ROLL                                                      T. Winter, Ed.
Internet-Draft
Intended status: Standards Track                         P. Thubert, Ed.
Expires: December 30, 2010 January 29, 2011                                  Cisco Systems
                                                         RPL Author Team
                                                            IETF ROLL WG
                                                            Jun
                                                           July 28, 2010

      RPL: IPv6 Routing Protocol for Low power and Lossy Networks
                         draft-ietf-roll-rpl-10
                         draft-ietf-roll-rpl-11

Abstract

   Low power and Lossy Networks (LLNs) are a class of network in which
   both the routers and their interconnect are constrained: LLN routers
   typically operate with constraints on (any subset of) processing
   power, memory and energy (battery), and their interconnects are
   characterized by (any subset of) high loss rates, low data rates and
   instability.  LLNs are comprised of anything from a few dozen and up
   to thousands of routers, and support point-to-point traffic (between
   devices inside the LLN), point-to-multipoint traffic (from a central
   control point to a subset of devices inside the LLN) and multipoint-
   to-point traffic (from devices inside the LLN towards a central
   control point).  This document specifies the IPv6 Routing Protocol
   for LLNs (RPL), which provides a mechanism whereby multipoint-to-
   point traffic from devices inside the LLN towards a central control
   point, as well as point-to-multipoint traffic from the central
   control point to the devices inside the LLN, is supported.  Support
   for point-to-point traffic is also available.

Status of this Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   6   7
     1.1.   Design Principles  . . . . . . . . . . . . . . . . . . .   6   7
     1.2.   Expectations of Link Layer Type  . . . . . . . . . . . .   7   8
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   8   9
   3.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .  11  12
     3.1.   Topology . . . . . . . . . . . . . . . . . . . . . . . .  11  12
       3.1.1.  Topology  RPL Identifiers . . . . . . . . . . . . . . . .  11 . . .  12
     3.2.   Instances, DODAGs, and DODAG Versions  . . . . . . . . .  11  12
     3.3.   Upward Routes and DODAG Construction . . . . . . . . . .  13  14
       3.3.1.  Objective Function (OF) . . . . . . . . . . . . . . .  14  15
       3.3.2.  DODAG Repair  . . . . . . . . . . . . . . . . . . . .  14  15
       3.3.3.  Security  . . . . . . . . . . . . . . . . . . . . . .  14  15
       3.3.4.  Grounded and Floating DODAGs  . . . . . . . . . . . .  14  16
       3.3.5.  Local DODAGs  . . . . . . . . . . . . . . . . . . . .  14  16
       3.3.6.  Administrative Preference . . . . . . . . . . . . . .  15  16
       3.3.7.  Datapath Validation and Loop Detection  . . . . . . .  15  16
       3.3.8.  Distributed Algorithm Operation . . . . . . . . . . .  15  17
     3.4.   Downward Routes and Destination Advertisement  . . . . .  15  17
     3.5.   Local DODAGs Route Discovery . . . . . . . . . . . . . .  16  17
     3.6.   Rank Properties  . . . . . . . . . . . . . . . . . . . .  18
       3.6.1.  Rank Comparison (DAGRank()) . . . . . . . . . . . . .  19
       3.6.2.  Rank Relationships  . . . . . . . . . . . . . . . . .  19
     3.7.   Routing Metrics and Constraints Used By RPL  . . . . . .  16
       3.6.1.  20
     3.8.   Loop Avoidance . . . . . . . . . . . . . . . . . . .  17
       3.6.2.  Rank Properties . .  21
       3.8.1.  Greediness and Instability  . . . . . . . . . . . . .  21
       3.8.2.  DODAG Loops . . . . . .  18
     3.7. . . . . . . . . . . . . . . .  23
       3.8.3.  DAO Loops . . . . . . . . . . . . . . . . . . . . . .  24
   4.  Traffic Flows Supported by RPL  . . . . . . . . . . . . .  20
       3.7.1. . .  25
     4.1.   Multipoint-to-Point Traffic  . . . . . . . . . . . . .  21
       3.7.2. .  25
     4.2.   Point-to-Multipoint Traffic  . . . . . . . . . . . . .  21
       3.7.3. .  25
     4.3.   Point-to-Point Traffic . . . . . . . . . . . . . . .  21
   4. . .  25
   5.  RPL Instance  . . . . . . . . . . . . . . . . . . . . . . . .  22
     4.1.  26
     5.1.   RPL Instance ID  . . . . . . . . . . . . . . . . . . . .  22
   5.  26
   6.  ICMPv6 RPL Control Message  . . . . . . . . . . . . . . . . .  24
     5.1.  28
     6.1.   RPL Security Fields  . . . . . . . . . . . . . . . . . .  25
     5.2.  29
     6.2.   DODAG Information Solicitation (DIS) . . . . . . . . . .  30
       5.2.1.  34
       6.2.1.  Format of the DIS Base Object . . . . . . . . . . . .  30
       5.2.2.  34
       6.2.2.  Secure DIS  . . . . . . . . . . . . . . . . . . . . .  31
       5.2.3.  34
       6.2.3.  DIS Options . . . . . . . . . . . . . . . . . . . . .  31
     5.3.  34
     6.3.   DODAG Information Object (DIO) . . . . . . . . . . . . .  31
       5.3.1.  35
       6.3.1.  Format of the DIO Base Object . . . . . . . . . . . .  31
       5.3.2.  35
       6.3.2.  Secure DIO  . . . . . . . . . . . . . . . . . . . . .  33
       5.3.3.  37
       6.3.3.  DIO Options . . . . . . . . . . . . . . . . . . . . .  33
     5.4.  37
     6.4.   Destination Advertisement Object (DAO) . . . . . . . . .  33
       5.4.1.  37
       6.4.1.  Format of the DAO Base Object . . . . . . . . . . . .  34
       5.4.2.  37
       6.4.2.  Secure DAO  . . . . . . . . . . . . . . . . . . . . .  34
       5.4.3.  39
       6.4.3.  DAO Options . . . . . . . . . . . . . . . . . . . . .  35
     5.5.  39
     6.5.   Destination Advertisement Object Acknowledgement
            (DAO-ACK)  . . . . . . . . . . . . . . . . . . . . . . .  35
       5.5.1.  39
       6.5.1.  Format of the DAO-ACK Base Object . . . . . . . . . .  35
       5.5.2.  39
       6.5.2.  Secure DAO-ACK  . . . . . . . . . . . . . . . . . . .  36
       5.5.3.  41
       6.5.3.  DAO-ACK Options . . . . . . . . . . . . . . . . . . .  36
     5.6.  41
     6.6.   Consistency Check (CC) . . . . . . . . . . . . . . . . .  36
       5.6.1.  41
       6.6.1.  Format of the CC Base Object  . . . . . . . . . . . .  36
       5.6.2.  41
       6.6.2.  CC Options  . . . . . . . . . . . . . . . . . . . . .  38
     5.7.  42
     6.7.   RPL Control Message Options  . . . . . . . . . . . . . .  38
       5.7.1.  43
       6.7.1.  RPL Control Message Option Generic Format . . . . . .  38
       5.7.2.  43
       6.7.2.  Pad1  . . . . . . . . . . . . . . . . . . . . . . . .  39
       5.7.3.  43
       6.7.3.  PadN  . . . . . . . . . . . . . . . . . . . . . . . .  39
       5.7.4.  44
       6.7.4.  Metric Container  . . . . . . . . . . . . . . . . . .  40
       5.7.5.  44
       6.7.5.  Route Information . . . . . . . . . . . . . . . . . .  40
       5.7.6.  45
       6.7.6.  DODAG Configuration . . . . . . . . . . . . . . . . .  42
       5.7.7.  47
       6.7.7.  RPL Target  . . . . . . . . . . . . . . . . . . . . .  43
       5.7.8.  49
       6.7.8.  Transit Information . . . . . . . . . . . . . . . . .  45
       5.7.9.  50
       6.7.9.  Solicited Information . . . . . . . . . . . . . . . .  46
       5.7.10.  53
       6.7.10. Prefix Information  . . . . . . . . . . . . . . . . .  48
   6.  55
       6.7.11. RPL Target descriptor . . . . . . . . . . . . . . . .  57
   7.  Sequence Counters . . . . . . . . . . . . . . . . . . . . . .  51
   7.  59
     7.1.   Sequence Counter Overview  . . . . . . . . . . . . . . .  59
     7.2.   Sequence Counter Operation . . . . . . . . . . . . . . .  60
   8.  Upward Routes . . . . . . . . . . . . . . . . . . . . . . . .  53
     7.1.  62
     8.1.   DIO Base Rules . . . . . . . . . . . . . . . . . . . . .  53
     7.2.  62
     8.2.   Upward Route Discovery and Maintenance . . . . . . . . .  53
       7.2.1.  62
       8.2.1.  Neighbors and Parents within a DODAG Version  . . . .  53
       7.2.2.  62
       8.2.2.  Neighbors and Parents across DODAG Versions . . . . .  54
       7.2.3.  63
       8.2.3.  DIO Message Communication . . . . . . . . . . . . . .  58
     7.3.  68
     8.3.   DIO Transmission . . . . . . . . . . . . . . . . . . . .  59
       7.3.1.  69
       8.3.1.  Trickle Parameters  . . . . . . . . . . . . . . . . .  60
     7.4.  69

     8.4.   DODAG Selection  . . . . . . . . . . . . . . . . . . . .  60
     7.5.  70
     8.5.   Operation as a Leaf Node . . . . . . . . . . . . . . . .  60
     7.6.  70
     8.6.   Administrative Rank  . . . . . . . . . . . . . . . . . .  61
   8.  71
   9.  Downward Routes . . . . . . . . . . . . . . . . . . . . . . .  62
     8.1.  72
     9.1.   Destination Advertisement Parents  . . . . . . . . . . .  62
     8.2.  72
     9.2.   Downward Route Discovery and Maintenance . . . . . . . .  62
     8.3.  73
       9.2.1.  Maintenance of Path Sequence  . . . . . . . . . . . .  73
       9.2.2.  Generation of DAO Messages  . . . . . . . . . . . . .  74
     9.3.   DAO Base Rules . . . . . . . . . . . . . . . . . . . . .  63
     8.4.  74
     9.4.   DAO Transmission Scheduling  . . . . . . . . . . . . . .  64
     8.5.  75
     9.5.   Triggering DAO Messages  . . . . . . . . . . . . . . . .  64
     8.6.  75
     9.6.   Structure of DAO Messages  . . . . . . . . . . . . . . .  65
     8.7.  76
     9.7.   Non-storing Mode . . . . . . . . . . . . . . . . . . . .  65
     8.8.  78
     9.8.   Storing Mode . . . . . . . . . . . . . . . . . . . . . .  66
     8.9.  79
     9.9.   Path Control . . . . . . . . . . . . . . . . . . . . . .  67
     8.10.  79
       9.9.1.  Path Control Example  . . . . . . . . . . . . . . . .  81
     9.10.  Multicast Destination Advertisement Messages . . . . . .  68
   9.  83
   10. Security Mechanisms . . . . . . . . . . . . . . . . . . . . .  69
     9.1.  84
     10.1.  Security Overview  . . . . . . . . . . . . . . . . . . .  69
     9.2.   Installing Keys  84
     10.2.  Joining a Secure Network . . . . . . . . . . . . . . . .  85
     10.3.  Installing Keys  . . . .  70
     9.3.   Joining a Secure Network . . . . . . . . . . . . . . . .  70
     9.4.   Counter and Counter Compression  86
     10.4.  Consistency Checks . . . . . . . . . . . .  71
       9.4.1.  Timestamp . . . . . . .  86
     10.5.  Counters . . . . . . . . . . . . . . . . .  72
     9.5.   Functional Description of Packet Protection . . . . . .  72
       9.5.1. .  87
     10.6.  Transmission of Outgoing Packets . . . . . . . . . .  72
       9.5.2. . .  88
     10.7.  Reception of Incoming Packets  . . . . . . . . . . . .  74
       9.5.3.  Cryptographic Mode of Operation .  89
       10.7.1. Timestamp Key Checks  . . . . . . . . . . .  76
     9.6. . . . . .  90
     10.8.  Coverage of Integrity and Confidentiality  . . . . . . .  77
   10. Packet Forwarding and Loop Avoidance/Detection  91
     10.9.  Cryptographic Mode of Operation  . . . . . . .  78
     10.1.  Suggestions for Packet Forwarding . . . . .  91
       10.9.1. Nonce . . . . . .  78
     10.2.  Loop Avoidance and Detection . . . . . . . . . . . . . .  79
       10.2.1. Source Node Operation . . . .  91
       10.9.2. Signatures  . . . . . . . . . . . .  80
       10.2.2. Router Operation . . . . . . . . .  92
   11. Packet Forwarding and Loop Avoidance/Detection  . . . . . . .  94
     11.1.  Suggestions for Packet Forwarding  . .  80
   11. Multicast Operation . . . . . . . . .  94
     11.2.  Loop Avoidance and Detection . . . . . . . . . . . .  83 . .  95
       11.2.1. Source Node Operation . . . . . . . . . . . . . . . .  96
       11.2.2. Router Operation  . . . . . . . . . . . . . . . . . .  96
   12. Multicast Operation . . . . . . . . . . . . . . . . . . . . .  99
   13. Maintenance of Routing Adjacency  . . . . . . . . . . . . . .  85
   13. 101
   14. Guidelines for Objective Functions  . . . . . . . . . . . . .  86
     13.1. 102
     14.1.  Objective Function Behavior  . . . . . . . . . . . . . .  86
   14. 102
   15. Suggestions for Interoperation with Neighbor Discovery  . . .  88
   15. 104
   16. RPL Constants and Variables . . . . . . . . . . . . . . . . .  89
   16. 105
   17. Manageability Considerations  . . . . . . . . . . . . . . . .  91
     16.1. 107
     17.1.  Introduction . . . . . . . . . . . . . . . . . . . . . .  91
     16.2. 107
     17.2.  Configuration Management . . . . . . . . . . . . . . . .  92
       16.2.1. 108
       17.2.1. Initialization Mode . . . . . . . . . . . . . . . . .  92
       16.2.2. 108
       17.2.2. DIO and DAO Base Message and Options Configuration  .  92
       16.2.3. 109
       17.2.3. Protocol Parameters to be configured on every
               router in the LLN . . . . . . . . . . . . . . . . . .  93
       16.2.4. 109

       17.2.4. Protocol Parameters to be configured on every
               non-root
               non-DODAG-root router in the LLN  . . . . . . . . . . . . .  93
       16.2.5. 110
       17.2.5. Parameters to be configured on the DODAG root . . . .  94
       16.2.6. 110
       17.2.6. Configuration of RPL Parameters related to
               DAO-based mechanisms  . . . . . . . . . . . . . . . .  95
       16.2.7. 111
       17.2.7. Default Values  . . . . . . . . . . . . . . . . . . .  96
     16.3. 112
     17.3.  Monitoring of RPL Operation  . . . . . . . . . . . . . .  96
       16.3.1. 112
       17.3.1. Monitoring a DODAG parameters . . . . . . . . . . . .  96
       16.3.2. 112
       17.3.2. Monitoring a DODAG inconsistencies and loop
               detection . . . . . . . . . . . . . . . . . . . . . .  97
     16.4. 113
     17.4.  Monitoring of the RPL data structures  . . . . . . . . .  98
       16.4.1. 114
       17.4.1. Candidate Neighbor Data Structure . . . . . . . . . .  98
       16.4.2. 114
       17.4.2. Destination Oriented Directed Acyclic Graph (DAG)
               Table . . . . . . . . . . . . . . . . . . . . . . . .  98
       16.4.3. 114
       17.4.3. Routing Table and DAO Routing Entries . . . . . . . .  99
     16.5. 115
     17.5.  Fault Management . . . . . . . . . . . . . . . . . . . . 100
     16.6. 116
     17.6.  Policy . . . . . . . . . . . . . . . . . . . . . . . . . 100
     16.7. 116
     17.7.  Liveness Detection and Monitoring  . . . . . . . . . . . 101
     16.8. 118
     17.8.  Fault Isolation  . . . . . . . . . . . . . . . . . . . . 102
     16.9. 118
     17.9.  Impact on Other Protocols  . . . . . . . . . . . . . . . 102
     16.10. 118
     17.10. Performance Management . . . . . . . . . . . . . . . . . 102
   17. 118
   18. Security Considerations . . . . . . . . . . . . . . . . . . . 104
     17.1. 120
     18.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . 104
   18. 120
   19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 106
     18.1. 122
     19.1.  RPL Control Message  . . . . . . . . . . . . . . . . . . 106
     18.2. 122
     19.2.  New Registry for RPL Control Codes . . . . . . . . . . . 106
     18.3. 122
     19.3.  New Registry for the Mode of Operation (MOP) DIO
            Control Field  . . . . . . . . . . . . . . . . . . . . . 107
     18.4. 123
     19.4.  RPL Control Message Option . . . . . . . . . . . . . . . 107
     18.5. 123
     19.5.  Objective Code Point (OCP) Registry  . . . . . . . . . . 108
     18.6. 124
     19.6.  New Registry for the  Security Section Flags . . . . . . 124
     19.7.  New Registry for the Key Identification Mode . . . . . . 125
     19.8.  New Registry for the KIM levels  . . . . . . . . . . . . 125
     19.9.  New Registry for the DIS (DODAG Informational
            Solicitation) Flags  . . . . . . . . . . . . . . . . . . 126
     19.10. New Registry for the DODAG Information Object (DIO)
            Flags  . . . . . . . . . . . . . . . . . . . . . . . . . 127
     19.11. New Registry for the Destination Advertisement Object
            (DAO) Flags  . . . . . . . . . . . . . . . . . . . . . . 127
     19.12. New Registry for the Destination Advertisement Object
            (DAO) Flags  . . . . . . . . . . . . . . . . . . . . . . 128
     19.13. New Registry for the Consistency Check (CC) Flags  . . . 128
     19.14. New Registry for the DODAG Configuration Option Flags  . 129
     19.15. New Registry for the RPL Target Option Flags . . . . . . 129
     19.16. New Registry for the Transit Information  Option Flags . 129
     19.17. New Registry for the Solicited Information Option
            Flags  . . . . . . . . . . . . . . . . . . . . . . . . . 130
     19.18. ICMPv6: Error in Source Routing Header . . . . . . . . . 108
     18.7. 131
     19.19. Link-Local Scope multicast address . . . . . . . . . . . 108
   19. 131
   20. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 110
   20. 132
   21. Contributors  . . . . . . . . . . . . . . . . . . . . . . . . 111
   21. 133
   22. References  . . . . . . . . . . . . . . . . . . . . . . . . . 113
     21.1. 135
     22.1.  Normative References . . . . . . . . . . . . . . . . . . 113
     21.2. 135
     22.2.  Informative References . . . . . . . . . . . . . . . . . 113 136
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 117 139

1.  Introduction

   Low power and Lossy Networks (LLNs) consist of largely of constrained
   nodes (with limited processing power, memory, and sometimes energy
   when they are battery operated). operated or energy scavenging).  These routers
   are interconnected by lossy links, typically supporting only low data
   rates, that are usually unstable with relatively low packet delivery
   rates.  Another characteristic of such networks is that the traffic
   patterns are not simply point-to-point, but in many cases point-to-multipoint point-to-
   multipoint or multipoint-to-point.  Furthermore such networks may
   potentially comprise up to thousands of nodes.  These characteristics
   offer unique challenges to a routing solution: the IETF ROLL Working
   Group has defined application-specific routing requirements for a Low
   power and Lossy Network (LLN) routing protocol, specified in
   [RFC5867], [RFC5826], [RFC5673], and [RFC5548].

   This document specifies the IPv6 Routing Protocol for Low power and
   lossy networks (RPL).  Note that although RPL was specified according
   to the requirements set forth in the aforementioned requirement
   documents, its use is in no way limited to these applications.

1.1.  Design Principles

   RPL was designed with the objective to meet the requirements spelled
   out in [RFC5867], [RFC5826], [RFC5673], and [RFC5548].

   A network may run multiple instances of RPL concurrently.  Each such
   instance may serve different and potentially antagonistic constraints
   or performance criteria.  This document defines how a single instance
   operates.

   In order to be useful in a wide range of LLN application domains, RPL
   separates packet processing and forwarding from the routing
   optimization objective.  Examples of such objectives include
   minimizing energy, minimizing latency, or satisfying constraints.
   This document describes the mode of operation of RPL.  Other
   companion documents specify routing objective functions.  A RPL
   implementation, in support of a particular LLN application, will
   include the necessary objective function(s) as required by the
   application.

   A set of companion documents to this specification will provide
   further guidance in the form of applicability statements specifying a
   set of operating points appropriate to the Building Automation, Home
   Automation, Industrial, and Urban application scenarios.

1.2.  Expectations of Link Layer Type

   In compliance with the layered architecture of IP, RPL does not rely
   on any particular features of a specific link layer technology.  RPL
   is designed to be able to operate over a variety of different link
   layers, including ones that are constrained, potentially lossy, or
   typically utilized in conjunction with highly constrained host or
   router devices, such as but not limited to, low power wireless or PLC
   (Power Line Communication) technologies.

   Implementers may find [RFC3819] a useful reference when designing a
   link layer interface between RPL and a particular link layer
   technology.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].

   Additionally, this document uses terminology from
   [I-D.ietf-roll-terminology], and introduces the following
   terminology:

   DAG:  Directed Acyclic Graph.  A directed graph having the property
         that all edges are oriented in such a way that no cycles exist.
         All edges are contained in paths oriented toward and
         terminating at one or more root nodes.

   DAG root:  A DAG root is a node within the DAG that has no outgoing
         edge.  Because the graph is acyclic, by definition all DAGs
         must have at least one DAG root and all paths terminate at a
         DAG root.

   Destination Oriented DAG (DODAG):  A DAG rooted at a single
         destination, i.e. at a single DAG root (the DODAG root) with no
         outgoing edges.

   DODAG root:  A DODAG root is the DAG root of a DODAG.

   Virtual DODAG root:  A Virtual DODAG root is the result of two or
         more RPL routers, most typically LBRs, coordinating to
         synchronize DODAG state and act in concert as if they are a
         single DODAG root (with multiple interfaces), with respect to
         the LLN.  The coordination most likely occurs between powered
         devices over a reliable transit link, and the details of that
         scheme are beyond the scope of this specification.

   Up:   Up refers to the direction from leaf nodes towards DODAG roots,
         following DODAG edges.  This follows the common terminology
         used in graphs and depth-first-search, where vertices further
         from the root are "deeper," or "down," and vertices closer to
         the root are "shallower," or "up." "up".

   Down: Down refers to the direction from DODAG roots towards leaf
         nodes, in the reverse direction of DODAG edges.  This follows
         the common terminology used in graphs and depth-first-search,
         where vertices further from the root are "deeper," or "down,"
         and vertices closer to the root are "shallower," or "up." "up".

   Rank: A node's Rank defines the node's individual position relative
         to other nodes with respect to a DODAG root.  Rank strictly
         increases in the down Down direction and strictly decreases in the
         up
         Up direction.  The exact way Rank is computed depends on the
         DAG's Objective Function (OF).  The Rank may analogously track
         a simple topological distance, may be calculated as a function
         of link metrics, and may consider other properties such as
         constraints.

   Objective Function (OF):  Defines which how routing metrics, optimization
         objectives, and related functions a DAG uses are used to compute Rank.
         Furthermore, the OF dictates how parents in the DODAG are
         selected and thus the DODAG formation itself.

   Objective Code Point (OCP):  An identifier that indicates which
         Objective Function the DODAG uses.

   RPLInstanceID:  A unique identifier within a network.  Two  DODAGs with
         the same RPLInstanceID share the same Objective Function.

   RPL Instance:  A set of one or more DODAGs that share a
         RPLInstanceID.  A RPL node can belong to at most one DODAG in a
         RPL Instance.  Each RPL Instance operates independently of
         other RPL Instances.  This document describes operation within
         a single RPL Instance.

   DODAGID:  The identifier of a DODAG root.  The DODAGID must be is unique
         within the scope of a RPL Instance in the LLN.  The tuple
         (RPLInstanceID, DODAGID) uniquely identifies a DODAG.

   DODAG Version:  A specific sequence number iteration ("version") ("Version") of a DODAG with a
         given DODAGID.

   DODAGVersionNumber:  A sequential counter that is incremented by the
         root to form a new Version of a DODAG.  A DODAG Version is
         identified uniquely by the (RPLInstanceID, DODAGID,
         DODAGVersionNumber) tuple.

   Goal: The Goal is a an application specific goal that is defined
         outside the scope of RPL.  Any node that roots a DODAG will
         need to know about this Goal to decide if the Goal can be
         satisfied or not.  A typical Goal is to construct the DODAG
         according to a specific objective function and to keep
         connectivity to a set of hosts (e.g. to use an objective
         function that minimizes ETX a metric and to be connected to a
         specific database host to store the collected data).

   Grounded:  A DODAG is grounded when the DODAG root can satisfy the
         Goal.

   Floating:  A DODAG is floating if it is not Grounded.  A floating
         DODAG is not expected to have the properties required to
         satisfy the goal.  It may, however, provide connectivity to
         other nodes within the DODAG.

   DODAG parent:  A parent of a node within a DODAG is one of the
         immediate successors of the node on a path towards the DODAG
         root.  A DODAG parent's Rank is lower than the node's.  (See
         Section 3.6.2.1). 3.6.1).

   Sub-DODAG  The sub-DODAG of a node is the set of other nodes whose
         paths to the DODAG root pass through that node.  Nodes in the
         sub-DODAG of a node have a greater Rank than that node itself.
         (See Section 3.6.2.1)

   As they form networks, LLN devices often 3.6.1).

   Local DODAG:  Local DODAGs contain one and only one root node, and
         allows that single root node to allocate and manage a RPL
         Instance, identified by a local RPLInstanceID, without
         coordination with other nodes.  This is typically done in order
         to optimize routes to a destination withing the LLN.  See
         Section 5.

   Global DODAG:  A Global DODAG uses a global RPLInstanceID that may be
         coordinated among several other nodes.  See Section 5.

   As they form networks, LLN devices often mix the roles of 'host' and
   'router' when compared to traditional IP networks.  In this document,
   'host' refers to an LLN device that can generate but does not forward
   RPL traffic, 'router' refers to an LLN device that can forward as
   well as generate RPL traffic, and 'node' refers to any RPL device,
   either a host or a router.

3.  Protocol Overview

   The aim of this section is to describe RPL in the spirit of
   [RFC4101].  Protocol details can be found in further sections.

3.1.  Topology

   This section describes how the basic RPL topologies, topologies that may be formed,
   and the rules by which these are constructed, i.e. the rules
   governing DODAG formation.

3.1.1.  Topology  RPL Identifiers

   RPL uses four identifiers values to identify and maintain the a topology:

   o  The first is a RPLInstanceID.  A RPLInstanceID identifies a set of
      one or more DODAGs.  All DODAGs in the same RPL Instance use the
      same Objective Function. Destination Oriented DAGs (DODAGs).  A network may
      have multiple RPLInstanceIDs, each of which defines an independent
      set of DODAGs, which may be optimized for different OFs Objective
      Functions (OFs) and/or applications.  The set of DODAGs identified
      by a RPLInstanceID is called a RPL Instance.  All DODAGs in the
      same RPL Instance use the same OF.

   o  The second is a DODAGID.  The scope of a DODAGID is a RPL
      Instance.  The combination of RPLInstanceID and DODAGID uniquely
      identifies a single DODAG in the network.  A RPL Instance may have
      multiple DODAGs, each of which has an unique DODAGID.

   o  The third is a DODAGVersionNumber.  The scope of a
      DODAGVersionNumber is a DODAG.  A DODAG is sometimes reconstructed
      from the DODAG root, by incrementing the DODAGVersionNumber.  The
      combination of RPLInstanceID, DODAGID, and DODAGVersionNumber
      uniquely identifies a DODAG Version.

   o  The fourth is Rank.  The scope of Rank is a DODAG Version.  Rank
      establishes a partial order over a DODAG Version, defining
      individual node positions with respect to the DODAG root.

3.2.  Instances, DODAGs, and DODAG Versions

   A RPL Instance contains one or more Destination Oriented DAG (DODAG) DODAG roots.  A RPL Instance may
   provide routes to certain destination prefixes, reachable via the
   DODAG roots or alternate paths within the DODAG.  These roots may
   operate independently, or may coordinate over a non-LLN backchannel. network that is not
   necessarily as constrained as a LLN.

   A RPL Instance may comprise:

   o  a single DODAG with a single root

      *  For example, a DODAG optimized to minimize latency rooted at a
         single centralized lighting controller in a home automation
         application.

   o  multiple uncoordinated DODAGs with independent roots (differing
      DODAGIDs)

      *  For example, multiple data collection points in an urban data
         collection application that do not have an always-on backbone suitable connectivity
         to coordinate to form a single DODAG, and further with each other, or that use the formation of
         multiple DODAGs as a means to dynamically and autonomously
         partition the network.

   o  a single DODAG with a single virtual root coordinating that coordinates LLN sinks
      (with the same DODAGID) over some non-LLN a backbone network.

      *  For example, multiple border routers operating with a reliable
         backbone,
         transit link, e.g. in support of a 6LowPAN application, that
         are capable to act as logically equivalent sinks interfaces to the
         sink of the same DODAG.

   o  a combination of the above as suited to some application scenario.

   Each RPL packet has meta-data that associates it is associated with a particular RPLInstanceID (see
   Section 11.2) and therefore RPL Instance.(Section 4). Instance (Section 5).  The
   provisioning or automated discovery of a mapping between a
   RPLInstanceID and a type or service of application traffic is beyond
   the scope of this specification.

   Figure 1 depicts an example of a RPL Instance comprising three DODAGs
   with DODAG Roots R1, R2, and R3.  Each of these DODAG Roots
   advertises the same RPLInstanceID.  The lines depict connectivity
   between parents and children.  Although tree-like DODAGs are depicted
   for simplicity, the DODAG structure allows for each node to have
   multiple parents when the connectivity supports it.

   Figure 2 depicts how a DODAG
   version Version number increment leads to a new
   DODAG Version.  This depiction illustrates a DODAG Version number
   increment that results in a different DODAG topology.  Note that a
   new DODAG Version does not always imply a different DODAG topology.
   To accommodate certain topology changes requires a new DODAG Version,
   as described later in this specification.

     +----------------------------------------------------------------+
     |                                                                |
     | +--------------+                                               |
     | |              |                                               |
     | |     (R1)     |            (R2)                   (R3)        |
     | |     /  \     |            /| \                  / |  \       |
     | |    /    \    |           / |  \                /  |   \      |
     | |  (A)    (B)  |         (C) |  (D)     ...    (F) (G)  (H)    |
     | |  /|\     |\  |         /   |   |\             |   |    |     |
     | | : : :    : : |        :   (E)  : :            :   :    :     |
     | |              |            / \                                |
     | +--------------+           :   :                               |
     |      DODAG                                                     |
     |                                                                |
     +----------------------------------------------------------------+
                                RPL Instance

                          Figure 1: RPL Instance

            +----------------+                +----------------+
            |                |                |                |
            |      (R1)      |                |      (R1)      |
            |      /  \      |                |      /         |
            |     /    \     |                |     /          |
            |   (A)    (B)   |         \      |   (A)          |
            |   /|\     |\   |    ------\     |   /|\          |
            |  : : (C)  : :  |           \    |  : : (C)       |
            |                |           /    |        \       |
            |                |    ------/     |         \      |
            |                |         /      |         (B)    |
            |                |                |          |\    |
            |                |                |          : :   |
            |                |                |                |
            +----------------+                +----------------+
                Version N                        Version N+1

                          Figure 2: DODAG Version

3.3.  Upward Routes and DODAG Construction

   RPL provisions routes up Up towards DODAG roots, forming a DODAG
   optimized according to an Objective Function (OF).  RPL nodes
   construct and maintain these DODAGs through DODAG Information Object
   (DIO) messages.

3.3.1.  Objective Function (OF)

   The Objective Function (OF) defines how RPL nodes select and optimize
   routes within a RPL Instance.  The OF is identified by an Objective
   Code Point (OCP) within the DIO Configuration option.  An OF defines
   how nodes translate one or more metrics and constraints, which are
   themselves defined in [I-D.ietf-roll-routing-metrics], into a value
   called Rank, which approximates the node's distance from a DODAG
   root.  An OF also defines how nodes select parents.  Further details
   may be found in Section 13, 14, [I-D.ietf-roll-routing-metrics],
   [I-D.ietf-roll-of0], and related companion specifications.

3.3.2.  DODAG Repair

   A DODAG Root institutes a global repair operation by incrementing the
   DODAG Version Number.  This initiates a new DODAG version. Version.  Nodes in
   the new DODAG version Version can choose a new position whose Rank is not
   constrained by their Rank within the old DODAG Version.

   RPL also supports mechanisms which may be used for local repair
   within the DODAG version. Version.  The DIO message specifies the necessary
   parameters as configured from the DODAG root, as and controlled by policy at the DODAG
   root.

3.3.3.  Security

   RPL supports message confidentiality and integrity.  It is designed
   such that link-layer mechanisms can be used when available and
   appropriate, yet in their absence RPL can use its own mechanisms.
   RPL has three basic security modes.

   In the first, called "unsecured," RPL control messages are sent
   without any additional security mechanisms.  Unsecured mode does not
   imply that the RPL network is unsecure: it could be using other
   present security primitives (e.g. link-layer security) to meet
   application security requirements.

   In the second, called "pre-installed," nodes joining a RPL Instance
   have pre-installed keys that enable them to process and generate
   secured RPL messages.

   The third mode is called "authenticated."  In authenticated mode,
   nodes have pre-installed keys as in pre-installed mode, but the pre-
   installed key may only be used to join a RPL Instance as a leaf.
   Joining an authenticated RPL Instance as a router requires obtaining
   a key from an authentication authority.  The process by which this
   key is obtained is outside the scope of this specification.

3.3.4.  Grounded and Floating DODAGs

   DODAGs can be grounded or floating: the DODAG root advertises which
   is the case.  A grounded DODAG offers connectivity to hosts that are
   required for satisfying the application-defined goal.  A floating
   DODAG is not expected to satisfy the goal and in most cases only
   provides routes to nodes within the DODAG.  Floating DODAGs may be
   used, for example, to preserve inner connectivity during repair.

3.3.5.  Local DODAGs

   RPL nodes can optimize routes to a destination within an LLN by
   forming a local DODAG whose DODAG Root is the desired destination.
   Unlike global DAGs, which can consist of multiple DODAGs, local DAGs
   have one and only one DODAG and therefore one DODAG Root.  Local
   DODAGs can be constructed on-demand.

3.3.6.  Administrative Preference

   An implementation/deployment may specify that some DODAG roots should
   be used over others through an administrative preference.
   Administrative preference offers a way to control traffic and
   engineer DODAG formation in order to better support application
   requirements or needs.

3.3.7.  Datapath Validation and Loop Detection

   RPL uses carries routing information in a hop-by-hop RPL Option contained in an IPv6 header to detect possible loops
   Hop-by-Hop Option as specified in [I-D.ietf-6man-rpl-option].  Such
   routing information is used, for example, for loop detection within a
   DODAG.
   DODAG as discussed in Section 11.2 and may be extended in future
   documents for additional features.

   Each data packet includes the Rank of the transmitter.  An
   inconsistency between the routing decision for a packet (upward or
   downward) and the Rank relationship between the two nodes indicates a
   possible loop.  On receiving such a packet, a node institutes a local
   repair operation.

   For example, if a node receives a packet flagged as moving in the
   upward direction, and if that packet records that the transmitter is
   of a lower (lesser) Rank than the receiving node, then the receiving
   node is able to conclude that the packet has not progressed in the
   upward direction and that the DODAG is inconsistent.

3.3.8.  Distributed Algorithm Operation

   A high level overview of the distributed algorithm, which constructs
   the DODAG, is as follows:

   o  Some nodes are configured to be DODAG roots, with associated DODAG
      configurations.

   o  Nodes advertise their presence, affiliation with a DODAG, routing
      cost, and related metrics by sending link-local multicast DIO
      messages.
      messages to all-RPL-nodes.

   o  Nodes listen for DIOs and use their information to join a new
      DODAG, or to maintain an existing DODAG, as according to the
      specified Objective Function and Rank of their neighbors.

   o  Nodes provision routing table entries, for the destinations
      specified by the DIO, DIO message, via their DODAG parents in the DODAG
      version.
      Version.  Nodes that decide to join a DODAG MUST provision a DODAG
      parent as a default route for the associated instance.  It is up
      to the end-to-end application to select the RPL instance to be
      associated to its traffic (should there be more than one instance)
      and thus the default route upwards when no longer-match exists.

3.4.  Downward Routes and Destination Advertisement

   RPL uses Destination Advertisement Object (DAO) messages to establish
   downward routes from DODAG roots. routes.  DAO messages are an optional feature for
   applications that require P2MP or P2P traffic.  RPL supports two
   modes of downward traffic: storing (fully stateful) or non-storing
   (fully source routed).  Any given RPL Instance is either storing or
   non-storing.  In both cases, P2P packets travel up to Up toward a DODAG
   Root then down Down to the final destination (unless the destination is on
   the upward route).

3.5.  Local DODAGs Route Discovery

   A RPL network can optionally support  In the non-storing case the packet will travel
   all the way to a DODAG root before traveling Down.  In the storing
   case the packet may be directed Down towards the destination by a
   common ancestor of the source and the destination prior to reaching a
   DODAG Root.

   This specification describes a basic mode of operation in support of
   P2P traffic.  Note that more optimized P2P solutions may be described
   in companion specifications.

3.5.  Local DODAGs Route Discovery

   A RPL network can optionally support on-demand discovery of DODAGs to
   specific destinations within an LLN.  Such local DODAGs behave
   slightly differently than global DODAGs.

3.6.  Routing Metrics and Constraints Used By RPL

   Routing metrics DODAGs: they are used uniquely defined by routing protocols to compute shortest
   paths.  Interior Gateway Protocols (IGPs) such as IS-IS ([RFC5120])
   and OSPF ([RFC4915]) use static link metrics.  Such link metrics can
   simply reflect the bandwidth or can also be computed according to a
   polynomial function of several metrics defining different link
   characteristics.  Some routing protocols support more than one
   metric: in
   the vast majority combination of the cases, one metric is used per
   (sub)topology.  Less often, DODAGID and RPLInstanceID.  The RPLInstanceID
   denotes whether a second metric may be used as DODAG is a tie-
   breaker in the presence of Equal Cost Multiple Paths (ECMP). local DODAG.

3.6.  Rank Properties

   The
   optimization rank of multiple metrics is known as an NP complete problem
   and a node is sometimes supported by some centralized path computation
   engine.

   In contrast, LLNs do require the support a scalar representation of both static and dynamic
   metrics.  Furthermore, both link and node metrics are required.  In the case location of RPL, it is virtually impossible to define one metric, or
   even a composite metric, that will satisfy all use cases.

   In addition, RPL supports constrained-based routing where constraints
   may be applied to both link and nodes.  If a link or a
   node does not
   satisfy within a required constraint, it DODAG Version.  The rank is 'pruned' from the candidate
   list, thus leading used to a constrained shortest path.

   An Objective Function specifies avoid and detect
   loops, and as such must demonstrate certain properties.  The exact
   calculation of the objectives used rank is left to compute the
   (constrained) path.  Upstream Objective Function, and Downstream metrics may be merged or
   advertised separately depending
   depend on the OF parents, link metrics, node metrics, and the node
   configuration and policies.

   The rank is not a path cost, although its value can be derived from
   and influenced by path metrics.  When they
   are advertised separately, it may happen  The rank has properties of its own
   that the set are not necessarily those of DIO parents all metrics:

   Type:   The rank is an abstract numeric value.

   Function:  The rank is different from the set expression of DAO parents (a DAO parent is a node to
   which unicast DAO messages are sent).  Yet, all are relative position within a
           DODAG parents Version with regards regard to neighbors and is not necessarily
           a good indication or a proper expression of a distance or a
           path cost to the rules for Rank computation. root.

   Stability:  The Objective Function itself is decoupled from stability of the rank determines the stability of the
           routing metrics
   and constraints used by RPL.  Indeed, whereas topology.  Some dampening or filtering is RECOMMENDED
           to keep the OF dictates rules
   such as DODAG parents selection, load balancing topology stable, and so on, thus the set of
   metrics and/or constraints used to select a DODAG parent and thus
   determine the preferred path are based on the information carried
   within the DAG container option in DIO messages.

   The set of supported link/node constraints and metrics is specified
   in [I-D.ietf-roll-routing-metrics].

   Example 1: Shortest path: path offering the shortest end-to-end delay

   Example 2: Constrained shortest path: the path that rank does not traverse
              any battery-operated node and that optimizes the path
              reliability

3.6.1.  Loop Avoidance

   RPL guarantees neither loop free path selection nor tight delay
   convergence times.  In order to reduce control overhead, however,
   such
           necessarily change as the cost of the count-to-infinity problem, RPL avoids
   creating loops when undergoing topology changes.  Furthermore, RPL
   includes rank-based datapath validation mechanisms for detecting
   loops when they do occur.  RPL uses this loop detection to ensure
   that packets make forward progress within the DODAG version and
   trigger repairs when necessary.

3.6.1.1.  Greediness and Rank-based Instabilities

   A fast as some link or node is greedy if it attempts to move deeper in the metrics
           would.  A new DODAG version,
   in order Version would be a good opportunity to increase the size of
           reconcile the parent set or improve some other
   metric.  Moving deeper in discrepancies that might form over time between
           metrics and ranks within a DODAG version in this manner could
   result Version.

   Properties:  The rank is incremented in instability a strictly monotonic fashion,
           and can be detrimental used to other nodes.

   Once validate a node has joined progression from or towards the
           root.  A metric, like bandwidth or jitter, does not
           necessarily exhibit this property.

   Abstract:  The rank does not have a DODAG version, RPL disallows certain
   behaviors, including greediness, in order physical unit, but rather a range
           of increment per hop, where the assignment of each increment
           is to prevent resulting
   instabilities in be determined by the Objective Function.

   The rank value feeds into DODAG version.

   Suppose a node is willing parent selection, according to receive and process a DIO messages from the
   RPL loop-avoidance strategy.  Once a node in its own sub-DODAG, parent has been added, and in general a
   rank value for the node deeper than
   itself.  In this case, a possibility exists that a feedback loop is
   created, wherein two or more within the DODAG has been advertised, the
   nodes continue further options with regard to try DODAG parent selection and move in
   movement within the DODAG version while attempting to optimize against each other.  In
   some cases, this will result are restricted in instability.  It is for this reason
   that RPL limits the cases where a node favor of loop avoidance.

3.6.1.  Rank Comparison (DAGRank())

   Rank may process DIO messages from
   deeper nodes to some forms be thought of local repair.  This approach creates an
   'event horizon', whereby as a node cannot be influenced beyond some
   limit into an instability by fixed point number, where the action position of nodes that may be
   the radix point between the integer part and the fractional part is
   determined by MinHopRankIncrease.  MinHopRankIncrease is the minimum
   increase in rank between a node and any of its
   own sub-DODAG.

3.6.1.2. DODAG Loops parents.  A
   DODAG loop may occur when Root provisions MinHopRankIncrease.  MinHopRankIncrease creates
   a node detaches from the DODAG tradeoff between hop cost precision and
   reattaches to a device in its prior sub-DODAG.  This may happen in
   particular when DIO messages are missed.  Strict use of the DODAG
   Version Number can eliminate this type of loop, but this type of loop
   may possibly be encountered when using some local repair mechanisms.

3.6.1.3.  DAO Loops

   A DAO loop may occur when the parent has a route installed upon
   receiving and processing a DAO message from a child, but the child
   has subsequently cleaned up the related DAO state.  This loop happens
   when a No-Path (a DAO message that invalidates a previously announced
   prefix) was missed and persists until all state has been cleaned up.
   RPL includes an optional mechanism to acknowledge DAO messages, which
   may mitigate the impact of a single DAO message being missed.  RPL
   includes loop detection mechanisms that may mitigate the impact of
   DAO loops and trigger their repair.

3.6.2.  Rank Properties

   The rank of a node is a scalar representation of the location of that
   node within a DODAG version.  The rank is used to avoid and detect
   loops, and as such must demonstrate certain properties.  The exact
   calculation of the rank is left to the Objective Function, and may
   depend on parents, link metrics, and the node configuration and
   policies.

   The rank is not a cost metric, although its value can be derived from
   and influenced by metrics.  The rank has properties of its own that
   are not necessarily those of all metrics:

   Type:   The rank is an abstract numeric value.

   Function:  The rank is the expression of a relative position within a
           DODAG version with regard to neighbors and is not necessarily
           a good indication or a proper expression of a distance or a
           cost to the root.

   Stability:  The stability of the rank determines the stability maximum number of the
           routing topology.  Some dampening or filtering might be
           applied to keep the topology stable, and thus the rank does
           not necessarily change as fast as some physical metrics
           would.  A new DODAG version would be a good opportunity to
           reconcile the discrepancies that might form over time between
           metrics and ranks within hops
   a DODAG version.

   Properties:  The rank is strictly monotonic, and network can be used to
           validate a progression from or towards the root. support.  A metric,
           like bandwidth or jitter, does not necessarily exhibit this
           property.

   Abstract:  The rank does not have a physical unit, but rather a range
           of increment per hop, where the assignment of each increment
           is to be determined by the Objective Function.

   The rank value feeds into DODAG parent selection, according to the
   RPL loop-avoidance strategy.  Once a parent has been added, and a
   rank value very large MinHopRankIncrease, for the node within the DODAG has been advertised, the
   nodes further options with regard to DODAG parent selection and
   movement within the DODAG are restricted in favor of loop avoidance.

3.6.2.1.  Rank Comparison (DAGRank())

   Rank may be thought of as a fixed point number, where the position example,
   allows precise characterization of
   the radix point between the integer part and the fractional part is
   determined by MinHopRankIncrease.  MinHopRankIncrease is the minimum
   increase in rank between a node and any of its DODAG parents. given hop's affect on Rank but
   cannot support many hops.

   When an objective function computes rank, the objective function
   operates on the entire (i.e. 16-bit) rank quantity.  When rank is
   compared, e.g. for determination of parent relationships or loop
   detection, the integer portion of the rank is to be used.  The
   integer portion of the Rank is computed by the DAGRank() macro as
   follows, where floor(x) is the function that evaluates to the
   greatest integer less than or equal to x:

              DAGRank(rank) = floor(rank/MinHopRankIncrease)

   MinHopRankIncrease

   For example, if a 16-bit rank quantity is provisioned at the DODAG Root decimal 27, and propagated in the DIO message.  The default value of
   MinHopRankIncrease is
   DEFAULT_MIN_HOP_RANK_INCREASE.  For efficient implementation the
   MinHopRankIncrease MUST be a power of 2.  An implementation may
   configure a value MinHopRankIncrease as appropriate to balance
   between the loop avoidance logic of RPL (i.e. selection decimal 16, then DAGRank(27) = floor(1.6875) =
   1.  The integer part of eligible
   parents) and the metrics in use.  A further effect of
   MinHopRankIncrease rank is to impact 1 and the number increments that are
   allowed before INFINITE_RANK fractional part is reached, i.e. to control how long it
   may take to count-to-infinity.
   11/16.

   By convention in this document, using the macro DAGRank(node) may be
   interpreted as DAGRank(node.rank), where node.rank is the rank value
   as maintained by the node.

   A node A has a rank less than the rank of a node B if DAGRank(A) is
   less than DAGRank(B).

   A node A has a rank equal to the rank of a node B if DAGRank(A) is
   equal to DAGRank(B).

   A node A has a rank greater than the rank of a node B if DAGRank(A)
   is greater than DAGRank(B).

3.6.2.2.

3.6.2.  Rank Relationships

   The computation of the rank MUST be done in such a way so as to

   Rank computations maintain the following properties for any nodes M
   and N that are neighbors in the LLN:

   DAGRank(M) is less than DAGRank(N):  In this case, the position of M
           is closer to the DODAG root than the position of N. Node M
           may safely be a DODAG parent for Node N without risk of
           creating a loop.  Further, for a node N, all parents in the
           DODAG parent set must be of rank less than DAGRank(N).  In
           other words, the rank presented by a node N MUST be greater
           than that presented by any of its parents.

   DAGRank(M) equals DAGRank(N):  In this case the positions of M and N
           within the DODAG and with respect to the DODAG root are
           similar (identical).  In some cases, Node M may be used as  Routing through a
           successor by Node N, which however entails the chance of
           creating node with equal Rank
           may cause a routing loop (which must be detected and resolved by some
           other means). (i.e., if that node chooses to route
           through a node with equal Rank as well).

   DAGRank(M) is greater than DAGRank(N):  In this case, the position of
           M is farther from the DODAG root than the position of N.
           Further, Node M may in fact be in the sub-DODAG of Node N. If
           node N selects node M as DODAG parent there is a risk to
           create a loop.

   As an example, the rank could be computed in such a way so as to
   closely track ETX (Expected Transmission Count, a fairly common
   routing metric used in LLN and defined in
   [I-D.ietf-roll-routing-metrics]) when the metric that an objective
   function minimizes is to
   minimize ETX, or latency when the objective function is to minimize latency, or in a more complicated way
   as appropriate to the objective function being used within the DODAG.

3.7.  Traffic Flows Supported by RPL

   RPL supports three basic traffic flows: Multipoint-to-Point (MP2P),
   Point-to-Multipoint (P2MP),  Routing Metrics and Point-to-Point (P2P).

3.7.1.  Multipoint-to-Point Traffic

   Multipoint-to-Point (MP2P) is a dominant traffic flow in many LLN
   applications ([RFC5867], [RFC5826], [RFC5673], [RFC5548]).  The
   destinations of MP2P flows Constraints Used By RPL

   Routing metrics are designated nodes that have some
   application significance, used by routing protocols to compute shortest
   paths.  Interior Gateway Protocols (IGPs) such as providing connectivity to IS-IS ([RFC5120])
   and OSPF ([RFC4915]) use static link metrics.  Such link metrics can
   simply reflect the
   larger Internet bandwidth or core private IP network.  RPL supports MP2P
   traffic by allowing MP2P destinations to can also be reached via DODAG roots.

3.7.2.  Point-to-Multipoint Traffic

   Point-to-multipoint (P2MP) is computed according to a traffic pattern required by
   polynomial function of several
   LLN applications ([RFC5867], [RFC5826], [RFC5673], [RFC5548]).  RPL
   supports P2MP traffic by using a destination advertisement mechanism
   that provisions routes toward destinations (prefixes, addresses, or
   multicast groups), and away from roots.  Destination advertisements
   can update metrics defining different link
   characteristics.  Some routing tables as the underlying DODAG topology changes.

3.7.3.  Point-to-Point Traffic

   RPL DODAGs provide a basic structure for point-to-point (P2P)
   traffic.  For a RPL network to protocols support P2P traffic, more than one
   metric: in the vast majority of the cases, one metric is used per
   (sub)topology.  Less often, a root must second metric may be
   able to route packets to used as a destination.  Nodes within tie-
   breaker in the network may
   also have routing tables to destinations.  A packet flows towards a
   root until it reaches an ancestor that has a presence of Equal Cost Multiple Paths (ECMP).  The
   optimization of multiple metrics is known route to as an NP complete problem
   and is sometimes supported by some centralized path computation
   engine.

   In contrast, LLNs do require the
   destination.  As pointed out later in this document, in support of both static and dynamic
   metrics.  Furthermore, both link and node metrics are required.  In
   the most
   constrained case (when nodes cannot store routes), of RPL, it is virtually impossible to define one metric, or
   even a composite metric, that common
   ancestor may be the DODAG root. will satisfy all use cases.

   In other cases it addition, RPL supports constrained-based routing where constraints
   may be a node
   closer applied to both the source link and destination.

   RPL also supports the case where nodes.  If a P2P destination link or a node does not
   satisfy a required constraint, it is 'pruned' from the candidate
   neighbor set, thus leading to a 'one-hop'
   neighbor.

   RPL neither constrained shortest path.

   An Objective Function specifies nor precludes additional mechanisms for
   computing and installing potentially more optimal routes the objectives used to compute the
   (constrained) path.  Furthermore, nodes are configured to support
   arbitrary P2P traffic.

4.  RPL Instance

   Within a given LLN, there may be multiple, logically independent RPL
   instances.  A RPL node may belong to multiple RPL instances,
   set of metrics and may
   act as a router in some constraints, and as a leaf select their parents in others.  This document
   describes how a single instance behaves.

   There are two types of RPL Instances: local and global.  Local RPL
   Instances are always a single the DODAG whose singular root owns
   according the
   corresponding DODAGID.  Local RPL Instances can be used for
   constructing DODAGs that may be used by future on-demand routing
   solutions that are outside of the scope of this document.  Global RPL
   Instances have one or more DODAGs metrics and are typically long-lived.  RPL
   divides constraints advertised in the RPLInstanceID space between global and local instances to
   allow for both coordinated DIO
   messages.  Upstream and unilateral allocation of
   RPLInstanceIDs.

   The definition Downstream metrics may be merged or
   advertised separately depending on the OF and provisioning of RPL instances are beyond the scope
   of this specification.  Those operations metrics.  When they
   are expected to be such advertised separately, it may happen that
   data packets coming from the outside set of DIO parents
   is different from the RPL network can
   unambiguously be associated to at least one RPL instance, and be
   safely routed over any instance that would match the packet.
   Information used to match set of DAO parents (a DAO parent is a packet node to a RPL instance can typically be
   taken from fields in the IPv6 header, like the flow label, TOS bits,
   or destination address.

   Control and data packets within RPL network
   which unicast DAO messages are tagged to
   unambiguously identify what RPL Instance they sent).  Yet, all are part of.

   Every RPL control message has a RPLInstanceID field.  Some RPL
   control messages, when referring DODAG parents
   with regards to a local RPLInstanceID as defined
   below, may also include a DODAGID.

   For data packets, the RPLInstanceID may be indicated in rules for Rank computation.

   The Objective Function itself is decoupled from the flow
   label routing metrics
   and constraints used by RPL.  Indeed, whereas the source of OF dictates rules
   such as DODAG parents selection, load balancing and so on, the packet.  If it is not, then it is inferred set of
   metrics and/or constraints used, and added by thus determine the RPL network ingress router in preferred
   path, are based on the RPL Hop-by-hop information carried within the DAG container
   option ([I-D.hui-6man-rpl-option]) as further described in
   Section 10.2

4.1.  RPL Instance ID

   A global RPLInstanceID MUST be unique to the whole LLN.  Mechanisms
   for allocating and provisioning global RPLInstanceID are out DIO messages.

   The set of scope
   for this document.  There can be up to 128 global instance in the
   whole network, supported link/node constraints and up 64 local instances per DODAGID.

   A global RPLinstanceID metrics is encoded specified
   in a RPLinstanceID field as
   follows:

        0 1 2 3 4 5 6 7
       +-+-+-+-+-+-+-+-+
       |0|     ID      |  Global RPLinstanceID in 0..127
       +-+-+-+-+-+-+-+-+

        Figure 3: RPL Instance ID field format for global instances

   A local RPLInstanceID is autoconfigured by [I-D.ietf-roll-routing-metrics].

   Example 1: Shortest path: path offering the shortest end-to-end
              delay.

   Example 2: Shortest Constrained path: the path that does not traverse
              any battery-operated node and that owns optimizes the
   DODAGID path
              reliability.

3.8.  Loop Avoidance

   RPL avoids creating loops when undergoing topology changes and it MUST be unique
   includes rank-based datapath validation mechanisms for that DODAGID. detecting
   loops when they do occur (see Section 11 for more details).  In
   practice, this means that case, the
   DODAGID MUST be RPL guarantees neither loop free path
   selection nor tight delay convergence times, but can detect and
   repair a valid address of the root that is used loop as an
   endpoint of all communications within that instance.

   A local RPLinstanceID is encoded in a RPLinstanceID field soon as follows:

        0 1 2 3 4 5 6 7
       +-+-+-+-+-+-+-+-+
       |1|D|   ID      |  Local RPLInstanceID in 0..63
       +-+-+-+-+-+-+-+-+

        Figure 4: RPL Instance ID field format for local instances

   The D flag in a Local RPLInstanceID it is always set to 0 in used.  RPL control
   messages.  It is used in data packets uses this loop detection to indicate whether the DODAGID
   is the source or the destination of the packet.  If
   ensure that packets make forward progress within the D flag DODAG Version
   and trigger repairs when necessary.

3.8.1.  Greediness and Instability

   A node is set greedy if it attempts to 1 then the destination address of the IPv6 packet MUST be the
   DODAGID.  If move deeper (increase Rank) in the D flag is clear then
   DODAG Version in order to increase the source address size of the IPv6
   packet MUST be the DODAGID.

5.  ICMPv6 parent set or
   improve some other metric.  Once a node has joined a DODAG Version,
   RPL Control Message

   This document defines disallows certain behaviors, including greediness, in order to
   prevent resulting instabilities in the RPL Control Message, DODAG Version.

   Suppose a new ICMPv6 message.
   A RPL Control Message node is identified by a code, willing to receive and composed of process a base
   that depends on the code, DIO message from a
   node in its own sub-DODAG, and in general a series of options.

   A RPL Control Message has the scope of node deeper than itself.
   In this case, a link.  The source address is possibility exists that a link local address.  The destination address feedback loop is either created,
   wherein two or more nodes continue to try and move in the DODAG
   Version while attempting to optimize against each other.  In some
   cases, this will result in instability.  It is for this reason that
   RPL
   routers multicast address or limits the cases where a link node may process DIO messages from
   deeper nodes to some forms of local address.  The RPL routers
   multicast address is a new address with repair.  This approach creates an
   'event horizon', whereby a requested value of
   FF02::1:A (to node cannot be confirmed by IANA).

   In accordance with [RFC4443], the RPL Control Message consists of influenced beyond some
   limit into an
   ICMPv6 header followed instability by a message body.  The message body is
   comprised of a message base and possibly a number the action of options as
   illustrated nodes that may be in Figure 5.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ its
   own sub-DODAG.

3.8.1.1.  Example: Greedy Parent Selection and Instability

         (A)                    (A)                    (A)
          |\                     |\                     |\
          |     Type `-----.              |     Code `-----.              |          Checksum `-----.
          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+        \             |        \             |
       .                             Base                              .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+        \
         (B)       (C)          (B)        \            |        (C)
                                  \        |            |
       .                           Option(s)                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+        /
                                   `-----. |            | .-----'
                                          \|            |/
                                          (C)          (B)

              -1-                    -2-                    -3-

                  Figure 5: RPL Control Message

   The 3: Greedy DODAG Parent Selection

   Figure 3 depicts a DODAG in 3 different configurations.  A usable
   link between (B) and (C) exists in all 3 configurations.  In
   Figure 3-1, Node (A) is a DODAG parent for Nodes (B) and (C).  In
   Figure 3-2, Node (A) is a DODAG parent for Nodes (B) and (C), and
   Node (B) is also a DODAG parent for Node (C).  In Figure 3-3, Node
   (A) is a DODAG parent for Nodes (B) and (C), and Node (C) is also a
   DODAG parent for Node (B).

   If a RPL Control message node is too greedy, in that it attempts to optimize for an ICMPv6 information message with a
   requested Type
   additional number of 155 (to be confirmed by IANA).

   The Code field identifies parents beyond its most preferred parents, then
   an instability can result.  Consider the type of RPL Control Message.  This
   document defines codes for DODAG illustrated in
   Figure 3-1.  In this example, Nodes (B) and (C) may most prefer Node
   (A) as a DODAG parent, but we will consider the following RPL Control Message types
   (all codes case when they are
   operating under the greedy condition that will try to optimize for 2
   parents.

   o  Let Figure 3-1 be confirmed by the IANA Section 18.2): initial condition.

   o  0x00:  Suppose Node (C) first is able to leave the DODAG Information Solicitation (Section 5.2)

   o  0x01: and rejoin at a
      lower rank, taking both Nodes (A) and (B) as DODAG Information Object (Section 5.3)

   o  0x02: Destination Advertisement Object (Section 5.4)
   o  0x03: Destination Advertisement Object Acknowledgment
      (Section 5.5)

   o  0x80: Secure parents as
      depicted in Figure 3-2.  Now Node (C) is deeper than both Nodes
      (A) and (B), and Node (C) is satisfied to have 2 DODAG Information Solicitation (Section 5.2.2) parents.

   o  0x81: Secure  Suppose Node (B), in its greediness, is willing to receive and
      process a DIO message from Node (C) (against the rules of RPL),
      and then Node (B) leaves the DODAG Information Object (Section 5.3.2) and rejoins at a lower rank,
      taking both Nodes (A) and (C) as DODAG parents.  Now Node (B) is
      deeper than both Nodes (A) and (C) and is satisfied with 2 DAG
      parents.

   o  0x82: Secure Destination Advertisement Object (Section 5.4.2)  Then Node (C), because it is also greedy, will leave and rejoin
      deeper, to again get 2 parents and have a lower rank then both of
      them.

   o  0x83: Secure Destination Advertisement Object Acknowledgment
      (Section 5.5.2)  Next Node (B) will again leave and rejoin deeper, to again get 2
      parents

   o  And again Node (C) leaves and rejoins deeper...

   o  0x8A: Consistency Check (Section 5.6)  The high order bit (0x80) of process will repeat, and the code denotes whether DODAG will oscillate between
      Figure 3-2 and Figure 3-3 until the RPL message
   has security enabled.  Secure RPL messages have a format nodes count to support
   confidentiality infinity and integrity, illustrated
      restart the cycle again.

   o  This cycle can be averted through mechanisms in Figure 6.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |     Code      |          Checksum             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                           Security                            .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                             Base                              .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                           Option(s)                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 6: Secure RPL Control Message

   The remainder of this section describes the currently defined RPL
   Control Message Base formats followed by the currently defined RPL
   Control Message Options.

5.1.  RPL Security Fields

   Each RPL message has RPL:

      *  Nodes (B) and (C) stay at a secure version.  The secure versions provide
   integrity rank sufficient to attach to their
         most preferred parent (A) and replay protection as well as optional confidentiality don't go for any deeper (worse)
         alternate parents (Nodes are not greedy)

      *  Nodes (B) and delay protection.  Because security covers the base message as
   well as options, in secured (C) do not process DIO messages from nodes deeper
         than themselves (because such nodes are possibly in their own
         sub-DODAGs)

3.8.2.  DODAG Loops

   A DODAG loop may occur when a node detaches from the security information lies
   between the checksum DODAG and base, as shown
   reattaches to a device in Figure Figure 6.

   The format its prior sub-DODAG.  This may happen in
   particular when DIO messages are missed.  Strict use of the security section is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |C|T| Rsrvd |Sec|KIM|Rsrvd| LVL |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
       |                            Counter                            |
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                  Message Authentication Code                  .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                        Key Identifier                         .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 7: Security Section

   All fields are considered as packet payload from a security
   processing perspective.  The exact placement and format DODAG
   Version Number can eliminate this type of message
   integrity/authentication codes has not yet been determined.

   Use loop, but this type of loop
   may possibly be encountered when using some local repair mechanisms.

   For example, consider the Security section is further detailed in Section 17.

   Security Control Field:  The Security Control Field has one flag and
         three fields:

         Counter Compression (C):  If the Counter Compression flag is
               set then the Counter field is compressed local repair mechanism that allows a node
   to detach from 4 bytes
               into 1 byte.  If the Counter Compression flag is clear
               then the Counter field is 4 bytes DODAG, advertise a rank of INFINITE_RANK (in order
   to poison its routes / inform its sub-DODAG), and uncompressed.

         Counter is Time (T):  If the Counter is Time flag is set then to re-attach
   to the Counter field is DODAG.  In that case the node may in some cases re-attach to
   its own prior-sub-DODAG, causing a timestamp.  If DODAG loop, because the flag is cleared
               then poisoning
   may fail if the Counter is an incrementing counter.  Section 9.4
               describes INFINITE_RANK advertisements are lost in the details of LLN
   environment.  (In this case the 'T' flag and Counter field.

         Security Mode (Sec):  The security algorithm field specifies
               what security mode rank-based datapath validation
   mechanisms would eventually detect and algorithms the network uses.
               Supported values trigger correction of this field are as follows:

                         +----+-----+-------------------+
                         | ID | Sec |     Algorithm     |
                         +----+-----+-------------------+
                         |  0 |  00 | CCM* with AES-128 |
                         |  1 |  01 |      Reserved     |
                         |  2 |  10 |      Reserved     |
                         |  3 |  11 |      Reserved     |
                         +----+-----+-------------------+

                           Security Mode (Sec) Encoding

         Key Identifier Mode (KIM):  The Key Identifier Mode field
               indicates whether the key used for packet protection is
               determined implicitly or explicitly
   loop)

3.8.3.  DAO Loops

   A DAO loop may occur when the parent has a route installed upon
   receiving and indicates processing a DAO message from a child, but the
               particular representation child
   has subsequently cleaned up the related DAO state.  This loop happens
   when a No-Path (a DAO message that invalidates a previously announced
   prefix) was missed and persists until all state has been cleaned up.
   RPL includes an optional mechanism to acknowledge DAO messages, which
   may mitigate the impact of a single DAO message being missed.  RPL
   includes loop detection mechanisms that may mitigate the Key Identifier field.
               The Key Identifier Mode impact of
   DAO loops and trigger their repair.

4.  Traffic Flows Supported by RPL

   RPL supports three basic traffic flows: Multipoint-to-Point (MP2P),
   Point-to-Multipoint (P2MP), and Point-to-Point (P2P).

4.1.  Multipoint-to-Point Traffic

   Multipoint-to-Point (MP2P) is set one a dominant traffic flow in many LLN
   applications ([RFC5867], [RFC5826], [RFC5673], [RFC5548]).  The
   destinations of MP2P flows are designated nodes that have some
   application significance, such as providing connectivity to the non-reserved
               values from the table below:

          +------+-----+-----------------------------+------------+
          | Mode | KIM |           Meaning           |    Key     |
          |      |     |                             | Identifier |
          |      |     |                             |   Length   |
          |      |     |                             |  (octets)  |
          +------+-----+-----------------------------+------------+
          |  0   | 00  | Group key used.             |     1      |
          |      |     | Key determined
   larger Internet or core private IP network.  RPL supports MP2P
   traffic by Key Index |            |
          |      |     | field.                      |            |
          |      |     |                             |            |
          |      |     | Key Source is not present.  |            |
          |      |     | Key Index allowing MP2P destinations to be reached via DODAG roots.

4.2.  Point-to-Multipoint Traffic

   Point-to-multipoint (P2MP) is present.       |            |
          +------+-----+-----------------------------+------------+
          |  1   | 01  | Per-pair key used.          |     0      |
          |      |     | Key determined a traffic pattern required by several
   LLN applications ([RFC5867], [RFC5826], [RFC5673], [RFC5548]).  RPL
   supports P2MP traffic by using a destination advertisement mechanism
   that provisions Down routes toward destinations (prefixes, addresses,
   or multicast groups), and away from roots.  Destination
   advertisements can update routing tables as the underlying DODAG
   topology changes.

4.3.  Point-to-Point Traffic

   RPL DODAGs provide a basic structure for point-to-point (P2P)
   traffic.  For a RPL network to support P2P traffic, a root must be
   able to route packets to a destination.  Nodes within the network may
   also have routing tables to destinations.  A packet flows towards a
   root until it reaches an ancestor that has a known route to the
   destination.  As pointed out later in this document, in the most
   constrained case (when nodes cannot store routes), that common
   ancestor may be the DODAG root.  In other cases it may be a node
   closer to both the source    |            |
          |      |     | and destination.

   RPL also supports the case where a P2P destination of packet.  |            |
          |      |     |                             |            |
          |      |     | Key Source is not present.  |            |
          |      |     | Key Index is not present.   |            |
          +------+-----+-----------------------------+------------+
          |  2   | 10  | Group key used.             |     9      |
          |      |     | Key determined by Key Index |            |
          |      |     | and Key Source Identifier.  |            |
          |      |     |                             |            |
          |      |     | Key Source is present.      |            |
          |      |     | Key Index is present.       |            |
          +------+-----+-----------------------------+------------+
          |  3   | 11  | Node's signature key used.  |    0/9     |
          |      |     | If packet is encrypted,     |
          |      |     | group key used. Group key   |            |
          |      |     | determined by Key Index a 'one-hop'
   neighbor.

   RPL neither specifies nor precludes additional mechanisms for
   computing and |            |
          |      |     | Key Source Identifier.      |            |
          |      |     |                             |            |
          |      |     | Key Source installing potentially more optimal routes to support
   arbitrary P2P traffic.

5.  RPL Instance

   Within a given LLN, there may be present.  |            |
          |      |     | Key Index multiple, logically independent RPL
   instances.  A RPL node may be present.   |            |
          +------+-----+-----------------------------+------------+

                          Key Identifier Mode (KIM) Encoding

         Security Level (LVL):  The Security Level field indicates the
               provided packet protection. belong to multiple RPL instances, and may
   act as a router in some and as a leaf in others.  This value can be adapted on document
   describes how a per-packet basis single instance behaves.

   There are two types of RPL Instances: local and allows global.  RPL divides
   the RPLInstanceID space between Global and Local instances to allow
   for varying levels both coordinated and unilateral allocation of data
               authenticity and, optionally, for data confidentiality.
               The KIM field indicates whether signatures RPLInstanceIDs.
   Global RPL Instances are used. coordinated, have one or more DODAGs, and
   are typically long-lived.  Local RPL Instances are always a single
   DODAG whose singular root owns the corresponding DODAGID and
   allocates the Local RPLInstanceID in a unilateral manner.  Local RPL
   Instances can be used, for example, for constructing DODAGs in
   support of a future on-demand routing solution.  The
               Security Level mode of
   operation of Local RPL Instances is set to one outside of the non-reserved values scope of this
   document and may be described in the table below:

                     +---------------------------+--------------------+
                     |      Without Signatures   |   With Signatures  |
          +----+-----+--------------------+------+--------------+-----+
          | ID | LVL |     Attributes     | Auth |  Attributes  | Sig |
          |    |     |                    | Len  |              | Len |
          +----+-----+--------------------+------+--------------+-----+
          |  0 | 000 |      Reserved      | N/A  |   Reserved   | N/A |
          |  1 | 001 |       MAC-32       |  4   |    Sign-32   | 40  |
          |  2 | 010 |       MAC-64       |  8   |    Sign-64   | 44  |
          |  3 | 011 |      Reserved      | N/A  |   Sign-128   | 52  |
          |  4 | 100 |      Reserved      | N/A  |   Reserved   | N/A |
          |  5 | 101 |     ENC-MAC-32     |  4   |  ENC-Sign-32 | 40  |
          |  6 | 110 |     ENC-MAC-64     |  8   |  ENC-Sign-64 | 44  |
          |  7 | 111 |      Reserved      | N/A  | ENC-Sign-128 | 52  |
          +----+-----+--------------------+------+-------------+------+

                         Security Level (LVL) Encoding

   Counter: other companion specifications.

   The Counter field indicates the non-repeating value (nonce)
         used with the cryptographic mechanism that implements packet
         protection definition and allows for provisioning of RPL instances are beyond the provision scope
   of semantic security.
         This value is compressed from 4 octets this specification.  Those operations are expected to 1 octet if be such that
   data packets coming from the
         Counter Compression field outside of the Security Control Field is set RPL network can
   unambiguously be associated to one.

   Message Authentication Code:  The Message Authentication Code field
         contains at least one RPL instance, and be
   safely routed over any instance that would match the packet.
   Information used to match a cryptographic MAC.  The length of packet to a RPL instance can typically be
   taken from fields in the MAC is IPv6 header, like the flow label,
   differentiated services (DS) field, or destination address.

   Control and data packets within RPL network are tagged to
   unambiguously identify what RPL Instance they are part of.

   Every RPL control message has a RPLInstanceID field.  Some RPL
   control messages, when referring to a local RPLInstanceID as defined
         by
   below, may also include a combination of DODAGID.

   Data packets that flow within the LVL RP network expose the RPLInstanceID
   in the RPL option that is specified in [I-D.ietf-6man-rpl-option],
   and Sec fields: it can be 0, 4, or
         8 octets long.  In further described in Section 11.2.  For data packets coming from
   outside the case of Security Modes where RPL network, the MAC RPLInstanceID is
         computed as part of determined by the ciphertext (as RPL
   network ingress router and placed in Security Mode 0,
         CCM*), the MAC field RPL option that is zero bytes long.

   Key Identifier:  The Key Identifier field indicates which key was
         used added to protect
   the packet.  This field provides various levels
         of granularity of packet protection, including peer-to-peer
         keys, group keys,

5.1.  RPL Instance ID

   A global RPLInstanceID MUST be unique to the whole LLN.  Mechanisms
   for allocating and signature keys.  This field provisioning global RPLInstanceID are out of scope
   for this document.  There can be up to 128 global instance in the
   whole network.  Local instances are always used in conjunction with a
   DODAGID (which is
         represented as indicated either given explicitly or implicitly in some
   cases), and up 64 local instances per DODAGID can be supported.
   Local instances are allocated and managed by the Key Identifier Mode field and node that owns the
   DODAGID, without any explicit coordination with other nodes, as
   further detailed below.

   A global RPLinstanceID is formatted encoded in a RPLinstanceID field as
   follows:

        0 1 2 3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
       +-+-+-+-+-+-+-+-+
       |0|     ID      |  Global RPLinstanceID in 0..127
       +-+-+-+-+-+-+-+-+

        Figure 4: RPL Instance ID field format for global instances

   A local RPLInstanceID is autoconfigured by the node that owns the
   DODAGID and it MUST be unique for that DODAGID.  The DODAGID used to
   configure the local RPLInstanceID MUST be a reachable IPv6 address of
   the node, and MUST be used as an endpoint of all communications
   within that local instance.

   A local RPLinstanceID is encoded in a RPLinstanceID field as follows:

        0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                          Key Source                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |
       +-+-+-+-+-+-+-+-+
       |1|D|   ID      |
       .                           Key Index                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  Local RPLInstanceID in 0..63
       +-+-+-+-+-+-+-+-+

        Figure 8: Key Identifier

         Key Source: 5: RPL Instance ID field format for local instances

   The Key Source field, when present, indicates the
               logical identifier of the originator of D flag in a group key.
               When present this field Local RPLInstanceID is 8 bytes always set to 0 in length.

         Key Index:  The Key Index field, when present, allows unique
               identification of different keys with the same
               originator. RPL control
   messages.  It is the responsibility of each key
               originator to make sure that actively used keys that it
               issues have distinct key indices and that all key indices
               have a value unequal in data packets to 0x00.  Value 0x00 indicate whether the DODAGID
   is reserved for
               a pre-installed, shared key.  When present this field the source or the destination of the packet.  If the D flag is set
   to 1 byte in length.

   Unassigned bits then the destination address of the Security section are reserved.  They IPv6 packet MUST be
   set to zero on transmission and the
   DODAGID.  If the D flag is cleared then the source address of the
   IPv6 packet MUST be ignored on reception.

5.2. the DODAGID.

   For example, consider a node A that is the DODAG Information Solicitation (DIS) Root of a local RPL
   Instance, and has allocated a local RPLInstanceID.  By definition,
   all traffic traversing that local RPL Instance will either originate
   or terminate at node A. The DODAG Information Solicitation (DIS) message may DODAGID in this case will be used the
   reachable IPv6 address of node A, and all traffic will contain the
   address of node A, thus the DODAGID, in either the source or
   destination address.  Thus the Local RPLInstanceID may indicate that
   the DODAGID is equivalent to
   solicit a DODAG Information Object from either the source address or the
   destination address by setting the D flag appropriately.

6.  ICMPv6 RPL Control Message

   This document defines the RPL Control Message, a new ICMPv6 message.
   A RPL node.  Its use Control Message is
   analogous to identified by a code, and composed of a base
   that depends on the code, and a series of options.

   A RPL Control Message has the scope of a Router Solicitation as specified in IPv6
   Neighbor Discovery; link.  The source address is
   a node may use DIS to probe its neighborhood for
   nearby DODAGs.  Section 7.3 describes how link local address.  The destination address is either the RPL
   nodes respond to multicast address or a DIS.

5.2.1.  Format unicast address.  The all-RPL-nodes
   multicast address is a new address with a requested value of FF02::1A
   (to be confirmed by IANA).

   In accordance with [RFC4443], the DIS Base Object RPL Control Message consists of an
   ICMPv6 header followed by a message body.  The message body is
   comprised of a message base and possibly a number of options as
   illustrated in Figure 6.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Reserved     Type      |   Option(s)...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     Code      |          Checksum             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                             Base                              .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                           Option(s)                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 9: 6: RPL Control Message

   The DIS Base Object

   Unassigned bits of the DIS Base are reserved.  They MUST be set to
   zero on transmission and MUST be ignored on reception.

5.2.2.  Secure DIS

   A Secure DIS RPL Control message follows the format in Figure Figure 6, where the
   base format is the DIS an ICMPv6 information message shown in Figure Figure 9.

5.2.3.  DIS Options with a
   requested Type of 155 (to be confirmed by IANA).

   The DIS message MAY carry valid options.

   This specification allows for the DIS message to carry Code field identifies the following
   options:
      0x00 Pad1
      0x01 PadN
      0x07 Solicited type of RPL Control Message.  This
   document defines codes for the following RPL Control Message types
   (all codes are to be confirmed by IANA Section 19.2):

   o  0x00: DODAG Information

5.3. Solicitation (Section 6.2)

   o  0x01: DODAG Information Object (DIO)

   The (Section 6.3)

   o  0x02: Destination Advertisement Object (Section 6.4)
   o  0x03: Destination Advertisement Object Acknowledgment
      (Section 6.5)

   o  0x80: Secure DODAG Information Solicitation (Section 6.2.2)

   o  0x81: Secure DODAG Information Object carries information that allows a node
   to discover a (Section 6.3.2)

   o  0x82: Secure Destination Advertisement Object (Section 6.4.2)

   o  0x83: Secure Destination Advertisement Object Acknowledgment
      (Section 6.5.2)

   o  0x8A: Consistency Check (Section 6.6)

   The high order bit (0x80) of the code denotes whether the RPL Instance, learn its configuration parameters,
   select message
   has security enabled.  Secure RPL messages have a DODAG parent set, format to support
   confidentiality and maintain the upward routing topology.

5.3.1.  Format of the DIO Base Object integrity, illustrated in Figure 7.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | RPLInstanceID     Type      |    Version     Code      |             Rank          Checksum             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |G|0| MOP
       | Prf                                                               |     DTSN
       .                           Security                            .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Reserved                                                               |
       .                             Base                              .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       .                           Option(s)                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 7: Secure RPL Control Message

   The remainder of this section describes the currently defined RPL
   Control Message Base formats followed by the currently defined RPL
   Control Message Options.

6.1.  RPL Security Fields

   Each RPL message has a secure variant.  The secure variants provide
   integrity and replay protection as well as optional confidentiality
   and delay protection.  Because security covers the base message as
   well as options, in secured messages the security information lies
   between the checksum and base, as shown in Figure 7.

   The level of security and the algorithms in use are indicated in the
   protocol messages as described below:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |T|    Level    |   Algorithm   |
       +                            DODAGID                            + KIM |Reserved |     Flags     |
       +                                                               +
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Counter                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Option(s)...
       +-+-+-+-+-+-+-+-+                                                               |
       .                        Key Identifier                         .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 10: The DIO Base Object 8: Security Section

   Message authentication codes (MACs) and signatures cover the entire
   ICMPv6 RPL message, while encryption starts after the Security
   section.  Use of the Security section is further detailed in
   Section 18.

   Security Control Field:  The DAG Security Control Field has three flags one flag and two
         three fields:

         Grounded (G):  The Grounded (G) flag indicates whether the
               DODAG advertised can satisfy the application-defined
               goal.

         Counter is Time (T):  If the Counter is Time flag is set, set then
               the DODAG Counter field is grounded. a timestamp.  If the flag is cleared, cleared
               then the DODAG Counter is floating.

         Mode an incrementing counter.
               Section 10.5 describes the details of Operation (MOP): the 'T' flag and
               Counter field.

         Security Level (Level):  The Mode of Operation (MOP) Security Level field
               identifies indicates the mode of operation
               provided packet protection.  This value can be adapted on
               a per-packet basis and allows for varying levels of the RPL Instance as
               administratively provisioned at data
               authenticity and, optionally, for data confidentiality.
               The KIM field indicates whether signatures are used and distributed by
               the
               DODAG Root.  All nodes who join meaning of the DODAG must be able Level field.  The Security Level is
               set to
               honor one of the MOP in order to fully participate as a router,
               or else they must only join as a leaf.  MOP is encoded as non-reserved values in the table tables
               below:

               +-----+-------------------------------------------------+

                      +---------------------------+
                      | MOP         KIM=0,1,2         | Meaning
              +-------+--------------------+------+
              |
               +-----+-------------------------------------------------+  LVL  | 000     Attributes     | No downward routes maintained by RPL MAC  |
              | 001       | Non storing mode                    | Len  | 010
              +-------+--------------------+------+
              | Storing without multicast support   0   |       MAC-32       | 011  4   | Storing with multicast support
              |   1   |     ENC-MAC-32     |  4   |
              |   2   | All other values are reserved       MAC-64       |
               +-----+-------------------------------------------------+

               A value of 000 indicates that destination advertisement
               messages are disabled and the DODAG maintains only upward
               routes

                           Mode of Operation (MOP)  8   |
              |   3   |     ENC-MAC-64     |  8   |
              | 4-127 |      Reserved      | N/A  |
              +-------+--------------------+------+

                            +---------------------+
                            |        KIM=3        |
                    +-------+---------------+-----+
                    |  LVL  |  Attributes   | Sig |
                    |       |               | Len |
                    +-------+---------------+-----+
                    |   0   |   Sign-3072   | 384 |
                    |   1   | ENC-Sign-3072 | 384 |
                    | 2-127 |   Reserved    | N/A |
                    +-------+---------------+-----+

                        Figure 9: Security Level (LVL) Encoding

         DODAGPreference (Prf):  A 3-bit unsigned integer

               The MAC attribute indicates that defines
               how preferable the root message has a
               Message Authentication Code of this DODAG is compared to
               other DODAG roots within the instance.  DAGPreference
               ranges from 0x00 (least preferred) to 0x07 (most
               preferred). specified length.  The default is 0 (least preferred).
               Section 7.2 describes how DAGPreference affects DIO
               processing.

   Version Number:  8-bit unsigned integer set by the DODAG root.
         Section 7.2 describes the rules for version numbers and how
         they affect DIO processing.

   Rank: 16-bit unsigned integer indicating the DODAG rank of the node
         sending the DIO message.  Section 7.2 describes how Rank is set
         and how it affects DIO processing.

   RPLInstanceID:  8-bit field set by the DODAG root that
               ENC attribute indicates
         which RPL Instance that the DODAG message is part of.

   Destination Advertisement Trigger Sequence Number (DTSN):  8-bit
         unsigned integer set by the node issuing the DIO message. encrypted.
               The
         Destination Advertisement Trigger Sequence Number (DTSN) flag
         is used as part of Sign attribute indicates that the procedure to maintain downward routes.
         The details of this process are described in Section 8.

   DODAGID:  128-bit unsigned integer set by a DODAG root which uniquely
         identifies message has a DODAG.  Possibly derived from the IPv6 address
               signature of the DODAG root.

   Unassigned bits of specified length.

         Security Algorithm (Algorithm):  The Security Algorithm field
               specifies the DIO Base are reserved.  They MUST be set to
   zero on transmission encryption, MAC, and MUST be ignored on reception.

5.3.2.  Secure DIO

   A Secure DIO message follows signature scheme the format in Figure
               network uses.  Supported values of this field are as
               follows:

    +-----------+-------------------+------------------------+
    | Algorithm |  Encryption/MAC   |        Signature       |
    +-----------+-------------------+------------------------+
    |     0     | CCM* with AES-128 |      RSA with SHA2     |
    |   1-255   |      Reserved     |         Reserved       |
    +-------+-------------------+----------------------------+

                  Figure 6, where the
   base format is 10: Security Algorithm (Algorithm) Encoding

               Section 10.9 describes the DIS message shown algorithms in Figure Figure 10.

5.3.3.  DIO Options greater detail.

         Key Identifier Mode (KIM):  The DIO message MAY carry valid options.

   This specification allows for the DIO message to carry Key Identifier Mode field
               indicates whether the following
   options:
      0x00 Pad1
      0x01 PadN
      0x02 Metric Container
      0x03 Routing Information
      0x04 DODAG Configuration
      0x08 Prefix Information

5.4.  Destination Advertisement Object (DAO)

   The Destination Advertisement Object (DAO) is key used to propagate
   destination information upwards along for packet protection is
               determined implicitly or explicitly and indicates the DODAG.
               particular representation of the Key Identifier field.
               The DAO message Key Identifier Mode is
   unicast by set one of the child to non-reserved
               values from the selected parent(s).  The DAO message table below:

          +------+-----+-----------------------------+------------+
          | Mode | KIM |           Meaning           |    Key     |
          |      |     |                             | Identifier |
          |      |     |                             |   Length   |
          |      |     |                             |  (octets)  |
          +------+-----+-----------------------------+------------+
          |  0   | 00  | Group key used.             |     1      |
          |      |     | Key determined by Key Index |            |
          |      |     | field.                      |            |
          |      |     |                             |            |
          |      |     | Key Source is not present.  |            |
          |      |     | Key Index is present.       |            |
          +------+-----+-----------------------------+------------+
          |  1   | 01  | Per-pair key used.          |     0      |
          |      |     | Key determined by source    |            |
          |      |     | and destination of packet.  |            |
          |      |     |                             |            |
          |      |     | Key Source is not present.  |            |
          |      |     | Key Index is not present.   |            |
          +------+-----+-----------------------------+------------+
          |  2   | 10  | Group key used.             |     9      |
          |      |     | Key determined by Key Index |            |
          |      |     | and Key Source Identifier.  |            |
          |      |     |                             |            |
          |      |     | Key Source is present.      |            |
          |      |     | Key Index is present.       |            |
          +------+-----+-----------------------------+------------+
          |  3   | 11  | Node's signature key used.  |    0/9     |
          |      |     | If packet is encrypted,     |
          |      |     | it uses a group key, Key    |            |
          |      |     | Index and Key Source        |            |
          |      |     | specify key.                |            |
          |      |     |                             |            |
          |      |     | Key Source may
   optionally, upon explicit request be present.  |            |
          |      |     | Key Index may be present.   |            |
          +------+-----+-----------------------------+------------+

                         Figure 11: Key Identifier Mode (KIM)
                                       Encoding

               In Mode 3 (KIM=11), the presence or error, absence of the Key
               Source and Key Identifier depends on the Security Level
               (LVL) described below.  If the Security Level indicates
               there is encryption, then the fields are present; if it
               indicates there is no encryption, then the fields are not
               present.

   Reserved:  5-bit unused field.  The field MUST be acknowledged initialized to zero
         by the
   parent sender and MUST be ignored by the receiver.

   Flags:  8-bit unused field reserved for flags.  The field MUST be
         initialized to zero by the sender and MUST be ignored by the
         receiver.

   Counter:  The Counter field indicates the non-repeating 4-octet value
         (nonce) used with a Destination Advertisement Acknowledgement (DAO-ACK)
   message back the cryptographic mechanism that implements
         packet protection and allows for the provision of semantic
         security.

   Key Identifier:  The Key Identifier field indicates which key was
         used to protect the child.

5.4.1.  Format packet.  This field provides various levels
         of granularity of packet protection, including peer-to-peer
         keys, group keys, and signature keys.  This field is
         represented as indicated by the DAO Base Object Key Identifier Mode field and
         is formatted as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | RPLInstanceID |K|D|         Reserved          | DAOSequence                                                               |
       .                          Key Source                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            DODAGID*                           +
       |                                                               |
       +                                                               +
       |                                                               |
       .                           Key Index                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Option(s)...
       +-+-+-+-+-+-+-+-+

                            Figure 11: 12: Key Identifier

         Key Source:  The DAO Base Object

   RPLInstanceID:  8-bit field indicating the topology instance
         associated with Key Source field, when present, indicates the DODAG, as learned from
               logical identifier of the DIO.

   K: originator of a group key.
               When present this field is 8 bytes in length.

         Key Index:  The 'K' flag indicates that Key Index field, when present, allows unique
               identification of different keys with the parent same
               originator.  It is expected the responsibility of each key
               originator to send a
         DAO-ACK back.

   D:    The 'D' flag indicates make sure that the DODAGID field actively used keys that it
               issues have distinct key indices and that all key indices
               have a value unequal to 0x00.  Value 0x00 is present.  This
         flag MUST be set when reserved for
               a local RPLInstanceID pre-installed, shared key.  When present this field is used.

   DAOSequence:  Incremented at each unique DAO message, echoed
               1 byte in length.

   Unassigned bits of the
         DAO-ACK message.

   DODAGID (optional):  128-bit unsigned integer Security section are reserved.  They MUST be
   set by a to zero on transmission and MUST be ignored on reception.

6.2.  DODAG root
         which uniquely identifies Information Solicitation (DIS)

   The DODAG Information Solicitation (DIS) message may be used to
   solicit a DODAG.  This field is only present
         when the 'D' flag is set.  This field is typically only present
         when DODAG Information Object from a local RPLInstanceID RPL node.  Its use is in use, in order
   analogous to identify the
         DODAGID that is associated with the RPLInstanceID.  When of a
         global RPLInstanceID is Router Solicitation as specified in IPv6
   Neighbor Discovery; a node may use this DIS to probe its neighborhood for
   nearby DODAGs.  Section 8.3 describes how nodes respond to a DIS.

6.2.1.  Format of the DIS Base Object

        0                   1                   2
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Flags     |   Reserved    |   Option(s)...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 13: The DIS Base Object

   Flags:  8-bit unused field need not reserved for flags.  The field MUST be present.
         initialized to zero by the sender and MUST be ignored by the
         receiver.

   Reserved:  8-bit unused field.  The field MUST be initialized to zero
         by the sender and MUST be ignored by the receiver.

   Unassigned bits of the DAO DIS Base are reserved.  They MUST be set to
   zero on transmission and MUST be ignored on reception.

5.4.2.

6.2.2.  Secure DAO DIS

   A Secure DAO DIS message follows the format in Figure Figure 6, 7, where the base
   format is the DAO DIS message shown in Figure Figure 11.

5.4.3.  DAO 13.

6.2.3.  DIS Options

   The DAO DIS message MAY carry valid options.

   This specification allows for the DAO DIS message to carry the following
   options:

      0x00 Pad1
      0x01 PadN
      0x05 RPL Target
      0x06 Transit
      0x07 Solicited Information

   A special case of the DAO message, termed a No-Path, is used to clear
   downward routing state that has been provisioned through DAO
   operation.  The No-Path carries a RPL Transit

6.3.  DODAG Information option,
   which identifies the destination to which the DAO is associated, with
   a lifetime of 0x00000000 to indicate a loss of reachability.

5.5.  Destination Advertisement Object Acknowledgement (DAO-ACK) (DIO)

   The DAO-ACK message is sent as a unicast packet by DODAG Information Object carries information that allows a DAO parent in
   response node
   to discover a unicast DAO message from RPL Instance, learn its configuration parameters,
   select a child.

5.5.1. DODAG parent set, and maintain the DODAG.

6.3.1.  Format of the DAO-ACK DIO Base Object

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | RPLInstanceID |D|  Reserved |Version Number | DAOSequence             Rank              |   Status
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |G|0| MOP | Prf |     DTSN      |  Flags        |  Reserved     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            DODAGID*                            DODAGID                            +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Option(s)...
       +-+-+-+-+-+-+-+-+

                      Figure 12: 14: The DAO ACK DIO Base Object

   RPLInstanceID:  8-bit field indicating the topology instance
         associated with the DODAG, as learned from the DIO.

   D:

   Control Field:  The 'D' DAG Control Field has three flags and two fields:

         Grounded (G):  The Grounded (G) flag indicates that whether the DODAGID field
               DODAG advertised can satisfy the application-defined
               goal.  If the flag is present.  This
         would typically only be set when a local RPLInstanceID set, the DODAG is used.

   DAOSequence:  Incremented grounded.  If the
               flag is cleared, the DODAG is floating.

         Mode of Operation (MOP):  The Mode of Operation (MOP) field
               identifies the mode of operation of the RPL Instance as
               administratively provisioned at each DAO message from and distributed by the
               DODAG Root.  All nodes who join the DODAG must be able to
               honor the MOP in order to fully participate as a given child,
         echoed router,
               or else they must only join as a leaf.  MOP is encoded as
               in the DAO-ACK figure below:

               +-----+-------------------------------------------------+
               | MOP | Meaning                                         |
               +-----+-------------------------------------------------+
               | 000 | No downward routes maintained by RPL            |
               | 001 | Non storing mode                                |
               | 010 | Storing without multicast support               |
               | 011 | Storing with multicast support                  |
               |     |                                                 |
               |     | All other values are reserved                   |
               +-----+-------------------------------------------------+

               A value of 000 indicates that destination advertisement
               messages are disabled and the parent.  The DAOSequence serves in DODAG maintains only upward
               routes

                      Figure 15: Mode of Operation (MOP) Encoding

         DODAGPreference (Prf):  A 3-bit unsigned integer that defines
               how preferable the parent-child communication and root of this DODAG is not compared to be confused with
               other DODAG roots within the Transit Information option Sequence that instance.  DAGPreference
               ranges from 0x00 (least preferred) to 0x07 (most
               preferred).  The default is associated 0 (least preferred).
               Section 8.2 describes how DAGPreference affects DIO
               processing.

   Version Number:  8-bit unsigned integer set by the DODAG root to a
         given target down the DODAG.

   Status:  Indicates
         DODAGVersionNumber.  Section 8.2 describes the completion. 0 is unqualified acceptance, above
         128 are rejection code rules for DODAG
         Version numbers and how they affect DIO processing.

   Rank: 16-bit unsigned integer indicating that the DODAG rank of the node should select
         an alternate parent.

   DODAGID (optional):  128-bit unsigned integer
         sending the DIO message.  Section 8.2 describes how Rank is set
         and how it affects DIO processing.

   RPLInstanceID:  8-bit field set by a the DODAG root that indicates
         which uniquely identifies a DODAG.  This field RPL Instance the DODAG is only present
         when part of.

   Destination Advertisement Trigger Sequence Number (DTSN):  8-bit
         unsigned integer set by the 'D' node issuing the DIO message.  The
         Destination Advertisement Trigger Sequence Number (DTSN) flag
         is set.  This field is typically only present
         when a local RPLInstanceID is in use, used as part of the procedure to maintain downward routes.
         The details of this process are described in order Section 9.

   Flags:  8-bit unused field reserved for flags.  The field MUST be
         initialized to identify zero by the
         DODAGID that is associated with sender and MUST be ignored by the RPLInstanceID.  When a
         global RPLInstanceID is in use this
         receiver.

   Reserved:  8-bit unused field.  The field need not MUST be present. initialized to zero
         by the sender and MUST be ignored by the receiver.

   DODAGID:  128-bit IPv6 address set by a DODAG root which uniquely
         identifies a DODAG.  The DODAGID MUST be a routable IPv6
         address belonging to the DODAG root.

   Unassigned bits of the DAO-ACK DIO Base are reserved.  They MUST be set to
   zero on transmission and MUST be ignored on reception.

5.5.2.

6.3.2.  Secure DAO-ACK DIO

   A Secure DAO-ACK DIO message follows the format in Figure Figure 6, 7, where the base
   format is the DAO-ACK DIO message shown in Figure Figure 12.

5.5.3.  DAO-ACK 14.

6.3.3.  DIO Options

   The DIO message MAY carry valid options.

   This specification does not define any options to be carried by allows for the
   DAO-ACK message.

5.6.  Consistency Check (CC)

   The CC DIO message to carry the following
   options:
      0x00 Pad1
      0x01 PadN
      0x02 Metric Container
      0x03 Routing Information
      0x04 DODAG Configuration
      0x08 Prefix Information

6.4.  Destination Advertisement Object (DAO)

   The Destination Advertisement Object (DAO) is used to check secure propagate
   destination information upwards along the DODAG.  In storing mode the
   DAO message counters and issue
   challenge/responses.  A CC is unicast by the child to the selected parent(s).  In
   non-storing mode the DAO message MUST is unicast to the DODAG root.  The
   DAO message may optionally, upon explicit request or error, be sent as
   acknowledged by its destination with a secured RPL
   message.

   A CC Destination Advertisement
   Acknowledgement (DAO-ACK) message (request or response) MUST NOT set back to the 'C' bit sender of the
   security section: CC messages always have full counters.

5.6.1. DAO.

6.4.1.  Format of the CC DAO Base Object
        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | RPLInstanceID |R| |K|D|   Flags   |   Reserved    |            Nonce DAOSequence   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            DODAGID                            DODAGID*                           +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Destination Counter                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Option(s)...
       +-+-+-+-+-+-+-+-+

   The '*' denotes that the DODAGID is not always present, as described
   below.

                      Figure 13: 16: The CC DAO Base Object

   RPLInstanceID:  8-bit field indicating the topology instance
         associated with the DODAG, as learned from the DIO.

   R:

   K:    The 'R' 'K' flag indicates whether that the CC message recipient is expected to send a response.  A
         message with the 'R'
         DAO-ACK back.  (See Section 9.3

   D:    The 'D' flag cleared is a request; a message with indicates that the 'R' DODAGID field is present.  This
         flag MUST be set is when a response.  A CC message with the R bit
         set local RPLInstanceID is used.

   Flags:  6-bit unused field reserved for flags.  The field MUST NOT compress be
         initialized to zero by the security Counter field: sender and MUST be ignored by the C bit of
         receiver.

   Reserved:  8-bit unused field.  The field MUST be initialized to zero
         by the security section sender and MUST be 0.

   Nonce:  16-bit unsigned integer set ignored by a CC request.  The
         corresponding CC response includes the same nonce value as receiver.

   DAOSequence:  Incremented at each unique DAO message from a node and
         echoed in the
         request.

   Destination Counter:  32-bit DAO-ACK message.

   DODAGID (optional):  128-bit unsigned integer value indicating the
         sender's estimate of the destination's current security Counter
         value.  If the sender does not have an estimate, it SHOULD set by a DODAG root
         which uniquely identifies a DODAG.  This field is only present
         when the Destination Counter 'D' flag is set.  This field is typically only present
         when a local RPLInstanceID is in use, in order to zero. identify the
         DODAGID that is associated with the RPLInstanceID.  When a
         global RPLInstanceID is in use this field need not be present.

   Unassigned bits of the CC DAO Base are reserved.  They MUST be set to
   zero on transmission and MUST be ignored on reception.

   The Destination Counter value allows new or recovered nodes to
   resynchronize through CC

6.4.2.  Secure DAO

   A Secure DAO message exchanges.  This is important to
   ensure that a Counter value is not repeated for a given security key
   even in follows the event of devices recovering from a failure that created a
   loss of Counter state.  For example, format in Figure 7, where a CC request or other RPL
   message is received with an initialized Counter within the message
   security section, the provision of the Incoming Counter within base
   format is the CC
   response DAO message allows the requesting node to reset its Outgoing
   Counter to a value greater than the last value received by the
   responding node; the Incoming Counter will also be updated from the
   received CC response.

5.6.2.  CC shown in Figure 16.

6.4.3.  DAO Options

   The CC DAO message MAY carry valid options.  In the scope of this
   specification, there are no valid options for a CC message.

   This specification allows for the CC DAO message to carry the following
   options:
      0x00 Pad1
      0x01 PadN

5.7.
      0x05 RPL Control Message Options

5.7.1. Target
      0x06 Transit Information
      0x09 RPL Control Message Option Generic Target Descriptor

   A special case of the DAO message, termed a No-Path, is used in
   storing mode to clear downward routing state that has been
   provisioned through DAO operation.  The No-Path carries a Target
   option and an associated Transit Information option with a lifetime
   of 0x00000000 to indicate a loss of reachability to that Target.

6.5.  Destination Advertisement Object Acknowledgement (DAO-ACK)

   The DAO-ACK message is sent as a unicast packet by a DAO recipient (a
   DAO parent or DODAG root) in response to a unicast DAO message.

6.5.1.  Format

   RPL Control Message Options all follow this format: of the DAO-ACK Base Object
        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Option Type RPLInstanceID |D|  Reserved   | Option Length  DAOSequence  | Option Data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -

                   Figure 14: RPL Option Generic Format

   Option Type:  8-bit identifier of the type of option.    Status     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            DODAGID*                           +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Option(s)...
       +-+-+-+-+-+-+-+-+

   The Option
         Type values are to be confirmed by '*' denotes that the IANA Section 18.4.

   Option Length: DODAGID is not always present, as described
   below.

                    Figure 17: The DAO ACK Base Object

   RPLInstanceID:  8-bit unsigned integer, representing field indicating the length in
         octets of topology instance
         associated with the option, not including DODAG, as learned from the Option Type and Length
         fields.

   Option Data:  A variable length field DIO.

   D:    The 'D' flag indicates that contains data specific to the option.

   When processing DODAGID field is present.  This
         would typically only be set when a RPL message containing an option for which the
   Option Type value local RPLInstanceID is not recognized by the receiver, the receiver used.

   Flags:  7-bit unused field reserved for flags.  The field MUST silently ignore the unrecognized option and continue be
         initialized to process
   the following option, correctly handling any remaining options in the
   message.

   RPL message options may have alignment requirements.  Following zero by the
   convention in IPv6, options with alignment requirements are aligned
   in a packet such that multi-octet values within sender and MUST be ignored by the Option Data field
   of each option fall on natural boundaries (i.e., fields of width n
   octets are placed
         receiver.

   DAOSequence:  Incremented at an integer multiple of n octets each DAO message from the start
   of the header, for n = 1, 2, 4, or 8).

5.7.2.  Pad1

   The Pad1 option may be present in DIS, DIO, DAO, a node, and echoed
         in the DAO-ACK
   messages, and its format is as follows:

        0
        0 1 2 3 4 5 6 7
       +-+-+-+-+-+-+-+-+
       |   Type = 0    |
       +-+-+-+-+-+-+-+-+

                   Figure 15: Format of by the Pad 1 Option recipient.  The Pad1 option DAOSequence is used to insert one or two octets of padding into
   the
         correlate a DAO message to enable options alignment.  If more than one octet of
   padding and a DAO ACK message and is required, the PadN option should not to be used rather than
   multiple Pad1 options.

   NOTE! the format of
         confused with the Pad1 Transit Information option Path Sequence that
         is associated to a special case - it has
   neither Option Length nor Option Data fields.

5.7.3.  PadN

   The PadN option may be present in DIS, DIO, DAO, given target Down the DODAG.

   Status:  Indicates the completion.  Status 0 is unqualified
         acceptance, 1 to 127 are reserved and DAO-ACK
   messages, undetermined, and its format 128 and
         greater are rejection codes used to indicate that the node
         should select an alternate parent.

   DODAGID (optional):  128-bit unsigned integer set by a DODAG root
         which uniquely identifies a DODAG.  This field is as follows:

        0                   1                   2
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
       |   Type = 1    | Option Length | 0x00 Padding...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -

                   Figure 16: Format of only present
         when the Pad N Option

   The PadN option 'D' flag is used set.  This field is typically only present
         when a local RPLInstanceID is in use, in order to insert two or more octets identify the
         DODAGID that is associated with the RPLInstanceID.  When a
         global RPLInstanceID is in use this field need not be present.

   Unassigned bits of padding into the message DAO-ACK Base are reserved.  They MUST be set
   to enable options alignment.  PadN Option data zero on transmission and MUST be ignored by on reception.

6.5.2.  Secure DAO-ACK

   A Secure DAO-ACK message follows the receiver.

   Option Type:  0x01 (to format in Figure 7, where the
   base format is the DAO-ACK message shown in Figure 17.

6.5.3.  DAO-ACK Options

   This specification does not define any options to be confirmed carried by IANA)

   Option Length:  For N (N > 1) octets of padding, the Option Length
         field contains
   DAO-ACK message.

6.6.  Consistency Check (CC)

   The CC message is used to check secure message counters and issue
   challenge/responses.  A CC message MUST be sent as a secured RPL
   message.

   A CC message (request or response) MUST NOT set the value N-2.

   Option Data:  For N (N > 1) octets 'C' bit of padding, the Option Data
         consists
   security section: CC messages always have full counters.

6.6.1.  Format of N-2 zero-valued octets.

5.7.4.  Metric Container

   The Metric Container option may be present in DIO messages, and its
   format is as follows: the CC Base Object

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Type = 2 RPLInstanceID |R|    Flags    | Option Length            Nonce              | Metric Data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            DODAGID                            +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Destination Counter                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Option(s)...
       +-+-+-+-+-+-+-+-+

                       Figure 17: Format of the Metric Container Option 18: The Metric Container is used to report metrics along CC Base Object

   RPLInstanceID:  8-bit field indicating the DODAG.  The
   Metric Container may contain a number of discrete node, link, and
   aggregate path metrics and constraints specified in
   [I-D.ietf-roll-routing-metrics] topology instance
         associated with the DODAG, as chosen by learned from the implementer. DIO.

   R:    The Metric Container MAY appear more than once in 'R' flag indicates whether the same RPL
   control message, for example to accommodate CC message is a use case where response.  A
         message with the
   Metric Data is longer than 256 bytes.  More information 'R' flag cleared is in
   [I-D.ietf-roll-routing-metrics]

   The processing and propagation of a request; a message with
         the Metric Container 'R' flag set is governed a response.  A CC message with the R bit
         set MUST NOT compress the security Counter field: the C bit of
         the security section MUST be 0.

   Flags:  7-bit unused field reserved for flags.  The field MUST be
         initialized to zero by
   implementation specific policy functions.

   Option Type:  0x02 (to the sender and MUST be confirmed ignored by IANA)

   Option Length: the
         receiver.

   Nonce:  16-bit unsigned integer set by a CC request.  The Option Length field contains
         corresponding CC response includes the length in octets same nonce value as the
         request.

   Destination Counter:  32-bit unsigned integer value indicating the
         sender's estimate of the Metric Data.

   Metric Data:  The order, content, and coding destination's current security Counter
         value.  If the sender does not have an estimate, it SHOULD set
         the Destination Counter field to zero.

   Unassigned bits of the Metric Container
         data is as specified in [I-D.ietf-roll-routing-metrics].

5.7.5.  Route Information

   The Route Information option may CC Base are reserved.  They MUST be present in DIO messages, set to
   zero on transmission and MUST be ignored on reception.

   The Destination Counter value allows new or recovered nodes to
   resynchronize through CC message exchanges.  This is
   equivalent in function important to the IPv6 ND Route Information option as
   defined
   ensure that a Counter value is not repeated for a given security key
   even in [RFC4191].  The format of the option event of devices recovering from a failure that created a
   loss of Counter state.  For example, where a CC request or other RPL
   message is modified slightly
   (Type, Length, Prefix) in order received with an initialized Counter within the message
   security section, the provision of the Incoming Counter within the CC
   response message allows the requesting node to reset its Outgoing
   Counter to a value greater than the last value received by the
   responding node; the Incoming Counter will also be carried as updated from the
   received CC response.

6.6.2.  CC Options

   The CC message MAY carry valid options.  In the scope of this
   specification, there are no valid options for a CC message.

   This specification allows for the CC message to carry the following
   options:
      0x00 Pad1
      0x01 PadN

6.7.  RPL option as
   follows: Control Message Options

6.7.1.  RPL Control Message Option Generic Format

   RPL Control Message Options all follow this format:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
       |  Option Type = 3  | Option Length | Prefix Length |Resvd|Prf|Resvd|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Route Lifetime                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                   Prefix (Variable Length)                    .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option Data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -

                   Figure 18: 19: RPL Option Generic Format

   Option Type:  8-bit identifier of the Route Information Option type of option.  The Route Information option is used to indicate that connectivity Option
         Type values are to be confirmed by IANA Section 19.4.

   Option Length:  8-bit unsigned integer, representing the specified destination prefix is available from length in
         octets of the DODAG root.

   In option, not including the event Option Type and Length
         fields.

   Option Data:  A variable length field that contains data specific to
         the option.

   When processing a RPL Control Message may need to specify
   connectivity to more than one destination, the Route Information message containing an option may be repeated.

   [RFC4191] should be consulted as the authoritative reference with
   respect to the Route Information option.  The field descriptions are
   transcribed here for convenience:

   Option Type:  0x03 (to be confirmed by IANA)

   Option Length:  Variable, length of the option in octets excluding which the
   Option Type and Length fields.  Note that this length value is expressed
         in units of single-octets, unlike in IPv6 ND.

   Prefix Length  8-bit unsigned integer.  The number of leading bits in not recognized by the Prefix that are valid.  The value ranges from 0 to 128.
         The Prefix field has receiver, the number of bytes inferred from receiver
   MUST silently ignore the
         Option Length field, that must be at least unrecognized option and continue to process
   the Prefix Length.
         Note that following option, correctly handling any remaining options in RPL this means that the Prefix field
   message.

   RPL message options may have
         lengths other than 0, 8, or 16.

   Prf:  2-bit signed integer.  The Route Preference indicates whether
         to prefer alignment requirements.  Following the router associated
   convention in IPv6, options with this prefix over others,
         when multiple identical prefixes (for different routers) have
         been received.  If the Reserved (10) value is received, the
         Route Information Option MUST be ignored.

   Resvd:  Two 3-bit unused fields.  They MUST be initialized to zero by
         the sender and MUST be ignored by the receiver.

   Route Lifetime  32-bit unsigned integer.  The length of time alignment requirements are aligned
   in
         seconds (relative to the time the a packet is sent) such that multi-octet values within the
         prefix is valid for route determination.  A value of all one
         bits (0xffffffff) represents infinity.

   Prefix  Variable-length Option Data field containing an IP address or a prefix
   of each option fall on natural boundaries (i.e., fields of width n
   octets are placed at an IP address.  The Prefix Length field contains integer multiple of n octets from the number start
   of
         valid leading bits in the prefix. header, for n = 1, 2, 4, or 8).

6.7.2.  Pad1

   The bits Pad1 option MAY be present in the prefix after
         the prefix length (if any) are reserved DIS, DIO, DAO, and MUST be initialized
         to zero by the sender DAO-ACK
   messages, and ignored by its format is as follows:

        0
        0 1 2 3 4 5 6 7
       +-+-+-+-+-+-+-+-+
       |   Type = 0    |
       +-+-+-+-+-+-+-+-+

                   Figure 20: Format of the receiver.  Note that
         in RPL this field may have lengths other than 0, 8, Pad 1 Option

   The Pad1 option is used to insert one or 16.

   Unassigned bits two octets of padding into
   the Route Information option are reserved.  They
   MUST be set message to zero on transmission and MUST enable options alignment.  If more than one octet of
   padding is required, the PadN option should be ignored on reception.

5.7.6.  DODAG Configuration used rather than
   multiple Pad1 options.

   NOTE! the format of the Pad1 option is a special case - it has
   neither Option Length nor Option Data fields.

6.7.3.  PadN

   The DODAG Configuration PadN option may MAY be present in DIO DIS, DIO, DAO, and DAO-ACK
   messages, and its format is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
       |   Type = 4 1    | Option Length | Resrvd|A| PCS | DIOIntDoubl.  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  DIOIntMin.   |   DIORedun.   |        MaxRankIncrease        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      MinHopRankIncrease       |              OCP              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0x00 Padding...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -

                   Figure 19: 21: Format of the DODAG Configuration Pad N Option

   The DODAG Configuration PadN option is used to distribute configuration
   information for DODAG Operation through the DODAG.

   The information communicated in this option is generally static and
   unchanging within insert two or more octets of padding into
   the DODAG, therefore it is not necessary message to include
   in every DIO.  This information is configured at the DODAG Root and
   distributed throughout the DODAG with the DODAG Configuration Option.
   Nodes other than the DODAG Root enable options alignment.  PadN Option data MUST NOT modify this information when
   propagating the DODAG Configuration option.  This option MAY be
   included occasionally by the DODAG Root (as determined
   ignored by the DODAG
   Root), and MUST be included in response to a unicast request, e.g. a
   unicast DODAG Information Solicitation (DIS) message. receiver.

   Option Type:  0x04  0x01 (to be confirmed by IANA)

   Option Length:  8 bytes

   Authentication Enabled (A):  One bit describing the security mode of
         the network.  The bit describe whether a node must authenticate
         with a key authority before joining the network as a router.
         If the DIO is not a secure DIO, the 'A' bit MUST be zero.

   Path Control Size (PCS):  3-bit unsigned integer used to configure
         the number  For N (N > 1) octets of bits that may be allocated to padding, the Path Control Option Length
         field (see Section 8.9).  Note that as used a value of 1 is
         added to this field, i.e. a PCS value of 0 results in 1 active
         bit in contains the Path Control field.  The default value N-2.

   Option Data:  For N (N > 1) octets of PCS is
         DEFAULT_PATH_CONTROL_SIZE.

   DIOIntervalDoublings:  8-bit unsigned integer used to configure Imax
         of the DIO trickle timer (see Section 7.3.1).

   DIOIntervalMin:  8-bit unsigned integer used to configure Imin of the
         DIO trickle timer (see Section 7.3.1).

   DIORedundancyConstant:  8-bit unsigned integer used to configure k of
         the DIO trickle timer (see Section 7.3.1).

   MaxRankIncrease:  16-bit unsigned integer used to configure
         DAGMaxRankIncrease, padding, the allowable increase in rank in support Option Data
         consists of local repair.  If DAGMaxRankIncrease is 0 then this
         mechanism is disabled.

   MinHopRankInc  16-bit unsigned integer used to configure
         MinHopRankIncrease as described in Section 3.6.2.1.

   Objective Code Point (OCP)  16-bit unsigned integer.  The OCP field
         identifies the OF and is managed by the IANA.

5.7.7.  RPL Target N-2 zero-valued octets.

6.7.4.  Metric Container

   The RPL Target Metric Container option MAY be present in DIO or DAO messages,
   and its format is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
       |   Type = 5 2    | Option Length |   Reserved    | Prefix Length |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                Target Prefix (Variable Length)                |
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Metric Data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -

             Figure 20: 22: Format of the RPL Target Metric Container Option

   The RPL Target Option Metric Container is used to indicate a target IPv6 address,
   prefix, or multicast group that is reachable or queried report metrics along the DODAG.  In  The
   Metric Container may contain a DIO, number of discrete node, link, and
   aggregate path metrics and constraints specified in
   [I-D.ietf-roll-routing-metrics] as chosen by the RPL Target Option identifies a resource that implementer.

   The Metric Container MAY appear more than once in the root is trying same RPL
   control message, for example to reach.  In accommodate a DAO, the RPL Target option
   indicates reachability.

   A set of one or more Transit Information options MAY directly follow use case where the Target option in a DAO message in support of constructing source
   routes
   Metric Data is longer than 256 bytes.  More information is in a non-storing mode of operation
   [I-D.hui-6man-rpl-routing-header].  When the same set of Transit
   Information options apply equally to a set
   [I-D.ietf-roll-routing-metrics].

   The processing and propagation of DODAG Target options, the group of Target options MUST appear first, followed Metric Container is governed by the
   Transit Information options which apply to those Targets.

   The RPL Target option may be repeated as necessary to indicate
   multiple targets.
   implementation specific policy functions.

   Option Type:  0x05  0x02 (to be confirmed by IANA)

   Option Length:  Variable, length of the option in octets excluding
         the Type and Length fields.

   Prefix Length:  8-bit unsigned integer.  Number of valid leading bits
         in the IPv6 Prefix.

   Target Prefix:  Variable-length field identifying an IPv6 destination
         address, prefix, or multicast group.  The Prefix Option Length field contains the number of valid leading bits length in octets
         of the prefix. Metric Data.

   Metric Data:  The
         bits in the prefix after the prefix length (if any) are
         reserved and MUST be set to zero on transmission order, content, and MUST be
         ignored on receipt.

5.7.8.  Transit coding of the Metric Container
         data is as specified in [I-D.ietf-roll-routing-metrics].

6.7.5.  Route Information

   The Transit Route Information option may MAY be present in DAO DIO messages, and
   its is
   equivalent in function to the IPv6 Neighbor Discovery (ND) Route
   Information option as defined in [RFC4191].  The format of the option
   is modified slightly (Type, Length, Prefix) in order to be carried as
   a RPL option as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Type = 6 3    | Option Length | Path Sequence | Path Control  | Prefix Length |Resvd|Prf|Resvd|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Path                        Route Lifetime                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                        Parent Address*                        +
       |                                                               |
       +                                                               +
       |                                                               |
       .                   Prefix (Variable Length)                    .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 21: 23: Format of the Transit Route Information option Option

   The Transit Route Information option is used for a node to indicate
   attributes for a path to one or more destinations.  The destinations
   are indicated as by one or more Target options that immediately
   precede the Transit Information option(s).

   The Transit Information option can used for a node to indicate its
   DODAG parents connectivity to an ancestor that is collecting DODAG routing
   information, typically for the purpose of constructing source routes.
   In the non-storing mode of operation this ancestor will be
   the DODAG
   Root, and this option specified destination prefix is carried by available from the DAO message.  The option
   length is used to determine whether DODAG root.

   In the Parent Address is present or
   not.

   A non-storing node event that has a RPL Control Message may need to specify
   connectivity to more than one DAO parent MAY include a
   Transit destination, the Route Information
   option for each DAO parent as part of the non-
   storing Destination Advertisement operation.  The node may code be repeated.

   [RFC4191] should be consulted as the
   Path Control field in order authoritative reference with
   respect to signal a preference among parents.

   One or more Transit the Route Information options MUST option.  The field descriptions are
   transcribed here for convenience:

   Option Type:  0x03 (to be preceded confirmed by one or
   more RPL Target options.  In this manner IANA)

   Option Length:  Variable, length of the RPL Target option
   indicates in octets excluding
         the child node, Type and the Transit Information option(s)
   enumerate the DODAG parents.

   A typical non-storing node will use multiple Transit Information
   options, and it will send the DAO thus formed to only one parent Length fields.  Note that
   will forward it to the root.  A typical storing node with use one
   Transit Information option with no parent field, and will send the
   DAO thus formed to multiple parents.

   Option Type:  0x06 (to be confirmed by IANA)

   Option Length:  Variable, depending on whether or not Parent Address this length is present.

   Path-Sequence: expressed
         in units of single-octets, unlike in IPv6 ND.

   Prefix Length  8-bit unsigned integer.  When a RPL Target option is
         issued by the node that owns  The number of leading bits in
         the Target Prefix (i.e. in a DAO
         message), that node sets the Path-Sequence and increments the
         Path-Sequence each time it issues a RPL Target option.

   Path Control:  8-bit bitfield. are valid.  The Path Control value ranges from 0 to 128.
         The Prefix field limits has the number of DAO-Parents to which a DAO message advertising
         connectivity to a specific destination may bytes inferred from the
         Option Length field, that must be sent, as well as
         providing some indication of relative preference.  The limit
         provides some bound on overall DAO fan-out at least the Prefix Length.
         Note that in RPL this means that the LLN. Prefix field may have
         lengths other than 0, 8, or 16.

   Prf:  2-bit signed integer.  The
         leftmost bit is Route Preference indicates whether
         to prefer the router associated with a path this prefix over others,
         when multiple identical prefixes (for different routers) have
         been received.  If the Reserved (10) value is received, the
         Route Information Option MUST be ignored.  As per [RFC4191],
         the Reserved (10) value MUST NOT be sent.  ([RFC4191] restricts
         the Preference to just three values to reinforce that contains it is not
         a most-
         preferred link, and the subsequent bits are ordered down metric).

   Resvd:  Two 3-bit unused fields.  They MUST be initialized to zero by
         the
         rightmost bit which is least preferred.

   Path Lifetime: sender and MUST be ignored by the receiver.

   Route Lifetime  32-bit unsigned integer.  The length of time in
         seconds (relative to the time the packet is sent) that the
         prefix is valid for route determination.  A value of all one
         bits (0xFFFFFFFF) (0xffffffff) represents infinity.  A value of all zero
         bits (0x00000000) indicates

   Prefix  Variable-length field containing an IP address or a loss prefix of reachability.  This is
         referred as a No-Path in this document.

   Parent Address (optional):
         an IPv6 Address of address.  The Prefix Length field contains the DODAG Parent number
         of valid leading bits in the
         node originally issuing prefix.  The bits in the Transit Information Option.  This
         field may not prefix
         after the prefix length (if any) are reserved and MUST be present, as according
         initialized to zero by the DODAG Mode of
         Operation sender and indicated ignored by the Transit Information option
         length. receiver.
         Note that in RPL this field may have lengths other than 0, 8,
         or 16.

   Unassigned bits of the Transit Route Information option are reserved.  They
   MUST be set to zero on transmission and MUST be ignored on reception.

5.7.9.  Solicited Information

6.7.6.  DODAG Configuration

   The Solicited Information DODAG Configuration option may MAY be present in DIS DIO messages, and
   its format is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Type = 7    | Option 4    |Opt Length = 14| Flags |A| PCS | RPLInstanceID |V|I|D|  Rsvd DIOIntDoubl.  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  DIOIntMin.   |
       +                                                               +
       |   DIORedun.   |
       +                            DODAGID                            +        MaxRankIncrease        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |
       +                                                               +      MinHopRankIncrease       |              OCP              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Version   Reserved    |
       +-+-+-+-+-+-+-+-+ Def. Lifetime |      Lifetime Unit            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 22: 24: Format of the Solicited Information DODAG Configuration Option

   The Solicited Information DODAG Configuration option is used for a node to request DIO
   messages from a subset of neighboring nodes. distribute configuration
   information for DODAG Operation through the DODAG.

   The Solicited
   Information information communicated in this option may specify a number of predicate criteria to be
   matched by a receiving node.  These predicates affect whether a node
   resets its DIO trickle timer, as described is generally static and
   unchanging within the DODAG, therefore it is not necessary to include
   in Section 7.3 every DIO.  This information is configured at the DODAG Root and
   distributed throughout the DODAG with the DODAG Configuration Option.
   Nodes other than the DODAG Root MUST NOT modify this information when
   propagating the DODAG Configuration option.  This option MAY be
   included occasionally by the DODAG Root (as determined by the DODAG
   Root), and MUST be included in response to a unicast request, e.g. a
   unicast DODAG Information Solicitation (DIS) message.

   Option Type:  0x07  0x04 (to be confirmed by IANA)

   Option Length:  19 bytes

   Control Field:  The Solicited Information option Control Field has
         three flags:

         V:    If the V flag is set then the Version field is valid and
               a node matches the predicate if its DODAGVersionNumber
               matches the requested version.  If the V flag is clear
               then the Version  14

   Flags:  4-bit unused field is not valid and the Version reserved for flags.  The field MUST be set
         initialized to zero on transmission by the sender and MUST be ignored upon
               receipt.

         I:    If by the I
         receiver.

   Authentication Enabled (A):  One bit flag is set then describing the RPLInstanceID field is
               valid and security
         mode of the network.  The bit describe whether a node matches the predicate if it matches must
         authenticate with a key authority before joining the
               requested RPLInstanceID. network as
         a router.  If the I flag is clear then the
               RPLInstanceID field DIO is not valid and a secure DIO, the RPLInstanceID
               field 'A' bit MUST be set
         zero.

   Path Control Size (PCS):  3-bit unsigned integer used to zero on transmission and ignored
               upon receipt.

         D:    If configure
         the D flag is set then number of bits that may be allocated to the DODAGID Path Control
         field (see Section 9.9).  Note that when PCS is valid and
               a node matches the predicate if it matches the requested
               DODAGID.  If consulted to
         determine the D flag is clear then width of the DODAGID Path Control field a value of 1 is not valid and
         added, i.e. a PCS value of 0 results in 1 active bit in the DODAGID field MUST be set to zero on
               transmission and ignored upon receipt.

   Version:
         Path Control field.  The default value of PCS is
         DEFAULT_PATH_CONTROL_SIZE.

   DIOIntervalDoublings:  8-bit unsigned integer containing used to configure Imax
         of the DODAG Version number
         that DIO trickle timer (see Section 8.3.1).  The default
         value of DIOIntervalDoublings is being solicited when valid.

   RPLInstanceID:
         DEFAULT_DIO_INTERVAL_DOUBLINGS.

   DIOIntervalMin:  8-bit unsigned integer containing used to configure Imin of the RPLInstanceID
         that
         DIO trickle timer (see Section 8.3.1).  The default value of
         DIOIntervalMin is being solicited when valid.

   DODAGID:  128-bit DEFAULT_DIO_INTERVAL_MIN.

   DIORedundancyConstant:  8-bit unsigned integer containing the DODAGID that is
         being solicited when valid.

   Unassigned bits used to configure k of
         the Solicited Information option are reserved.
   They MUST be set to zero on transmission and MUST be ignored on
   reception.

5.7.10.  Prefix Information

   The Prefix Information option may be present in DIO messages, and trickle timer (see Section 8.3.1).  The default value
         of DIORedundancyConstant is
   equivalent in function DEFAULT_DIO_REDUNDANCY_CONSTANT.

   MaxRankIncrease:  16-bit unsigned integer used to configure
         DAGMaxRankIncrease, the IPv6 ND Prefix Information option as
   defined allowable increase in [RFC4861].  The format rank in support
         of the option local repair.  If DAGMaxRankIncrease is modified slightly
   (Type, Length, Prefix) in order 0 then this
         mechanism is disabled.

   MinHopRankInc  16-bit unsigned integer used to be carried configure
         MinHopRankIncrease as a described in Section 3.6.1.  The default
         value of MinHopRankInc is DEFAULT_MIN_HOP_RANK_INCREASE.

   Default Lifetime:  8-bit unsigned integer.  This is the lifetime that
         is used as default for all RPL routes.  It is expressed in
         units of Lifetime Units, e.g. the default lifetime in seconds
         is (Default Lifetime) * (Lifetime Unit).

   Lifetime Unit:  16-bit unsigned integer.  Provides the unit in
         seconds that is used to express route lifetimes in RPL.  For
         very stable networks, it can be hours to days.

   Objective Code Point (OCP)  16-bit unsigned integer.  The OCP field
         identifies the OF and is managed by the IANA.

6.7.7.  RPL Target

   The RPL Target option MAY be present in DAO messages, and its format
   is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Type = 8 5    | Option Length |   Flags       | Prefix Length |L|A| Reserved1 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Valid Lifetime                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Preferred Lifetime                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Reserved2 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                Target Prefix                             +
       |                                                               |
       +                                                               +
       | (Variable Length)                |
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 23: 25: Format of the Prefix Information RPL Target Option

   The Prefix Information option may be RPL Target Option is used to distribute indicate a target IPv6 address,
   prefix, or multicast group that is reachable or queried along the prefix in
   use inside
   DODAG.  In a DAO, the DODAG, e.g. for address autoconfiguration.

   [RFC4861] should RPL Target option indicates reachability.

   A RPL Target Option May optionally be consulted as the authoritative reference paired with
   respect to a RPL Target
   Descriptor Option (Figure 30) that qualifies the Prefix target.

   A set of one or more Transit Information option. options (Section 6.7.8) MAY
   directly follow a set of one or more Target option in a DAO message
   (where each Target Option MAY be paired with a RPL Target Descriptor
   Option as above).  The field descriptions structure of the DAO message, detailing how
   Target options are
   transcribed here for convenience: used in conjunction with Transit Information
   options, is further described in Section 9.6.

   The RPL Target option may be repeated as necessary to indicate
   multiple targets.

   Option Type:  0x08  0x05 (to be confirmed by IANA)

   Option Length:  30.  Note that this  Variable, length is expressed in units of
         single-octets, unlike the option in IPv6 ND.

   Prefix octets excluding
         the Type and Length fields.

   Flags:  8-bit unsigned integer.  The number of leading bits in
         the Prefix that are valid.  The value ranges from 0 to 128.
         The prefix length unused field provides necessary information for on-
         link determination (when combined with the L flag in the prefix
         information option).  It also assists with address
         autoconfiguration as specified in [RFC4862], for which there
         may be more restrictions on the prefix length.

   L     1-bit on-link flag.  When set, indicates that this prefix can
         be used for on-link determination.  When not set the
         advertisement makes no statement about on-link or off-link
         properties of the prefix.  In other words, if the L flag is not
         set a host MUST NOT conclude that an address derived from the
         prefix is off-link.  That is, it MUST NOT update a previous
         indication that the address is on-link.

   A     1-bit autonomous address-configuration flag.  When set
         indicates that this prefix can be used reserved for stateless address
         configuration as specified in [RFC4862].

   Reserved1  6-bit unused field.  It flags.  The field MUST be
         initialized to zero by the sender and MUST be ignored by the
         receiver.

   Valid Lifetime  32-bit

   Prefix Length:  8-bit unsigned integer.  The length  Number of time valid leading bits
         in
         seconds (relative to the time the packet is sent) that the
         prefix is valid for the purpose of on-link determination.  A
         value of all one bits (0xffffffff) represents infinity.  The
         Valid Lifetime is also used by [RFC4862].

   Preferred Lifetime  32-bit unsigned integer.  The length of time in
         seconds (relative to the time the packet is sent) that
         addresses generated from the prefix via stateless address
         autoconfiguration remain preferred [RFC4862].  A value of all
         one bits (0xffffffff) represents infinity.  See [RFC4862].

         Note that the value of this field MUST NOT exceed the Valid
         Lifetime field to avoid preferring addresses that are no longer
         valid.

   Reserved2  This field is unused.  It MUST be initialized to zero by
         the sender and MUST be ignored by the receiver.

   Prefix  An IP address or a prefix of an IP address.  The Prefix
         Length field contains IPv6 Prefix.

   Target Prefix:  Variable-length field identifying an IPv6 destination
         address, prefix, or multicast group.  The Prefix Length field
         contains the number of valid leading bits in the prefix.  The
         bits in the prefix after the prefix length (if any) are
         reserved and MUST be initialized set to zero by the sender on transmission and MUST be
         ignored by the receiver.  A router SHOULD NOT send a prefix on receipt.

6.7.8.  Transit Information

   The Transit Information option for the link-local prefix and a host SHOULD ignore such
         a prefix option.  A non-storing node SHOULD refrain from
         advertising a prefix till it owns an address of that prefix,
         and then it SHOULD advertise its full address in this field, to MAY be used by its children present in DAO messages, and
   its format is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Type = 6    | Option Length |E|    Flags    | Path Control  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Path Sequence | Path Lifetime |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
       |                                                               |
       +                                                               +
       |                                                               |
       +                        Parent Address*                        +
       |                                                               |
       +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The '*' denotes that the Parent Address field is not always present, as
   described below.

            Figure 26: Format of the Transit Information Option

   Unassigned bits of the Prefix option

   The Transit Information option are reserved.  They
   MUST be set is used for a node to zero on transmission and MUST be ignored on reception.

6.  Sequence Counters

   This section describes the general scheme indicate
   attributes for bootstrap and operation
   of sequence counters in RPL, such as the DODAGVersionNumber in the
   DIO message, the DAOSequence in the DAO message, and the Path-
   Sequence in a path to one or more destinations.  The destinations
   are indicated by one or more Target options that immediately precede
   the Transit Information option.

   RPL sequence counters are subdivided in a 'lollipop' fashion
   ([Perlman83]), where the values from 128 and greater are option(s).

   The Transit Information option can be used as for a
   linear sequence node to indicate a restart and bootstrap its
   DODAG parents to an ancestor that is collecting DODAG routing
   information, typically for the counter, and purpose of constructing source routes.
   In the values less than or equal to 127 used as a circular sequence
   number space non-storing mode of size 128 as in [RFC1982].  Consideration operation this ancestor will be the DODAG
   Root, and this option is given to carried by the DAO message.  In the storing
   mode of operation when transitioning from the linear region to Parent Address is not needed, since the circular region.  Finally, when operating in DAO
   message is sent directly to the circular region,
   if sequence numbers are detected to be too far apart then they are
   not comparable, as detailed below.

   A window of comparison, SEQUENCE_WINDOW = 16, is configured based on
   a value of 2^N, where N=4.

   For a given sequence counter,

   1. parent.  The sequence counter SHOULD be initialized option length is used to an implementation
       defined value which
   determine whether the Parent Address is 128 present or greater prior to use. not.

   A
       recommended value is 240 (256 - SEQUENCE_WINDOW).

   2.  When non-storing node that has more than one DAO parent MAY include a sequence counter increment would cause
   Transit Information option for each DAO parent as part of the sequence
       counter to increment beyond its maximum value, non-
   storing destination advertisement operation.  The node may distribute
   the sequence
       counter MUST wrap back bits in the Path Control field among different groups of DAO
   parents in order to zero.  When incrementing signal a sequence
       counter greater than or equal to 128, preference among parents.  That
   preference may influence the maximum value is 255.
       When incrementing a sequence counter less than 128, decision of the maximum
       value is 127.

   3.  When comparing two sequence counters, DODAG root when
   selecting among the following rules alternate parents/paths for constructing downward
   routes.

   One or more Transit Information options MUST be
       applied:

       1.  When a first sequence counter A is in preceded by one or
   more RPL Target options.  In this manner the interval [0..127] RPL Target option
   indicates the child node, and a second sequence counter B is the Transit Information option(s)
   enumerate the DODAG parents.  The structure of the DAO message,
   further detailing how Target options are used in [128..255]:

           1.  If B-A is less than or equal to SEQUENCE_WINDOW, then B conjunction with
   Transit Information options, is greater than A, further described in Section 9.6.

   A is less than B, typical non-storing node will use multiple Transit Information
   options, and it will send the two are not
               equal.

           2.  If B-A is greater than SEQUENCE_WINDOW, then DAO message thus formed directly to the
   root.  A is greater
               than B, B is less than A, typical storing node will use one Transit Information option
   with no parent field, and will send the two are not equal.

       2.  In the case where both sequence counters DAO message thus formed, with
   additional adjustments to be compared are
           less than or equal Path Control as detailed later, to 127, and one or
   multiple parents.

   For example, in a non-storing mode of operation let Tgt(T) denote a
   Target option for a target T. Let Trnst(P) denote a Transit
   Information option that contains a parent address P. Consider the
   case where both
           sequence counters to be compared are greater than or equal to
           128:

           1.  If the absolute magnitude of difference between the two
               sequence counters is less than or equal to
               SEQUENCE_WINDOW, then a comparison as described in
               [RFC1982] is used to determine non-storing node N that advertises the relationships greater
               than, less than, self-owned targets
   N1 and N2 and equal

           2.  If the absolute magnitude of difference of the two
               sequence counters is greater than SEQUENCE_WINDOW, then a
               desynchronization has occurred parents P1, P2, and P3.  In that case the two sequence
               numbers are not comparable.

   4.  If two sequence numbers are determined to DAO
   message would be not comparable, i.e. expected to contain the results of sequence ( (Tgt(N1),
   Tgt(N2)), (Trnst(P1), Trnst(P2), Trnst(P3)) ), such that the comparison group of
   Target options {N1, N2} are not defined, then a node should
       consider described by the comparison as if it has evaluated in such a way so Transit Information
   options as to give precedence to the sequence number that has most
       recently been observed to increment.  Failing this, having the parents {P1, P2, P3}.  The non-storing node
       should consider the comparison as if it has evaluated in such a
       way so as
   would then address that DAO message directly to minimize the resulting changes to its own state.

7.  Upward Routes

   This section describes how RPL discovers DODAG root, and maintains upward routes.
   It describes the use
   forward that DAO message through one of DODAG Information Objects (DIOs), the
   messages used to discover and maintain these routes.  It specifies
   how RPL generates and responds to DIOs.  It also describes DODAG
   Information Solicitation (DIS) messages, which are used parents P1, P2, or
   P3.

   Option Type:  0x06 (to be confirmed by IANA)

   Option Length:  Variable, depending on whether or not Parent Address
         is present.

   External (E):  1-bit flag.  The 'E' flag is set to trigger
   DIO transmissions.

7.1.  DIO Base Rules

   1.  For the following DIO Base fields, a node indicate that is not a DODAG
       root MUST advertise the same values as its preferred DODAG
         parent
       (defined in Section 7.2.1).  Therefore, if router redistributes external targets into the RPL
         network.  An external target is a DODAG root does not
       change these values, every node target that has been learned
         through an alternate protocol.  The external targets are listed
         in a route to the target options that DODAG root
       eventually advertises immediately precede the same values Transit
         Information option.  An external target is not expected to
         support RPL messages and options.

   Flags:  7-bit unused field reserved for these fields.  These
       fields are:
       1.  Grounded (G)
       2.  Mode of Operation (MOP)
       3.  DAGPreference (Prf)
       4.  Version
       5.  RPLInstanceID
       6.  DODAGID

   2.  A node MAY update the following fields at each hop:
       1.  Rank
       2.  DTSN

   3. flags.  The DODAGID field each root sets MUST be unique within the RPL
       Instance.

7.2.  Upward Route Discovery and Maintenance

   Upward route discovery allows a node
         initialized to join a DODAG zero by discovering
   neighbors that are members of the DODAG of interest and identifying a
   set of parents.  The exact policies for selecting neighbors and
   parents is implementation-dependent sender and driven MUST be ignored by the OF.  This
   section specifies
         receiver.

   Path Control:  8-bit bitfield.  The Path Control field limits the set
         number of rules those policies must follow for
   interoperability.

7.2.1.  Neighbors and Parents within DAO-Parents to which a DODAG Version

   RPL's upward route discovery algorithms and processing are in terms
   of three logical sets of link-local nodes.  First, the candidate
   neighbor set is DAO message advertising
         connectivity to a subset specific destination may be sent, as well as
         providing some indication of relative preference.  The limit
         provides some bound on overall DAO message fan-out in the nodes that can be reached via link-
   local multicast. LLN.
         The selection of this set is implementation-
   dependent assignment and OF-dependent.  Second, the parent set is a restricted
   subset ordering of the candidate neighbor set.  Finally, bits in the preferred parent,
   a set of size one, is an element path control
         also serves to communicate preference.  Not all of these bits
         may be enabled as according the parent set that is the
   preferred next hop PCS in upward routes.

   More precisely:

   1.  The DODAG parent set MUST be a subset of the candidate neighbor
       set.

   2.  A DODAG root MUST have a DODAG parent set of size zero.

   3.  A node that
         Configuration.  The Path Control field is not a DODAG root MAY maintain a DODAG parent set
       of size greater than or equal to one.

   4.  A node's divided into four
         subfields which contain two bits each: PC1, PC2, PC3, and PC4,
         as illustrated in Figure 27.  The subfields are ordered by
         preference, with PC1 being the most preferred DODAG parent MUST be a member of its DODAG
       parent set.

   5.  A node's rank MUST be greater than all elements of its DODAG
       parent set.

   6.  When Neighbor Unreachability Detection (NUD), or an equivalent
       mechanism, determines that and PC4 being the
         least preferred.  Within a neighbor subfield there is no longer reachable, a
       RPL node MUST NOT consider this node in order of
         preference.  By grouping the candidate neighbor
       set when calculating parents (as in ECMP) and advertising routes until it determines
       that it is again reachable.  Routes through an unreachable
       neighbor MUST ordering
         them, the parents may be removed from associated with specific bits in the routing table.

   These rules ensure
         Path Control field in a way that there is communicates preference.

                                    0 1 2 3 4 5 6 7
                                   +-+-+-+-+-+-+-+-+
                                   |PC1|PC2|PC3|PC4|
                                   +-+-+-+-+-+-+-+-+

              Figure 27: Path Control Preference Sub-field Encoding

   Path Sequence:  8-bit unsigned integer.  When a consistent partial order on nodes
   within RPL Target option is
         issued by the DODAG.  As long as node ranks do not change, following the
   above rules ensures that every node's route to a DODAG root is loop-
   free, as rank decreases on each hop to owns the root.

   The OF can guide candidate neighbor set and parent set selection, as
   discussed Target Prefix (i.e. in [I-D.ietf-roll-routing-metrics] and [I-D.ietf-roll-of0].

7.2.2.  Neighbors a DAO
         message), that node sets the Path Sequence and Parents across DODAG Versions

   The above rules govern increments the
         Path Sequence each time it issues a single DODAG version. RPL Target option with
         updated information.

   Path Lifetime:  8-bit unsigned integer.  The rules length of time in this
   section define how RPL operates when there are multiple DODAG
   versions:

7.2.2.1.  DODAG Version

   1.
         Lifetime Units (obtained from the Configuration option) that
         the prefix is valid for route determination.  The tuple (RPLInstanceID, DODAGID, DODAGVersionNumber) uniquely
       defines period starts
         when a DODAG Version.  Every element new Path Sequence is seen.  A value of all one bits
         (0xFF) represents infinity.  A value of all zero bits (0x00)
         indicates a node's DODAG parent
       set, as conveyed by the last heard DIO loss of reachability.  A DAO message from each DODAG
       parent, MUST belong to the same DODAG version.  Elements that contains
         a Transit Information option with a Path Lifetime of 0x00 for a
       node's candidate neighbor set MAY belong to different DODAG
       Versions.

   2.  A node
         Target is referred as a member No-Path (for that Target) in this
         document.

   Parent Address (optional):  IPv6 Address of a the DODAG version if every element Parent of its
       DODAG parent set belongs the
         node originally issuing the Transit Information Option.  This
         field may not be present, as according to that the DODAG version, Mode of
         Operation (storing or if that node
       is non-storing) and indicated by the root Transit
         Information option length.

   Unassigned bits of the corresponding DODAG.

   3.  A node Transit Information option are reserved.  They
   MUST NOT send DIOs for DODAG versions of which it is not a
       member.

   4.  DODAG roots MAY increment the DODAGVersionNumber that they
       advertise and thus move be set to zero on transmission and MUST be ignored on reception.

6.7.9.  Solicited Information

   The Solicited Information option MAY be present in DIS messages, and
   its format is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Type = 7    |Opt Length = 19| RPLInstanceID |V|I|D|  Flags  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            DODAGID                            +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Version Number |
       +-+-+-+-+-+-+-+-+

           Figure 28: Format of the Solicited Information Option

   The Solicited Information option is used for a new DODAG version.  When node to request DIO
   messages from a DODAG
       root increments its DODAGVersionNumber, it MUST follow subset of neighboring nodes.  The Solicited
   Information option may specify a number of predicate criteria to be
   matched by a receiving node.  This is used by the
       conventions requester to limit
   the number of Serial Number Arithmetic replies from "non-interesting" nodes.  These predicates
   affect whether a node resets its DIO trickle timer, as described in
   Section 6.

   5.  Within a given DODAG, a node 8.3.

   Option Type:  0x07 (to be confirmed by IANA)

   Option Length:  19

   Control Field:  The control field contains flags that is indicate which
         predicates a not node should check when deciding whether to reset
         its Trickle timer.  A node resets its Trickle timer when all
         predicates are true.  If a root flag is set, then the RPL node MUST NOT
       advertise a DODAGVersionNumber higher than
         check the highest
       DODAGVersionNumber it has heard.  Higher associated predicate.  If a flag is defined as cleared, then the
       greater-than operator in Section 6.

   6.  Once a
         RPL node has advertised a DODAG version by sending a DIO, it MUST NOT be member of a previous DODAG version of check the same DODAG
       (i.e. with associated predicate and assume the same RPLInstanceID,
         predicate is true.  The Solicited Information option Control
         Field has three flags:

         V:    The V flag is the same DODAGID, and a lower
       DODAGVersionNumber).  Lower Version predicate.  The Version
               predicate is defined as true if the less-than operator
       in Section 6.

   When receiver's DODAGVersionNumber
               matches the DODAG parent requested Version Number.  If the V flag is
               cleared then the Version field is not valid and the
               Version field MUST be set becomes empty to zero on a node that transmission and
               ignored upon receipt.

         I:    The I flag is not a root,
   (i.e. the last parent has been removed, causing InstanceID predicate.  The InstanceID
               predicate is true when the node to no longer
   be associated with that DODAG), RPL node's current
               RPLInstanceID matches the requested RPLInstanceID.  If
               the I flag is cleared then the DODAG information should RPLInstanceID field is not
   be suppressed until after
               valid and the expiration of an implementation-
   specific local timer in order RPLInstanceID field MUST be set to observe zero on
               transmission and ignored upon receipt.

         D:    The D flag is the DODAGID predicate.  The DODAGID
               predicate is true if the DODAGVersionNumber RPL node's parent set has been incremented, should any new parents appear for the DODAG.
   This will help protect against
               same DODAGID as the possibility of loops that may
   occur of that node were to inadvertently rejoin DODAGID field.  If the old DODAG version
   in its own prior sub-DODAG.

   As D flag is
               cleared then the DODAGVersionNumber DODAGID field is incremented, a new DODAG Version spreads
   outward from the DODAG root.  A parent that advertises not valid and the new
   DODAGVersionNumber cannot belong
               DODAGID field MUST be set to the sub-DODAG of a node
   advertising an older DODAGVersionNumber.  Therefore a node can safely
   add a parent of any Rank with a newer DODAGVersionNumber without
   forming a loop.

   Exactly when a DODAG Root increments the DODAGVersionNumber is
   implementation and application-dependent zero on transmission and outside the scope of
   this document.  Examples include incrementing the DODAGVersionNumber
   periodically,
               ignored upon administrative intervention, or on application-
   level detection of lost connectivity or DODAG inefficiency.

   After a node transitions receipt.

         Flags:  5-bit unused field reserved for flags.  The field MUST
               be initialized to and advertises a new DODAG Version, zero by the
   rules above make it unable to advertise sender and MUST be ignored
               by the previous DODAG receiver.

   Version
   (prior DODAGVersionNumber) once it has committed to advertising the
   new DODAG Version.

7.2.2.2.  DODAG Roots

   1.  A DODAG root without possibility to satisfy the application-
       defined goal MUST NOT set Number:  8-bit unsigned integer containing the Grounded bit.

   2.  A DODAG root MUST advertise a rank value of ROOT_RANK.

   3.  A node whose DODAG parent set
         DODAGVersionNumber that is empty MAY become being solicited when valid.

   RPLInstanceID:  8-bit unsigned integer containing the DODAG Root
       of a floating DODAG.  It MAY also set its DAGPreference such RPLInstanceID
         that
       it is less preferred.

   In a deployment being solicited when valid.

   DODAGID:  128-bit unsigned integer containing the DODAGID that uses a backbone link to federate a number of LLN
   roots, it is possible
         being solicited when valid.

   Unassigned bits of the Solicited Information option are reserved.
   They MUST be set to run RPL over that backbone zero on transmission and use one
   router as a "backbone root". MUST be ignored on
   reception.

6.7.10.  Prefix Information

   The backbone root Prefix Information option MAY be present in DIO messages, and is
   equivalent in function to the virtual root
   of the DODAG, and exposes a rank IPv6 ND Prefix Information option as
   defined in [RFC4861].  The format of BASE_RANK over the backbone.  All the LLN roots that are parented option is modified slightly
   (Type, Length, Prefix) in order to that backbone root, including the
   backbone root if it also serves be carried as LLN root itself, expose a rank RPL option as
   follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Type = 8    |Opt Length = 30| Prefix Length |L|A|R|Reserved1|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Valid Lifetime                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Preferred Lifetime                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Reserved2                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            Prefix                             +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 29: Format of
   ROOT_RANK the Prefix Information Option

   The Prefix Information option may be used to distribute the LLN.  These virtual roots are part of prefix in
   use inside the same DODAG DODAG, e.g. for address autoconfiguration.

   [RFC4861] and advertise [RFC3775] should be consulted as the same DODAGID.  They coordinate DODAGVersionNumbers
   and other DODAG parameters authoritative
   reference with respect to the virtual root over the backbone.

7.2.2.3.  DODAG Selection Prefix Information option.  The objective function of a DAG determines how a node selects its
   neighbor set, parent set, and preferred parents.  This selection
   implicitly also decides the DODAG within a DAG.  Such selection can
   include administrative preference (Prf) as well as metrics or other
   considerations.

   If a node has field
   descriptions are transcribed here for convenience:

   Option Type:  0x08 (to be confirmed by IANA)

   Option Length:  30.  Note that this length is expressed in units of
         single-octets, unlike in IPv6 ND.

   Prefix Length  8-bit unsigned integer.  The number of leading bits in
         the option Prefix that are valid.  The value ranges from 0 to join a more preferred DODAG while still
   meeting other optimization objectives, then 128.
         The prefix length field provides necessary information for on-
         link determination (when combined with the node will generally
   seek to join L flag in the more preferred DODAG prefix
         information option).  It also assists with address
         autoconfiguration as determined by specified in [RFC4862], for which there
         may be more restrictions on the OF.  All
   else being equal, it is left to prefix length.

   L     1-bit on-link flag.  When set, indicates that this prefix can
         be used for on-link determination.  When not set the implementation to determine which
   DODAG is most preferred.

7.2.2.4.  Rank and Movement within a DODAG Version

   1.  A node MUST NOT advertise a Rank less than
         advertisement makes no statement about on-link or equal to any member off-link
         properties of its parent set within the DODAG Version.

   2.  A node MAY advertise a Rank lower than its prior advertisement
       within prefix.  In other words, if the DODAG Version.

   3.  Let L be the lowest rank within a DODAG version that flag is not
         set a given node
       has advertised.  Within the same DODAG Version, that node host MUST NOT advertise conclude that an effective rank higher than L +
       DAGMaxRankIncrease.  INFINITE_RANK address derived from the
         prefix is an exception to this rule:
       a node MAY advertise an INFINITE_RANK within a DODAG version
       without restriction.  If a node's Rank would be higher than
       allowed by L + DAGMaxRankIncrease, when it advertises Rank off-link.  That is, it MUST advertise its Rank as INFINITE_RANK.

   4.  A node MAY, at any time, choose to join a different DODAG within
       a RPL Instance.  Such NOT update a join has no rank restrictions, unless previous
         indication that different DODAG the address is a DODAG Version of which on-link.

   A     1-bit autonomous address-configuration flag.  When set
         indicates that this node has
       previously been a member, prefix can be used for stateless address
         configuration as specified in which case [RFC4862].

   R     1-bit Router address flag.  When set, indicates that the rule of Prefix
         field contains a complete IPv6 address assigned to the previous
       bullet (3) must sending
         router that can be observed.  Until a node transmits used as parent in a DIO
       indicating its new DODAG membership, it MUST forward packets
       along target option.  The
         indicated prefix is the previous DODAG.

   5.  A node MAY, at any time after hearing first Prefix Length bits of the next DODAGVersionNumber
       advertised from suitable DODAG parents, choose to migrate to Prefix
         field.  The router IPv6 address has the
       next DODAG Version within same scope and conforms
         to the DODAG.

   Conceptually, an implementation is maintaining a DODAG parent set
   within same lifetime values as the DODAG Version.  Movement entails changes to advertised prefix.  This use
         of the DODAG
   parent set.  Moving up does not present Prefix field is compatible with its use in advertising
         the risk to create a loop but
   moving down might, so that operation prefix itself, since Prefix Advertisement uses only the
         leading bits.  Interpretation of this flag bit is subject to additional
   constraints.

   When a node migrates to thus
         independent of the next DODAG Version, processing required for the DODAG parent set
   needs On-Link (L) and
         Autonomous Address-Configuration (A) flag bits.

   Reserved1  5-bit unused field.  It MUST be initialized to zero by the
         sender and MUST be rebuilt for ignored by the new version.  An implementation could
   defer to migrate for some reasonable amount receiver.

   Valid Lifetime  32-bit unsigned integer.  The length of time, to see if some
   other neighbors with potentially better metrics but higher rank
   announce themselves.  Similarly, when a node jumps into a new DODAG
   it needs to construct new a DODAG parent set for this new DODAG.

   If a node needs time in
         seconds (relative to move down a DODAG the time the packet is sent) that it the
         prefix is attached to,
   increasing its Rank, then it MAY poison its routes and delay before
   moving as described in Section 7.2.2.5.

7.2.2.5.  Poisoning

   1. valid for the purpose of on-link determination.  A node poisons routes
         value of all one bits (0xffffffff) represents infinity.  The
         Valid Lifetime is also used by advertising a Rank [RFC4862].

   Preferred Lifetime  32-bit unsigned integer.  The length of INFINITE_RANK.

   2. time in
         seconds (relative to the time the packet is sent) that
         addresses generated from the prefix via stateless address
         autoconfiguration remain preferred [RFC4862].  A node value of all
         one bits (0xffffffff) represents infinity.  See [RFC4862].
         Note that the value of this field MUST NOT have any nodes with exceed the Valid
         Lifetime field to avoid preferring addresses that are no longer
         valid.

   Reserved2  This field is unused.  It MUST be initialized to zero by
         the sender and MUST be ignored by the receiver.

   Prefix  An IPv6 address or a Rank prefix of INFINITE_RANK in
       its parent set.

   Although an implementation may advertise INFINITE_RANK for IPv6 address.  The Prefix
         Length field contains the
   purposes number of poisoning, doing so is not valid leading bits in the same as setting Rank to
   INFINITE_RANK.  For example, a node may continue
         prefix.  The bits in the prefix after the prefix length are
         reserved and MUST be initialized to zero by the sender and
         ignored by the receiver.  A router SHOULD NOT send data packets
   whose meta-data include a Rank that is not INFINITE_RANK yet still
   advertise INFINITE_RANK in its DIOs.

7.2.2.6.  Detaching

   1.  A node unable to stay connected to prefix
         option for the link-local prefix and a DODAG within host SHOULD ignore such
         a given DODAG
       version MAY detach from this DODAG version. prefix option.  A non-storing node that detaches
       becomes root SHOULD refrain from
         advertising a prefix till it owns an address of its own floating DODAG that prefix,
         and then it SHOULD immediately advertise this new situation its full address in a DIO as an alternate to
       poisoning.

7.2.2.7.  Following a Parent

   1.  If this field,
         with the 'R' flag set.  The children of a node receives that so
         advertises a DIO from one of its DODAG parents,
       indicating full address with the 'R' flag set may then use
         that address to determine the parent has left content of the DODAG, that node SHOULD
       stay in its current DODAG through an alternative DODAG parent, if
       possible.  It MAY follow Parent Address
         field of the leaving parent.

   A DODAG parent may have moved, migrated Transit Information Option.

   Unassigned bits of the Prefix Information option are reserved.  They
   MUST be set to zero on transmission and MUST be ignored on reception.

6.7.11.  RPL Target descriptor

   The RPL Target option MAY be immediately followed by one opaque
   descriptor that qualifies that specific target.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Type = 9    |Opt Length = 4 |           Descriptor          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Descriptor (cont.)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 30: Format of the next DODAG Version, or
   jumped RPL Target Descriptor Option

   The RPL Target Descriptor Option is used to qualify a different DODAG.  A target,
   something that is sometimes called tagging.

   There can be at most one descriptor per target.  The descriptor is
   set by the node should give some preference to
   remaining that injects the target in the current DODAG, if possible via an alternate parent, RPL network.  It MUST
   be copied but ought to follow the parent if there are no other options.

7.2.3.  DIO Message Communication

   When an DIO message is received, the receiving node must first
   determine whether or not modified by routers that propagate the DIO message should target Up
   the DODAG in DAO messages.

   Option Type:  0x09 (to be accepted confirmed by IANA)

   Option Length:  4

   Descriptor:  32-bit unsigned integer.  Opaque.

7.  Sequence Counters

   This section describes the general scheme for
   further processing, bootstrap and subsequently present operation
   of sequence counters in RPL, such as the DIO message for
   further processing if eligible.

   1.  If DODAGVersionNumber in the
   DIO message is malformed, then message, the DIO message is not
       eligible for further processing DAOSequence in the DAO message, and a node MUST silently discard
       it.

   2.  If the sender of Path
   Sequence in the DIO message is a member of Transit Information option.

7.1.  Sequence Counter Overview

   This specification utilizes three different sequence numbers to
   validate the candidate
       neighbor set freshness and the DIO message synchronization of protocol
   information:

   DODAGVersionNumber:   This sequence counter is not malformed, the node MUST
       process present in the DIO.

7.2.3.1.  DIO Message Processing

   As DIO messages are received from candidate neighbors, the neighbors
   may be promoted
         base to DODAG parents by following indicate the rules Version of the DODAG
   discovery as described in Section 7.2.  When a node places being formed.  The
         DODAGVersionNumber is monotonically incremented by the root
         each time the root decides to form a neighbor
   into new Version of the DODAG parent set,
         in order to revalidate the node becomes attached integrity and allow a global repairs
         to occur.  The DODAGVersionNumber is propagated unchanged Down
         the DODAG
   through as routers join the new DODAG parent node. Version.  The most preferred parent should be used to restrict which other
   nodes may become DODAG parents.  Some nodes
         DODAGVersionNumber is globally significant in the a DODAG parent set
   may be and
         indicates the Version of the DODAG that a rank less than or equal router is operating
         in.  An older (lesser) value indicates that the originating
         router has not migrated to the most preferred new DODAG
   parent.  (This case may occur, for example, if an energy constrained
   device is at a lesser rank but should Version and can not be avoided
         used as per an
   optimization objective, resulting in a more preferred parent at a
   greater rank).

7.3.  DIO Transmission

   RPL nodes transmit DIOs using a Trickle timer
   ([I-D.ietf-roll-trickle]).  A DIO from a sender with a lower DAGRank
   that causes no changes to the recipient's parent set, preferred
   parent, or Rank SHOULD be considered consistent with respect to once the
   Trickle timer.

   The following packets and events MUST be considered inconsistencies
   with respect receiving node has migrated to the Trickle timer, and cause
         newer DODAG Version.

   DAOSequence:   This sequence counter is present in the Trickle timer DAO base to
   reset:

   o  When a node detects an inconsistency when forwarding a packet, as
      detailed in Section 10.2.

   o  When a node receives
         correlate a multicast DIS DAO message without a Solicited
      Information option.

   o  When a node receives a multicast DIS with a Solicited Information
      option and the node matches all of the predicates in the Solicited
      Information option.

   o  When a node joins a new DODAG Version (e.g. by updating its
      DODAGVersionNumber, joining a new RPL Instance, etc.)

   Note that this list DAO ACK message.  The DAOSequence
         number is not exhaustive, and an implementation MAY
   consider other messages or events to be inconsistencies.

   A node SHOULD NOT reset its DIO trickle timer in response to unicast
   DIS messages.  When a node receives a unicast DIS without a Solicited
   Information option, it MUST unicast a DIO locally significant to the sender in response.
   This DIO MUST include a DODAG Configuration option.  When a node
   receives that issues a unicast DIS DAO
         message with a Solicited Information option,
   if it satisfies for its own consumption to detect the predicates loss of a DAO
         message and enable retries.

   Path Sequence:   This sequence counter is present in the Solicited Transit
         Information option it
   MUST unicast in a DIO DAO message.  The purpose of this
         counter is to the sender in response.  This unicast DIO MUST
   include differentiate a DODAG Configuration Option.  Thus movement where a node may transmit newer route
         supersedes a
   unicast DIS message to stale one from a potential DODAG parent route redundancy scenario where
         multiple routes exist in order to probe parallel for a same target.  The Path
         Sequence is globally significant in a DODAG Configuration and other parameters.

7.3.1.  Trickle Parameters

   The configuration parameters indicates the
         freshness of the trickle timer are specified as
   follows:

   Imin: learned from route to the DIO message as (2^DIOIntervalMin)ms.  The
         default associated target.  An older
         (lesser) value of DIOIntervalMin is DEFAULT_DIO_INTERVAL_MIN.

   Imax: learned received from an originating router indicates
         that the DIO message originating router holds stale routing states and the
         originating router should not be considered anymore as DIOIntervalDoublings. a
         potential next-hop for the target.  The
         default value of DIOIntervalDoublings Path Sequence is
         DEFAULT_DIO_INTERVAL_DOUBLINGS.

   k:    learned from
         computed by the DIO message as DIORedundancyConstant.  The
         default value of DIORedundancyConstant node that advertises the target, that is
         DEFAULT_DIO_REDUNDANCY_CONSTANT.  In RPL, when k has the value
         target itself or a router that advertises a target on behalf of 0x00 this
         a host, and is to be treated unchanged as the DAO content is propagated
         towards the root by parent routers.  If a redundancy constant of
         infinity in RPL, i.e.  Trickle never suppresses messages.

7.4.  DODAG Selection

   The DODAG selection host does not pass a
         counter to its router, then the router is implementation in charge of
         computing the Path Sequence on behalf of the host and OF dependent.  Nodes SHOULD
   prefer the host
         can only register to join DODAGs one router for RPLInstanceIDs advertising OCPs and
   destinations compatible with their implementation specific
   objectives.  In order to limit erratic movements, and all metrics
   being equal, nodes SHOULD keep their previous selection.  Also, nodes
   SHOULD provide that purpose.  If a means to filter out DAO
         message containing a parent whose availability same target is
   detected as fluctuating, at least when more stable choices are
   available.

   When connection issued to multiple parents
         at a grounded DODAG is not possible or preferable given point of time for
   security or other reasons, scattered DODAGs MAY aggregate as much as
   possible into larger DODAGs in order to allow connectivity within the
   LLN.

   A node SHOULD verify that bidirectional connectivity and adequate
   link quality purpose of route redundancy,
         then the Path Sequence is available with a candidate neighbor before it
   considers the same in all the DAO messages for
         that candidate as a DODAG parent.

7.5. same target.

7.2.  Sequence Counter Operation as a Leaf Node

   In some cases a

   RPL node may attach to sequence counters are subdivided in a DODAG 'lollipop' fashion
   ([Perlman83]), where the values from 128 and greater are used as a leaf node only.
   One example of such a case is when
   linear sequence to indicate a node does not understand restart and bootstrap the RPL
   Instance's OF counter, and
   the values less than or advertised metric/constraint.  As specified in
   Section 16.6 related equal to policy function, the node may either join the
   DODAG 127 used as a leaf node or may not join the DODAG.  As mentioned circular sequence
   number space of size 128 as in
   Section 16.5, it [RFC1982].  Consideration is then recommended given to log a fault.

   A leaf node does not extend DODAG connectivity but in some cases
   the
   leaf node may still need mode of operation when transitioning from the linear region to transmit DIOs on occasion, in particular
   the circular region.  Finally, when operating in the leaf node may circular region,
   if sequence numbers are detected to be too far apart then they are
   not have always been acting comparable, as detailed below.

   A window of comparison, SEQUENCE_WINDOW = 16, is configured based on
   a leaf node and value of 2^N, where N is defined to be 4 in this specification.

   For a given sequence counter,

   1.  The sequence counter SHOULD be initialized to an inconsistency implementation
       defined value which is detected. 128 or greater prior to use.  A node operating as
       recommended value is 240 (256 - SEQUENCE_WINDOW).

   2.  When a leaf node must obey sequence counter increment would cause the following rules:

   1.  It MUST NOT transmit DIOs containing sequence
       counter to increment beyond its maximum value, the DAG Metric Container.

   2.  Its DIOs sequence
       counter MUST advertise wrap back to zero.  When incrementing a DAGRank of INFINITE_RANK. sequence
       counter greater than or equal to 128, the maximum value is 255.
       When incrementing a sequence counter less than 128, the maximum
       value is 127.

   3.  It MAY suppress DIO transmission, except DIO transmission  When comparing two sequence counters, the following rules MUST
       NOT be suppressed when DIO transmission has been triggered due to
       detection of inconsistency when
       applied:

       1.  When a packet first sequence counter A is being forwarded or in
       response to a unicast DIS message.

   4.  It MAY transmit unicast DAOs as described in Section 8.2.

   5.  It MAY transmit multicast DAOs to the '1 hop' neighborhood as
       described in Section 8.10.

   A particular case that requires a leaf node to send interval [0..127]
           and a DIO second sequence counter B is if that
   leaf node was a prior member of another DODAG in [128..255]:

           1.  If B-A is less than or equal to SEQUENCE_WINDOW, then B
               is greater than A, A is less than B, and another node
   forwards a message assuming the old topology, triggering an
   inconsistency.  The leaf node needs two are not
               equal.

           2.  If B-A is greater than SEQUENCE_WINDOW, then A is greater
               than B, B is less than A, and the two are not equal.

       2.  In the case where both sequence counters to transmit a DIO in order be compared are
           less than or equal to
   repair 127, and in the inconsistency.  Note that due case where both
           sequence counters to be compared are greater than or equal to
           128:

           1.  If the lossy nature absolute magnitude of LLNs,
   even though difference between the leaf node may have optimistically poisoned its routes
   by advertising two
               sequence counters is less than or equal to
               SEQUENCE_WINDOW, then a rank of INFINITE_RANK comparison as described in the old DODAG prior
               [RFC1982] is used to
   becoming a leaf node, that advertisement may have become lost determine the relationships greater
               than, less than, and equal.

           2.  If the absolute magnitude of difference of the two
               sequence counters is greater than SEQUENCE_WINDOW, then a
   leaf node must be capable to send a DIO later in order
               desynchronization has occurred and the two sequence
               numbers are not comparable.

   4.  If two sequence numbers are determined to repair be not comparable, i.e.
       the
   inconsistency.

   In general it is results of the comparison are not expected that such defined, then a leaf node would advertise
   itself should
       consider the comparison as a router.

7.6.  Administrative Rank

   In some cases if it might be beneficial has evaluated in such a way so
       as to give precedence to adjust the rank advertised by
   a node beyond sequence number that computed by the OF based on some implementation
   specific policy and properties of has most
       recently been observed to increment.  Failing this, the node.  For example, a node that
   has limited battery
       should be a leaf unless there is no other choice,
   and may then augment the rank computation specified by consider the OF comparison as if it has evaluated in
   order such a
       way so as to expose an exaggerated rank. minimize the resulting changes to its own state.

8.  Downward  Upward Routes

   This section describes how RPL discovers and maintains downward upward routes.  RPL constructs and maintains downward routes with
   Destination Advertisement Object (DAO) messages.  Downward routes
   support of P2MP flows, from
   It describes the use of DODAG roots toward Information Objects (DIOs), the leaves.
   Downward routes also support P2P flows: P2P
   messages can flow used to a
   DODAG Root through an upward route, then away from the discover and maintain these routes.  It specifies
   how RPL generates and responds to DIOs.  It also describes DODAG Root
   Information Solicitation (DIS) messages, which are used to trigger
   DIO transmissions.

8.1.  DIO Base Rules

   1.  For the following DIO Base fields, a destination through node that is not a downward route.

   This specification describes DODAG
       root MUST advertise the two modes a RPL Instance may choose
   from for maintaining downward routes. same values as its preferred DODAG parent
       (defined in Section 8.2.1).  In this way these values will
       propagate Down the first mode, call
   "storing," nodes store downward routing tables for their sub-DODAG.
   Each hop on DODAG unchanged and advertised by every node
       that has a downward route in a storing network examines its
   routing table to decide on that DODAG root.  These fields are:
       1.  Grounded (G)
       2.  Mode of Operation (MOP)
       3.  DAGPreference (Prf)
       4.  Version
       5.  RPLInstanceID
       6.  DODAGID

   2.  A node MAY update the next hop.  In following fields at each hop:
       1.  Rank
       2.  DTSN

   3.  The DODAGID field each root sets MUST be unique within the second mode, called
   "non-storing," nodes do not store downward routing tables.  Downward
   packets are routed with source routes populated by a DODAG Root. RPL allows a simple one-hop P2P optimization for both storing
       Instance and
   non-storing networks.  A node may send MUST be a P2P packet destined routable IPv6 address belonging to the
       root.

8.2.  Upward Route Discovery and Maintenance

   Upward route discovery allows a
   one-hop neighbor directly node to join a DODAG by discovering
   neighbors that node.

8.1.  Destination Advertisement Parents

   To establish downward routes, RPL nodes send DAO messages upwards.
   The next hop destinations of these DAO messages are called DAO
   parents.  The collection members of the DODAG of interest and identifying a node's DAO
   set of parents.  The exact policies for selecting neighbors and
   parents is called implementation-dependent and driven by the OF.  This
   section specifies the DAO
   parent set.

   o  A node's DAO parent set MUST be of rules those policies must follow for
   interoperability.

8.2.1.  Neighbors and Parents within a DODAG Version

   RPL's upward route discovery algorithms and processing are in terms
   of three logical sets of link-local nodes.  First, the candidate
   neighbor set is a subset of its DODAG parent set.

   o  A node MUST NOT unicast DAOs to the nodes that are not DAO parents.

   o  A node MAY link-local multicast DAO messages.

   o can be reached via link-
   local multicast.  The IPv6 Source Address selection of a DAO message MUST be this set is implementation-
   dependent and OF-dependent.  Second, the link local
      address parent set is a restricted
   subset of the sending node.

   o  If candidate neighbor set.  Finally, the preferred parent
   is a node sends member of the parent set that is the preferred next hop in
   upward routes.  The preferred parent is conceptually a DAO to one DAO parent, single parent
   although it MUST send may be a DAO with
      the same DAOSequence to all other DAO parents.

   The selection set of DAO multiple parents is implementation and objective function
   specific.

8.2.  Downward Route Discovery if those parents are
   equally preferred and Maintenance

   Destination Advertisement may be configured to have identical rank.

   More precisely:

   1.  The DODAG parent set MUST be entirely disabled,
   or operate in either a storing or non-storing mode, as reported in
   the MOP in subset of the DIO message.

   1.  All nodes who join a candidate neighbor
       set.

   2.  A DODAG root MUST abide by the MOP setting from the
       root.  Nodes that do not have the capability to fully participate
       as a router MAY join the DODAG as a leaf.

   2.  If the MOP parent set of size zero.

   3.  A node that is 000, indicating no downward routing, nodes MUST NOT
       transmit DAO messages, and not a DODAG root MAY ignore DAO messages.

   3.  In non-storing mode, the maintain a DODAG Root parent set
       of size greater than or equal to one.

   4.  A node's preferred DODAG parent MUST store source routing
       table entries for all destinations learned from DAOs.

   4.  In storing mode, all non-root, non-leaf nodes be a member of its DODAG
       parent set.

   5.  A node's rank MUST store routing
       table entries for be greater than all destinations learned from DAOs.

   A DODAG can have one of several possible modes elements of operation, as
   defined by its DODAG
       parent set.

   6.  When Neighbor Unreachability Detection (NUD) [RFC4861], or an
       equivalent mechanism, determines that a neighbor is no longer
       reachable, a RPL node MUST NOT consider this node in the MOP field.  Either
       candidate neighbor set when calculating and advertising routes
       until it does not support downward
   routes, determines that it supports downward routes is again reachable.  Routes through source routing
       an unreachable neighbor MUST be removed from DODAG
   Roots, or it supports downward routes through in-network routing
   tables.  When downward routes are supported through in-network
   routing tables, the multicast operation defined in this specification
   may or may not be supported, also as indicated by routing table.

   These rules ensure that there is a consistent partial order on nodes
   within the MOP field. DODAG.  As
   of this specification RPL does long as node ranks do not support mixed-mode operation,
   where some nodes source change, following the
   above rules ensures that every node's route and other store routing tables: future
   extensions to RPL may support this mode of operation.

8.3.  DAO Base Rules

   1.  Each time a node generates a new DAO, the DAOSequence field MUST
       increment by at least one since DODAG root is loop-
   free, as rank decreases on each hop to the last generated DAO.

   2.  Each time root.

   The OF can guide candidate neighbor set and parent set selection, as
   discussed in [I-D.ietf-roll-of0].

8.2.2.  Neighbors and Parents across DODAG Versions

   The above rules govern a node link-local multicasts single DODAG Version.  The rules in this
   section define how RPL operates when there are multiple DODAG
   Versions:

8.2.2.1.  DODAG Version

   1.  The tuple (RPLInstanceID, DODAGID, DODAGVersionNumber) uniquely
       defines a DAO, the DAOSequence
       field MUST increment DODAG Version.  Every element of a node's DODAG parent
       set, as conveyed by one since the last link local multicast
       DAO.

   3.  The RPLInstanceID and DODAGID fields of a DAO heard DIO message from each DODAG
       parent, MUST be belong to the same
       value as the members DODAG Version.  Elements of the a
       node's parent candidate neighbor set and the DIOs it
       transmits.

   4. MAY belong to different DODAG
       Versions.

   2.  A node MAY set the K flag in is a unicast DAO message to solicit member of a
       unicast DAO-ACK in response in order DODAG Version if every element of its
       DODAG parent set belongs to confirm the attempt.  A that DODAG Version, or if that node receiving a unicast DAO message with
       is the K flag set SHOULD
       respond with a DAO-ACK. root of the corresponding DODAG.

   3.  A node receiving a DAO message without
       the K flag set MAY respond with a DAO-ACK, especially to report
       an error condition.

   5.  Nodes SHOULD ignore DAOs without newer sequence numbers and MUST NOT process them further.

   Unlike the Version field send DIOs for DODAG Versions of a DIO, which it is incremented only by not a
       member.

   4.  DODAG Root roots MAY increment the DODAGVersionNumber that they
       advertise and repeated unchanged by other nodes, DAOSequence values
   are unique thus move to each node.  The sequence number space for unicast and
   multicast DAO messages can be either the same or distinct.

8.4.  DAO Transmission Scheduling

   Because DAOs flow upwards, receiving a unicast DAO can trigger
   sending a unicast DAO.

   1.  On receiving new DODAG Version.  When a unicast DAO with DODAG
       root increments its DODAGVersionNumber, it MUST follow the
       conventions of Serial Number Arithmetic as described in
       Section 7.  Events triggering the increment of the
       DODAGVersionNumber are described later in this section and in
       Section 17.

   5.  Within a new DAOSequence, given DODAG, a node SHOULD
       send that is a DAO.  It SHOULD not a root MUST NOT send this DAO immediately.  It SHOULD
       delay sending
       advertise a DODAGVersionNumber higher than the DAO in order to aggregate DAO information from
       other nodes for which highest
       DODAGVersionNumber it has heard.  Higher is defined as the
       greater-than operator in Section 7.

   6.  Once a DAO parent.

   2.  A node SHOULD delay has advertised a DODAG Version by sending a DAO with DIO, it
       MUST NOT be a timer (DelayDAO).
       Receiving member of a DAO starts previous DODAG Version of the DelayDAO timer.  DAOs received while same
       DODAG (i.e. with the DelayDAO timer same RPLInstanceID, the same DODAGID, and a
       lower DODAGVersionNumber).  Lower is active do not reset defined as the timer. less-than
       operator in Section 7.

   When the
       DelayDAO timer expires, the node sends a DAO.

   3.  When a node adds a node to its DAO DODAG parent set, it SHOULD schedule set becomes empty on a DAO transmission.

   DelayDAO's value and calculation is implementation-dependent.

8.5.  Triggering DAO Messages

   Nodes can trigger their sub-DODAG to send DAO messages.  Each node
   maintains a DAO Trigger Sequence Number (DTSN), which it communicates
   through DIO messages.

   1.  If that is not a node hears one of its DAO parents increment its DTSN, root,
   (i.e. the last parent has been removed, causing the node MUST schedule a DAO transmission using rules to no longer
   be associated with that DODAG), then the DODAG information should not
   be suppressed until after the expiration of an implementation-
   specific local timer in Section 8.3
       and Section 8.4.

   2.  In non-storing mode, order to observe if a node hears one of its DAO the DODAGVersionNumber
   has been incremented, should any new parents
       increment its DTSN, appear for the node MUST increment its own DTSN.

   In a storing mode DODAG.
   This will help protect against the possibility of operation, a storing loops that may
   occur if that node MAY increment DTSN in
   order were to reliably trigger a set of DAO updates from inadvertently rejoin the old DODAG Version
   in its immediate
   children, as part of routine routing table updates and maintenance.
   In a storing mode of operation it own prior sub-DODAG.

   As the DODAGVersionNumber is not necessary to trigger DAO
   updates incremented, a new DODAG Version spreads
   outward from the entire sub-DODAG, since that state information will
   percolate hop-by-hop up the DODAG in root.  A parent that advertises the storing mode of operation.

   In a non-storing mode of operation, a DTSN increment will also cause new
   DODAGVersionNumber cannot belong to the immediate children sub-DODAG of a node to increment their DTSN in turn,
   triggering
   advertising an older DODAGVersionNumber.  Therefore a set of DAO updates from the entire sub-DODAG.  In node can safely
   add a non-
   storing mode parent of operation typically only the root would independently
   increment the DTSN when any Rank with a DAO refresh is needed but newer DODAGVersionNumber without
   forming a global repair
   (such as by incrementing DODAGVersionNumber) is not desired.  In loop.

   For example, suppose that a
   non-storing mode of operation typically all non-root nodes would only
   increment their DTSN when their parent(s) are observed node has left a DODAG with
   DODAGVersionNumber N. Suppose that node had a sub-DODAG, and did
   attempt to do so.

   In the case of triggered DAOs, selecting poison that sub-DODAG by advertising a proper DAODelay can
   greatly reduce the number rank of DAOs transmitted.  The trigger flows
   down the DODAG;
   INFINITE_RANK, but those advertisements may have become lost in the best case the DAOs flow up
   LLN.  Then, if the DODAG such that
   leaves send DAOs first, with each node sending did observe a DAO only once.  Such candidate neighbor advertising
   a scheduling position in that original DODAG at DODAGVersionNumber N, that
   candidate neighbor could be approximated by setting DAODelay inversely
   proportional possibly have been in the node's former sub-
   DODAG and there is a possible case where to Rank.  Note add that candidate
   neighbor as a parent could cause a loop.  If that candidate neighbor
   in this suggestion case is intended as an
   optimization observed to allow efficient aggregation -- advertise a DODAGVersionNumber N+1, then
   that candidate neighbor is certain to be safe, since it is certain
   not required for
   correct operation to be in that original node's sub-DODAG as it has been able to
   increment the general case.

8.6.  Structure of DAO Messages

   DAOs follow DODAGVersionNumber by hearing from the DODAG root while
   that original node was detached.  It is for this reason that it is
   useful for the detached node to remember the original DODAG
   information, including the DODAGVersionNumber N.

   Exactly when a common structure in both storing DODAG Root increments the DODAGVersionNumber is
   implementation and non-storing
   networks.  Later sections describe further details for each mode application-dependent and outside the scope of
   operation.

   1.  RPL nodes MUST
   this document.  Examples include one incrementing the DODAGVersionNumber
   periodically, upon administrative intervention, or more RPL Target Options in each DAO
       they transmit.  One RPL Target Option MUST have on application-
   level detection of lost connectivity or DODAG inefficiency.

   After a prefix that
       includes the node's IPv6 address if that node needs transitions to and advertises a new DODAG Version, the
   rules above make it unable to advertise the previous DODAG Version
   (prior DODAGVersionNumber) once it has committed to
       provision downward routes advertising the
   new DODAG Version.

8.2.2.2.  DODAG Roots

   1.  A DODAG root without possibility to that node. satisfy the application-
       defined goal MUST NOT set the Grounded bit.

   2.  A RPL Target Option in a unicast DAO DODAG root MUST be followed by advertise a
       Transit Information Option. rank of ROOT_RANK.

   3.  Multicast DAOs MUST NOT include Transit Information options.

   4.  If a  A node receives whose DODAG parent set is empty MAY become the DODAG Root
       of a DAO floating DODAG.  It MAY also set its DAGPreference such that does not follow the above three
       rules,
       it MUST discard the DAO without further processing.

8.7.  Non-storing Mode is less preferred.

   In non-storing mode, RPL routes messages downward using source
   routing.  The following rule applies to nodes a deployment that are in non-storing
   mode.  Storing mode has uses non-RPL links to federate a separate set of rules, described in
   Section 8.8.

   1.  The Parent Address field number of a Transit Information Option MUST
       contain one or more addresses.  All of these addresses MUST be
       addresses of DAO parents LLN
   roots, it is possible to run RPL over those non-RPL links and use one
   router as a "backbone root".  The backbone root is the virtual root
   of the sender.

   2.  On receiving a unicast DAO, DODAG, and exposes a node MUST forward rank of BASE_RANK over the DAO upwards.
       This forwarding MAY use any parent in backbone.  All
   the parent set.  Note LLN roots that
       this forwarding may be delayed in support of aggregation as
       described below, but are parented to that such a delay is not required backbone root, including the
   backbone root if it also serves as LLN root itself, expose a
       node's resources do not support it.

   3.  When rank of
   ROOT_RANK to the LLN.  These virtual roots are part of the same DODAG
   and advertise the same DODAGID.  They coordinate DODAGVersionNumbers
   and other DODAG parameters with the virtual root over the backbone.
   The method of coordination is outside the scope of this
   specification.

8.2.2.3.  DODAG Selection

   The objective function and the set of advertised routing metrics and
   constraints of a node removes DAG determines how a node from selects its DAO neighbor set,
   parent set, it MAY
       generate a new DAO with an updated Transit Information option.

   In non-storing mode, a node uses DAOs to report its DAO parents to and preferred parents.  This selection implicitly also
   determines the DODAG Root.  The DODAG Root within a DAG.  Such selection can piece together include
   administrative preference (Prf) as well as metrics or other
   considerations.

   If a downward route node has the option to join a more preferred DODAG while still
   meeting other optimization objectives, then the node will generally
   seek to join the more preferred DODAG as determined by using DAO parent sets from each node in the route.  The
   purpose of this per-hop route calculation OF.  All
   else being equal, it is left to minimize traffic when
   DAO parents change.  If nodes reported complete source routes, then
   on a DAO parent change the entire sub-DODAG would have to send new
   DAOs implementation to the determine which
   DODAG Root.  Therefore, in non-storing mode, is most preferred (since, as a reminder, a node can
   send must only join
   one DODAG per RPL Instance).

8.2.2.4.  Rank and Movement within a DODAG Version

   1.  A node MUST NOT advertise a single DAO, although it might choose to send more Rank less than one
   DAO or equal to each any member
       of multiple DAO parents.

   Nodes aggregate DAOs by sending a single DAO with multiple RPL Target
   Options.  Each RPL Target Option has its own, immediately following,
   Transit Information options.

8.8.  Storing Mode

   In storing mode, RPL routes messages downward by parent set within the IPv6 destination
   address.  The following rule apply to nodes that are in storing mode:

   1.  The Parent Address field of a Transmit Information option MUST be
       empty. DODAG Version.

   2.  On receiving a unicast DAO, a  A node MUST compute if MAY advertise a Rank lower than its prior advertisement
       within the DAO would
       change DODAG Version.

   3.  Let L be the set of prefixes lowest rank within a DODAG Version that the a given node itself advertises.  If
       so,
       has advertised.  Within the same DODAG Version, that node MUST generate a new DAO and transmit it, following
       the rules in Section 8.4.  Such a change includes receiving a No-
       Path DAO.

   3.  When
       NOT advertise an effective rank higher than L +
       DAGMaxRankIncrease.  INFINITE_RANK is an exception to this rule:
       a node generates MAY advertise an INFINITE_RANK within a new DAO, DODAG version
       without restriction.  If a node's Rank were to be higher than
       allowed by L + DAGMaxRankIncrease, when it SHOULD unicast advertises Rank it to each of
       its DAO parents.  It
       MUST NOT unicast the DAO advertise its Rank as INFINITE_RANK.

   4.  A node MAY, at any time, choose to nodes join a different DODAG within
       a RPL Instance.  Such a join has no rank restrictions, unless
       that are
       not DAO parents.

   4.  When different DODAG is a DODAG Version of which this node removes has
       previously been a member, in which case the rule of the previous
       bullet (3) must be observed.  Until a node from transmits a DIO
       indicating its DAO parent set, new DODAG membership, it SHOULD
       send a No-Path DAO (Section 5.4.3) to that removed DAO parent to
       invalidate MUST forward packets
       along the existing route. previous DODAG.

   5.  If messages to an  A node MAY, at any time after hearing the next DODAGVersionNumber
       advertised downwards address suffer from a
       forwarding error, neighbor unreachable detected (NUD), or similar
       failure, a node MAY mark suitable DODAG parents, choose to migrate to the address as unreachable and generate
       next DODAG Version within the DODAG.

   Conceptually, an appropriate No-Path DAO.

   DAOs advertise what destination addresses and prefixes implementation is maintaining a node has
   routes to.  Unlike in non-storing mode, these DAOs do DODAG parent set
   within the DODAG Version.  Movement entails changes to the DODAG
   parent set.  Moving Up does not communicate
   information about present the routes themselves: risk to create a loop but
   moving Down might, so that information is stored
   within the network and operation is implicit from the IPv6 source address. subject to additional
   constraints.

   When a storing node generates a DAO, it uses migrates to the stored state next DODAG Version, the DODAG parent set
   needs to be rebuilt for the new Version.  An implementation could
   defer to migrate for some reasonable amount of DAOs time, to see if some
   other neighbors with potentially better metrics but higher rank
   announce themselves.  Similarly, when a node jumps into a new DODAG
   it has received needs to produce construct a new DODAG parent set of RPL Target options and their
   associated Transmit Information options.

   Because for this information is stored within new DODAG.

   If a network, in storing mode
   DAOs are communicated directly node needs to DAO parents, who store this
   information.

8.9.  Path Control

   A DAO message from move Down a DODAG that it is attached to,
   increasing its Rank, then it MAY poison its routes and delay before
   moving as described in Section 8.2.2.5.

   A node contains one or more Target Options.  Each
   Target Option specifies either the node's prefix, a prefix of
   addresses reachable outside the LLN, or is allowed to join any DODAG Version that it has never been a destination in the node's
   sub-DODAG.  The Path Control field
   prior member of without any restrictions, but if the Transit Information option
   allows nodes to request multiple downward routes.  A node constructs
   the Path Control field of has been a Transit Information option as follows:

   1.  The bit width
   prior member of the path control field MUST be equal DODAG Version then it must continue to observe
   the
       value (PCS + 1), where PCS is specified in the control field of
       the DODAG Configuration Option.  Bits greater than or equal to
       the value (PCS + 1) MUST be cleared on transmission and MUST be
       ignored on reception.  Bits below rule that value are considered
       "active" bits.

   2.  For a RPL Target option describing a node's own address or a
       prefix outside the LLN, it may not advertise an effective rank higher than
   L+DAGMaxRankIncrease at least one active bit of any point in the Path
       Control field MUST be set.  More active bits life of the Path Control
       field MAY DODAG Version.
   This rule must be set.

   3.  If observed so as not to create a node receives multiple DAOs with the same RPL Target option,
       it MUST bitwise-OR the Path Control fields it receives.  This
       aggregated bitwise-OR represents the number of downward routes loophole that would
   allow the prefix requests.

   4.  When a node sends a DAO to one of effectively increment its DAO parents, it MUST select
       one or more of the set, active bits in rank all the aggregated Path
       Control field.  The DAO it transmits way to its parent MUST
   INFINITE_RANK, which may have
       these active bits set and all impact on other active bits cleared.

   5.  For the RPL Target option nodes and DAOSequence number, the DAOs create a
   resource-wasting count-to-infinity scenario.

8.2.2.5.  Poisoning

   1.  A node
       sends to different DAO parents MUST have disjoint sets poisons routes by advertising a Rank of active
       Path Control bits. INFINITE_RANK.

   2.  A node MUST NOT set the same active bit on
       DAOs to two different DAO parents.

   6.  Path control bits SHOULD be allocated in order have any nodes with a Rank of preference,
       such that INFINITE_RANK in
       its parent set.

   Although an implementation may advertise INFINITE_RANK for the most significant bits, or groupings
   purposes of bits, are
       allocated to poisoning, doing so is not the most preferred DAO parents same as determined by the
       node.

   7.  In a non-storing mode of operation, setting Rank to
   INFINITE_RANK.  For example, a node MAY pass DAOs through
       without performing any further processing on the Path Control
       field.

   8.  A node MUST NOT unicast may continue to send data packets
   whose RPL option ([I-D.ietf-6man-rpl-option]) includes a DAO Rank that has no active bits is
   not INFINITE_RANK, yet still advertise INFINITE_RANK in the Path
       Control field set.

   The Path Control field allows its DIOs.

   When a node to bound how many downward
   routes will be generated (former) parent is observed to it.  It sets advertise a number Rank of bits in the Path
   Control field equal to
   INFINITE_RANK, that (former) parent has detached from the maximum number of downward routes it
   prefers.  Each bit DODAG and
   is sent to at most one DAO parent; clusters of
   bits can be sent no longer able to act as a single DAO parent for it to divide among its
   own DAO parents.

8.10.  Multicast Destination Advertisement Messages

   A special case of DAO operation, distinct from unicast DAO operation, parent, nor is multicast DAO operation which there any why that
   another node may be used considered to populate '1-hop'
   routing table entries. have a Rank greater-than
   INFINITE_RANK.  Therefore that (former) parent cannot act as a parent
   any longer and is removed from the parent set.

8.2.2.6.  Detaching
   1.  A node MAY multicast a DAO message unable to the link-local scope all-
       nodes multicast address FF02::1.

   2.  A multicast DAO message MUST be used only to advertise
       information about self, i.e. prefixes directly stay connected to or
       owned by this node, such as a multicast group DODAG within a given DODAG
       Version, i.e. that cannot retain non-empty parent set without
       violating the rules of this specification, MAY detach from this
       DODAG Version.  A node is
       subscribed to or that detaches becomes root of its own
       floating DODAG and SHOULD immediately advertise this new
       situation in a global address owned by the node.

   3.  A multicast DAO message MUST NOT be used DIO as an alternate to relay connectivity
       information learned (e.g. through unicast DAO) from another node.

   4.  Information obtained from poisoning.

8.2.2.7.  Following a multicast DAO MAY be installed in the
       routing table and MAY be propagated by Parent

   1.  If a node in unicast DAOs.

   5.  A node MUST NOT perform any other DAO related processing on a
       received multicast DAO, in particular receives a DIO from one of its DODAG parents,
       indicating that the parent has left the DODAG, that node MUST NOT perform SHOULD
       stay in its current DODAG through an alternative DODAG parent, if
       possible.  It MAY follow the
       actions of a DAO leaving parent.

   A DODAG parent upon receipt of a multicast DAO.

   o  The multicast DAO may be used have moved, migrated to enable direct P2P communication,
      without needing the RPL routing structure next DODAG Version, or
   jumped to relay a different DODAG.  A node ought to give some preference to
   remaining in the packets.

   o  The multicast DAO does not presume any DODAG relationship between current DODAG, if possible via an alternate parent,
   but ought to follow the emitter and parent if there are no other options.

8.2.3.  DIO Message Communication

   When an DIO message is received, the receiver.

9.  Security Mechanisms

   This section describes receiving node must first
   determine whether or not the generation DIO message should be accepted for
   further processing, and subsequently present the DIO message for
   further processing of secure RPL
   messages.  The high order bit of if eligible.

   1.  If the RPL DIO message code identifies
   whether a RPL is malformed, then the DIO message is secure or not.  In addition to secure
   versions of basic control messages (DIS, DIO, DAO, DAO-Ack), RPL has
   several messages which are relevant only in networks with security
   enabled.

9.1.  Security Overview

   RPL supports three security modes:

   o  Insecure.  In this security mode, RPL uses insecure DIS, DIO, DAO, not
       eligible for further processing and DAO-Ack messages.

   o  Pre-installed.  In this security mode, RPL uses secure messages.
      To join a RPL Instance, a node must have a pre-installed key.
      Nodes use this to provide MUST silently discard
       it.  (See Section 17 for error logging).

   2.  If the sender of the DIO message confidentiality, integrity, is a member of the candidate
       neighbor set and
      authenticity.  A the DIO message is not malformed, the node may, using this preinstalled key, join MUST
       process the
      RPL network DIO.

8.2.3.1.  DIO Message Processing

   As DIO messages are received from candidate neighbors, the neighbors
   may be promoted to DODAG parents by following the rules of DODAG
   discovery as either a host or a router.

   o  Authenticated.  In this security mode, RPL uses secure messages.
      To join a RPL Instance, described in Section 8.2.  When a node must have a pre-installed key.
      Node use this key to provide message confidentiality, integrity,
      and authenticity.  Using this preinstalled key, places a neighbor
   into the DODAG parent set, the node becomes attached to the DODAG
   through the new DODAG parent node.

   The most preferred parent should be used to restrict which other
   nodes may join become DODAG parents.  Some nodes in the network as DODAG parent set
   may be of a host only.  To join rank less than or equal to the network most preferred DODAG
   parent.  (This case may occur, for example, if an energy constrained
   device is at a lesser rank but should be avoided as per an
   optimization objective, resulting in a router, more preferred parent at a
      node must obtain
   greater rank).

8.3.  DIO Transmission

   RPL nodes transmit DIOs using a second key Trickle timer
   ([I-D.ietf-roll-trickle]).  A DIO from a key authority.  This key
      authority can authenticate sender with a lesser DAGRank
   that causes no changes to the requester is allowed recipient's parent set, preferred
   parent, or Rank SHOULD be considered consistent with respect to the
   Trickle timer.

   The following packets and events MUST be a
      router before providing it considered inconsistencies
   with respect to the second key.

   Whether or not Trickle timer, and cause the RPL Instance uses insecure mode is signaled by
   whether it uses secure RPL messages.  Whether Trickle timer to
   reset:

   o  When a secured network uses
   the pre-installed or authenticated mode is signaled by node detects an inconsistency when forwarding a packet, as
      detailed in Section 11.2.

   o  When a node receives a multicast DIS message without a Solicited
      Information option, unless a DIS flag restricts this behavior.

   o  When a node receives a multicast DIS with a Solicited Information
      option and the 'A' bit node matches all of the DAG Configuration option.

   RPL uses CCM* -- Counter with CBC-MAC (Cipher Block Chaining Message
   Authentication Code) -- as predicates in the cryptographic basis for its
   security[RFC3610].  In Solicited
      Information option, unless a DIS flag restricts this specification, CCM uses AES-128 as behavior.

   o  When a node joins a new DODAG Version (e.g. by updating its
   underlying cryptographic algorithm.  There are bits reserved in the
   security section to specify other algorithms in the future.

   All secured RPL messages have
      DODAGVersionNumber, joining a message authentication code (MAC).
   Secured RPL messages optionally also have encryption protection for
   confidentiality.  Secured new RPL message formats support both integrated
   encryption/authentication schemes (e.g., CCM*) as well as schemes Instance, etc.).

   Note that separately encrypt this list is not exhaustive, and authenticate packets.

9.2.  Installing Keys

   Authenticated mode requires a would-be router an implementation MAY
   consider other messages or events to dynamically install
   new keys once they have joined be inconsistencies.

   A node SHOULD NOT reset its DIO trickle timer in response to unicast
   DIS messages.  When a network as node receives a host.

   The exact message exchange to obtain such keys is TBD.  It will
   involve communication with unicast DIS without a key authority, possibly, using the pre-
   installed shared key.  The key authority can apply Solicited
   Information option, it MUST unicast a security policy
   to decide whether DIO to grant the would-be-router a new key.  These keys
   may have lifetimes (start and end times) associated with them, which
   nodes that support timestamps (described sender in Section 9.4.1) can use.

9.3.  Joining response.
   This DIO MUST include a Secure Network

   RPL security assumes that DODAG Configuration option.  When a node wishing to join
   receives a secured network
   has been preconfigured unicast DIS message with a shared key for communicating with
   neighbors Solicited Information option
   and matches the RPL root.  To join a secure RPL network, a node
   either listens for secure DIOs or triggers secure DIOs by sending predicates of that Solicited Information option, it
   MUST unicast a
   secure DIS.  In addition DIO to the DIO/DIS rules sender in Section 7, secure response.  This unicast DIO and DIS messages have these rules:

   1.  If sent, this initial secure DIS MUST NOT set the C bit, MUST set
       the KIM field to 0 (00), and MUST set the LVL field to 1 (001).
       The key used MUST be the preconfigured group key (Key Index
       0x00).

   2.  When
   include a DODAG Configuration Option.  Thus a node resets its Trickle timer in response to MAY transmit a secure
   unicast DIS
       (Section 7.3), the next DIO it transmits MUST be message to a secure DIO
       with the same security potential DODAG parent in order to probe for
   DODAG Configuration and other parameters.

8.3.1.  Trickle Parameters

   The configuration parameters of the trickle timer are specified as
   follows:

   Imin: learned from the secure DIS.  If a
       node receives multiple secure DIS messages before it transmits a
       DIO, DIO message as (2^DIOIntervalMin)ms.  The
         default value of DIOIntervalMin is DEFAULT_DIO_INTERVAL_MIN.

   Imax: learned from the secure DIO MUST have message as DIOIntervalDoublings.  The
         default value of DIOIntervalDoublings is
         DEFAULT_DIO_INTERVAL_DOUBLINGS.

   k:    learned from the same security configuration DIO message as DIORedundancyConstant.  The
         default value of DIORedundancyConstant is
         DEFAULT_DIO_REDUNDANCY_CONSTANT.  In RPL, when k has the last DIS it value
         of 0x00 this is responding to.

   3.  When a node sends a DIO in response to a unicast secure DIS
       (Section 7.3), the DIO MUST be treated as a secure DIO. redundancy constant of
         infinity in RPL, i.e.  Trickle never suppresses messages.

8.4.  DODAG Selection

   The above rules allow DODAG selection is implementation and OF dependent.  In order to
   limit erratic movements, and all metrics being equal, nodes SHOULD
   keep their previous selection.  Also, nodes SHOULD provide a node means to join
   filter out a secured RPL Instance using the
   preconfigured shared key.  Once parent whose availability is detected as fluctuating, at
   least when more stable choices are available.

   When connection to a node has joined the grounded DODAG using the
   preconfigured shared key, the 'A' bit of the Configuration option
   determines its capabilities.  If the 'A' bit of the Configuration is
   cleared, then nodes can use this preinstalled, shared key not possible or preferable for
   security or other reasons, scattered DODAGs MAY aggregate as much as
   possible into larger DODAGs in order to exchange
   messages normally: it can issue DIOs, DAOs, etc.

   If the 'A' bit of allow connectivity within the Configuration option is set:

   1.
   LLN.

   A node MUST NOT advertise a Rank besides INFINITE_RANK in secure
       DIOs secured with Key Index 0x00.  If a node receives a secure
       DIO SHOULD verify that advertises a Rank besides INFINITE_RANK bidirectional connectivity and adequate
   link quality is secured available with Key Index 0x00, a candidate neighbor before it MUST discard the message without further
       processing.

   2.  Secure DAOs using Key Index 0x00 MUST NOT have
   considers that candidate as a DODAG parent.

8.5.  Operation as a Leaf Node

   In some cases a RPL Target
       option with node may attach to a prefix besides the node's address.  If DODAG as a leaf node
       receives only.
   One example of such a secured DAO using the preinstalled, shared key where
       the RPL Target option case is when a node does not match the IPv6 source address, it
       MUST discard understand or does
   not support (policy) the secured DAO without further processing.

   The above rules mean that in RPL Instances where Instance's OF or advertised metric/
   constraint.  As specified in Section 17.6 related to policy function,
   the 'A' bit is set,
   using Key Index 0x00 a node can may either join the RPL Instance DODAG as a host but leaf node or may not join the
   DODAG.  As mentioned in Section 17.5, it is then recommended to log a router.
   fault.

   A leaf node must communicate with a key authority to obtain
   a key that will enable it does not extend DODAG connectivity but in some cases the
   leaf node may still need to act as a router.  Obtaining this key
   might require authentication on one or both ends.  This message
   exchange is TBD.

9.4.  Counter and Counter Compression

   Every secured RPL packet has a Counter field.  Depending transmit DIOs on whether occasion, in particular
   when the 'C' bit is set, this Counter field can be 1 or 4 bits.  RPL nodes
   send CC messages to force uncompressed Counter values, protect
   against replay attacks and synchronize counters.

   1.  If leaf node may not have always been acting as a leaf node and
   an inconsistency is sending detected.

   A node operating as a secured RPL packet, and leaf node must obey the Counter value following rules:

   1.  It MUST NOT transmit DIOs containing the DAG Metric Container.

   2.  Its DIOs MUST advertise a DAGRank of INFINITE_RANK.

   3.  It MAY suppress DIO transmission, unless the DIO transmission has
       been triggered due to detection of inconsistency when a packet is more than 255 greater than the last secured
       packet
       being forwarded or in response to a unicast DIS message, in which
       case the destination address, the node DIO transmission MUST NOT set the 'C'
       bit of the security section of be suppressed.

   4.  It MAY transmit unicast DAOs as described in Section 9.2.

   5.  It MAY transmit multicast DAOs to the packet.

   2.  If '1 hop' neighborhood as
       described in Section 9.10.

   A particular case that requires a leaf node receives to send a secure RPL message with the C bit set and DIO is
       uncertain if that
   leaf node was a prior member of the 32-bit counter value, it MAY send another DODAG and another node
   forwards a CC message
       with assuming the R bit cleared to obtain old topology, triggering an uncompressed counter value.
   inconsistency.  The Nonce field of the CC message SHOULD be a random or
       pseudorandom number.

   3.  If a leaf node receives a unicast CC message with the R bit cleared,
       and it is needs to transmit a member of or is DIO in the process of joining the
       associated DODAG, it SHOULD respond with a unicast CC message order to
   repair the sender.  This response MUST have inconsistency.  Note that due to the C bit lossy nature of LLNs,
   even though the security
       section cleared, MUST leaf node may have optimistically poisoned its routes
   by advertising a rank of INFINITE_RANK in the R bit set, and MUST old DODAG prior to
   becoming a leaf node, that advertisement may have the same
       Nonce, RPLInstanceID become lost and DODAGID fields as the message it
       received.

   4.  If a
   leaf node receives must be capable to send a multicast CC message, it MUST discard DIO later in order to repair the
       message with no further processing.

   These rules allow nodes to compress the Counter when destinations who
   received
   inconsistency.

   In the prior packet can determine general case, the full counter value.  If a leaf node cannot determine the full counter value, it can request the full
   counter with MUST NOT advertise itself as a CC message.

9.4.1.  Timestamp Counters
   router (i.e. send DIOs).

8.6.  Administrative Rank

   In some cases it might be beneficial to adjust the simplest case, the Counter value is an unsigned integer that rank advertised by
   a node increments beyond that computed by one or more the OF based on each secured RPL transmission.  The
   Counter MAY represent some implementation
   specific policy and properties of the node.  For example, a timestamp node that
   has the following properties:

   1.  The timestamp MUST be at least six octets long.

   2.  The timestamp MUST be in 1kHz (millisecond) granularity.

   3.  The timestamp start time MUST be January 1, 2010, 12:00:00AM UTC.

   4.  If the Counter represents such as timestamp, the Counter value
       MUST limited battery should be a value computed as follows.  Let T be the timestamp, S
       be the start time of the key in use, leaf unless there is no other choice,
   and E be may then augment the end time of rank computation specified by the
       key OF in use.  Both S
   order to expose an exaggerated rank.

9.  Downward Routes

   This section describes how RPL discovers and E are represented using maintains downward
   routes.  RPL constructs and maintains downward routes with
   Destination Advertisement Object (DAO) messages.  Downward routes
   support P2MP flows, from the same 3 rules
       as DODAG roots toward the timestamp described above.  If E > T < S, leaves.  Downward
   routes also support P2P flows: P2P messages can flow toward a DODAG
   Root (or a common ancestor) through an upward route, then away from
   the Counter
       is invalid and DODAG Root to a node MUST NOT generate destination through a packet.  Otherwise, downward route.

   This specification describes the
       Counter value is equal to T-S.

   5.  If two modes a RPL Instance may choose
   from for maintaining downward routes.  In the Counter represents such first mode, called
   "storing", nodes store downward routing tables for their sub-DODAG.
   Each hop on a timestamp, downward route in a node MAY set the
       'T' flag of storing network examines its
   routing table to decide on the security section of secured RPL packets.

   6.  If next hop.  In the Counter field does second mode, called
   "non-storing", nodes do not present such store downward routing tables.  Downward
   packets are routed with source routes populated by a timestamp, then DODAG Root
   [I-D.ietf-6man-rpl-routing-header].

   RPL allows a simple one-hop P2P optimization for both storing and
   non-storing networks.  A node MUST NOT set the 'T' flag.

   7.  If may send a node does not have P2P packet destined to a local timestamp
   one-hop neighbor directly to that satisfies node.

9.1.  Destination Advertisement Parents

   To establish downward routes, RPL nodes send DAO messages upwards.
   The next hop destinations of these DAO messages are called DAO
   parents.  The collection of a node's DAO parents is called the
       above requirements, it DAO
   parent set.

   1.  A node's DAO parent set MUST ignore the 'T' flag.

   If be a node supports such timestamps and it receives a message with the
   'T' flag set, it MAY apply the temporal check on the received message
   described in Section 9.5.2.1.  If subset of its DODAG parent set.

   2.  In storing mode operation, a node receives MUST NOT address unicast DAO
       messages to nodes that are not DAO parents.

   3.  In non-storing mode operation, a message without
   the 'T' flag set, it node MUST NOT apply this temporal check. address unicast
       DAO messages to nodes that are not DODAG roots.

   4.  A node's
   security policy MAY, for application reasons, include rejecting all node MUST NOT forward unicast DAO messages without to nodes that are
       not DAO parents.

   5.  A node MAY send DAO messages using the 'T' flag set.

9.5.  Functional Description of Packet Protection

9.5.1.  Transmission of Outgoing Packets

   Given all-RPL-nodes multicast
       address, which is an outgoing RPL control packet and required security
   protection, this section describes how RPL generates the secured
   packet optimization to transmit.  It also describes the order provision on-hop routing.
       The 'K' bit MUST be cleared on transmission of cryptographic
   operations to provide the required protection. multicast DAO.

   6.  The requirement for security protection and the level IPv6 Source Address of security to
   be applied to an outgoing RPL packet shall a DAO message MUST be determined by the
   node's security policy database. link local
       address of the sending node.

   The configuration selection of this security
   policy database for outgoing packet processing DAO parents is TBD (it may, for
   example, implementation and objective function
   specific.

9.2.  Downward Route Discovery and Maintenance

   Destination Advertisement may be defined through DIO Configuration or through out-of-band
   administrative router configuration).

   Where secured RPL messages are configured to be transmitted, entirely disabled,
   or operate in either a RPL node MUST set
   the security section (C, T, Sec, KIM, and LVL) storing or non-storing mode, as reported in
   the outgoing RPL
   packet to describe the protection level and security settings that
   are applied (see Section 5.1).  The Security subfield bit of the RPL
   message Code field MUST be set to indicate the secure RPL message.

   The Counter value used MOP in constructing the Nonce to secure the
   outgoing packet DIO message.

   1.  All nodes who join a DODAG MUST be an increment of the last Counter transmitted
   to abide by the particular destination address.  Where a Counter for MOP setting from the
   intended destination address has
       root.  Nodes that do not been established, have the Counter
   value MUST be initialized capability to zero and sent fully participate
       as a Full Counter for the
   initial RPL message transmission.

   Where a Counter is currently maintained for outgoing messages to the
   intended destination address, the Compressed Counter (indicated with router, e.g. that does not match the 'C' bit set) MUST be transmitted within advertised MOP, MAY
       join the secured RPL message,
   provided DODAG as a leaf.

   2.  If the message MOP is not a RPL Consistency Check message.  The
   current Full Counter (indicated with 000, indicating no downward routing, nodes MUST NOT
       transmit DAO messages, and MAY ignore DAO messages.

   3.  In non-storing mode, the 'C' bit cleared) DODAG Root SHOULD store source routing
       table entries for the
   given destination address SHALL always be used when the outgoing
   packet is a Consistency Check (challenge or response) message.  Where
   a Counter destinations learned from DAOs.

   4.  In storing mode, all non-root, non-leaf nodes MUST store routing
       table entries for destinations learned from DAOs.

   A DODAG can have one of several possible modes of operation, as
   defined by the intended destination address MOP field.  Either it does not exist, the
   initialized (zero-value), Full Counter MUST be transmitted within support downward
   routes, it supports downward routes through source routing from DODAG
   Roots, or it supports downward routes through in-network routing
   tables.  When downward routes are supported through in-network
   routing tables, the
   initial RPL control message.  Where security policy specifies multicast operation defined in this specification
   may or may not be supported, also as indicated by the
   application MOP field.  As
   of delay protection, this specification RPL does not support mixed-mode operation,
   where some nodes source route and other store routing tables: future
   extensions to RPL may support this mode of operation.

9.2.1.  Maintenance of Path Sequence

   For each Target that is associated with (owned by) a node, that node
   is responsible to emit DAO messages in order to provision the Timestamp Counter used
   downward routes.  The Target+Transit information contained in
   constructing those
   DAO messages subsequently propagates Up the Nonce to secure DODAG.  The Path Sequence
   counter in the outgoing packet MUST be
   incremented according Transit information option is used to the rules indicate
   freshness and update stale downward routing information as described
   in Section 9.4.1.  Where 7.

   For a
   Timestamp Counter Target that is applied (indicated associated with the 'T' flag set) the
   locally maintained Time Counter (owned by) a node, that node
   MUST be included as part of the
   transmitted secured RPL message.

   The cryptographic algorithm used in securing the outgoing packet
   shall be specified by increment the node's security policy database Path Sequence counter, and MUST generate a new DAO
   message, when:

   1.  The Path Lifetime is to be
   indicated in the value of the Sec field set within the outgoing
   message. updated (e.g. a refresh or a no-Path)

   2.  The security policy for the outgoing packet shall determine the
   applicable Key Identifier Mode (KIM) and Key Identifier specifying
   the security key Parent Address list is to be used for changed

   For a Target that is associated with (owned by) a node, that node MAY
   increment the cryptographic packet processing,
   including Path Sequence counter, and generate a new DAO message,
   on occasion in order to refresh the optional use of signature keys (see Section 5.1).  The
   security policy will also specify downward routing information.  In
   storing mode, the level node generates such DAO to each of protection (LVL) its DAO parents
   in
   the form of authentication or authentication and encryption, and
   potential use of signatures that shall apply order to enable multipath.  All DAOs generated at the outgoing packet.

   Where encryption is applied, same time
   for a node same target MUST replace the original packet
   payload be sent with that payload encrypted using the security protection,
   key, and nonce specified same path sequence in the security section
   transit information.

9.2.2.  Generation of the packet.

   All secured RPL messages include integrity protection.  In
   conjunction with the security algorithm processing, a DAO Messages

   A node derives a
   Message Authentication Code (MAC) that MUST be included might send DAO messages when it receives DAO messages, as part of
   the outgoing secured RPL packet.

9.5.2.  Reception a
   result of Incoming Packets

   This section describes changes in its DAO parent set, or in response to another
   event such as the reception and processing expiry of a secured RPL
   packet.  Given an incoming secured RPL packet, where related prefix lifetime.  In the Security
   subfield bit case
   of receiving DAOs, it matters whether the RPL DAO message Code field is set, this section
   describes how RPL generates an unencrypted version of the packet and
   validates its integrity.

   The receiver uses the RPL security control fields to determine the
   necessary packet security processing.  If the described level of
   security for the "new," or
   contains new information.  In non-storing mode, every DAO message type and originator does not meet locally
   maintained security policies, a
   node MAY discard the packet without
   further processing.  These policies can include security levels, keys
   used, source identifiers, or the lack of timestamp-based counters (as
   indicated by the 'T' flag).  The configuration of the security policy
   database for incoming packet processing receives is TBD (it may, "new."  In storing mode, a DAO message is "new" if
   it satisfies any of these criteria for example,
   be defined through DIO Configuration a contained Target:

   1.  it has a newer Path Sequence number,

   2.  it has additional Path Control bits, or through out-of-band
   administrative router configuration).

   Where the

   3.  is a No-Path DAO message security level (LVL) indicates an encrypted RPL
   message, the node uses the key information identified through the KIM
   field as well as that removes the Nonce as input last downward route to the
       a prefix.

   A node that receives a DAO message payload decryption
   processing.  The Nonce shall be derived from the its sub-DODAG MAY suppress
   scheduling a DAO message Counter
   field and other received and locally maintained transmission if that DAO message is not new.

9.3.  DAO Base Rules

   1.  If a node sends a DAO message with newer or different information (see
   Section 9.5.3.1).  The plaintext
       than the prior DAO message contents shall be obtained
   by invoking transmission, it MUST increment the inverse cryptographic mode of operation specified
       DAOSequence field by at least one.  A DAO message transmission
       that is identical to the Sec field of prior DAO message transmission MAY
       increment the received packet. DAOSequence field.

   2.  The receiver shall use the Nonce RPLInstanceID and identified key information to
   check the integrity DODAGID fields of the incoming packet.  If the integrity check
   fails against the received message authentication code (MAC), a node DAO message MUST discard the packet.

   If a Compressed Counter is received and be the node does not currently
   have an incoming Counter currently maintained for
       same value as the originator members of the message, node's parent set and the DIOs
       it transmits.

   3.  A node MUST send a Consistency Check request to the
   message source to update MAY set the Counters.

   If an initialized (zero value) Full Counter is received 'K' flag in a secured
   RPL unicast DAO message and the receiving node currently has an incoming Counter
   currently maintained for the originator of the message, the node MUST
   initiate a Counter resynchronization by sending to solicit a Consistency Check
       unicast DAO-ACK in response message (see Section 5.6.1) in order to confirm the attempt.

   4.  A node receiving a unicast DAO message source.  The
   Consistency Check response message shall be protected with the
   current full outgoing Counter maintained for the particular 'K' flag set
       SHOULD respond with a DAO-ACK.  A node
   address.  That outgoing Counter will be included within the security
   section of the receiving a DAO message while
       without the incoming Counter will be included
   within 'K' flag set MAY respond with a DAO-ACK, especially
       to report an error condition.

   5.  A node that sets the Consistency Check 'K' flag in a unicast DAO message payload.

   Based on the specified security policy but does
       not receive a node DAO-ACK in response MAY apply replay
   protection reschedule the DAO message
       transmission for a received RPL message.  The replay check another attempt, up until an implementation-
       specific number of retries.

   6.  Nodes SHOULD ignore DAOs without newer sequence numbers and MUST be
   performed following
       NOT process them further.

   Unlike the authentication Version field of the received packet. a DIO, which is incremented only by a
   DODAG Root and repeated unchanged by other nodes, DAOSequence values
   are unique to each node.  The
   full Counter, as obtained from the incoming packet or as derived from
   the received Compressed Counter shall sequence number space for unicast and
   multicast DAO messages can be compared against the
   watermark of either the incoming Counter maintained for same or distinct.  It is
   RECOMMENDED to use the given
   origination same sequence number space.

9.4.  DAO Transmission Scheduling

   Because DAOs flow upwards, receiving a unicast DAO can trigger
   sending a unicast DAO to a DAO parent.

   1.  On receiving a unicast DAO message with updated information, such
       as containing a Transit Information option with a new Path
       Sequence, a node address.  If SHOULD send a DAO.  It SHOULD NOT send this DAO
       message immediately.  It SHOULD delay sending the received DAO message Counter value in
       order to aggregate DAO information from other nodes for which it
       is
   non-zero and less than the maintained incoming Counter watermark a
   potential packet replay is indicated and the DAO parent.

   2.  A node MUST discard the
   incoming packet.

   If SHOULD delay protection is specified as part of the incoming packet
   security policy checks, the Timestamp Counter is used to validate the
   timeliness of the received RPL message.  If the incoming sending a DAO message
   Timestamp Counter value indicates with a timer
       (DelayDAO).  Receiving a DAO message transmission time prior
   to starts the locally maintained transmission time Counter for DelayDAO timer.
       DAO messages received while the
   originator address, a replay violation DelayDAO timer is indicated and active do not
       reset the node MUST
   discard timer.  When the incoming packet.  If DelayDAO timer expires, the received Timestamp Counter value
   indicates node sends
       a DAO.

   3.  When a node adds a node to its DAO parent set, it SHOULD schedule
       a DAO message transmission time that transmission.

   DelayDAO's value and calculation is earlier than the
   Current time less the acceptable packet delay, implementation-dependent.

9.5.  Triggering DAO Messages

   Nodes can trigger their sub-DODAG to send DAO messages.  Each node
   maintains a delay violation is
   indicated and DAO Trigger Sequence Number (DTSN), which it communicates
   through DIO messages.

   1.  If a node hears one of its DAO parents increment its DTSN, the
       node MUST discard the incoming packet.

   Once schedule a DAO message has been decrypted, where applicable, and has
   successfully passed its integrity check, replay, transmission using rules in
       Section 9.3 and optionally delay
   protection checks, the Section 9.4.

   2.  In non-storing mode, if a node can update hears one of its local security
   information, such as DAO parents
       increment its DTSN, the source's expected Counter value for counter
   compression and replay comparison.

   A node MUST NOT update increment its security information on receipt of own DTSN.

   In a
   message that fails security policy checks or other applied integrity,
   replay, or delay checks.

9.5.2.1.  Timestamp Key Checks

   If the 'T' flag storing mode of a message is set operation, as part of routine routing table
   updates and maintenance, a storing node has a local timestamp
   that follows the requirements MAY increment DTSN in Section 9.4.1, then order
   to reliably trigger a node MAY check
   the temporal consistency set of the message.  The node computes the
   transmit time DAO updates from its immediate children.
   In a storing mode of the message by adding the Counter value operation it is not necessary to trigger DAO
   updates from the start
   time of the associated key.  If this transmit time is past entire sub-DODAG, since that state information will
   propagate hop-by-hop Up the end
   time DODAG.

   In a non-storing mode of operation, a DTSN increment will also cause
   the key, the immediate children of a node MAY discard the message without further
   processing.  If the transmit time is too far in the past or future
   compared to the local time on the receiver, it MAY discard the
   message without further processing.

9.5.3.  Cryptographic Mode of Operation

   The cryptographic mode increment their DTSN in turn,
   triggering a set of operation used is based on DAO updates from the CCM entire sub-DODAG.  In a non-
   storing mode of operation and typically only the block-cipher AES-128[RFC3610].  This mode of
   operation root would independently
   increment the DTSN when a DAO refresh is widely supported needed but a global repair
   (such as by existing implementations and
   coincides with the CCM* incrementing DODAGVersionNumber) is not desired.  In a
   non-storing mode of operation[CCMStar].  CCM mode
   requires operation typically all non-root nodes would
   increment their DTSN only when their parent(s) are observed to do so.

   In the general, a nonce.

9.5.3.1.  Nonce

   A RPL node constructs a CCM nonce as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                       Source Identifier                       +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Counter                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Reserved | LVL |
       +-+-+-+-+-+-+-+-+

                           Figure 24: CCM* Nonce

   Source Identifier:  8 bytes.  Source Identifier is set may trigger DAO updates according to
   implementation specific logic, such as based on the logical
         identifier detection of a
   downward route inconsistency or occasionally based upon an internal
   timer.

   In the originator case of triggered DAOs, selecting a proper DAODelay can
   greatly reduce the protected packet.

   Counter:  4 bytes.  Counter is set to the (uncompressed) value number of DAOs transmitted.  The trigger flows
   Down the
         corresponding field DODAG; in the Security option of best case the RPL control
         message.

   Security Level (LVL):  3 bits.  Security Level DAOs flow Up the DODAG such that
   leaves send DAOs first, with each node sending a DAO message only
   once.  Such a scheduling could be approximated by setting DAODelay
   inversely proportional to Rank.  Note that this suggestion is set
   intended as an optimization to allow efficient aggregation (it is not
   required for correct operation in the value general case).

9.6.  Structure of
         the corresponding field DAO Messages

   DAOs follow a common structure in both storing and non-storing
   networks.  In the Security option most general form, a DAO message may include
   several groups of the RPL
         control message.

   Unassigned bits options, where each group consists of the nonce are reserved.  They MUST be set one or more
   Target options followed by one or more Transit Information options.
   The entire group of Transit Information options applies to zero
   when constructing the nonce.

   All fields entire
   group of the nonce shall be represented is most-significant-
   octet and most-significant-bit first order.

9.5.3.2.  Signatures

   If the Key Identification Mode (KIM) mode indicates the use of
   signatures (a value Target options.  Later sections describe further details for
   each mode of 3), then a node appends operation.

   1.  RPL nodes MUST include one or more RPL Target Options in each DAO
       message they transmit.  One RPL Target Option MUST have a signature to prefix
       that includes the
   data payload of node's IPv6 address if that node needs the packet.
       DODAG to provision downward routes to that node.  The Security Level (LVL) field describes RPL Target
       Option MAY be immediately followed by an opaque RPL Target
       Descriptor Option that qualifies it.

   2.  When a node updates the length of this signature.

   The signature scheme information in RPL a Transit Information
       option for Security Mode 00 is an instantiation a Target option that covers one of its addresses, it
       MUST increment the ECPVS signature scheme[X9.92].  It uses as an elliptic curve
   the named curve K-283[X9.92].  It uses CCM* mode[CCMStar] as the
   encryption scheme with M=0 (as Path Sequence number in that Transit
       Information option.  The Path Sequence number MAY be incremented
       occasionally to cause a stream-cipher).  It uses the Matyas-
   Meyer-Oseas unkeyed hash function[AppliedCryptography].  It uses refresh to the
   key derivation function based on this unkeyed hash function specified downward routes.

   3.  One or more RPL Target Option in Section 5.6.3 of [X9.63-2001], and the a unicast DAO message encoding rule of
   Section 7.8 MUST be
       followed by one or ANSI X9.92 [X9.92].  PadLen is a non-negative integer
   set more Transit Information Option.  All the
       transit options apply to M-OctCurve, where OctCurve is all the byte-length of target options that immediately
       precede them.

   4.  Multicast DAOs MUST NOT include the curve Parent Address in
   question (with K-283, one has OctCurve=36).

   Let 'a' be a concatenation of a six-byte representation of Counter Transit
       Information options.

   5.  A node that receives and the message header.  The packet payload is processes a concatenation of
   packet data 'c' and the signature 's'.  This signature scheme is
   invoked with visible and recoverable DAO message parts containing
       information for a specific Target, and c, whereas that has prior information
       for that Target, MUST use the signature verification is invoked Path Sequence number in the Transit
       Information option associated with as received visible and that Target in order to
       determine whether or not the DAO message representative a, c, and with signature s.

9.6.  Coverage of Integrity and Confidentiality

   For contains updated
       information as per Section 7.

   6.  If a RPL ICMPv6 message, node receives a DAO message that does not follow the entire packet is within above
       rules, it MUST discard the scope of
   RPL security.  The DAO message authentication code is calculated over without further
       processing.

   In non-storing mode additional rules apply to ensure the
   entire IPv6 packet.  This calculation is done before any compression
   that lower layers may apply.  The IPv6 and ICMPv6 headers are never
   encrypted.  The body continuity
   of end-to-end source route path:

   1.  The address used as transit parent by the RPL ICMPv6 message MAY children MUST be encrypted,
   starting taken
       from a PIO with the first byte after the security section and
   continuing to the end of the packet.

10.  Packet Forwarding and Loop Avoidance/Detection

10.1.  Suggestions 'R' flag set from that parent but is not
       necessarily on link for Packet Forwarding

   When forwarding the children.

   2.  The router that advertises an address as parent in a packet to PIO MUST
       also advertise that address as target in a destination, precedence DAO message.

   3.  An address that is given to
   selection of a next-hop successor advertised as follows:

   1.  This specification only covers how target in a successor is selected from DAO MUST be
       collocated or reachable onlink by the DODAG version parent that matches the RPLInstanceID marked is indicated in
       the
       IPv6 header of the packet being forwarded.  Routing outside the
       instance can be done as long as additional rules associated transit information.

   4.  A router might have targets that are put in place
       such as strict ordering of instances and routing protocols not known to
       protect against loops.

   2.  If a local administrative preference favors be onlink for a route
       parent, either because they are addresses located on an alternate
       interface or because they belong to nodes that has been
       learned from a different routing protocol than are external to
       RPL, then use that
       successor.

   3.  If the packet header specifies for instance connected hosts.  In order to inject such a source route, then use that
       route [I-D.hui-6man-rpl-routing-header].  If
       target in the node fails to
       forward RPL network, the packet with router MUST advertise itself as
       the Parent Address in the Transit Information option for that specified source route, then
       target, using an address that
       packet SHOULD be dropped.  The node MAY log is onlink for that nodes DAO
       parent.  If the target belongs to an error.  The external node
       MAY send an ICMPv6 Error in Source Routing Header message to then the
       source of
       router MUST set the packet Section 18.6.

   4.  If there is an entry External 'E' flag in the routing table matching the
       destination transit information.

9.7.  Non-storing Mode

   In non-storing mode, RPL routes messages downward using IP source
   routing.  The following rule applies to nodes that are in non-storing
   mode.  Storing mode has been learned from a multicast destination
       advertisement (e.g. separate set of rules, described in
   Section 9.8.

   1.  The Parent Address field of a Transit Information Option MUST
       contain one or more addresses.  All of these addresses MUST be
       addresses of DAO parents of the destination is sender.

   2.  On receiving a one-hop neighbor), then unicast DAO, a node MUST propagate the updated
       downward route information upwards.  The node MAY use that successor.

   5.  If there is an entry any parent
       in the routing table matching parent set.  The downward route information in the
       destination that has been learned DAO
       message MAY be aggregated with other DAOs before being propagated
       upwards, which MAY entail to delay the propagation as described
       below.

   3.  When a node removes a node from its DAO parent set, it MAY
       generate a unicast destination
       advertisement (e.g. the destination is located down the sub-
       DODAG), then use that successor.  If there are new DAO Path Control
       bits associated message with multiple successors, then consult the Path
       Control bits an updated Transit Information
       option.

   In non-storing mode, a node uses DAOs to report its DAO parents to order
   the successors by preference when choosing.

   6.  If there is a DODAG version offering Root.  The DODAG Root can piece together a downward route
   to a prefix matching node by using DAO parent sets from each node in the destination, then select one route.  The
   Path Sequence information may be used to detect stale DAO
   information.  The purpose of those DODAG this per-hop route calculation is to
   minimize traffic when DAO parents as change.  If nodes reported complete
   source routes, then on a
       successor according to the OF and routing metrics.

   7.  Any other as-yet-unattempted DODAG DAO parent may be chosen for change the
       next attempt entire sub-DODAG would
   have to send new DAOs to forward a unicast packet when no better match
       exists.

   8.  Finally the packet is dropped.  ICMP Destination Unreachable may
       be invoked (an inconsistency is detected).

   TTL must be decremented when forwarding.

   Note that the chosen successor MUST NOT be the neighbor that was the
   predecessor of the packet (split horizon), except DODAG Root.  Therefore, in the case where non-storing
   mode, a node can send a single DAO, although it is intended for the packet to change from an up might choose to an down flow,
   such as switching from DIO routes send
   more than one DAO message to each of multiple DAO parents.

   Nodes pack DAOs by sending a single DAO message with multiple RPL
   Target Options.  Each RPL Target Option has its own, immediately
   following, Transit Information options.

9.8.  Storing Mode

   In storing mode, RPL routes as messages downward by the IPv6 destination is
   neared.

10.2.  Loop Avoidance and Detection

   RPL loop avoidance mechanisms are kept simple and designed
   address.  The following rule apply to
   minimize churn and states.  Loops may form for a number of reasons,
   e.g. control packet loss.  RPL includes a reactive loop detection
   technique that protects from meltdown and triggers repair of broken
   paths.

   RPL loop detection uses information nodes that is placed into the packet.
   A future version are in storing mode:

   1.  The Parent Address field of this specification will detail how this
   information is carried with the packet (e.g. a hop-by-hop Transmit Information option
   ([I-D.hui-6man-rpl-option]) or summarized somehow into MUST be
       empty.

   2.  On receiving a unicast DAO, a node MUST compute if the flow
   label).  For DAO would
       change the purpose set of prefixes that the node itself advertises.  This
       computation SHOULD include consultation of RPL operations, the Path Sequence
       information carried
   with a packet is constructed follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |O|R|F|0|0|0|0|0| RPLInstanceID |          SenderRank           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          RPL Packet in the Transit Information

   Down 'O' bit:  1-bit flag indicating whether options associated with
       the packet is expected DAO, to progress up or down.  A router sets the 'O' bit when determine if the
         packet is expect to progress down (using DAO routes), and
         resets it when forwarding towards message contains newer
       information that supersedes the root of information already stored at the
       node.  If so, the DODAG
         version.  A host or RPL leaf node MUST set the bit to 0.

   Rank-Error 'R' bit:  1-bit flag indicating whether a rank error was
         detected.  A rank error is detected when there is generate a mismatch in
         the relative ranks new DAO message and
       transmit it, following the direction as indicated rules in the 'O'
         bit.  A host or RPL leaf Section 9.4.  Such a change
       includes receiving a No-Path DAO.

   3.  When a node generates a new DAO, it SHOULD unicast it to each of
       its DAO parents.  It MUST set NOT unicast the bit DAO message to 0.

   Forwarding-Error 'F' bit:  1-bit flag indicating nodes
       that this node can are not forward the packet further towards the destination.  The
         'F' bit might be set by DAO parents.

   4.  When a child node that does not have a route
         to destination for removes a packet with the down 'O' bit set.  A host
         or RPL leaf node MUST set the bit to 0.

   RPLInstanceID:  8-bit field indicating the DODAG instance along which
         the packet is sent.

   SenderRank:  16-bit field set to zero by the source and to
         DAGRank(rank) by from its DAO parent set, it SHOULD
       send a router that forwards inside the RPL network.

10.2.1.  Source Node Operation

   If the source is aware of the RPLInstanceID No-Path DAO message (Section 6.4.3) to that is preferred for the
   packet, then it MUST set the RPLInstanceID field associated with the
   packet accordingly, otherwise it MUST set it removed DAO
       parent to invalidate the
   RPL_DEFAULT_INSTANCE.

10.2.2.  Router Operation

10.2.2.1.  Instance Forwarding

   Instance IDs are used existing route.

   5.  If messages to avoid loops between DODAGs an advertised downwards address suffer from different
   origins.  DODAGs that constructed for antagonistic constraints might
   contain paths that, if mixed together, would yield loops.  Those
   loops are avoided by a
       forwarding error, neighbor unreachable detected (NUD), or similar
       failure, a packet along node MAY mark the DODAG address as unreachable and generate
       an appropriate No-Path DAO.

   DAOs advertise what destination addresses and prefixes a node has
   routes to.  Unlike in non-storing mode, these DAOs do not communicate
   information about the routes themselves: that information is
   associated to a given instance.

   The RPLInstanceID stored
   within the network and is associated by implicit from the IPv6 source with the packet.  This
   RPLInstanceID MUST match the RPL Instance onto which the packet is
   placed by any node, be it address.
   When a host or router.  For traffic originating
   outside of the RPL domain there may be storing node generates a mapping occurring at the
   gateway into the RPL domain, possibly based on an encoding within DAO, it uses the
   flow label.  This aspect stored state of RPL operation is DAOs
   it has received to be clarified in produce a
   future version of this specification.

   The source of the packet might be aware set of the RPL network, of the
   constraints imposed on OFs, Target options and of their
   associated Instance IDs.  In that
   case, the source of the packet MAY tag the flow label with the
   RPLInstanceID, in which case it Transmit Information options.

   Because this information is used in that form stored within the RPL
   network. each node's routing tables,
   in storing mode DAOs are communicated directly to DAO parents, who
   store this information.

9.9.  Path Control

   A router that injects DAO message from a data packet into node contains one or more Target Options.  Each
   Target Option specifies either the RPL network MUST tag node's prefix, a prefix of
   addresses reachable outside the
   packet by inserting LLN, or a RPL Hop-by-hop option as specified destination in
   [I-D.hui-6man-rpl-option].  If the RPLInstanceID is not present in
   flow label node's
   sub-DODAG.  The Path Control field of the data packet, the ingress router that injects the
   packet into the RPL network MUST add a RPLInstanceID field Transit Information option
   allows nodes to the RPL
   Hop-by-hop option. request or allow for multiple downward routes.  A router that forwards
   node constructs the Path Control field of a packet to outside Transit Information
   option as follows:

   1.  The bit width of the RPL network path control field MUST
   remove the RPL Hop-by-hop option.

   When a router receives a packet that specifies a given RPLInstanceID
   and be equal to the node can forward
       value (PCS + 1), where PCS is specified in the packet along control field of
       the DODAG associated Configuration Option.  Bits greater than or equal to
   that instance, then
       the router value (PCS + 1) MUST do so be cleared on transmission and leave the RPLInstanceID MUST be
       ignored on reception.  Bits below that value unchanged.

   If any are considered
       "active" bits.

   2.  The node can not forward a packet along MUST logically construct groupings of its DAO parents
       while populating the DODAG associated Path Control field, where each group
       consists of DAO parents of equal preference.  Those groups MUST
       then be ordered according to preference, which allows for a
       logical mapping of DAO parents onto Path Control subfields (See
       Figure 27).  Groups MAY be repeated in order to extend over the RPLInstanceID, then
       entire bit width of the node SHOULD discard patch control field, but the packet and send
   an ICMP error message.

10.2.2.2.  DAG Inconsistency Loop Detection

   The DODAG order,
       including repeated groups, MUST be retained so that preference is inconsistent if the direction of a packet does not match
   the rank relationship.  A receiver detects an inconsistency if it
   receives
       properly communicated.

   3.  For a packet with either:

      the 'O' bit set (to down) from RPL Target option describing a node of node's own address or a higher rank.
       prefix outside the 'O' LLN, at least one active bit reset (for up) from a node of a lesser rank.

   When the DODAG root increments Path
       Control field MUST be set.  More active bits of the DODAGVersionNumber Path Control
       field MAY be set.

   4.  If a temporary
   rank discontinuity may form between the next version and node receives multiple DAOs with the prior
   version, in particular if nodes are adjusting their rank in same RPL Target option,
       it MUST bitwise-OR the next
   version and deferring their migration into Path Control fields it receives.  This
       aggregated bitwise-OR represents the next version.  A
   router that is still a member number of downward routes
       the prior version may choose to
   forward prefix requests.

   5.  When a packet to node sends a (future) parent that is in the next version.
   In some cases this could cause the parent DAO message to detect an inconsistency
   because one of its DAO parents, it
       MUST select one or more of the rank-ordering bits that are set active in the prior version
       subfield that is not necessarily the
   same as in the next version and the packet may be judged mapped to not be
   making forward progress.  If the sending router is aware group containing that DAO parent
       from the
   chosen successor has already joined the next version, then the
   sending router MUST update the SenderRank to INFINITE_RANK aggregated Path Control field.  A given bit can only be
       presented as active to one parent.  The DAO message it
   forwards the packets across the discontinuity into the next DODAG
   version in order transmits
       to avoid a false detection of rank inconsistency.

   One inconsistency along its parent MUST have these active bits set and all other
       active bits cleared.

   6.  For the path is not considered as a critical
   error RPL Target option and DAOSequence number, the packet may continue.  But DAOs a second detection along the
   path node
       sends to different DAO parents MUST have disjoint sets of a same packet should not occur and the packet is dropped.

   This process is controlled by active
       Path Control bits.  A node MUST NOT set the Rank-Error same active bit associated with the
   packet.  When an inconsistency is detected on a packet, if the Rank-
   Error bit was not set then the Rank-Error bit is set.  If it was set
       DAOs to two different DAO parents.

   7.  Path control bits SHOULD be allocated according to the packet is discarded and preference
       mapping of DAO parents onto Path Control subfields, such that the trickle timer is reset.

10.2.2.3.
       active Path Control bits, or groupings of bits, that belong to a
       particular Path Control subfield are allocated to DAO Inconsistency Loop Detection and Recovery parents
       within the group that was mapped to that subfield.

   8.  In a non-storing mode of operation, a node MAY pass DAOs through
       without performing any further processing on the Path Control
       field.

   9.  A node MUST NOT unicast a DAO inconsistency happens when router message that has an down DAO route
   via a child that no active bits in
       the Path Control field set.  It is possible that, for a remnant from an obsolete state given
       Target option, that is a node does not
   matched in the child.  With DAO inconsistency loop recovery, have enough aggregate Path
       Control bits to send a packet
   can be used DAO message containing that Target to recursively explore and cleanup the obsolete each
       of its DAO
   states along a sub-DODAG.

   In a general manner, Parents, in which case those least preferred DAO
       Parents may not get a packet that goes down should never go up
   again.  If DAO inconsistency loop recovery is applied, then the
   router SHOULD send the packet back to the parent message for that passed it with
   the Forwarding-Error 'F' bit set and the 'O' bit left untouched.
   Otherwise the router MUST silently discard the packet.

10.2.2.4.  Forward Target.

   The Path Recovery

   Upon receiving a packet with Control field allows a Forwarding-Error bit set, the node
   MUST remove to bound how many downward
   routes will be generated to it.  It sets a number of bits in the routing states that caused forwarding Path
   Control field equal to that
   neighbor, clear the Forwarding-Error maximum number of downward routes it
   prefers.  Each bit and attempt is sent to send the
   packet again.  The packet may at most one DAO parent; clusters of
   bits can be sent to an alternate neighbor.  If a single DAO parent for it to divide among its
   own DAO parents.

   A node that provisions a DAO route for a Target that alternate neighbor still has an inconsistent DAO state via this
   node, the process will recurse, this node will set the Forwarding-
   Error 'F' bit and
   associated Path Control field SHOULD use the routing state content of that Path
   Control field in the alternate neighbor will be
   cleaned up as well.

11.  Multicast Operation

   This section describes further the multicast routing operations over
   an IPv6 RPL network, and specifically how unicast DAOs can be used order to
   relay group registrations up.  Wherever the following text mentions
   Multicast Listener Discovery (MLD), one can read MLDv1 ([RFC2710]) or
   MLDv2 ([RFC3810]).

   Nodes determine an order of preference among
   multiple alternative DAO routes for that support Target.  The Path Control
   field assignment is derived from preference (of the RPL storing mode of operation SHOULD also
   support multicast DAO operations parents), as described below.  Nodes that only
   support
   determined on the non-storing mode basis of operation are not expected to support this section.

   The multicast operation is controlled by node's best knowledge of the MOP field "end-to-
   end" aggregated metrics in the DIO.

      If the MOP field requires multicast support, then a node that
      joins "downward" direction as per the RPL network as a router must operate as described in
      this section for multicast signaling and forwarding within
   objective function.  In non storing mode the RPL
      network.  A node that does not support root can determine the multicast operation
      required
   downward route by aggregating the MOP field can only join as information from each received DAO,
   which includes the Path Control indications of preferred DAO parents.

9.9.1.  Path Control Example

   Suppose that there is an LLN operating in storing mode that contains
   a leaf.

      If Node N with four parents, P1, P2, P3, and P4.  Let N have three
   children, C1, C2, and C3 in its sub-DODAG.  Let PCS be 7, such that
   there will be 8 active bits in the MOP Path Control field: 11111111b.
   Consider the following example:

   The Path Control field does not require multicast support, then
      multicast is handled by some other way split into 4 subfields, PC1 (11000000b),
   PC2 (00110000b), PC3 (00001100b), and PC4 (00000011b), such that is out
   those 4 subfields represent 4 different levels of scope for
      this specification.  (Examples may include preference as a series per
   Figure 27.  The implementation at Node N, in this example, groups
   {P1, P2} to be of unicast
      copies or limited-scope flooding)

   As equal preference to each other, and the most
   preferred group overall. {P3} is traditional, a listener uses a protocol such as MLD with a
   router less preferred to register {P1, P2}, and more
   preferred to a multicast group.

   Along the {P4}.  Let Node N then perform its path between control mapping
   such that:

              {P1, P2} -> PC1 (11000000b) in the router and Path Control field
              {P3}     -> PC2 (00110000b) in the DODAG root, MLD requests
   are mapped and transported as DAO messages within Path Control field
              {P4}     -> PC3 (00001100b) in the RPL protocol;
   each hop coalesces Path Control field
              {P4}     -> PC4 (00000011b) in the multiple requests for a same group as Path Control field

   Note that the implementation repeated {P4} in order to get complete
   coverage of the Path Control field.

   1.   Let C1 send a single DAO message to containing a Target T with a Path Control
        10000000b.  Node N stores an entry associating 10000000b with
        the parent(s), in Path Control field for C1 and Target T.

   2.   Let C2 send a fashion similar to proxy IGMP, but
   recursively between child router DAO containing a Target T with a Path Control
        00010000b.  Node N stores an entry associating 00010000b with
        the Path Control field for C1 and parent up to Target T.

   3.   Let C3 send a DAO containing a Target T with a Path Control
        00001100b.  Node N stores an entry associating 00001100b with
        the root.

   A router might select to pass Path Control field for C1 and Target T.

   4.   At some later time, Node N generates a listener registration DAO message to
   its preferred parent only, in which case multicast packets coming
   back might be lost for all Target T. Node N
        will construct an aggregate Path Control field by ORing together
        the contribution from each of its sub-DODAG if the transmission fails
   over children that link.  Alternatively have given a DAO
        for Target T. The aggregate Path Control field thus has the router might select to copy
   additional
        active bits set as: 10011100b.

   5.   Node N then distributes the aggregate Path Control bits among
        its parents as it would do for DAO messages advertising
   unicast destinations, P1, P2, P3, and P4 in which case there might be duplicates that order to prepare the router will need DAO
        messages.

   6.   P1 and P2 are eligible to prune.

   As a result, multicast routing states receive active bits from the most
        preferred subfield (11000000b).  Those bits are installed 10000000b in each router on the way from
        aggregate Path Control field.  Node N must the listeners bit to one of the root, enabling the root
        two parents only.  In this case, Node P1 is allocated the bit,
        and gets the Path Control field 10000000b for its DAO.  There
        are no bits left to copy allocate to Node P2, thus Node P2 would have
        a
   multicast packet Path Control field of 00000000b and a DAO cannot be generated
        to all its children routers that had issued Node P2 since there are no active bits.

   7.   The second-most preferred subfield (00110000b) has the active
        bits 00010000b.  Node N has mapped P3 to this subfield.  Node N
        may allocates the active bit to P3, constructing a DAO
   message including for P3
        containing Target T with a Path Control of 00010000b.

   8.   The third-most preferred subfield (00001100b) has the active
        bits 00001100b.  Node N has mapped P4 to this subfield.  Node N
        may allocate both bits to P4, constructing a DAO for that multicast group, as well as all P4
        containing Target T with a Path Control of 00001100b.

   9.   The least preferred subfield (00000011b) has no active bits.
        Had there been active bits, those bits would have been added to
        the
   attached nodes that registered over MLD.

   For unicast traffic, it is expected that Path Control field of the grounded root DAO constructed for P4.

   10.  The process of an
   DODAG terminates RPL and MAY redistribute populating the RPL routes over DAO messages destined for P1, P2,
        P3, P4 with other targets (other than T) proceeds as according
        the
   external infrastructure using whatever routing protocol aggregate path control fields collected for those targets.

9.10.  Multicast Destination Advertisement Messages

   A special case of DAO operation, distinct from unicast DAO operation,
   is multicast DAO operation which may be used in
   the other to populate '1-hop'
   routing domain.  For multicast traffic, the root table entries.

   1.  A node MAY proxy
   MLD for all the nodes attached multicast a DAO message to the RPL domain (this would be
   needed if the link-local scope all-
       RPL-nodes multicast source is located in address.

   2.  A multicast DAO message MUST be used only to advertise
       information about the external
   infrastructure).  For node itself, i.e. prefixes directly
       connected to or owned by this node, such a source, the packet will be replicated as
   it flows down the DODAG based on the multicast routing table entries
   installed from the DAO message.

   For a source inside the DODAG, multicast group
       that the packet node is passed subscribed to or a global address owned by the preferred
   parents, and if that fails then
       node.

   3.  A multicast DAO message MUST NOT be used to the alternates relay connectivity
       information learned (e.g. through unicast DAO) from another node.

   4.  A node MUST NOT perform any other DAO related processing on a
       received multicast DAO message, in particular a node MUST NOT
       perform the DODAG. actions of a DAO parent upon receipt of a multicast
       DAO.

   o  The
   packet is also copied multicast DAO may be used to all the registered children, except for the
   one that passed the packet.  Finally, if there is a listener in the
   external infrastructure then enable direct P2P communication,
      without needing the DODAG root has to further propagate
   the packet into the external infrastructure.

   As a result, relay the DODAG Root acts as an automatic proxy Rendezvous
   Point for packets.

10.  Security Mechanisms

   This section describes the RPL network, generation and as source towards the Internet for all
   multicast flows started in the processing of secure RPL LLN.  So regardless
   messages.  The high order bit of whether the
   root is actually attached to the Internet, and regardless of RPL message code identifies
   whether
   the DODAG a RPL message is grounded or floating, the root can serve inner multicast
   streams at all times.

12.  Maintenance of Routing Adjacency

   The selection of successors, along the default paths up along the
   DODAG, secure or along the paths learned from destination advertisements
   down along the DODAG, leads not.  In addition to the formation secure
   versions of routing adjacencies
   that require maintenance.

   In IGPs basic control messages (DIS, DIO, DAO, DAO-Ack), RPL has
   several messages which are relevant only in networks with security
   enabled.

   Implementation complexity and size is a core concern for LLNs such as OSPF [RFC4915]
   that it may be economically or IS-IS [RFC5120], the maintenance of physically impossible to include
   sophisticated security provisions in a routing adjacency involves RPL implementation.
   Furthermore, many deployments can utilize link-layer or other
   security mechanisms to meet their security requirements without
   requiring the use of Keepalive mechanisms (Hellos)
   or other protocols such as BFD ([RFC5880]) and MANET Neighborhood
   Discovery Protocol (NHDP [I-D.ietf-manet-nhdp]).  Unfortunately, such
   an approach is not desirable security in constrained environments such as LLN
   and would lead to excessive control traffic RPL itself.

   Therefore, the security features described in light this document are
   OPTIONAL to implement.  A given implementation MAY support a subset
   (including the empty set) of the data
   traffic with a negative impact on both link loads described security features, for
   example it could support integrity and nodes
   resources.  Overhead confidentiality, but not
   signatures.  An implementation SHOULD clearly specify which security
   mechanisms are supported, and deployers are RECOMMENDED to maintain carefully
   consider their security requirements and the routing adjacency should availability of security
   mechanisms in their network.

10.1.  Security Overview

   RPL supports three security modes:

   o  Unsecured.  In this security mode, RPL uses basic DIS, DIO, DAO,
      and DAO-Ack messages, which do not have security sections.  As a
      network could be
   minimized.  Furthermore, it is using other security mechanisms, such as link-
      layer security, unsecured mode does not always possible imply all messages are
      sent without any protection.

   o  Pre-installed.  In this security mode, RPL uses secure messages.
      To join a RPL Instance, a node must have a pre-installed key.
      Nodes use this to rely on provide message confidentiality, integrity, and
      authenticity.  A node may, using this preinstalled key, join the
   link
      RPL network as either a host or transport layer a router.

   o  Authenticated.  In this security mode, RPL uses secure messages.
      To join a RPL Instance, a node must have a pre-installed key.
      Node use this key to provide information of message confidentiality, integrity,
      and authenticity.  Using this preinstalled key, a node may join
      the associated link
   state.  The network layer needs to fall back on its own mechanism.

   Thus RPL makes use of as a different approach consisting of probing host only.  To join the
   neighbor using network as a Neighbor Solicitation message (see [RFC4861]).  The
   reception of router, a Neighbor Advertisement (NA) message with
      node must obtain a second key from a key authority.  This key
      authority can authenticate that the
   "Solicited Flag" set requester is used allowed to verify the validity of the routing
   adjacency.  Such mechanism MAY be used prior to sending a data
   packet.  This allows for detecting whether
      router before providing it with the second key.

   Whether or not the routing
   adjacency RPL Instance uses unsecured mode is still valid, and should signaled by
   whether it not be uses secure RPL messages.  Whether a secured network uses
   the case, select
   another feasible successor to forward pre-installed or authenticated mode is signaled by the packet.

13.  Guidelines for Objective Functions

   An Objective Function (OF) allows 'A' bit of
   the DAG Configuration option.

   This specification specifies CCM* -- Counter with CBC-MAC (Cipher
   Block Chaining Message Authentication Code) -- as the cryptographic
   basis for RPL security[RFC3610].  In this specification, CCM uses
   AES-128 as its underlying cryptographic algorithm.  There are bits
   reserved in the selection of a DODAG security section to
   join, specify other algorithms in the
   future.

   All secured RPL messages have either a message authentication code
   (MAC) or a signature.  Secured RPL messages optionally also have
   encryption protection for confidentiality.  Secured RPL message
   formats support both integrated encryption/authentication schemes
   (e.g., CCM*) as well as schemes that separately encrypt and
   authenticate packets.

10.2.  Joining a number of peers in Secure Network

   RPL security assumes that DODAG as parents.  The OF is used
   to compute an ordered list of parents.  The OF is also responsible a node wishing to
   compute the rank of join a secured network
   has been preconfigured with a shared key for communicating with
   neighbors and the device within RPL root.  To join a secure RPL network, a node
   either listens for secure DIOs or triggers secure DIOs by sending a
   secure DIS.  In addition to the DODAG version.

   The Objective Function is indicated DIO/DIS rules in the Section 8, secure
   DIO message using an
   Objective Code Point (OCP), and indicates DIS messages have these rules:

   1.  If sent, this initial secure DIS MUST set the method that must be
   used Key Identifier Mode
       field to construct 0 (00) and MUST set the DODAG. Security Level field to 1 (001).
       The Objective Code Points are specified key used MUST be the preconfigured group key (Key Index
       0x00).

   2.  When a node resets its Trickle timer in [I-D.ietf-roll-of0], and related companion specifications.

13.1.  Objective Function Behavior

   Most Objective Functions are expected response to follow the same abstract
   behavior:

   o  The parent selection is triggered each time an event indicates
      that a potential next hop information is updated.  This might
      happen upon secure DIS
       (Section 8.3), the reception of next DIO it transmits MUST be a secure DIO message,
       with the same security configuration as the secure DIS.  If a timer elapse, all
      DODAG parents are unavailable, or
       node receives multiple secure DIS messages before it transmits a trigger indicating that
       DIO, the
      state of a candidate neighbor has changed.

   o  An OF scans all secure DIO MUST have the interfaces on same security configuration as
       the device.  Although there may
      typically be only one interface last DIS it is responding to.

   3.  When a node sends a DIO in most application scenarios,
      there might be multiple of them and an interface might be
      configured response to be usable or not for RPL operation.  An interface
      can also be configured with a preference or dynamically learned to
      be better than another by some heuristics that might unicast secure DIS
       (Section 8.3), the DIO MUST be link-layer
      dependent and are out of scope.  Finally an interface might or not
      match a required criterion for an Objective Function, for instance secure DIO.

   The above rules allow a degree of security.  As node to join a result some interfaces might be
      completely excluded from secured RPL Instance using the computation, while others might be
      more or less preferred.

   o  An OF scans all
   preconfigured shared key.  Once a node has joined the candidate neighbors on DODAG using the possible interfaces
   preconfigured shared key, the 'A' bit of the Configuration option
   determines its capabilities.  If the 'A' bit of the Configuration is
   cleared, then nodes can use this preinstalled, shared key to check whether they exchange
   messages normally: it can act as a router for a DODAG.  There
      might be multiple issue DIOs, DAOs, etc.

   If the 'A' bit of them the Configuration option is set and the RPL
   Instance is operating in authenticated mode:

   1.  A node MUST NOT advertise a candidate neighbor might need Rank besides INFINITE_RANK in secure
       DIOs secured with Key Index 0x00.  When processing DIO messages
       secured with Key Index 0x00, a processing node MUST consider the
       advertised Rank to
      pass some validation tests before it can be used.  In particular,
      some link layers require experience on INFINITE_RANK.  Any other value results in
       the activity message being discarded.

   2.  Secure DAOs using Key Index 0x00 MUST NOT have a RPL Target
       option with a router
      to enable prefix besides the router as node's address.  If a next hop.

   o  An OF computes self's rank by adding to the rank of the candidate node
       receives a value representing secured DAO message using the relative locations of self and preinstalled, shared key
       where the
      candidate in RPL Target option does not match the DODAG version.

      * IPv6 source
       address, it MUST discard the secured DAO message without further
       processing.

   The increase in rank must be at least MinHopRankIncrease.

      *  To keep loop avoidance and metric optimization above rules mean that in alignment, RPL Instances where the increase in rank should reflect any increase in 'A' bit is set,
   using Key Index 0x00 a node can join the metric
         value.  For example, RPL Instance as a host but
   not a router.  A node must communicate with a purely additive metric such key authority to obtain
   a key that will enable it to act as ETX,
         the increase in rank can be made proportional a router.

10.3.  Installing Keys

   Authenticated mode requires a would-be router to dynamically install
   new keys once they have joined a network as a host.  Having joined as
   a host, the increase
         in the metric.

      *  Candidate neighbors that would cause self's rank node uses standard IP messaging to increase
         are not considered for parent selection

   o  Candidate neighbors that advertise an OF incompatible communicate with an
   authorization server, which can provide new keys.

   The protocol to obtain such keys is the set subject of OF specified by a future standard.

10.4.  Consistency Checks

   RPL nodes send Consistency Check (CC) messages to protect against
   replay attacks and synchronize counters.

   1.  If a node receives a unicast CC message with the policy functions are ignored.

   o  As R bit cleared,
       and it scans all the candidate neighbors, is a member of or is in the OF keeps process of joining the current
      best parent and compares its capabilities
       associated DODAG, it SHOULD respond with the current
      candidate neighbor.  The OF defines a number of tests that are
      critical unicast CC message to reach
       the objective.  A test between sender.  This response MUST have the routers
      determines an order relation.

      *  If R bit set, and MUST have
       the routers are equal for that relation then the next test
         is attempted between the routers,

      *  Else the best of the two routers becomes the current best
         parent same Nonce, RPLInstanceID and DODAGID fields as the scan continues with message
       it received.

   2.  If a node receives a multicast CC message, it MUST discard the next candidate neighbor

      *  Some OFs may include
       message with no further processing.

   Consistency Check messages allow nodes to issue a test challenge-response
   to compare the ranks that would
         result if the node joined either router

   o  When validate a node's current Counter value.  Because the scan CC Nonce is complete,
   generated by the preferred parent is elected and
      self's rank challenger, an adversary replaying messages is computed as the preferred parent rank plus the step
      in rank with that parent.

   o  Other rounds of scans might
   unlikely to be necessary able to elect alternate
      parents.  In the next rounds:

      *  Candidate neighbors that are not generate a correct response.  The Counter in
   the same DODAG are ignored

      *  Candidate neighbors that are of greater rank than self are
         ignored

      *  Candidate neighbors of an equal rank Consistency Check response allows the challenger to self are ignored for
         parent selection

      *  Candidate neighbors of a lesser rank than self are preferred

14.  Suggestions for Interoperation with Neighbor Discovery

   This specification directly borrows validate the Prefix Information Option
   (PIO) and
   Counter values it hears.

10.5.  Counters

   In the Routing Information Option (RIO) from IPv6 ND.  It simplest case, the Counter value is
   envisioned that as future specifications build on this base an unsigned integer that
   there may be additional cause to leverage parts of IPv6 ND.  This
   section provides some suggestions for future specifications.

   First and foremost RPL is a routing protocol.  One should take great
   care to preserve architecture when mapping functionalities between
   RPL and ND.  RPL is for routing only.  That said, there may be
   persuading technical reasons to allow for sharing options between
   node increments by one or more on each secured RPL
   and IPv6 ND in transmission.  The
   Counter MAY represent a particular implementation/deployment.

   In general timestamp that has the following guidelines apply:

   o  RPL Type codes must properties:

   1.  The timestamp MUST be allocated from the RPL Control Message
      Options registry.

   o  RPL Length fields must at least six octets long.

   2.  The timestamp MUST be expressed in units of single octets, as
      opposed to ND Length fields which are expressed in units of 8
      octets.

   o  RPL Options are generally not required to 1024Hz (binary millisecond) granularity.

   3.  The timestamp start time MUST be aligned to 8 octet
      boundaries.

   o  When mapping/transposing an IPv6 ND option for redistribution January 1, 1970, 12:00:00AM UTC.

   4.  If the Counter represents such as timestamp, the Counter value
       MUST be a
      RPL option, any padding octets should value computed as follows.  Let T be removed when possible.
      For example, the Prefix Length field in the PIO is sufficient to
      describe timestamp, S
       be the length start time of the Prefix field.  When mapping/transposing
      a RPL option for redistribution as an IPv6 ND option, any such
      padding octets should be restored.  This procedure must be
      unambiguous.

15.  RPL Constants key in use, and Variables

   Following is a summary E be the end time of RPL constants the
       key in use.  Both S and variables:

   BASE_RANK  This is E are represented using the rank for same 3 rules
       as the timestamp described above.  If E > T < S, then the Counter
       is invalid and a virtual root that might be used to
         coordinate multiple roots.  BASE_RANK has node MUST NOT generate a packet.  Otherwise, the
       Counter value of 0.

   ROOT_RANK  This is equal to T-S.

   5.  If the rank for Counter represents such a DODAG root.  ROOT_RANK has timestamp, a value node MAY set the
       'T' flag of MinHopRankIncrease (as advertised by the DODAG root), security section of secured RPL packets.

   6.  If the Counter field does not present such a timestamp, then a
       node MUST NOT set the 'T' flag.

   7.  If a node does not have a local timestamp that DAGRank(ROOT_RANK) is 1.

   INFINITE_RANK  This is satisfies the constant maximum for
       above requirements, it MUST ignore the rank.
         INFINITE_RANK has 'T' flag.

   If a value of 0xFFFF.

   RPL_DEFAULT_INSTANCE  This is node supports such timestamps and it receives a message with the RPLInstanceID that is used by this
         protocol by
   'T' flag set, it MAY apply the temporal check on the received message
   described in Section 10.7.1.  If a node without any overriding policy.
         RPL_DEFAULT_INSTANCE has receives a value of 0.

   DEFAULT_PATH_CONTROL_SIZE  This is message without
   the default value used 'T' flag set, it MUST NOT apply this temporal check.  A node's
   security policy MAY, for application reasons, include rejecting all
   messages without the 'T' flag set.

   The 'T' flag is present because many LLNs today already maintain
   global time synchronization at sub-millisecond granularity for
   security, application, and other reasons.  Allowing RPL to
         configure PCS in leverage
   this existing functionality when present greatly simplifies solutions
   to some security problems, such as delay protection.

10.6.  Transmission of Outgoing Packets

   Given an outgoing RPL control packet and required security
   protection, this section describes how RPL generates the DODAG Configuration Option, which dictates secured
   packet to transmit.  It also describes the number order of significant bits in cryptographic
   operations to provide the Path Control field of required protection.

   The requirement for security protection and the
         Transit Information option.  DEFAULT_PATH_CONTROL_SIZE has a
         value level of 0.  This configures the simplest case-- limiting security to
   be applied to an outgoing RPL packet shall be determined by the
         fan-out
   node's security policy database.  The configuration of this security
   policy database for outgoing packet processing is implementation
   specific.

   Where secured RPL messages are to 1 and limiting be transmitted, a RPL node MUST set
   the security section (T, Sec, KIM, and LVL) in the outgoing RPL
   packet to send a DAO describe the protection level and security settings that
   are applied (see Section 6.1).  The Security subfield bit of the RPL
   message Code field MUST be set to only
         one parent.

   DEFAULT_DIO_INTERVAL_MIN  This is indicate the default secure RPL message.

   The Counter value used in constructing the Nonce to configure
         Imin for secure the DIO trickle timer.  DEFAULT_DIO_INTERVAL_MIN has a
         value
   outgoing packet MUST be an increment of 3.  This configuration results in Imin the last Counter transmitted
   to the particular destination address.

   Where security policy specifies the application of 8ms.

   DEFAULT_DIO_INTERVAL_DOUBLINGS  This is delay protection,
   the default value Timestamp Counter used in constructing the Nonce to
         configure Imax for secure the DIO trickle timer.
         DEFAULT_DIO_INTERVAL_DOUBLINGS has a value of 20.  This
         configuration results
   outgoing packet MUST be incremented according to the rules in
   Section 10.5.  Where a maximum interval of 2.3 hours.

   DEFAULT_DIO_REDUNDANCY_CONSTANT  This Timestamp Counter is applied (indicated with
   the default value 'T' flag set) the locally maintained Time Counter MUST be
   included as part of the transmitted secured RPL message.

   The cryptographic algorithm used to
         configure k for in securing the outgoing packet
   shall be specified by the node's security policy database and MUST be
   indicated in the DIO trickle timer.
         DEFAULT_DIO_REDUNDANCY_CONSTANT has a value of 10.  This
         configuration is a conservative value the Sec field set within the outgoing
   message.

   The security policy for trickle suppression
         mechanism.

   DEFAULT_MIN_HOP_RANK_INCREASE  This is the default value outgoing packet shall determine the
   applicable Key Identifier Mode (KIM) and Key Identifier specifying
   the security key to be used for the cryptographic packet processing,
   including the optional use of
         MinHopRankIncrease.  DEFAULT_MIN_HOP_RANK_INCREASE has a value signature keys (see Section 6.1).  The
   security policy will also specify the algorithm (Algorithm) and level
   of 256.  This configuration results protection (Level) in an 8-bit wide integer
         part the form of Rank.

   DIO Timer  One instance per DODAG authentication or authentication
   and encryption, and potential use of signatures that a node shall apply to
   the outgoing packet.

   Where encryption is applied, a member of.  Expiry
         triggers DIO message transmission.  Trickle timer node MUST replace the original packet
   payload with variable
         interval in [0, DIOIntervalMin..2^DIOIntervalDoublings].  See
         Section 7.3.1

   DAG Version Increment Timer  Up to one instance per DODAG that payload encrypted using the
         node is acting as DODAG root of.  May not be supported in all
         implementations.  Expiry triggers increment of
         DODAGVersionNumber, causing a new series of updated DIO message
         to be sent.  Interval should be chosen appropriate to
         propagation time of DODAG security protection,
   key, and as appropriate to application
         requirements (e.g. response time vs. overhead).

   DelayDAO Timer  Up to one instance per DAO parent (the subset of
         DODAG parents chosen to receive destination advertisements) per
         DODAG.  Expiry triggers sending nonce specified in the security section of DAO message to the DAO
         parent.  See Section 8.4

   RemoveTimer  Up to one instance per DAO entry per neighbor (i.e.
         those neighbors that have given DAO packet.

   All secured RPL messages to this node as include integrity protection.  In
   conjunction with the security algorithm processing, a
         DODAG parent) Expiry triggers node derives
   either a change in state for the DAO
         entry, setting up to do unreachable (No-Path) advertisements Message Authentication Code (MAC) or
         immediately deallocating the DAO entry if there are no DAO
         parents.

16.  Manageability Considerations

   The aim signature that MUST be
   included as part of this section is to give consideration to the manageability
   of RPL, and how outgoing secured RPL will be operated in a LLN.  The scope packet.

10.7.  Reception of this Incoming Packets

   This section is to consider describes the following aspects of manageability:
   configuration, monitoring, fault management, accounting, reception and
   performance processing of a secured RPL
   packet.  Given an incoming secured RPL packet, where the protocol in light Security
   subfield bit of the recommendations set forth
   in [RFC5706].

16.1.  Introduction

   Most RPL message Code field is set, this section
   describes how RPL generates an unencrypted variant of the existing IETF management standards are Structure of
   Management Information (SMI) based data models (MIB modules) to
   monitor packet and manage networking devices.

   For a number of protocols, the IETF community has used
   validates its integrity.

   The receiver uses the IETF
   Standard Management Framework, including RPL security control fields to determine the Simple Network
   Management Protocol [RFC3410],
   necessary packet security processing.  If the Structure described level of Management
   Information [RFC2578], and MIB data models
   security for managing new
   protocols.

   As pointed out in [RFC5706], the common policy in terms of operation
   and management has been expanded to a policy that is more open to a
   set of tools message type and management protocols rather than strictly relying on originator does not meet locally
   maintained security policies, a single protocol such as SNMP.

   In 2003, node MAY discard the Internet Architecture Board (IAB) held a workshop on
   Network Management [RFC3535] that discussed packet without
   further processing.  These policies can include security levels, keys
   used, source identifiers, or the strengths and
   weaknesses lack of some IETF network management protocols and compared
   them to operational needs, especially configuration.

   One issue discussed was timestamp-based counters (as
   indicated by the user-unfriendliness 'T' flag).  The configuration of the binary format
   of SNMP [RFC3410].  In security policy
   database for incoming packet processing is outside the case scope of LLNs, it must this
   specification (it may, for example, be noted that at the
   time of writing, defined through DIO
   Configuration or through out-of-band administrative router
   configuration).

   Where the CoRE Working Group is actively working on
   resource management of devices in LLNs.  Still, it is felt that this
   section provides important guidance on how message security level (LVL) indicates an encrypted RPL should be deployed,
   operated, and managed.

   As stated in [RFC5706], "A management
   message, the node uses the key information model should
   include a discussion of what is manageable, which aspects of identified through the
   protocol need KIM
   field as well as the Nonce as input to the message payload decryption
   processing.  The Nonce shall be configured, what types of operations are allowed,
   what protocol-specific events might occur, which events can be
   counted, derived from the message Counter
   field and for which events an operator should other received and locally maintained information (see
   Section 10.9.1).  The plaintext message contents shall be notified".  These
   aspects are discussed in detail in obtained by
   invoking the following sections.

   RPL will be used on a variety inverse cryptographic mode of devices that may have resources such
   as memory varying from a very few Kbytes to several hundreds operation specified by the
   Sec field of
   Kbytes the received packet.

   The receiver shall use the Nonce and even Mbytes.  When memory is highly constrained, it may
   not be possible identified key information to satisfy all
   check the requirements listed in this
   section.  Still it is worth listing all of these in an exhaustive
   fashion, and implementers will then determine which integrity of these
   requirements could be satisfied according to the available resources
   on incoming packet.  If the device.

16.2.  Configuration Management

16.2.1.  Initialization Mode

   "Architectural Principles of integrity check
   fails against the Internet" [RFC1958], Section 3.8,
   states: "Avoid options and parameters whenever possible.  Any options
   and parameters should be configured or negotiated dynamically rather
   than manually.  This especially true in LLNs where received message authentication code (MAC), a node
   MUST discard the number of
   devices may be large and manual configuration is infeasible.  This packet.

   If the received message has been taken into account in an initialized (zero value) Counter value
   and the design of RPL whereby receiver has an incoming Counter currently maintained for the DODAG
   root provides a number
   originator of parameters to the devices joining message, the
   DODAG, thus avoiding cumbersome configuration on the routers and
   potential sources of misconfiguration (e.g. values of trickle timers,
   ...).  Still there are additional RPL parameters that receiver MUST initiate a RPL
   implementation should allow to be configured, which are discussed in
   this section.

16.2.1.1.  DIS mode of operation upon boot-up

   When Counter
   resynchronization by sending a node is first powered up:

   1.  The node may decide to stay silent, waiting Consistency Check response message
   (see Section 6.6) to receive DIO
       messages from DODAG of interest (advertising a supported OF and
       metrics/constraints) and not send any multicast DIO messages
       until it has joined a DODAG.

   2. the message source.  The node may decide to send one or more DIS messages (optionally
       requesting DIO for a specific DODAG) Consistency Check
   response message as an initial probe shall be protected with the current full outgoing
   Counter maintained for nearby DODAGs, and in the absence of DIO messages in reply
       after some configurable period particular node address.  That outgoing
   Counter will be included within the security section of time, the message
   while the incoming Counter will be included within the Consistency
   Check message payload.

   Based on the specified security policy a node may decide to
       root MAY apply replay
   protection for a floating DODAG and start sending multicast DIO messages.

   A received RPL implementation message.  The replay check SHOULD allow configuring be
   performed before the preferred mode authentication of
   operation listed above along with the required parameters (in received packet.  The
   Counter as obtained from the
   second mode: incoming packet shall be compared
   against the number watermark of DIS messages and related timer).

16.2.2.  DIO and DAO Base Message the incoming Counter maintained for the
   given origination node address.  If the received message Counter
   value is non-zero and Options Configuration

   RPL specifies less than the maintained incoming Counter
   watermark a number of protocol parameters considering potential packet replay is indicated and the large
   spectrum node MUST
   discard the incoming packet.

   If delay protection is specified as part of applications where it will be used.  That said,
   particular attention has been given the incoming packet
   security policy checks, the Timestamp Counter is used to limiting validate the number
   timeliness of these
   parameters that must be configured on each the received RPL router.  Instead, a
   number of message.  If the default values can be used, and when required these
   parameters can be provided by incoming message
   Timestamp Counter value indicates a message transmission time prior
   to the DODAG root thus allowing locally maintained transmission time Counter for
   dynamic parameter setting.

   A RPL implementation SHOULD allow configuring the following routing
   protocol parameters.  As pointed out above, note that
   originator address, a large set of
   parameters replay violation is configured on indicated and the DODAG root.

16.2.3.  Protocol Parameters to be configured on every router in node MUST
   discard the LLN

   o  RPLInstanceID [DIO message, in DIO base message].  Although incoming packet.  If the
      RPLInstanceID must be configured on received Timestamp Counter value
   indicates a message transmission time that is earlier than the DODAG root, it must also
      be configured as
   Current time less the acceptable packet delay, a policy on every node in order to determine
      whether or not delay violation is
   indicated and the node should join a particular DODAG.  Note that
      a second RPLInstance can be configured on MUST discard the node, should it
      become root of a floating DODAG.

   o  Objective Code Point (OCP)

   o  List of supported metrics: [I-D.ietf-roll-routing-metrics]
      specifies incoming packet.

   Once a number of metrics message has been decrypted, where applicable, and constraints used for has
   successfully passed its integrity check, replay, and optionally delay
   protection checks, the DODAG
      formation.  Thus a RPL implementation should allow configuring node can update its local security
   information, such as the
      list source's expected Counter value for replay
   comparison.

   A node MUST NOT update its security information on receipt of metrics that a node can accept and understand.
   message that fails security policy checks or other applied integrity,
   replay, or delay checks.

10.7.1.  Timestamp Key Checks

   If the 'T' flag of a DIO message is received with set and a metric and/or constraint node has a local timestamp
   that is not understood
      or supported, as specified follows the requirements in Section 7.5, 10.5, then a node MAY check
   the temporal consistency of the message.  The node would join as
      a leaf node.

   o  DODAGID [DIO, DIO base option] and [DAO message when computes the D flag
   transmit time of the DAO message is set).

   o  Route Information (and preference) [DIO message, in Route
      Information option]

   o  Solicited Information [DIS message, in Solicited Information
      option].  Note that an RPL implementation SHOULD allow configuring
      when such messages should be sent and under which circumstances,
      along with by adding the Counter value of the RPLInstance ID, V/I/D flags.

   o  K flag [DAO message, in DAO base message].

   o  MOP (Mode of Operation) [DIO message, in DIO base message]

16.2.4.  Protocol Parameters to be configured on every non-root router
         in the LLN

   o  Target prefix [DAO, in RPL Target option and DIO messages]
   o  Transit information [DAO, Transit information option]: A RPL
      implementation SHOULD allow configuring whether a non-storing node
      provides start
   time of the transit information in DAO messages.

   A node whose DODAG parent set associated key.  If this transmit time is empty may become past the DODAG root end
   time of a
   floating DODAG.  It may also set its DAGPreference such that it is
   less preferred.  Thus a RPL implementation MUST allow configuring the
   set of actions that key, the node should initiate in this case:

   o  Start its own (floating) DODAG: MAY discard the new DODAGID must be configured message without further
   processing.  If the transmit time is too far in addition the past or future
   compared to its DAGPreference

   o  Poison the broken path (see procedure in Section 7.2.2.5)

   o  Trigger a local repair

16.2.5.  Parameters to be configured time on the DODAG root

   In addition, several other parameters are configured only on receiver, it MAY discard the
   DODAG root
   message without further processing.

10.8.  Coverage of Integrity and advertised in options carried in DIO messages.

   As specified in Section 7.3, Confidentiality

   For a RPL implementation makes use of
   trickle timers to govern the sending of DIO messages.  The operation
   of ICMPv6 message, the trickle algorithm entire packet is determined by a set within the scope of configurable
   parameters, which MUST be configurable
   RPL security.

   Message authentication codes (MAC) and that signatures are then advertised
   by calculated over
   the DODAG root along entire IPv6 packet.  MAC and signature calculations are performed
   before any compression that lower layers may apply.

   When a RPL ICMPv6 message is encrypted, encryption starts at the DODAG in DIO messages.

   o  DIOIntervalDoublings [DIO, in DODAG configuration option]

   o  DIOIntervalMin [DIO, in DODAG configuration option]

   o  DIORedundancyConstant [DIO, in DODAG configuration option]

   In addition, a RPL implementation SHOULD allow for configuring the
   following set of RPL parameters:

   o  Path Control Size [DIO, in DODAG configuration option]

   o  MinHopRankIncrease [DIO, in DODAG configuration option]

   o  The following fields: MOP (Mode of Operation), DODAGPreference
      field [DIO message, DIO Base object]

   o  Route information (list of prefixes with preference) [DIO message,
      in Route Information option]

   o  The T flag allows for triggering a refresh of the downward routes.
      A RPL implementation SHOULD support manual setting of the T flag
      or upon the occurrence of a set of event such as
   first byte after the expiration of
      a configurable periodic timer.

   o  List of metrics security section and constraints used for continues to the DODAG.

   o  Prefix information along with valid and preferred lifetime and last byte
   of the
      L packet.  The IPv6 header, ICMPv6 header, and A flags.  [DIO message, Prefix Information option].  A RPL
      implementation SHOULD allow configuring if the Prefix Information
      Option must be carried with the DIO message Up to distribute the
      prefix information for auto-configuration.  In that case, the RPL
      implementation MUST allow
   the list end of prefixes to be advertised in the Prefix Information Option along with the corresponding flags.

   DAG Root behavior: in some cases, a node may security section are not want to permanently
   act encrypted, as a floating DODAG root if it cannot join a grounded DODAG.  For
   example a battery-operated node may not want they are needed
   to act as a floating
   DODAG root for a long period of time.  Thus a RPL implementation MAY
   support correctly decrypt the ability to configure whether or not packet.

   For example, a node could act as a
   floating DODAG root for a configured period of time.

   DAG Version Number Increment: sending a RPL implementation may allow by
   configuration at message with LVL=5, KIM=0, and
   Algorithm=0 uses the DODAG root CCM* algorithm[CCMStar] to refresh create a packet with
   attributes ENC-MAC-32: it encrypts the DODAG states packet and appends a 32-bit
   MAC.  The block cipher key is determined by
   updating the DODAGVersionNumber.  A RPL implementation SHOULD allow
   configuring whether or not periodic or event triggered mechanisms are
   used by Key Index; the DODAG root to control DODAGVersionNumber change (which
   triggers a global repair Nonce
   is computed as specified described in Section 3.3.2.

16.2.6.  Configuration of RPL Parameters related to DAO-based mechanisms

   DAO messages are optional and used in DODAGs that require downward
   routing operation.  This section deals with 10.9.1; the set of parameters
   related to DAO message to
   authenticate and provides recommendations on their
   configuration.

   An implementation SHOULD bound encrypt is the time that RPL message starting at the entry is allocated
   in first
   byte after the UNREACHABLE state.  Upon security section and ends with the equivalent expiry last byte of the related
   timer (RemoveTimer),
   packet; the entry SHOULD be suppressed.  Thus a RPL
   implementation MAY allow for additional authentication data starts with the configuration beginning
   of the RemoveTimer.

   While the entry is in IPv6 header and ends with the UNREACHABLE state a node SHOULD make a
   reasonable attempt to report a No-Path to each last byte of the DAO parents.
   That number RPL security
   section.

10.9.  Cryptographic Mode of attempts MAY be configurable.

   When the associated Retry Counter for a REACHABLE(Pending) entry
   reaches a maximum threshold, the entry Operation

   The cryptographic mode of operation described in this specification
   (Algorithm = 0) is placed into the UNREACHABLE
   state based on CCM and No-Path should be scheduled to send to the node's DAO
   Parents.  The maximum threshold MAY be configurable.

   An implementation should support rate-limiting block-cipher AES-
   128[RFC3610].  This mode of operation is widely supported by existing
   implementations and coincides with the sending CCM* mode of DAO
   messages.  The related parameters MAY be configurable.

   When scheduling to send
   operation[CCMStar].  CCM mode requires a DAO, an implementation should equivalently
   start nonce.

10.9.1.  Nonce

   A RPL node constructs a timer (DelayDAO) CCM nonce as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                       Source Identifier                       +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Counter                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Reserved | LVL |
       +-+-+-+-+-+-+-+-+

                           Figure 31: CCM* Nonce

   Source Identifier:  8 bytes.  Source Identifier is set to delay sending the DAO, thus helping to
   potentially aggregate DAOs.  The DelayDAO timer MAY be configurable.

16.2.7.  Default Values

   This document specifies default values for logical
         identifier of the following set originator of RPL
   variables:
      DEFAULT_PATH_CONTROL_SIZE
      DEFAULT_DIO_INTERVAL_MIN
      DEFAULT_DIO_INTERVAL_DOUBLINGS
      DEFAULT_DIO_REDUNDANCY_CONSTANT
      DEFAULT_MIN_HOP_RANK_INCREASE

   It the protected packet.

   Counter:  4 bytes.  Counter is recommended set to specify default values in protocols; that being
   said, as discussed the (uncompressed) value of the
         corresponding field in [RFC5706], default values may make less and
   less sense. the Security option of the RPL control
         message.

   Security Level (LVL):  3 bits.  Security Level is a routing protocol that is expected set to be used in
   a number of contexts where network characteristics such as the number value of nodes, link and nodes types are expected to vary significantly.
   Thus, these default values are likely to change with the context and
   as the technology will evolve.  Indeed, LLNs' related technology
   (e.g. hardware, link layers) have been evolving dramatically over
         the
   past few years and such technologies are expected to change and
   evolve considerably corresponding field in the coming years.

   The proposed values are not based on extensive best current practices
   and are considered to be conservative.

16.3.  Monitoring Security option of the RPL Operation

   Several RPL parameters should
         control message.

   Unassigned bits of the nonce are reserved.  They MUST be monitored set to verify zero
   when constructing the correct
   operation nonce.

   All fields of the routing protocol nonce are represented in most-significant-octet and
   most-significant-bit first order.

10.9.2.  Signatures

   If the network itself.  This
   section lists Key Identification Mode (KIM) mode indicates the set use of monitoring parameters
   signatures (a value of interest.

16.3.1.  Monitoring 3), then a DODAG parameters

   A RPL implementation SHOULD provide information about the following
   parameters:

   o  DODAG Version number [DIO message, in DIO base message]

   o  Status of node appends a signature to the G flag [DIO message, in DIO base message]

   o  Status
   data payload of the MOP packet.  The Security Level (LVL) field [DIO message, in DIO base message]
   o  Value of describes
   the DTSN [DIO message, length of this signature.

   The signature scheme in DIO base message]

   o  Value RPL for Security Mode 3 is an instantiation
   of the rank [DIO message, in DIO base message]

   o  DAOSequence: Incremented at each unique DAO message, echoed in RSA algorithm [RFC3447].  It uses as public key the
      DAO-ACK message [DAO pair
   (n,e), where n is a 3072-bit RSA modulus and DAO-ACK messages]

   o  Route Information [DIO message, Route Information option] (list of
      IPv6 prefixes per parent along where e=2^{16}+1.  It
   uses CCM* mode[CCMStar] as the encryption scheme with lifetime and preference]

   o  Trickle parameters:

      *  DIOIntervalDoublings [DIO, in DODAG configuration option]

      *  DIOIntervalMin [DIO, in DODAG configuration option]

      *  DIORedundancyConstant [DIO, in DODAG configuration option]

   o  Path Control Size [DIO, in DODAG configuration option]

   o  MinHopRankIncrease [DIO, in DODAG configuration option]

   Values that may be monitored only on M=0 (as a
   stream-cipher).  It uses the DODAG root

   o  Transit Information [DAO, Transit Information option]: A RPL
      implementation SHOULD allow configuring whether SHA-2 hash function [sha2].  It uses the set
   message encoding rule of
      received Transit Information options should [RFC3447].

   Let 'a' be displayed on the
      DODAG root.  In this case, the RPL database a concatenation of received Transit
      Information should also contain: the path-sequence, path control,
      path lifetime and parent address.

16.3.2.  Monitoring a DODAG inconsistencies and loop detection

   Detection six-byte representation of DODAG inconsistencies is particularly critical in RPL
   networks.  Thus it Counter
   and the message header.  The packet payload is recommended for a RPL implementation to provide
   appropriate monitoring tools.  A RPL implementation SHOULD provide a
   counter reporting the number right-
   concatenation of a times packet data 'm' and the node has detected an
   inconsistency signature 's'.  This
   signature scheme is invoked with respect to a DODAG parent, e.g. if the DODAGID has
   changed.

   When possible more granular information about inconsistency detection
   should be provided.  A RPL implementation MAY provide counters
   reporting the number right-concatenation of following inconsistencies:

   o  Packets received with O bit set (to down) from a node with a
      higher rank

   o  Packets received with O bit reset (to up) from a node with the
   message parts a lower
      rank

   o  Number of packets with and m, whereas the F bit set

   o  Number of packets signature verification is invoked
   with the R bit set

16.4.  Monitoring right-concatenation of the RPL data structures

16.4.1.  Candidate Neighbor Data Structure

   A node in the candidate neighbor list is message parts a node discovered by the
   some means and qualified to potentially become a parent (with high
   enough local confidence).  A RPL implementation SHOULD provide a way
   to monitor the candidate neighbor list m, and with some metric reflecting
   local confidence (the degree of stability
   signature s.

   RSA signatures of the neighbors) as
   measured by some metrics.

   A RPL implementation MAY this form provide a counter reporting sufficient protection for RPL
   networks.  If needed, alternative signature schemes which produce
   more concise signatures may be the number subject of
   times a candidate neighbor has been ignored, should the number of
   candidate neighbors exceeds the maximum authorized value.

16.4.2.  Destination Oriented Directed Acyclic Graph (DAG) Table

   For each DODAG, future work.

11.  Packet Forwarding and Loop Avoidance/Detection

11.1.  Suggestions for Packet Forwarding

   When forwarding a RPL implementation packet to a destination, precedence is expected given to keep track
   selection of a next-hop successor as follows:

   1.  This specification only covers how a successor is selected from
       the
   following DODAG table values:

   o  RPLInstanceID

   o  DODAGID

   o  DODAGVersionNumber

   o  Rank

   o  Objective Code Point

   o  A set of DODAG Parents

   o  A set of prefixes offered upwards along Version that matches the DODAG

   o  Trickle timers used to govern RPLInstanceID marked in the sending
       IPv6 header of DIO messages for the
      DODAG

   o  List of DAO parents

   o  DTSN
   o  Node status (router versus leaf)

   A RPL implementation SHOULD allow for monitoring packet being forwarded.  Routing outside the set
       instance can be done as long as additional rules are put in place
       such as strict ordering of
   parameters listed above.

16.4.3.  Routing Table instances and DAO Routing Entries

   A RPL implementation maintains several information elements related routing protocols to the DODAG and the DAO entries (for storing nodes).  In the case of
       protect against loops.  Such rules may be defined in a non storing node, separate
       document.

   2.  If a limited amount of information is maintained
   (the routing table is mostly reduced to local administrative preference favors a set of DODAG parents along
   with characteristics of route that has been
       learned from a different routing protocol than RPL, then use that
       successor.

   3.  If the DODAG packet header specifies a source route by including a RH4
       header as mentioned above) whereas specified in [I-D.ietf-6man-rpl-routing-header], then
       use that route.  If the
   case of storing nodes, this information is augmented node fails to forward the packet with routing
   entries.

   A RPL implementation
       that specified source route, then that packet SHOULD provide the ability be dropped.
       The node MAY log an error.  The node MAY send an ICMPv6 Error in
       Source Routing Header message to monitor the
   following parameters:

   o  Next Hop (DODAG parent)

   o  Next Hop Interface

   o  Path metrics value for each DODAG parent

   A DAO Routing Table Entry conceptually contains source of the following
   elements (for storing nodes only):

   o  Advertising Neighbor Information

   o  IPv6 Address

   o  Interface ID to which DAO Parents has this packet (See
       Section 19.18).

   4.  If there is an entry in the routing table matching the
       destination that has been reported

   o  Retry Counter

   o  Logical equivalent of DAO Content:

      *  DAO Sequence

      *  DAO Lifetime

      *  DAO Path Control

   o  Destination Prefix (or Address or Mcast Group)

   A RPL implementation SHOULD provide information about learned from a multicast destination
       advertisement (e.g. the state of
   each DAO Routing Table entry states.

16.5.  Fault Management

   Fault management destination is a critical component used for troubleshooting,
   verification of one-hop neighbor), then
       use that successor.

   5.  If there is an entry in the correct mode of operation of routing table matching the protocol,
   network design, and is also
       destination that has been learned from a key component of network performance
   monitoring.  A RPL implementation SHOULD allow providing unicast destination
       advertisement (e.g. the
   following information related to fault managements:

   o  Memory overflow along destination is located Down the sub-
       DODAG), then use that successor.  If there are DAO Path Control
       bits associated with multiple successors, then consult the cause (e.g. routing tables
      overflow, ...)

   o  Number of times Path
       Control bits to order the successors by preference when choosing.
       If, for a packet could not given DAO Path Control bit, multiple successors are
       recorded as having asserted that bit, precedence should be sent given
       to the successor who most recently asserted that bit.

   6.  If there is a DODAG parent
      flagged as valid

   o  Number of times a packet has been received for which the router
      did not have Version offering a corresponding RPLInstanceID

   o  Number of times route to a local repair procedure was triggered

   o  Number prefix matching
       the destination, then select one of times those DODAG parents as a global repair was triggered by
       successor according to the OF and routing metrics.

   7.  Any other as-yet-unattempted DODAG root

   o  Number of received malformed messages

   o  Number of seconds with packets parent may be chosen for the
       next attempt to forward and a unicast packet when no next hop (DODAG
      parent)

   o  Number of seconds without next hop (DODAG parent)

   o  Number better match
       exists.

   8.  Finally the packet is dropped.  ICMP Destination Unreachable MAY
       be invoked (an inconsistency is detected).

   Hop Limit MUST be decremented when forwarding as per [RFC2460].

   Note that the chosen successor MUST NOT be the neighbor that was the
   predecessor of times the packet (split horizon), except in the case where
   it is intended for the packet to change from an upward to a downward
   flow, as determined by the routing table of the node has joined a DODAG making the
   change, such as a leaf because it
      received a switching from DIO with metric/constraint not understood and it was
      configured routes to join DAO routes as a leaf node in this case (see Section 16.6).

   It the
   destination is RECOMMENDED neared in order to report faults via at least error log messages.
   Other protocols may be used continue traveling toward the
   destination.

11.2.  Loop Avoidance and Detection

   RPL loop avoidance mechanisms are kept simple and designed to report such faults.

16.6.  Policy

   Policy rules can be used by
   minimize churn and states.  Loops may form for a number of reasons,
   e.g. control packet loss.  RPL implementation to determine whether
   or not includes a reactive loop detection
   technique that protects from meltdown and triggers repair of broken
   paths.

   RPL loop detection uses information that contained within the node data
   packet using the RPL Option [I-D.ietf-6man-rpl-option]) in an IPv6
   Hop-by-Hop Option header.  The RPL Option is allowed to join a particular DODAG advertised by generic container for
   a
   neighbor by means list of DIO messages. TLVs.  This document specifies operation within specification defines a single DODAG.  A DODAG new RPL Option type,
   called the RPL Loop Detection.  The RPL Loop Detection TLV is
   characterized placed
   in the RPL Option with Option Type = 1 (to be confirmed by IANA),
   Option Data Length = 4 octets, and the Value has the following tuple (RPLInstanceID, DODAGID).
   Furthermore, as pointed out above, DIO messages are used to advertise
   other DODAG characteristics such as
   format:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |O|R|F|0|0|0|0|0| RPLInstanceID |          SenderRank           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 32: RPL Packet Information

   Down 'O':  1-bit flag indicating whether the routing metrics and
   constraints used to build packet is expected to
         progress Up or Down.  A router sets the DODAG and 'O' flag when the Objective Function in
   use (specified by OCP).

   The first policy rules consists of specifying
         packet is expected to progress Down (using DAO routes), and
         clears it when forwarding toward the following
   conditions that DODAG root (to a RPL node must satisfy to join with
         a DODAG:

   o  RPLInstanceID

   o  DODAGID

   o  List of supported routing metrics and constraints

   o  Objective Function (OCP values) lower rank).  A host or RPL implementation MUST allow configuring these parameters and
   SHOULD specify whether the leaf node must simply ignore the DIO if MUST set the
   advertised DODAG 'O' flag
         to 0.

   Rank-Error 'R':  1-bit flag indicating whether a rank error was
         detected.  A rank error is not compliant with detected when there is a mismatch in
         the local policy or whether relative ranks and the node should join direction as indicated in the 'O'
         bit.  A host or RPL leaf node if only MUST set the list of supported
   routing metrics and constraints, and the OF is 'R' bit to 0.

   Forwarding-Error 'F':  1-bit flag indicating that this node can not supported.

   A RPL implementation SHOULD allow configuring
         forward the packet further towards the destination.  The 'F'
         bit might be set of acceptable
   or preferred Objective Functions (OF) referenced by their Objective
   Codepoints (OCPs) for a child node to join that does not have a DODAG, and what action should
   be taken if none of route to
         destination for a node's candidate neighbors advertise one of packet with the
   configured allowable Objective Functions, Down 'O' bit set.  A host or if the advertised
   metrics/constraint is not understood/supported.  Two actions can be
   taken in this case:

   o  The
         RPL leaf node joins MUST set the 'F' bit to 0.

   RPLInstanceID:  8-bit field indicating the DODAG as instance along which
         the packet is sent.

   SenderRank:  16-bit field set to zero by the source and to
         DAGRank(rank) by a leaf node as specified in
      Section 7.5

   o  The node does not join router that forwards inside the DODAG

   A node in an LLN may learn routing information RPL network.

11.2.1.  Source Node Operation

   If the source is aware of the RPLInstanceID that is preferred for the
   packet, then it MUST set the RPLInstanceID field associated with the
   packet accordingly, otherwise it MUST set it to the
   RPL_DEFAULT_INSTANCE.

11.2.2.  Router Operation

11.2.2.1.  Instance Forwarding

   RPLInstanceIDs are used to avoid loops between DODAGs from different routing
   protocols including RPL.  It
   origins.  DODAGs that are constructed for antagonistic constraints
   might contain paths that, if mixed together, would yield loops.
   Those loops are avoided by forwarding a packet along the DODAG that
   is in this case desirable associated to control via
   administrative preference a given instance.

   The RPLInstanceID is associated by the source with the packet.  This
   RPLInstanceID MUST match the RPL Instance onto which route should be favored.  An
   implementation SHOULD allow for specifying an administrative
   preference for the routing protocol packet is
   placed by any node, be it a host or router.

   For a packet that is originated from which outside the route was learned.

   Internal Data Structures: some RPL implementations may limit network, the size
   source of the candidate neighbor list in order to bound the memory usage, in
   which case some otherwise viable candidate neighbors may not packet might be
   considered and simply dropped from aware of the candidate neighbor list.

   A RPL implementation MAY provide an indicator network, of the
   constraints imposed on OFs, and of associated RPLInstanceIDs.  In
   that case, the size source of the
   candidate neighbor list.

16.7.  Liveness Detection and Monitoring

   By contrast packet MAY tag the flow label with several other routing protocols, the
   RPLInstanceID.

   A RPL does not define
   any 'keep-alive' mechanisms to detect routing adjacency failure: this
   is in most cases, because such router that forwards a mechanism may be too expensive packet in
   terms of bandwidth and even more importantly energy (a battery
   operated device could the RPL network MUST check if
   the packet includes the RPL Loop Detection TLV in a RPL Option within
   the IPv6 Hop-by-Hop Option header.  If one does not afford to send periodic Keep alive).  Still exist, the RPL requires mechanisms to detect that
   router MUST insert a neighbor is no longer
   reachable: this can be performed by using mechanisms such RPL Loop Detection type as NUD
   (Neighbor Unreachability Detection) or even some form of Keep-alive
   that are outside of this document.

16.8.  Fault Isolation

   It is RECOMMENDED to quarantine neighbors that start emitting
   malformed messages at unacceptable rates.

16.9.  Impact on Other Protocols

   RPL has very limited impact on other protocols.  Where more than one
   routing protocol is required on a specified in

   [I-D.ietf-6man-rpl-option].  If the router such as a LBR, it is
   expected for the device to support routing redistribution functions
   between an ingress router that
   injects the routing protocols to allow for reachability between packet into the
   two routing domains.  Such redistribution SHOULD be governed by RPL network, the
   use of user configurable policy.

   With regards to router MUST set the impact
   RPLInstanceID field in terms of traffic on the network, RPL
   has been designed Loop Detection TLV.

   A router that forwards a packet to limit outside the control traffic thanks to mechanisms
   such as Trickle timers (Section 7.3).  Thus RPL network MUST
   remove the impact of RPL on
   other protocols should be extremely limited.

16.10.  Performance Management

   Performance management is always an important aspect of Option as specified in [I-D.ietf-6man-rpl-option].

   When a protocol router receives a packet that specifies a given RPLInstanceID
   and RPL is not an exception.  Several metrics of interest have been
   specified by the IP Performance Monitoring (IPPM) Working Group: node can forward the packet along the DODAG associated to
   that
   being said, they will be hardly applicable instance, then the router MUST do so and leave the RPLInstanceID
   value unchanged.

   If any node can not forward a packet along the DODAG associated to LLN considering
   the
   cost of monitoring these metrics in terms of resources on RPLInstanceID, then the devices
   and required bandwidth.  Still, RPL implementation MAY support some
   of these, and other parameters of interest are listed below:

   o  Number of repairs node SHOULD discard the packet and time to repair in seconds (average,
      variance)

   o  Number send
   an ICMP error message.

11.2.2.2.  DAG Inconsistency Loop Detection

   The DODAG is inconsistent if the direction of times and duration during which a devices could packet does not
      forward match
   the rank relationship.  A receiver detects an inconsistency if it
   receives a packet because with either:

      the 'O' bit set (to Down) from a node of a lack higher rank.

      the 'O' bit cleared (for Up) from a node of reachable neighbor a lesser rank.

   When the DODAG root increments the DODAGVersionNumber, a temporary
   rank discontinuity may form between the next DODAG Version and the
   prior DODAG Version, in its
      routing table

   o  Monitoring of resources consumption by RPL itself particular if nodes are adjusting their rank
   in terms of
      bandwidth and required memory

   o  Number of RPL control messages sent the next DODAG Version and received

17.  Security Considerations

17.1.  Overview

   From deferring their migration into the next
   DODAG Version.  A router that is still a security perspective, RPL networks are no different from any
   other network.  They are vulnerable member of the prior DODAG
   Version may choose to passive eavesdropping attacks
   and potentially even active tampering when physical access forward a packet to a wire (future) parent that is not required to participate
   in communications.  The very nature of
   ad hoc networks and their cost objectives impose additional security
   constraints, which perhaps make these networks the most difficult
   environments next DODAG Version.  In some cases this could cause the parent
   to secure.  Devices are low-cost and have limited
   capabilities detect an inconsistency because the rank-ordering in terms of computing power, available storage, and
   power drain; the prior
   DODAG Version is not necessarily the same as in the next DODAG
   Version and it cannot always the packet may be assumed they have neither a
   trusted computing base nor a high-quality random number generator
   aboard.  Communications cannot rely on judged to not be making forward
   progress.  If the online availability of a
   fixed infrastructure and might involve short-term relationships
   between devices sending router is aware that may never have communicated before.  These
   constraints might severely limit the choice of cryptographic
   algorithms and protocols and influence chosen successor
   has already joined the design of next DODAG Version, then the security
   architecture because sending router
   MUST update the establishment and maintenance of trust
   relationships between devices need SenderRank to be addressed with care.  In
   addition, battery lifetime and cost constraints put severe limits on INFINITE_RANK as it forwards the security overhead these networks can tolerate, something that is
   of far less concern with higher bandwidth networks.  Most of these
   security architectural elements can be implemented at higher layers
   and may, therefore, be considered to be outside
   packets across the scope of this
   standard.  Special care, however, needs to be exercised with respect
   to interfaces to these higher layers.

   The security mechanisms discontinuity into the next DODAG Version in this standard are based on symmetric-key
   and public-key cryptography and use keys that are order
   to be provided by
   higher layer processes.  The establishment and maintenance avoid a false detection of these
   keys are outside rank inconsistency.

   One inconsistency along the scope of this standard.  The mechanisms assume path is not considered a
   secure implementation of cryptographic operations and secure critical error
   and
   authentic storage of keying material.

   The security mechanisms specified provide particular combinations the packet may continue.  But a second detection along the path
   of a same packet should not occur and the following security services:

   Data confidentiality:  Assurance that transmitted information packet MUST be dropped.

   This process is only
               disclosed to parties for which it controlled by the Rank-Error bit associated with the
   packet.  When an inconsistency is intended.

   Data authenticity:  Assurance of detected on a packet, if the source of transmitted
               information (and, hereby, that information Rank-
   Error bit was not
               modified in transit).

   Replay protection:  Assurance that a duplicate of transmitted
               information set then the Rank-Error bit is detected.

   Timeliness (delay protection):  Assurance that transmitted
               information set.  If it was received in a timely manner.

   The actual protection provided can set
   the packet MUST be adapted on a per-packet basis discarded and allows for varying levels of data authenticity (to minimize
   security overhead in transmitted packets where required) the trickle timer MUST be reset.

11.2.2.3.  DAO Inconsistency Loop Detection and for
   optional data confidentiality.  When nontrivial protection is
   required, replay protection is always provided.

   Replay protection is provided Recovery

   A DAO inconsistency happens when a router has a downward route that
   was previously learned from a DAO message via the use of a non-repeating value
   (nonce) child, but that
   downward route is not longer valid in the child, e.g. because that
   related state in the child has been cleaned up.  With DAO
   inconsistency loop recovery, a packet protection process can be used to recursively
   explore and storage of some status
   information for each originating device on the receiving device,
   which allows detection of whether this particular nonce value was
   used previously by cleanup the originating device. obsolete DAO states along a sub-DODAG.

   In addition, so-called
   delay protection a general manner, a packet that goes Down should never go Up
   again.  If DAO inconsistency loop recovery is provided amongst those devices applied, then the
   router SHOULD send the packet back to the parent that have passed it with
   the Forwarding-Error 'F' bit set and the 'O' bit left untouched.
   Otherwise the router MUST silently discard the packet.

11.2.2.4.  Forward Path Recovery

   Upon receiving a
   loosely synchronized clock on board. packet with a Forwarding-Error bit set, the node
   MUST remove the routing states that caused forwarding to that
   neighbor, clear the Forwarding-Error bit and attempt to send the
   packet again.  The acceptable time delay can packet may be adapted on sent to an alternate neighbor, after
   the expiration of a per-packet basis user-configurable implementation specific timer.
   If that alternate neighbor still has an inconsistent DAO state via
   this node, the process will recurse, this node will set the
   Forwarding-Error 'F' bit and allows for varying latencies (to
   facilitate longer latencies the routing state in packets transmitted the alternate
   neighbor will be cleaned up as well.

12.  Multicast Operation

   This section describes further the multicast routing operations over
   an IPv6 RPL network, and specifically how unicast DAOs can be used to
   relay group registrations up.  Wherever the following text mentions
   Multicast Listener Discovery (MLD), one can read MLDv1 ([RFC2710]) or
   MLDv2 ([RFC3810]).

   Nodes that support the RPL storing mode of operation SHOULD also
   support multicast DAO operations as described below.  Nodes that only
   support the non-storing mode of operation are not expected to support
   this section.

   The multicast operation is controlled by the MOP field in the DIO.

      If the MOP field requires multicast support, then a multi-hop
   communication path).

   Cryptographic protection node that
      joins the RPL network as a router must operate as described in
      this section for multicast signaling and forwarding within the RPL
      network.  A node that does not support the multicast operation
      required by the MOP field can only join as a leaf.

      If the MOP field does not require multicast support, then
      multicast is handled by some other way that is out of scope for
      this specification.  (Examples may use include a key shared between two peer
   devices (link key) series of unicast
      copies or limited-scope flooding).

   As is traditional, a key shared among listener uses a group of devices (group
   key), thus allowing some flexibility protocol such as MLD with a
   router to register to a multicast group.

   Along the path between the router and application-specific
   tradeoffs the DODAG root, MLD requests
   are mapped and transported as DAO messages within RPL; each hop
   coalesces the multiple requests for a same group as a single DAO
   message to the parent(s), in a fashion similar to proxy IGMP, but
   recursively between key storage child router and key maintenance costs versus parent Up to the DODAG root.

   A router might select to pass a listener registration DAO message to
   its preferred parent only, in which case multicast packets coming
   back might be lost for all of its sub-DODAG if the transmission fails
   over that link.  Alternatively the router might select to copy
   additional parents as it would do for DAO messages advertising
   unicast destinations, in which case there might be duplicates that
   the router will need to prune.

   As a result, multicast routing states are installed in each router on
   the way from the listeners to the DODAG root, enabling the root to
   copy a multicast packet to all its children routers that had issued a
   DAO message including a Target option for that multicast group, as
   well as all the attached nodes that registered over MLD.

   For unicast traffic, it is expected that the grounded DODAG root acts
   as an LBR and MAY redistribute the RPL routes over the external
   infrastructure using whatever routing protocol is used in the other
   routing domain.  For multicast traffic, the root MAY proxy MLD for
   all the nodes attached to the RPL domain (this would be needed if the
   multicast source is located in the external infrastructure).  For
   such a source, the packet will be replicated as it flows Down the
   DODAG based on the multicast routing table entries installed from the
   DAO message.

   For a multicast packet sourced from inside the DODAG, the packet is
   passed to the preferred parents, and if that fails then to the
   alternates in the DODAG.  The packet is also copied to all the
   registered children, except for the one that passed the packet.
   Finally, if there is a listener in the external infrastructure then
   the DODAG root has to further propagate the packet into the external
   infrastructure.

   As a result, the DODAG Root acts as an automatic proxy Rendezvous
   Point for the RPL network, and as source towards the non-RPL domain
   for all multicast flows started in the RPL domain.  So regardless of
   whether the root is actually attached to a non-RPL domain, and
   regardless of whether the DODAG is grounded or floating, the root can
   serve inner multicast streams at all times.

13.  Maintenance of Routing Adjacency

   The selection of successors, along the default paths Up along the
   DODAG, or along the paths learned from destination advertisements
   Down along the DODAG, leads to the formation of routing adjacencies
   that require maintenance.

   In IGPs such as OSPF [RFC4915] or IS-IS [RFC5120], the maintenance of
   a routing adjacency involves the use of Keepalive mechanisms (Hellos)
   or other protocols such as BFD ([RFC5880]) and MANET Neighborhood
   Discovery Protocol (NHDP [I-D.ietf-manet-nhdp]).  Unfortunately, such
   an approach is not desirable in constrained environments such as LLN
   and would lead to excessive control traffic in light of the data
   traffic with a negative impact on both link loads and nodes
   resources.  Overhead to maintain the routing adjacency should be
   minimized.  Furthermore, it is not always possible to rely on the
   link or transport layer to provide information of the associated link
   state.  The network layer needs to fall back on its own mechanism.

   Thus RPL makes use of a different approach consisting of probing the
   neighbor using a Neighbor Solicitation message (see [RFC4861]).  The
   reception of a Neighbor Advertisement (NA) message with the
   "Solicited Flag" set is used to verify the validity of the routing
   adjacency.  Such mechanism MAY be used prior to sending a data
   packet.  This allows for detecting whether or not the routing
   adjacency is still valid, and should it not be the case, select
   another feasible successor to forward the packet.  Under specific
   circumstances and according to the network resources, a RPL
   implementation MAY decide to augment this mechanism with Keep-Alive
   messages.

14.  Guidelines for Objective Functions

   An Objective Function (OF), in conjunction with routing metrics and
   constraints, allows for the selection of a DODAG to join, and a
   number of peers in that DODAG as parents.  The OF is used to compute
   an ordered list of parents.  The OF is also responsible to compute
   the rank of the device within the DODAG Version.

   The Objective Function is indicated in the DIO message using an
   Objective Code Point (OCP), and indicates the method that must be
   used to construct the DODAG.  The Objective Code Points are specified
   in [I-D.ietf-roll-of0], and related companion specifications.

14.1.  Objective Function Behavior

   Most Objective Functions are expected to follow the same abstract
   behavior:

   o  The parent selection is triggered each time an event indicates
      that a potential next hop information is updated.  This might
      happen upon the reception of a DIO message, a timer elapse, all
      DODAG parents are unavailable, or a trigger indicating that the
      state of a candidate neighbor has changed.

   o  An OF scans all the interfaces on the device.  Although there may
      typically be only one interface in most application scenarios,
      there might be multiple of them and an interface might be
      configured to be usable or not for RPL operation.  An interface
      can also be configured with a preference or dynamically learned to
      be better than another by some heuristics that might be link-layer
      dependent and are out of scope.  Finally an interface might or not
      match a required criterion for an Objective Function, for instance
      a degree of security.  As a result, some interfaces might be
      completely excluded from the computation, for example if those
      interfaces cannot satisfy some advertised constraints, while
      others might be more or less preferred.

   o  An OF scans all the candidate neighbors on the possible interfaces
      to check whether they can act as a router for a DODAG.  There
      might be multiple of them and a candidate neighbor might need to
      pass some validation tests before it can be used.  In particular,
      some link layers require experience on the activity with a router
      to enable the router as a next hop.

   o  An OF computes self's rank by adding to the rank of the candidate
      a value representing the relative locations of self and the
      candidate in the DODAG Version.

      *  The increase in rank must be at least MinHopRankIncrease.

      *  To keep loop avoidance and metric optimization in alignment,
         the increase in rank should reflect any increase in the metric
         value.  For example, with a purely additive metric such as ETX,
         the increase in rank can be made proportional to the increase
         in the metric.

      *  Candidate neighbors that would cause self's rank to increase
         are not considered for parent selection.

   o  Candidate neighbors that advertise an OF incompatible with the set
      of OF specified by the policy functions are ignored.

   o  As it scans all the candidate neighbors, the OF keeps the current
      best parent and compares its capabilities with the current
      candidate neighbor.  The OF defines a number of tests that are
      critical to reach the objective.  A test between the routers
      determines an order relation.

      *  If the routers are equal for that relation then the next test
         is attempted between the routers,

      *  Else the best of the two routers becomes the current best
         parent and the scan continues with the next candidate neighbor.

      *  Some OFs may include a test to compare the ranks that would
         result if the node joined either router.

   o  When the scan is complete, the preferred parent is elected and
      self's rank is computed as the preferred parent rank plus the step
      in rank with that parent.

   o  Other rounds of scans might be necessary to elect alternate
      parents.  In the next rounds:

      *  Candidate neighbors that are not in the same DODAG are ignored.

      *  Candidate neighbors that are of greater rank than self are
         ignored.

      *  Candidate neighbors of an equal rank to self are ignored for
         parent selection.

      *  Candidate neighbors of a lesser rank than self are preferred.

15.  Suggestions for Interoperation with Neighbor Discovery

   This specification directly borrows the Prefix Information Option
   (PIO) and the Routing Information Option (RIO) from IPv6 ND.  It is
   envisioned that, as future specifications build on this base, there
   may be additional cause to leverage parts of IPv6 ND.  This section
   provides some suggestions for future specifications.

   First and foremost RPL is a routing protocol.  One should take great
   care to preserve architecture when mapping functionalities between
   RPL and ND.  RPL is for routing only.  That said, there may be
   persuading technical reasons to allow for sharing options between RPL
   and IPv6 ND in a particular implementation/deployment.

   In general the following guidelines apply:

   o  RPL Type codes must be allocated from the RPL Control Message
      Options registry.

   o  RPL Length fields must be expressed in units of single octets, as
      opposed to ND Length fields which are expressed in units of 8
      octets.

   o  RPL Options are generally not required to be aligned to 8 octet
      boundaries.

   o  When mapping/transposing an IPv6 ND option for redistribution as a
      RPL option, any padding octets should be removed when possible.
      For example, the Prefix Length field in the PIO is sufficient to
      describe the length of the Prefix field.  When mapping/transposing
      a RPL option for redistribution as an IPv6 ND option, any such
      padding octets should be restored.  This procedure must be
      unambiguous.

16.  RPL Constants and Variables

   Following is a summary of RPL constants and variables:

   BASE_RANK  This is the rank for a virtual root that might be used to
         coordinate multiple roots.  BASE_RANK has a value of 0.

   ROOT_RANK  This is the rank for a DODAG root.  ROOT_RANK has a value
         of MinHopRankIncrease (as advertised by the DODAG root), such
         that DAGRank(ROOT_RANK) is 1.

   INFINITE_RANK  This is the constant maximum for the rank.
         INFINITE_RANK has a value of 0xFFFF.

   RPL_DEFAULT_INSTANCE  This is the RPLInstanceID that is used by this
         protocol by a node without any overriding policy.
         RPL_DEFAULT_INSTANCE has a value of 0.

   DEFAULT_PATH_CONTROL_SIZE  This is the default value used to
         configure PCS in the DODAG Configuration Option, which dictates
         the number of significant bits in the Path Control field of the
         Transit Information option.  DEFAULT_PATH_CONTROL_SIZE has a
         value of 0.  This configures the simplest case limiting the
         fan-out to 1 and limiting a node to send a DAO message to only
         one parent.

   DEFAULT_DIO_INTERVAL_MIN  This is the default value used to configure
         Imin for the DIO trickle timer.  DEFAULT_DIO_INTERVAL_MIN has a
         value of 3.  This configuration results in Imin of 8ms.

   DEFAULT_DIO_INTERVAL_DOUBLINGS  This is the default value used to
         configure Imax for the DIO trickle timer.
         DEFAULT_DIO_INTERVAL_DOUBLINGS has a value of 20.  This
         configuration results in a maximum interval of 2.3 hours.

   DEFAULT_DIO_REDUNDANCY_CONSTANT  This is the default value used to
         configure k for the DIO trickle timer.
         DEFAULT_DIO_REDUNDANCY_CONSTANT has a value of 10.  This
         configuration is a conservative value for trickle suppression
         mechanism.

   DEFAULT_MIN_HOP_RANK_INCREASE  This is the default value of
         MinHopRankIncrease.  DEFAULT_MIN_HOP_RANK_INCREASE has a value
         of 256.  This configuration results in an 8-bit wide integer
         part of Rank.

   DIO Timer  One instance per DODAG that a node is a member of.  Expiry
         triggers DIO message transmission.  Trickle timer with variable
         interval in [0, DIOIntervalMin..2^DIOIntervalDoublings].  See
         Section 8.3.1

   DAG Version Increment Timer  Up to one instance per DODAG that the
         node is acting as DODAG root of.  May not be supported in all
         implementations.  Expiry triggers increment of
         DODAGVersionNumber, causing a new series of updated DIO message
         to be sent.  Interval should be chosen appropriate to
         propagation time of DODAG and as appropriate to application
         requirements (e.g. response time vs. overhead).

   DelayDAO Timer  Up to one timer per DAO parent (the subset of DODAG
         parents chosen to receive destination advertisements) per
         DODAG.  Expiry triggers sending of DAO message to the DAO
         parent.  See Section 9.4

   RemoveTimer  Up to one timer per DAO entry per neighbor (i.e. those
         neighbors that have given DAO messages to this node as a DODAG
         parent) Expiry may trigger No-Path advertisements or
         immediately deallocate the DAO entry if there are no DAO
         parents.

17.  Manageability Considerations

   The aim of this section is to give consideration to the manageability
   of RPL, and how RPL will be operated in a LLN.  The scope of this
   section is to consider the following aspects of manageability:
   configuration, monitoring, fault management, accounting, and
   performance of the protocol in light of the recommendations set forth
   in [RFC5706].

17.1.  Introduction

   Most of the existing IETF management standards are Structure of
   Management Information (SMI) based data models (MIB modules) to
   monitor and manage networking devices.

   For a number of protocols, the IETF community has used the IETF
   Standard Management Framework, including the Simple Network
   Management Protocol [RFC3410], the Structure of Management
   Information [RFC2578], and MIB data models for managing new
   protocols.

   As pointed out in [RFC5706], the common policy in terms of operation
   and management has been expanded to a policy that is more open to a
   set of tools and management protocols rather than strictly relying on
   a single protocol such as SNMP.

   In 2003, the Internet Architecture Board (IAB) held a workshop on
   Network Management [RFC3535] that discussed the strengths and
   weaknesses of some IETF network management protocols and compared
   them to operational needs, especially configuration.

   One issue discussed was the user-unfriendliness of the binary format
   of SNMP [RFC3410].  In the case of LLNs, it must be noted that at the
   time of writing, the CoRE Working Group is actively working on
   resource management of devices in LLNs.  Still, it is felt that this
   section provides important guidance on how RPL should be deployed,
   operated, and managed.

   As stated in [RFC5706], "A management information model should
   include a discussion of what is manageable, which aspects of the
   protocol need to be configured, what types of operations are allowed,
   what protocol-specific events might occur, which events can be
   counted, and for which events an operator should be notified".  These
   aspects are discussed in detail in the following sections.

   RPL will be used on a variety of devices that may have resources such
   as memory varying from a few Kbytes to several hundreds of Kbytes and
   even Mbytes.  When memory is highly constrained, it may not be
   possible to satisfy all the requirements listed in this section.
   Still it is worth listing all of these in an exhaustive fashion, and
   implementers will then determine which of these requirements could be
   satisfied according to the available resources on the device.

17.2.  Configuration Management

   This section discusses the configuration management, listing the
   protocol parameters for which configuration management is relevant.

   Some of the RPL parameters are optional.  The requirements for
   configuration are only applicable for the options that are used.

17.2.1.  Initialization Mode

   "Architectural Principles of the Internet" [RFC1958], Section 3.8,
   states: "Avoid options and parameters whenever possible.  Any options
   and parameters should be configured or negotiated dynamically rather
   than manually.  This is especially true in LLNs where the number of
   devices may be large and manual configuration is infeasible.  This
   has been taken into account in the design of RPL whereby the DODAG
   root provides a number of parameters to the devices joining the
   DODAG, thus avoiding cumbersome configuration on the routers and
   potential sources of misconfiguration (e.g. values of trickle timers,
   ...).  Still there are additional RPL parameters that a RPL
   implementation should allow to be configured, which are discussed in
   this section.

17.2.1.1.  DIS mode of operation upon boot-up

   When a node is first powered up:

   1.  The node may decide to stay silent, waiting to receive DIO
       messages from DODAG of interest (advertising a supported OF and
       metrics/constraints) and not send any multicast DIO messages
       until it has joined a DODAG.

   2.  The node may decide to send one or more DIS messages (optionally
       requesting DIO for a specific DODAG) as an initial probe for
       nearby DODAGs, and in the absence of DIO messages in reply after
       some configurable period of time, the node may decide to root a
       floating DODAG and start sending multicast DIO messages.

   A RPL implementation SHOULD allow configuring the preferred mode of
   operation listed above along with the required parameters (in the
   second mode: the number of DIS messages and related timer).

17.2.2.  DIO and DAO Base Message and Options Configuration

   RPL specifies a number of protocol parameters considering the large
   spectrum of applications where it will be used.  That said,
   particular attention has been given to limiting the number of these
   parameters that must be configured on each RPL router.  Instead, a
   number of the default values can be used, and when required these
   parameters can be provided by the DODAG root thus allowing for
   dynamic parameter setting.

   A RPL implementation SHOULD allow configuring the following routing
   protocol parameters.  As pointed out above, note that a large set of
   parameters is configured on the DODAG root.

17.2.3.  Protocol Parameters to be configured on every router in the LLN

   A RPL implementation MUST allow configuring the following RPL
   parameters:

   o  RPLInstanceID [DIO message, in DIO base message].  Although the
      RPLInstanceID must be configured on the DODAG root, it must also
      be configured as a policy on every node in order to determine
      whether or not the node should join a particular DODAG.  Note that
      a second RPLInstance can be configured on the node, should it
      become root of a floating DODAG.

   o  List of supported Objective Code Points (OCPs)

   o  List of supported metrics: [I-D.ietf-roll-routing-metrics]
      specifies a number of metrics and constraints used for the DODAG
      formation.  Thus a RPL implementation should allow configuring the
      list of metrics that a node can accept and understand.  If a DIO
      is received with a metric and/or constraint that is not understood
      or supported, as specified in Section 8.5, the node would join as
      a leaf node.

   o  Prefix information, along with valid and preferred lifetime and
      the L and A flags.  [DIO message, Prefix Information option].  A
      RPL implementation SHOULD allow configuring if the Prefix
      Information Option must be carried with the DIO message to
      distribute the prefix information for auto-configuration.  In that
      case, the RPL implementation MUST allow the list of prefixes to be
      advertised in the Prefix Information Option along with the
      corresponding flags.

   o  Solicited Information [DIS message, in Solicited Information
      option].  Note that an RPL implementation SHOULD allow configuring
      when such messages should be sent and under which circumstances,
      along with the value of the RPLInstance ID, V/I/D flags.

   o  'K' flag: when a node should set the 'K' flag in a DAO message
      [DAO message, in DAO base message].

   o  MOP (Mode of Operation) [DIO message, in DIO base message].

   o  Route Information (and preference) [DIO message, in Route
      Information option]

17.2.4.  Protocol Parameters to be configured on every non-DODAG-root
         router in the LLN

   A RPL implementation MUST allow configuring the Target prefix [DAO
   message, in RPL Target option].

   Furthermore, there are circumstances where a node may want to
   designate a Target to allow for specific processing of the Target
   (prioritization, ...).  Such processing rules are out of the scope of
   this document.  When used, a RPL implementation SHOULD allow
   configuring the Target Descriptor on a per-Target basis (for example
   using access lists).

   A node whose DODAG parent set is empty may become the DODAG root of a
   floating DODAG.  It may also set its DAGPreference such that it is
   less preferred.  Thus a RPL implementation MUST allow configuring the
   set of actions that the node should initiate in this case:

   o  Start its own (floating) DODAG: the new DODAGID must be configured
      in addition to its DAGPreference.

   o  Poison the broken path (see procedure in Section 8.2.2.5).

   o  Trigger a local repair.

17.2.5.  Parameters to be configured on the DODAG root

   In addition, several other parameters are configured only on the
   DODAG root and advertised in options carried in DIO messages.

   As specified in Section 8.3, a RPL implementation makes use of
   trickle timers to govern the sending of DIO messages.  The operation
   of the trickle algorithm is determined by a set of configurable
   parameters, which MUST be configurable and that are then advertised
   by the DODAG root along the DODAG in DIO messages.

   o  DIOIntervalDoublings [DIO message, in DODAG configuration option]

   o  DIOIntervalMin [DIO message, in DODAG configuration option]

   o  DIORedundancyConstant [DIO message, in DODAG configuration option]

   In addition, a RPL implementation SHOULD allow for configuring the
   following set of RPL parameters:

   o  Path Control Size [DIO message, in DODAG configuration option]

   o  MinHopRankIncrease [DIO message, in DODAG configuration option]

   o  The DODAGPreference field [DIO message, DIO Base object]

   o  DODAGID [DIO message, in DIO base option] and [DAO message, when
      the 'D' flag of the DAO message is set]

   DAG Root behavior: in some cases, a node may not want to permanently
   act as a floating DODAG root if it cannot join a grounded DODAG.  For
   example a battery-operated node may not want to act as a floating
   DODAG root for a long period of time.  Thus a RPL implementation MAY
   support the ability to configure whether or not a node could act as a
   floating DODAG root for a configured period of time.

   DAG Version Number Increment: a RPL implementation may allow by
   configuration at the DODAG root to refresh the DODAG states by
   updating the DODAGVersionNumber.  A RPL implementation SHOULD allow
   configuring whether or not periodic or event triggered mechanisms are
   used by the DODAG root to control DODAGVersionNumber change (which
   triggers a global repair as specified in Section 3.3.2.

17.2.6.  Configuration of RPL Parameters related to DAO-based mechanisms

   DAO messages are optional and used in DODAGs that require downward
   routing operation.  This section deals with the set of parameters
   related to DAO message and provides recommendations on their
   configuration.

   As stated in Section 9.4, it is recommended to delay the sending of
   DAO message to DAO parents in order to maximize the chances to
   perform route aggregation.  Upon receiving a DAO message, the node
   should thus start a DelayDAO timer.  A RPL implementation MAY allow
   for configuring the DelayDAO timer.

   In a storing mode of operation, a storing node may increment DTSN in
   order to reliably trigger a set of DAO updates from its immediate
   children, as part of routine routing table updates and maintenance.

   A RPL implementation MAY allow for configuring a set of rules
   specifying the triggers for DTSN increment (manual or event-based).

   When a DAO entry times out or is invalidated, a node SHOULD make a
   reasonable attempt to report a No-Path to each of the DAO parents.
   That number of attempts MAY be configurable.

   An implementation should support rate-limiting the sending of DAO
   messages.  The related parameters MAY be configurable.

17.2.7.  Default Values

   This document specifies default values for the following set of RPL
   variables:
      DEFAULT_PATH_CONTROL_SIZE
      DEFAULT_DIO_INTERVAL_MIN
      DEFAULT_DIO_INTERVAL_DOUBLINGS
      DEFAULT_DIO_REDUNDANCY_CONSTANT
      DEFAULT_MIN_HOP_RANK_INCREASE

   It is recommended to specify default values in protocols; that being
   said, as discussed in [RFC5706], default values may make less and
   less sense.  RPL is a routing protocol that is expected to be used in
   a number of contexts where network characteristics such as the number
   of nodes, link and nodes types are expected to vary significantly.
   Thus, these default values are likely to change with the context and
   as the technology will evolve.  Indeed, LLNs' related technology
   (e.g. hardware, link layers) have been evolving dramatically over the
   past few years and such technologies are expected to change and
   evolve considerably in the coming years.

   The proposed values are not based on extensive best current practices
   and are considered to be conservative.

17.3.  Monitoring of RPL Operation

   Several RPL parameters should be monitored to verify the correct
   operation of the routing protocol and the network itself.  This
   section lists the set of monitoring parameters of interest.

17.3.1.  Monitoring a DODAG parameters

   A RPL implementation SHOULD provide information about the following
   parameters:

   o  DODAG Version number [DIO message, in DIO base message]
   o  Status of the G flag [DIO message, in DIO base message]

   o  Status of the MOP field [DIO message, in DIO base message]

   o  Value of the DTSN [DIO message, in DIO base message]

   o  Value of the rank [DIO message, in DIO base message]

   o  DAOSequence: Incremented at each unique DAO message, echoed in the
      DAO-ACK message [DAO and DAO-ACK messages]

   o  Route Information [DIO message, Route Information option] (list of
      IPv6 prefixes per parent along with lifetime and preference]

   o  Trickle parameters:

      *  DIOIntervalDoublings [DIO message, in DODAG configuration
         option]

      *  DIOIntervalMin [DIO message, in DODAG configuration option]

      *  DIORedundancyConstant [DIO message, in DODAG configuration
         option]

   o  Path Control Size [DIO message, in DODAG configuration option]

   o  MinHopRankIncrease [DIO message, in DODAG configuration option]

   Values that may be monitored only on the DODAG root

   o  Transit Information [DAO, Transit Information option]: A RPL
      implementation SHOULD allow configuring whether the set of
      received Transit Information options should be displayed on the
      DODAG root.  In this case, the RPL database of received Transit
      Information should also contain: the path-sequence, path control,
      path lifetime and parent address.

17.3.2.  Monitoring a DODAG inconsistencies and loop detection

   Detection of DODAG inconsistencies is particularly critical in RPL
   networks.  Thus it is recommended for a RPL implementation to provide
   appropriate monitoring tools.  A RPL implementation SHOULD provide a
   counter reporting the number of a times the node has detected an
   inconsistency with respect to a DODAG parent, e.g. if the DODAGID has
   changed.

   When possible more granular information about inconsistency detection
   should be provided.  A RPL implementation MAY provide counters
   reporting the number of following inconsistencies:

   o  Packets received with 'O' bit set (to Down) from a node with a
      higher rank

   o  Packets received with 'O' bit cleared (to Up) from a node with a
      lower rank

   o  Number of packets with the 'F' bit set

   o  Number of packets with the 'R' bit set

17.4.  Monitoring of the RPL data structures

17.4.1.  Candidate Neighbor Data Structure

   A node in the candidate neighbor list is a node discovered by the
   some means and qualified to potentially become a parent (with high
   enough local confidence).  A RPL implementation SHOULD provide a way
   to monitor the candidate neighbor list with some metric reflecting
   local confidence (the degree of stability of the neighbors) as
   measured by some metrics.

   A RPL implementation MAY provide a counter reporting the number of
   times a candidate neighbor has been ignored, should the number of
   candidate neighbors exceeds the maximum authorized value.

17.4.2.  Destination Oriented Directed Acyclic Graph (DAG) Table

   For each DODAG, a RPL implementation is expected to keep track of the
   following DODAG table values:

   o  RPLInstanceID

   o  DODAGID

   o  DODAGVersionNumber

   o  Rank

   o  Objective Code Point

   o  A set of DODAG Parents

   o  A set of prefixes offered upwards along the DODAG

   o  Trickle timers used to govern the sending of DIO messages for the
      DODAG

   o  List of DAO parents

   o  DTSN

   o  Node status (router versus leaf)

   A RPL implementation SHOULD allow for monitoring the set of
   parameters listed above.

17.4.3.  Routing Table and DAO Routing Entries

   A RPL implementation maintains several information elements related
   to the DODAG and the DAO entries (for storing nodes).  In the case of
   a non storing node, a limited amount of information is maintained
   (the routing table is mostly reduced to a set of DODAG parents along
   with characteristics of the DODAG as mentioned above) whereas in the
   case of storing nodes, this information is augmented with routing
   entries.

   A RPL implementation SHOULD provide the ability to monitor the
   following parameters:

   o  Next Hop (DODAG parent)

   o  Next Hop Interface

   o  Path metrics value for each DODAG parent

   A DAO Routing Table Entry conceptually contains the following
   elements (for storing nodes only):

   o  Advertising Neighbor Information

   o  IPv6 Address

   o  Interface ID to which DAO Parents has this entry been reported

   o  Retry Counter

   o  Logical equivalent of DAO Content:

      *  DAO-Sequence

      *  Path Sequence

      *  DAO Lifetime
      *  DAO Path Control

   o  Destination Prefix (or Address or Mcast Group)

   A RPL implementation SHOULD provide information about the state of
   each DAO Routing Table entry states.

17.5.  Fault Management

   Fault management is a critical component used for troubleshooting,
   verification of the correct mode of operation of the protocol,
   network design, and is also a key component of network performance
   monitoring.  A RPL implementation SHOULD allow providing the
   following information related to fault managements:

   o  Memory overflow along with the cause (e.g. routing tables
      overflow, ...)

   o  Number of times a packet could not be sent to a DODAG parent
      flagged as valid

   o  Number of times a packet has been received for which the router
      did not have a corresponding RPLInstanceID

   o  Number of times a local repair procedure was triggered

   o  Number of times a global repair was triggered by the DODAG root

   o  Number of received malformed messages

   o  Number of seconds with packets to forward and no next hop (DODAG
      parent)

   o  Number of seconds without next hop (DODAG parent)

   o  Number of times a node has joined a DODAG as a leaf because it
      received a DIO with metric/constraint not understood and it was
      configured to join as a leaf node in this case (see Section 17.6).

   It is RECOMMENDED to report faults via at least error log messages.
   Other protocols may be used to report such faults.

17.6.  Policy

   Policy rules can be used by a RPL implementation to determine whether
   or not the node is allowed to join a particular DODAG advertised by a
   neighbor by means of DIO messages.

   This document specifies operation within a single DODAG.  A DODAG is
   characterized by the following tuple (RPLInstanceID, DODAGID).
   Furthermore, as pointed out above, DIO messages are used to advertise
   other DODAG characteristics such as the routing metrics and
   constraints used to build to the DODAG and the Objective Function in
   use (specified by OCP).

   The first policy rules consist of specifying the following conditions
   that a RPL node must satisfy to join a DODAG:

   o  RPLInstanceID

   o  List of supported routing metrics and constraints

   o  Objective Function (OCP values)

   A RPL implementation MUST allow configuring these parameters and
   SHOULD specify whether the node must simply ignore the DIO if the
   advertised DODAG is not compliant with the local policy or whether
   the node should join as the leaf node if only the list of supported
   routing metrics and constraints, and the OF is not supported.
   Additionally a RPL implementation SHOULD allow for the addition of
   the DODAGID as part of the policy.

   A RPL implementation SHOULD allow configuring the set of acceptable
   or preferred Objective Functions (OF) referenced by their Objective
   Codepoints (OCPs) for a node to join a DODAG, and what action should
   be taken if none of a node's candidate neighbors advertise one of the
   configured allowable Objective Functions, or if the advertised
   metrics/constraint is not understood/supported.  Two actions can be
   taken in this case:

   o  The node joins the DODAG as a leaf node as specified in
      Section 8.5

   o  The node does not join the DODAG

   A node in an LLN may learn routing information from different routing
   protocols including RPL.  It is in this case desirable to control via
   administrative preference which route should be favored.  An
   implementation SHOULD allow for specifying an administrative
   preference for the routing protocol from which the route was learned.

   Internal Data Structures: some RPL implementations may limit the size
   of the candidate neighbor list in order to bound the memory usage, in
   which case some otherwise viable candidate neighbors may not be
   considered and simply dropped from the candidate neighbor list.

   A RPL implementation MAY provide an indicator on the size of the
   candidate neighbor list.

17.7.  Liveness Detection and Monitoring

   By contrast with several other routing protocols, RPL does not define
   any 'keep-alive' mechanisms to detect routing adjacency failure: this
   is in most cases, because such a mechanism may be too expensive in
   terms of bandwidth and even more importantly energy (a battery
   operated device could not afford to send periodic Keep alive).  Still
   RPL requires mechanisms to detect that a neighbor is no longer
   reachable: this can be performed by using mechanisms such as NUD
   (Neighbor Unreachability Detection) or even some form of Keep-alive
   that are outside of this document.

17.8.  Fault Isolation

   It is RECOMMENDED to quarantine neighbors that start emitting
   malformed messages at unacceptable rates.

17.9.  Impact on Other Protocols

   RPL has very limited impact on other protocols.  Where more than one
   routing protocol is required on a router such as a LBR, it is
   expected for the device to support routing redistribution functions
   between the routing protocols to allow for reachability between the
   two routing domains.  Such redistribution SHOULD be governed by the
   use of user configurable policy.

   With regards to the impact in terms of traffic on the network, RPL
   has been designed to limit the control traffic thanks to mechanisms
   such as Trickle timers (Section 8.3).  Thus the impact of RPL on
   other protocols should be extremely limited.

17.10.  Performance Management

   Performance management is always an important aspect of a protocol
   and RPL is not an exception.  Several metrics of interest have been
   specified by the IP Performance Monitoring (IPPM) Working Group: that
   being said, they will be hardly applicable to LLN considering the
   cost of monitoring these metrics in terms of resources on the devices
   and required bandwidth.  Still, RPL implementation MAY support some
   of these, and other parameters of interest are listed below:

   o  Number of repairs and time to repair in seconds (average,
      variance)

   o  Number of times and duration during which a devices could not
      forward a packet because of a lack of reachable neighbor in its
      routing table

   o  Monitoring of resources consumption by RPL itself in terms of
      bandwidth and required memory

   o  Number of RPL control messages sent and received

18.  Security Considerations

18.1.  Overview

   From a security perspective, RPL networks are no different from any
   other network.  They are vulnerable to passive eavesdropping attacks
   and potentially even active tampering when physical access to a wire
   is not required to participate in communications.  The very nature of
   ad hoc networks and their cost objectives impose additional security
   constraints, which perhaps make these networks the most difficult
   environments to secure.  Devices are low-cost and have limited
   capabilities in terms of computing power, available storage, and
   power drain; and it cannot always be assumed they have neither a
   trusted computing base nor a high-quality random number generator
   aboard.  Communications cannot rely on the online availability of a
   fixed infrastructure and might involve short-term relationships
   between devices that may never have communicated before.  These
   constraints might severely limit the choice of cryptographic
   algorithms and protocols and influence the design of the security
   architecture because the establishment and maintenance of trust
   relationships between devices need to be addressed with care.  In
   addition, battery lifetime and cost constraints put severe limits on
   the security overhead these networks can tolerate, something that is
   of far less concern with higher bandwidth networks.  Most of these
   security architectural elements can be implemented at higher layers
   and may, therefore, be considered to be outside the scope of this
   standard.  Special care, however, needs to be exercised with respect
   to interfaces to these higher layers.

   The security mechanisms in this standard are based on symmetric-key
   and public-key cryptography and use keys that are to be provided by
   higher layer processes.  The establishment and maintenance of these
   keys are outside the scope of this standard.  The mechanisms assume a
   secure implementation of cryptographic operations and secure and
   authentic storage of keying material.

   The security mechanisms specified provide particular combinations of
   the following security services:

   Data confidentiality:  Assurance that transmitted information is only
               disclosed to parties for which it is intended.

   Data authenticity:  Assurance of the source of transmitted
               information (and, hereby, that information was not
               modified in transit).

   Replay protection:  Assurance that a duplicate of transmitted
               information is detected.

   Timeliness (delay protection):  Assurance that transmitted
               information was received in a timely manner.

   The actual protection provided can be adapted on a per-packet basis
   and allows for varying levels of data authenticity (to minimize
   security overhead in transmitted packets where required) and for
   optional data confidentiality.  When nontrivial protection is
   required, replay protection is always provided.

   Replay protection is provided via the use of a non-repeating value
   (nonce) in the packet protection process and storage of some status
   information for each originating device on the receiving device,
   which allows detection of whether this particular nonce value was
   used previously by the originating device.  In addition, so-called
   delay protection is provided amongst those devices that have a
   loosely synchronized clock on board.  The acceptable time delay can
   be adapted on a per-packet basis and allows for varying latencies (to
   facilitate longer latencies in packets transmitted over a multi-hop
   communication path).

   Cryptographic protection may use a key shared between two peer
   devices (link key) or a key shared among a group of devices (group
   key), thus allowing some flexibility and application-specific
   tradeoffs between key storage and key maintenance costs versus the
   cryptographic protection provided.  If a group key is used for peer-
   to-peer communication, protection is provided only against outsider
   devices and not against potential malicious devices in the key-
   sharing group.

   Data authenticity may be provided using symmetric-key based or
   public-key based techniques.  With public-key based techniques (via
   signatures), one corroborates evidence as to the unique originator of
   transmitted information, whereas with symmetric-key based techniques
   data authenticity is only provided relative to devices in a key-
   sharing group.  Thus, public-key based authentication may be useful
   in scenarios that require a more fine-grained authentication than can
   be provided with symmetric-key based authentication techniques alone,
   such as with group communications (broadcast, multicast), or in
   scenarios that require non-repudiation.

19.  IANA Considerations

19.1.  RPL Control Message

   The RPL Control Message is an ICMP information message type that is
   to be used carry DODAG Information Objects, DODAG Information
   Solicitations, and Destination Advertisement Objects in support of
   RPL operation.

   IANA has defined an ICMPv6 Type Number Registry.  The suggested type
   value for the RPL Control Message is 155, to be confirmed by IANA.

19.2.  New Registry for RPL Control Codes

   IANA is requested to create a registry, RPL Control Codes, for the
   Code field of the ICMPv6 RPL Control Message.

   New codes may be allocated only by an IETF Consensus action.  Each
   code should be tracked with the following qualities:

   o  Code

   o  Description

   o  Defining RFC

   Three codes are currently defined:

   +------+----------------------------------------------+-------------+
   | Code | Description                                  | Reference   |
   +------+----------------------------------------------+-------------+
   | 0x00 | DODAG Information Solicitation               | This        |
   |      |                                              | document    |
   |      |                                              |             |
   | 0x01 | DODAG Information Object                     | This        |
   |      |                                              | document    |
   |      |                                              |             |
   | 0x02 | Destination Advertisement Object             | This        |
   |      |                                              | document    |
   |      |                                              |             |
   | 0x03 | Destination Advertisement Object             | This        |
   |      | Acknowledgment                               | document    |
   |      |                                              |             |
   | 0x80 | Secure DODAG Information Solicitation        | This        |
   |      |                                              | document    |
   |      |                                              |             |
   | 0x81 | Secure DODAG Information Object              | This        |
   |      |                                              | document    |
   | 0x82 | Secure Destination Advertisement Object      | This        |
   |      |                                              | document    |
   |      |                                              |             |
   | 0x83 | Secure Destination Advertisement Object      | This        |
   |      | Acknowledgment                               | document    |
   +------+----------------------------------------------+-------------+

                             RPL Control Codes

19.3.  New Registry for the Mode of Operation (MOP) DIO Control Field

   IANA is requested to create a registry for the Mode of Operation
   (MOP) DIO Control Field, which is contained in the DIO Base.

   New fields may be allocated only by an IETF Consensus action.  Each
   field should be tracked with the following qualities:

   o  Mode of Operation

   o  Capability description

   o  Defining RFC

   Three values are currently defined:

   +-----+----------------------------------------------+--------------+
   | MOP | Description                                  | Reference    |
   +-----+----------------------------------------------+--------------+
   | 000 | No downward routes maintained by RPL         | This         |
   |     |                                              | document     |
   |     |                                              |              |
   | 001 | Non-Storing mode of operation                | This         |
   |     |                                              | document     |
   |     |                                              |              |
   | 010 | Storing mode of operation with no multicast  | This         |
   |     | support                                      | document     |
   |     |                                              |              |
   | 011 | Storing mode of operation with multicast     | This         |
   |     | support                                      | document     |
   +-----+----------------------------------------------+--------------+

                           DIO Mode of operation

19.4.  RPL Control Message Option

   IANA is requested to create a registry for the RPL Control Message
   Options
             +-------+-----------------------+---------------+
             | Value | Meaning               | Reference     |
             +-------+-----------------------+---------------+
             |   0   | Pad1                  | This document |
             |       |                       |               |
             |   1   | PadN                  | This document |
             |       |                       |               |
             |   2   | DAG Metric Container  | This Document |
             |       |                       |               |
             |   3   | Routing Information   | This Document |
             |       |                       |               |
             |   4   | DODAG Configuration   | This Document |
             |       |                       |               |
             |   5   | RPL Target            | This Document |
             |       |                       |               |
             |   6   | Transit Information   | This Document |
             |       |                       |               |
             |   7   | Solicited Information | This Document |
             |       |                       |               |
             |   8   | Prefix Information    | This Document |
             |       |                       |               |
             |   9   | Target Descriptor     | This Document |
             +-------+-----------------------+---------------+

                        RPL Control Message Options

19.5.  Objective Code Point (OCP) Registry

   IANA is requested to create a registry to manage the codespace of the
   Objective Code Point (OCP) field.

   No OCP codepoints are defined in this specification.

19.6.  New Registry for the  Security Section Flags

   IANA is requested to create a registry for the 8-bit Security Section
   Flag Field.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   No bit is currently defined for the Security Section Flags.

19.7.  New Registry for the Key Identification Mode

   IANA is requested to create a registry for the 3-bit Key
   Identification Mode Field.

   New values may be allocated only by an IETF Consensus action.  Each
   value should be tracked with the following qualities:

   o  Value

   o  Description

   o  Defining RFC

   The following values are currently defined:

                 +-------+---------------+---------------+
                 | Value | Description   | Reference     |
                 +-------+---------------+---------------+
                 |   0   | See Figure 11 | This document |
                 |       |               |               |
                 |   1   | See Figure 11 | This document |
                 |       |               |               |
                 |   2   | See Figure 11 | This document |
                 |       |               |               |
                 |   3   | See Figure 11 | This document |
                 +-------+---------------+---------------+

                          Key Identification Mode

19.8.  New Registry for the KIM levels

   IANA is requested to create one registry for the 7-bit KIM level
   Field per allocated KIM value.

   For a given KIM value, new levels may be allocated only by an IETF
   Consensus action.  Each level should be tracked with the following
   qualities:

   o  Level

   o  KIM value

   o  Description

   o  Defining RFC

   The following levels pre KIM value are currently defined:

           +-------+-----------+--------------+---------------+
           | Level | KIM value | Description  | Reference     |
           +-------+-----------+--------------+---------------+
           |   0   |     0     | See Figure 9 | This document |
           |       |           |              |               |
           |   1   |     0     | See Figure 9 | This document |
           |       |           |              |               |
           |   2   |     0     | See Figure 9 | This document |
           |       |           |              |               |
           |   3   |     0     | See Figure 9 | This document |
           |       |           |              |               |
           |   0   |     1     | See Figure 9 | This document |
           |       |           |              |               |
           |   1   |     1     | See Figure 9 | This document |
           |       |           |              |               |
           |   2   |     1     | See Figure 9 | This document |
           |       |           |              |               |
           |   3   |     1     | See Figure 9 | This document |
           |       |           |              |               |
           |   0   |     2     | See Figure 9 | This document |
           |       |           |              |               |
           |   1   |     2     | See Figure 9 | This document |
           |       |           |              |               |
           |   2   |     2     | See Figure 9 | This document |
           |       |           |              |               |
           |   3   |     2     | See Figure 9 | This document |
           |       |           |              |               |
           |   0   |     3     | See Figure 9 | This document |
           |       |           |              |               |
           |   1   |     3     | See Figure 9 | This document |
           +-------+-----------+--------------+---------------+

                                KIM levels

19.9.  New Registry for the DIS (DODAG Informational Solicitation) Flags

   IANA is requested to create a registry for the DIS (DODAG
   Informational Solicitation) Flag Field.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the
   cryptographic protection provided.  If a group key following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC
   No bit is used currently defined for peer-
   to-peer communication, protection the DIS (DODAG Informational
   Solicitation) Flags.

19.10.  New Registry for the DODAG Information Object (DIO) Flags

   IANA is provided only against outsider
   devices and not against potential malicious devices in requested to create a registry for the key-
   sharing group.

   Data authenticity 8-bit DODAG
   Information Object (DIO) Flag Field.

   New bit numbers may be provided using symmetric-key based or
   public-key based techniques.  With public-key based techniques (via
   signatures), one corroborates evidence allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as to the unique originator of
   transmitted information, whereas with symmetric-key based techniques
   data authenticity most significant bit)

   o  Capability description

   o  Defining RFC

   No bit is only provided relative currently defined for the DIS (DODAG Informational
   Solicitation) Flags.

19.11.  New Registry for the Destination Advertisement Object (DAO)
        Flags

   IANA is requested to devices in create a key-
   sharing group.  Thus, public-key based authentication registry for the 8-bit Destination
   Advertisement Object (DAO) Flag Field.

   New bit numbers may be useful
   in scenarios that require a more fine-grained authentication than can allocated only by an IETF Consensus action.
   Each bit should be provided tracked with symmetric-key based authentication techniques alone,
   such the following qualities:

   o  Bit number (counting from bit 0 as with group communications (broadcast, multicast), or in
   scenarios that require non-repudiation.

18.  IANA Considerations

18.1.  RPL Control Message the most significant bit)

   o  Capability description

   o  Defining RFC

   The RPL Control Message following bits are currently defined:

         +------------+--------------------------+---------------+
         | Bit number | Description              | Reference     |
         +------------+--------------------------+---------------+
         |      0     | DAO-ACK request          | This document |
         |            |                          |               |
         |      1     | DODAGID field is an ICMP information message type that present | This document |
         +------------+--------------------------+---------------+

                              DAO Base Flags

19.12.  New Registry for the Destination Advertisement Object (DAO)
        Flags

   IANA is requested to be used carry DODAG Information Objects, DODAG Information
   Solicitations, and create a registry for the 8-bit Destination
   Advertisement Objects in support of
   RPL operation.

   IANA has defined Object (DAO) Flag Field.

   New bit numbers may be allocated only by an ICMPv6 Type Number Registry. IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   The suggested type
   value following bit is currently defined:

         +------------+--------------------------+---------------+
         | Bit number | Description              | Reference     |
         +------------+--------------------------+---------------+
         |      0     | DODAGID field is present | This document |
         +------------+--------------------------+---------------+

                            DAO-Ack Base Flags

19.13.  New Registry for the RPL Control Message Consistency Check (CC) Flags

   IANA is 155, requested to create a registry for the 8-bit Consistency
   Check (CC) Flag Field.

   New bit numbers may be confirmed allocated only by IANA.

18.2. an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   The following bit is currently defined:

               +------------+-------------+---------------+
               | Bit number | Description | Reference     |
               +------------+-------------+---------------+
               |      0     | CC Response | This document |
               +------------+-------------+---------------+

                       Consistency Check Base Flags

19.14.  New Registry for RPL Control Codes the DODAG Configuration Option Flags

   IANA is requested to create a registry, RPL Control Codes, registry for the
   Code field of the ICMPv6 RPL Control Message. 8-bit DODAG
   Configuration Option Flag Field.

   New codes bit numbers may be allocated only by an IETF Consensus action.
   Each
   code bit should be tracked with the following qualities:

   o  Code  Bit number (counting from bit 0 as the most significant bit)

   o  Description  Capability description

   o  Defining RFC

   Three codes

   The following bits are currently defined:

   +------+----------------------------------------------+-------------+

          +------------+------------------------+---------------+
          | Code Bit number | Description            | Reference     |
   +------+----------------------------------------------+-------------+
   | 0x00 | DODAG Information Solicitation               | This        |
   |      |                                              | document    |
   |      |                                              |             |
   | 0x01 | DODAG Information Object                     | This        |
   |      |                                              | document    |
   |      |                                              |             |
   | 0x02 | Destination Advertisement Object             | This        |
   |      |                                              | document    |
   |      |                                              |
          +------------+------------------------+---------------+
          |      4     | 0x03 | Destination Advertisement Object Authentication Enabled | This        |
   |      | Acknowledgment                               | document |
          |            |                        |               |
          | 0x80     5-7    | Secure DODAG Information Solicitation Path Control Size      | This        |
   |      |                                              | document |
   |      |                                              |             |
   | 0x81 | Secure
          +------------+------------------------+---------------+

                     DODAG Information Object              | This        |
   |      |                                              | document    |
   | 0x82 | Secure Destination Advertisement Object      | This        |
   |      |                                              | document    |
   |      |                                              |             |
   | 0x83 | Secure Destination Advertisement Object      | This        |
   |      | Acknowledgment                               | document    |
   +------+----------------------------------------------+-------------+

                             RPL Control Codes

18.3. Configuration Option Flags

19.15.  New Registry for the Mode of Operation (MOP) DIO Control Field RPL Target Option Flags

   IANA is requested to create a registry for the Mode of Operation
   (MOP) DIO Control Field, which 8-bit RPL Target
   Option Flag Field.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   No bit is contained in currently defined for the DIO Base. RPL Target Option Flags.

19.16.  New fields Registry for the Transit Information  Option Flags

   IANA is requested to create a registry for the 8-bit Transit
   Information Option (RIO) Flag Field.

   New bit numbers may be allocated only by an IETF Consensus action.

   Each
   field bit should be tracked with the following qualities:

   o  Mode of Operation  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   Three values

   The following bits are currently defined:

   +-----+----------------------------------------------+--------------+

               +------------+-------------+---------------+
               | MOP Bit number | Description | Reference     |
   +-----+----------------------------------------------+--------------+
   | 000 | No downward routes maintained by RPL         | This         |
   |     |                                              | document     |
   |     |                                              |              |
   | 001 | Non-Storing mode of operation                | This         |
   |     |                                              | document     |
   |
               +------------+-------------+---------------+
               |      0     |              |
   | 010 | Storing mode of operation with no multicast  | This         |
   |     | support                                      | document     |
   |     |                                              |              |
   | 011 | Storing mode of operation with multicast External    | This         |
   |     | support                                      | document |
   +-----+----------------------------------------------+--------------+

                              DIO Base
               +------------+-------------+---------------+

                     Transit Information Option Flags

18.4.  RPL Control Message

19.17.  New Registry for the Solicited Information Option Flags

   IANA is requested to create a registry for the RPL Control Message
   Options
             +-------+-----------------------+---------------+ 8-bit Solicited
   Information Option (RIO) Flag Field.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   The following bits are currently defined:

        +------------+----------------------------+---------------+
        | Value Bit number | Meaning Description                | Reference     |
             +-------+-----------------------+---------------+
        +------------+----------------------------+---------------+
        |      0     | Pad1                  | This document |
             |       |                       |               |
             |   1   | PadN                  | This document |
             |       |                       |               |
             |   2   | DAG Metric Container  | This Document |
             |       |                       |               |
             |   3   | Routing Information   | This Document |
             |       |                       |               |
             |   4   | DODAG Configuration   | This Document |
             |       |                       |               |
             |   5   | RPL Target            | This Document |
             |       |                       |               |
             |   6   | Transit Information   | Version Predicate match    | This Document document |
        |            |                            |               |
        |   7      1     | Solicited Information InstanceID Predicate match | This Document document |
        |            |                            |               |
        |   8      2     | Prefix Information DODAGID Predicate match    | This Document document |
             +-------+-----------------------+---------------+

                        RPL Control Message Options

18.5.  Objective Code Point (OCP) Registry

   IANA is requested to create a registry to manage the codespace of the
   Objective Code Point (OCP) field.

   No OCP codepoints are defined in this specification.

18.6.
        +------------+----------------------------+---------------+

                    Solicited Information Option Flags

19.18.  ICMPv6: Error in Source Routing Header

   In some cases RPL will return an ICMPv6 error message when a message
   cannot be delivered as specified by its source routing header.  This
   ICMPv6 error message is "Error in Source Routing Header" Header".

   IANA has defined an ICMPv6 "Code" Fields Registry for ICMPv6 Message
   Types.  ICMPv6 Message Type 1 describes "Destination Unreachable"
   codes.  The "Error in Source Routing Header" code is suggested to be
   allocated from the ICMPv6 Code Fields Registry for ICMPv6 Message
   Type 1, with a suggested code value of 7, to be confirmed by IANA.

18.7.

19.19.  Link-Local Scope multicast address

   The rules for assigning new IPv6 multicast addresses are defined in
   [RFC3307].  This specification requires the allocation of a new
   permanent multicast address with a link local scope for RPL routers, nodes
   called all-RPL-nodes, with a suggested value of FF02::1:A, FF02::1A, to be
   confirmed by IANA.

19.

20.  Acknowledgements

   The authors would like to acknowledge the review, feedback, and
   comments from Roger Alexander, Emmanuel Baccelli, Dominique Barthel,
   Yusuf Bashir, Yoav Ben-Yehezkel, Phoebus Chen, Mischa Dohler,
   Mathilde Durvy, Joakim Eriksson, Omprakash Gnawali, Manhar Goindi,
   Mukul Goyal, Ulrich Herberg, Anders Jagd, JeongGil (John) Ko, Ajay
   Kumar, Quentin Lampin, Jerry Martocci, Matteo Paris, Alexandru
   Petrescu, Joseph Reddy, Michael Richardson, Don Sturek, Joydeep
   Tripathi, and Nicolas Tsiftes.

   The authors would like to acknowledge the guidance and input provided
   by the ROLL Chairs, David Culler and JP Vasseur.

   The authors would like to acknowledge prior contributions of Robert
   Assimiti, Mischa Dohler, Julien Abeille, Ryuji Wakikawa, Teco Boot,
   Patrick Wetterwald, Bryan Mclaughlin, Carlos J. Bernardos, Thomas
   Watteyne, Zach Shelby, Caroline Bontoux, Marco Molteni, Billy Moon,
   Jim Bound, Yanick Pouffary, Henning Rogge and Arsalan Tavakoli, whom
   have provided useful design considerations to RPL.

   RPL Security Design, found in Section 9, 10, Section 17, 18, and elsewhere
   throughout the document, is primarily the contribution of the
   Security Design Team: Tzeta Tsao, Roger Alexander, Dave Ward, Philip
   Levis, Kris Pister, and Rene Struik.

20.

21.  Contributors

   RPL is the result of the contribution of the following members of the
   RPL Author Team, including the editors, and additional contributors
   as listed below:

   JP Vasseur
   Cisco Systems, Inc
   11, Rue Camille Desmoulins
   Issy Les Moulineaux,   92782
   France below in alphabetical order:

   Anders Brandt
   Sigma Designs
   Emdrupvej 26A, 1.
   Copenhagen, DK-2100
   Denmark

   Email: jpv@cisco.com abr@sdesigns.dk

   Thomas Heide Clausen
   LIX, Ecole Polytechnique, France

   Phone: +33 6 6058 9349
   EMail: T.Clausen@computer.org
   URI:   http://www.ThomasClausen.org/

   Philip Levis
   Stanford University
   358 Gates

   Stephen Dawson-Haggerty
   UC Berkeley
   Soda Hall, Stanford University
   Stanford, UC Berkeley
   Berkeley, CA  94305-9030
   USA

   Email: pal@cs.stanford.edu

   Richard Kelsey
   Ember Corporation
   Boston, MA  94720
   USA

   Phone: +1 617 951 1225

   Email: kelsey@ember.com stevedh@cs.berkeley.edu

   Jonathan W. Hui
   Arch Rock Corporation
   501 2nd St. Ste. 410
   San Francisco, CA  94107
   USA

   Email: jhui@archrock.com

   Richard Kelsey
   Ember Corporation
   Boston, MA
   USA

   Phone: +1 617 951 1225
   Email: kelsey@ember.com
   Philip Levis
   Stanford University
   358 Gates Hall, Stanford University
   Stanford, CA  94305-9030
   USA

   Email: pal@cs.stanford.edu

   Kris Pister
   Dust Networks
   30695 Huntwood Ave.
   Hayward,   94544
   USA

   Email: kpister@dustnetworks.com

   Anders Brandt
   Sigma Designs
   Emdrupvej 26A, 1.
   Copenhagen, DK-2100
   Denmark

   Email: abr@sdesigns.dk

   R. Struik

   Email: rstruik.ext@gmail.com

   Stephen Dawson-Haggerty
   UC Berkeley
   Soda Hall, UC Berkeley
   Berkeley, CA  94720
   USA

   JP Vasseur
   Cisco Systems, Inc
   11, Rue Camille Desmoulins
   Issy Les Moulineaux,   92782
   France

   Email: stevedh@cs.berkeley.edu

21. jpv@cisco.com

22.  References

21.1.

22.1.  Normative References

   [I-D.ietf-6man-rpl-option]
              Hui, J. and J. Vasseur, "RPL Option for Carrying RPL
              Information in Data-Plane Datagrams",
              draft-ietf-6man-rpl-option-00 (work in progress),
              July 2010.

   [I-D.ietf-6man-rpl-routing-header]
              Hui, J., Vasseur, J., and D. Culler, "An IPv6 Routing
              Header for Source Routes with RPL",
              draft-ietf-6man-rpl-routing-header-00 (work in progress),
              July 2010.

   [I-D.ietf-roll-routing-metrics]
              Vasseur, J., Kim, M., Networks, D., Dejean, N., and D.
              Barthel, "Routing Metrics used for Path Calculation in Low
              Power and Lossy Networks",
              draft-ietf-roll-routing-metrics-08 (work in progress),
              July 2010.

   [I-D.ietf-roll-trickle]
              Levis, P., Gnawali, O., Clausen, T., Hui, J., and J. Ko,
              "The Trickle Algorithm", draft-ietf-roll-trickle-02 (work
              in progress), July 2010.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

21.2.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, February 2003.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, November 2005.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

22.2.  Informative References

   [AppliedCryptography]
              Menzes, AJ., van Oorschot, PC., and SA. Vanstone,
              "Handbook of Applied Cryptography", CRC Press , 1997.

   [CCMStar]  IEEE, "IEEE Std. 802.15.4-2006, IEEE Standard for
              Information Technology - Telecommunications and
              Information Exchange between Systems - Local and
              Metropolitan Area Networks - Specific requirements Part
              15.4: Wireless Medium Access Control (MAC) and Physical
              Layer (PHY) Specifications for Low-Rate Wireless Personal
              Area Networks (WPANs)", IEEE Press Revision of IEEE Std
              802.15.4-2003, 2006.

   [I-D.hui-6man-rpl-option]
              Hui, J. and J. Vasseur, "RPL Option for Carrying RPL
              Information in Data-Plane Datagrams",
              draft-hui-6man-rpl-option-01 (work in progress),
              June 2010.

   [I-D.hui-6man-rpl-routing-header]
              Hui, J., Vasseur, J., and D. Culler, "An IPv6 Routing
              Header for Source Routes with RPL",
              draft-hui-6man-rpl-routing-header-02 (work in progress),
              June 2010.

   [I-D.ietf-manet-nhdp]
              Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
              Network (MANET) Neighborhood Discovery Protocol (NHDP)",
              draft-ietf-manet-nhdp-12
              draft-ietf-manet-nhdp-14 (work in progress), March July 2010.

   [I-D.ietf-roll-of0]
              Thubert, P., "RPL Objective Function 0",
              draft-ietf-roll-of0-02 (work in progress), June 2010.

   [I-D.ietf-roll-routing-metrics]
              Vasseur, J., Kim, M., Networks, D., and H. Chong, "Routing
              Metrics used for Path Calculation in Low Power and Lossy
              Networks", draft-ietf-roll-routing-metrics-07
              draft-ietf-roll-of0-03 (work in progress), June July 2010.

   [I-D.ietf-roll-terminology]
              Vasseur, J., "Terminology in Low power And Lossy
              Networks", draft-ietf-roll-terminology-03 (work in
              progress), March 2010.

   [I-D.ietf-roll-trickle]
              Levis, P., Clausen, T., Hui, J., and J. Ko, "The Trickle
              Algorithm", draft-ietf-roll-trickle-01 (work in progress),
              April 2010.

   [Perlman83]
              Perlman, R., "Fault-Tolerant Broadcast of Routing
              Information", North-Holland Computer Networks 7: 395-405,
              1983, <http://www.cs.illinois.edu/~pbg/courses/cs598fa09/
              readings/p83.pdf>.

   [RFC1958]  Carpenter, B., "Architectural Principles of the Internet",
              RFC 1958, June 1996.

   [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
              August 1996.

   [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Structure of Management Information
              Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.

   [RFC2710]  Deering, S., Fenner, W., and B. Haberman, "Multicast
              Listener Discovery (MLD) for IPv6", RFC 2710,
              October 1999.

   [RFC3307]  Haberman, B., "Allocation Guidelines for IPv6 Multicast
              Addresses", RFC 3307, August 2002.

   [RFC3410]  Case, J., Mundy, R., Partain, D., and B. Stewart,
              "Introduction and Applicability Statements for Internet-
              Standard Management Framework", RFC 3410, December 2002.

   [RFC3535]  Schoenwaelder, J., "Overview of the 2002 IAB Network
              Management Workshop", RFC 3535, May 2003.

   [RFC3610]  Whiting, D., Housley, R., and N. Ferguson, "Counter with
              CBC-MAC (CCM)", RFC 3610, September 2003.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

   [RFC3819]  Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
              Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
              Wood, "Advice for Internet Subnetwork Designers", BCP 89,
              RFC 3819, July 2004.

   [RFC4101]  Rescorla, E. and IAB, "Writing Protocol Models", RFC 4101,
              June 2005.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, November 2005.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, June 2007.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120, February 2008.

   [RFC5548]  Dohler, M., Watteyne, T., Winter, T., and D. Barthel,
              "Routing Requirements for Urban Low-Power and Lossy
              Networks", RFC 5548, May 2009.

   [RFC5673]  Pister, K., Thubert, P., Dwars, S., and T. Phinney,
              "Industrial Routing Requirements in Low-Power and Lossy
              Networks", RFC 5673, October 2009.

   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions",
              RFC 5706, November 2009.

   [RFC5826]  Brandt, A., Buron, J., and G. Porcu, "Home Automation
              Routing Requirements in Low-Power and Lossy Networks",
              RFC 5826, April 2010.

   [RFC5867]  Martocci, J., De Mil, P., Riou, N., and W. Vermeylen,
              "Building Automation Routing Requirements in Low-Power and
              Lossy Networks", RFC 5867, June 2010.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, June 2010.

   [X9.63-2001]
              "ANSI X9.63-2001, Public Key Cryptography for the
              Financial Services Industry - Key Agreement and Key
              Transport Using Elliptic Curve Cryptography", 2001.

   [X9.92]    "ANSI X9.92, Public Key Cryptography for the Financial
              Services Industry - Digital Signature Algorithms Giving
              Partial Message Recovery - Part 1: Elliptic Curve Pintsov-
              Vanstone Signatures (ECPVS)", 2009.

   [sha2]     "FIPS Pub 180-3, Secure Hash Standard (SHS)",  ,
              February 2008.

Authors' Addresses

   Tim Winter (editor)

   Email: wintert@acm.org

   Pascal Thubert (editor)
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis  06410
   FRANCE

   Phone: +33 497 23 26 34
   Email: pthubert@cisco.com

   RPL Author Team
   IETF ROLL WG

   Email: rpl-authors@external.cisco.com