Networking Working Group
ROLL                                                      T. Winter, Ed.
Internet-Draft
Intended status: Standards Track                         P. Thubert, Ed.
Expires: September 9, November 29, 2010                                 Cisco Systems
                                                        ROLL Design
                                                         RPL Author Team
                                                            IETF ROLL WG
                                                           March 8,
                                                            May 28, 2010

      RPL: IPv6 Routing Protocol for Low power and Lossy Networks
                         draft-ietf-roll-rpl-07
                         draft-ietf-roll-rpl-08

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 LLN 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 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 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.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  6
     1.1.  Design Principles  . . . . . . . . . . . . . . . . . . . .  6
     1.2.  Expectations of Link Layer Type  . . . . . . . . . . . . .  7
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  9
     3.1.  Topology . . . . . . . . . . . . . . . . . . . . . . . . .  9
       3.1.1.  Topology Identifiers . . . . . . . . . . . . . . . . .  9
       3.1.2. 10
     3.2.  Instances, DODAGs, and DODAG Information Versions  . . . . . . . . . . 10
     3.3.  Upward Routes and DODAG Construction . . . . . . . . 10
     3.2.  Instances, DODAGs, and DODAG Iterations . . . 12
       3.3.1.  DAG Repair . . . . . . 11
     3.3.  Traffic Flows . . . . . . . . . . . . . . . . 12
       3.3.2.  Grounded and Floating DODAGs . . . . . . 13
       3.3.1.  Multipoint-to-Point Traffic . . . . . . . 12
       3.3.3.  Administrative Preference  . . . . . . 13
       3.3.2.  Point-to-Multipoint Traffic . . . . . . . . 13
       3.3.4.  Objective Function (OF)  . . . . . 13
       3.3.3.  Point-to-Point Traffic . . . . . . . . . . 13
       3.3.5.  Distributed Algorithm Operation  . . . . . . 13
     3.4.  Upward Routes and DODAG Construction . . . . . 13
     3.4.  Downward Routes and Destination Advertisement  . . . . . . 13
       3.4.1.  DODAG Information Object (DIO) 14
     3.5.  Routing Metrics and Constraints Used By RPL  . . . . . . . 14
       3.5.1.  Loop Avoidance . . . . . 14
       3.4.2.  DAG Repair . . . . . . . . . . . . . . . 15
       3.5.2.  Rank Properties  . . . . . . . 14
       3.4.3.  Grounded and Floating DODAGs . . . . . . . . . . . . 16
     3.6.  Traffic Flows Supported by RPL . . 15
       3.4.4.  Administrative Preference . . . . . . . . . . . . 19
       3.6.1.  Multipoint-to-Point Traffic  . . 15
       3.4.5.  Objective Function (OF) . . . . . . . . . . . 19
       3.6.2.  Point-to-Multipoint Traffic  . . . . 15
       3.4.6.  Distributed Algorithm Operation . . . . . . . . . 19
       3.6.3.  Point-to-Point Traffic . . 15
     3.5.  Downward Routes and Destination Advertisement . . . . . . 16
       3.5.1.  Destination Advertisement Object (DAO) . . . . . . . . 16
     3.6.  Routing Metrics and Constraints Used By 19
   4.  RPL Instance . . . . . . . 17
       3.6.1.  Loop Avoidance . . . . . . . . . . . . . . . . . . 20
     4.1.  RPL Instance ID  . . 18
       3.6.2.  Rank Properties . . . . . . . . . . . . . . . . . . . 19
   4. 20
   5.  ICMPv6 RPL Control Message . . . . . . . . . . . . . . . . . . 21
   5.  Upward Routes
     5.1.  RPL Security Fields  . . . . . . . . . . . . . . . . . . . 23
     5.2.  DODAG Information Solicitation (DIS) . . . . . 22
     5.1.  DODAG Information Object (DIO) . . . . . . 26
       5.2.1.  Format of the DIS Base Object  . . . . . . . . 22
       5.1.1.  DIO Base Format . . . . 26
       5.2.2.  Secure DIS . . . . . . . . . . . . . . . 22
       5.1.2.  DIO Base Rules . . . . . . . 27
       5.2.3.  DIS Options  . . . . . . . . . . . . . 24
       5.1.3.  DIO Suboptions . . . . . . . . 27
     5.3.  DODAG Information Object (DIO) . . . . . . . . . . . . 25
     5.2.  DODAG Information Solicitation (DIS) . . 27
       5.3.1.  Format of the DIO Base Object  . . . . . . . . . 30
     5.3.  Upward Route Discovery and Maintenance . . . 27
       5.3.2.  Secure DIO . . . . . . . 30
       5.3.1.  RPL Instance . . . . . . . . . . . . . . . 29
       5.3.3.  DIO Options  . . . . . . 30
       5.3.2.  Neighbors and Parents within a DODAG Iteration . . . . 30
       5.3.3.  Neighbors and Parents across DODAG Iterations . . . . 31
       5.3.4.  DIO Message Communication . . . . . . . 29
     5.4.  Destination Advertisement Object (DAO) . . . . . . . 36
       5.3.5.  DIO Transmission . . . 30
       5.4.1.  Format of the DAO Base Object  . . . . . . . . . . . . 30
       5.4.2.  Secure DAO . . . . 36
       5.3.6.  DODAG Selection . . . . . . . . . . . . . . . . . . 31
       5.4.3.  DAO Options  . 39
     5.4.  Operation as a Leaf Node . . . . . . . . . . . . . . . . . 39
     5.5.  Administrative Rank . . . 31
     5.5.  Destination Advertisement Object Acknowledgement
           (DAO-ACK)  . . . . . . . . . . . . . . . . 40
     5.6.  Collision . . . . . . . . 31
       5.5.1.  Format of the DAO-ACK Base Object  . . . . . . . . . . 31
       5.5.2.  Secure DAO-ACK . . . . . . 40
   6.  Downward Routes . . . . . . . . . . . . . . 32
       5.5.3.  DAO-ACK Options  . . . . . . . . . 40
     6.1.  Destination Advertisement Object (DAO) . . . . . . . . . . 41
       6.1.1.  DAO Suboptions 32
     5.6.  RPL Control Message Options  . . . . . . . . . . . . . . . 32
       5.6.1.  RPL Control Message Option Generic Format  . . . . . 42
     6.2.  Downward Route Discovery and Maintenance . 32
       5.6.2.  Pad1 . . . . . . . . 43
       6.2.1.  Overview . . . . . . . . . . . . . . . . . 33
       5.6.3.  PadN . . . . . . 43
       6.2.2.  Mode of Operation . . . . . . . . . . . . . . . . . . 44
       6.2.3.  Destination Advertisement Parents . 33
       5.6.4.  Metric Container . . . . . . . . . 44
       6.2.4.  Operation of DAO Storing Nodes . . . . . . . . . . 34
       5.6.5.  Route Information  . . 45
       6.2.5.  Operation of DAO Non-storing Nodes . . . . . . . . . . 48
       6.2.6.  Scheduling to Send DAO (or no-DAO) . . . . . . 35
       5.6.6.  DODAG Configuration  . . . . 49
       6.2.7.  Triggering DAO Message from the Sub-DODAG . . . . . . 49
       6.2.8.  Sending DAO Messages to DAO Parents . . . . . . . 36
       5.6.7.  RPL Target . . 51
       6.2.9.  Multicast Destination Advertisement Messages . . . . . 52
   7.  Packet Forwarding and Loop Avoidance/Detection . . . . . . . . 52
     7.1.  Suggestions for Packet Forwarding . . . . . . . 37
       5.6.8.  Transit Information  . . . . . 53
     7.2.  Loop Avoidance and Detection . . . . . . . . . . . . 39
       5.6.9.  Solicited Information  . . . 54
       7.2.1.  Source Node Operation . . . . . . . . . . . . . 40
       5.6.10. Prefix Information . . . 55
       7.2.2.  Router Operation . . . . . . . . . . . . . . . 42
   6.  Upward Routes  . . . . 55
   8.  Multicast Operation . . . . . . . . . . . . . . . . . . . . 44
     6.1.  DIO Base Rules . 57
   9.  Maintenance of Routing Adjacency . . . . . . . . . . . . . . . 58
   10. Guidelines for Objective Functions . . . . . . 45
     6.2.  Upward Route Discovery and Maintenance . . . . . . . . 59
   11. RPL Constants and Variables . . 45
       6.2.1.  Neighbors and Parents within a DODAG Version . . . . . 45
       6.2.2.  Neighbors and Parents across DODAG Versions  . . . . . 46
       6.2.3.  DIO Message Communication  . . . . . 61
   12. Manageability Considerations . . . . . . . . . 51
     6.3.  DIO Transmission . . . . . . . . 62
     12.1. Control of Function and Policy . . . . . . . . . . . . . 52
       6.3.1.  Trickle Parameters . 62
       12.1.1. Initialization Mode . . . . . . . . . . . . . . . . . 62
       12.1.2. DIO Base option 52
     6.4.  DODAG Selection  . . . . . . . . . . . . . . . . . . . 63
       12.1.3. Trickle Timers . . . 53
     6.5.  Operation as a Leaf Node . . . . . . . . . . . . . . . . . 63
       12.1.4. DAG Sequence Number Increment 53
     6.6.  Administrative Rank  . . . . . . . . . . . . 64
       12.1.5. Destination Advertisement Timers . . . . . . . 53
   7.  Downward Routes  . . . . 64
       12.1.6. Policy Control . . . . . . . . . . . . . . . . . . . 54
     7.1.  Downward Route Discovery and Maintenance . 64
       12.1.7. Data Structures . . . . . . . . 54
       7.1.1.  Overview . . . . . . . . . . . 65
     12.2. Information and Data Models . . . . . . . . . . . . 54
       7.1.2.  Mode of Operation  . . . 65
     12.3. Liveness Detection and Monitoring . . . . . . . . . . . . 65
       12.3.1. Candidate Neighbor Data Structure . . . 55
       7.1.3.  Destination Advertisement Parents  . . . . . . . 65
       12.3.2. Directed Acyclic Graph (DAG) Table . . . 56
       7.1.4.  DAO Operation on Storing Nodes . . . . . . . 65
       12.3.3. Routing Table . . . . . 56
       7.1.5.  Operation of DAO Non-storing Nodes . . . . . . . . . . 60
       7.1.6.  Scheduling to Send DAO (or No-Path)  . . . . . 66
       12.3.4. Other RPL Monitoring Parameters . . . . 61
       7.1.7.  Triggering DAO Message from the Sub-DODAG  . . . . . . 61
       7.1.8.  Sending DAO Messages to DAO Parents  . 67
       12.3.5. RPL Trickle Timers . . . . . . . . 62
       7.1.9.  Multicast Destination Advertisement Messages . . . . . 63
   8.  Packet Forwarding and Loop Avoidance/Detection . . . . . 67
     12.4. Verifying Correct Operation . . . 64
     8.1.  Suggestions for Packet Forwarding  . . . . . . . . . . . . 67
     12.5. Requirements on Other Protocols 64
     8.2.  Loop Avoidance and Functional
           Components Detection . . . . . . . . . . . . . . . 65
       8.2.1.  Source Node Operation  . . . . . . . . . 67
     12.6. Impact on Network Operation . . . . . . . 66
       8.2.2.  Router Operation . . . . . . . . 67
   13. Security Considerations . . . . . . . . . . . 66
   9.  Multicast Operation  . . . . . . . . 67
   14. IANA Considerations . . . . . . . . . . . . . 68
   10. Maintenance of Routing Adjacency . . . . . . . . 67
     14.1. RPL Control Message . . . . . . . 69
   11. Guidelines for Objective Functions . . . . . . . . . . . . 68
     14.2. New Registry for RPL Control Codes . . 70
     11.1. Objective Function Behavior  . . . . . . . . . . 68
     14.3. New Registry for the Control Field of the DIO Base . . . . 68
     14.4. DODAG Information Object (DIO) Suboption . 70
   12. RPL Constants and Variables  . . . . . . . . 69
   15. Acknowledgements . . . . . . . . . 72
   13. Manageability Considerations . . . . . . . . . . . . . . 69
   16. Contributors . . . 73
     13.1. Control of Function and Policy . . . . . . . . . . . . . . 73
       13.1.1. Initialization Mode  . . . . . . . . 70
   17. References . . . . . . . . . 73
       13.1.2. DIO Base option  . . . . . . . . . . . . . . . . . 71
     17.1. Normative References . . 74
       13.1.3. Trickle Timers . . . . . . . . . . . . . . . . . 71
     17.2. Informative References . . . 74
       13.1.4. DAG Version Number Increment . . . . . . . . . . . . . 75
       13.1.5. Destination Advertisement Timers . . 72
   Appendix A.  Requirements . . . . . . . . . 75
       13.1.6. Policy Control . . . . . . . . . . . 74
     A.1.  Protocol Properties Overview . . . . . . . . . 75
       13.1.7. Data Structures  . . . . . . 74
       A.1.1.  IPv6 Architecture . . . . . . . . . . . . . 75
     13.2. Information and Data Models  . . . . . 74
       A.1.2.  Typical LLN Traffic Patterns . . . . . . . . . . 76
     13.3. Liveness Detection and Monitoring  . . . 74
       A.1.3.  Constraint Based Routing . . . . . . . . . 76
       13.3.1. Candidate Neighbor Data Structure  . . . . . . 74
     A.2.  Deferred Requirements . . . . 76
       13.3.2. Directed Acyclic Graph (DAG) Table . . . . . . . . . . 76
       13.3.3. Routing Table  . . . . 75
   Appendix B.  Examples . . . . . . . . . . . . . . . . 77
       13.3.4. Other RPL Monitoring Parameters  . . . . . . 75
     B.1.  DAO Operation When Only the Root Node Stores DAO
           Information . . . . . 77
       13.3.5. RPL Trickle Timers . . . . . . . . . . . . . . . . . . 75
     B.2.  DAO 78
     13.4. Verifying Correct Operation When All Nodes Fully Store DAO
           Information  . . . . . . . . . . . . . . . 78
     13.5. Requirements on Other Protocols and Functional
           Components . . . . . . . . 77
     B.3.  DAO . . . . . . . . . . . . . . . . 78
     13.6. Impact on Network Operation When Nodes Have Mixed Capabilities  . . . . . 79
   Appendix C.  Outstanding Issues . . . . . . . . . . 78
   14. Security Considerations  . . . . . . . 81
     C.1.  Additional Support for P2P Routing . . . . . . . . . . . . 81
     C.2.  Destination Advertisement / DAO Fan-out 78
     14.1. Overview . . . . . . . . . 81
     C.3.  Source Routing . . . . . . . . . . . . . . . . 78
     14.2. Functional Description of Packet Protection  . . . . . . 81
     C.4.  Address / Header Compression . 80
       14.2.1. Transmission of Outgoing Packets . . . . . . . . . . . 80
       14.2.2. Reception of Incoming Packets  . . . . . . . . . . . . 81
     C.5.  Managing Multiple Instances
       14.2.3. Cryptographic Mode of Operation  . . . . . . . . . . . 81
     14.3. Protecting RPL ICMPv6 messages . . . . . . . . . . . . . . 82
   Authors' Addresses
     14.4. Security State Machine . . . . . . . . . . . . . . . . . . 83
   15. IANA Considerations  . . . . . . 82

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).  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 unicast, but in many cases 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
   [I-D.ietf-roll-building-routing-reqs],
   [I-D.ietf-roll-home-routing-reqs], [RFC5673], and [RFC5548].  This
   document specifies the IPv6 Routing Protocol for Low power and lossy
   networks (RPL).

1.1.  Design Principles . . . . . . . . . . . . . . . 83
     15.1. RPL was designed with the objective to meet the requirements spelled
   out in [I-D.ietf-roll-building-routing-reqs],
   [I-D.ietf-roll-home-routing-reqs], [RFC5673], and [RFC5548].  Because
   those requirements are heterogeneous and sometimes incompatible in
   nature, the approach is first taken to design a protocol capable of
   supporting a core set of functionalities corresponding to the
   intersection of the requirements.  As the Control Message  . . . . . . . . . . . . . . . . . . . 83
     15.2. New Registry for RPL design evolves optional
   features may be added to address some application specific
   requirements.  This is a key protocol design decision providing a
   granular approach in order to restrict the core of Control Codes . . . . . . . . . . . . 84
     15.3. New Registry for the protocol to a
   minimal set of functionalities, and to allow each implementation Mode of
   the protocol to be optimized differently.  All "MUST" application
   requirements that cannot be satisfied by Operation (MOP) DIO
           Control Field  . . . . . . . . . . . . . . . . . . . . . . 84
     15.4. RPL will be specifically
   listed in the Appendix A, accompanied by a justification. Control Message Option . . . . . . . . . . . . . . . . 85
   16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 85
   17. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 86
   18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 88
     18.1. Normative References . . . . . . . . . . . . . . . . . . . 88
     18.2. Informative References . . . . . . . . . . . . . . . . . . 88
   Appendix A.  Requirements  . . . . . . . . . . . . . . . . . . . . 90
     A.1.  Protocol Properties Overview . . . . . . . . . . . . . . . 90
       A.1.1.  IPv6 Architecture  . . . . . . . . . . . . . . . . . . 90
       A.1.2.  Typical LLN Traffic Patterns . . . . . . . . . . . . . 90
       A.1.3.  Constraint Based Routing . . . . . . . . . . . . . . . 91
     A.2.  Deferred Requirements  . . . . . . . . . . . . . . . . . . 91
   Appendix B.  Outstanding Issues  . . . . . . . . . . . . . . . . . 91
     B.1.  Additional Support for P2P Routing . . . . . . . . . . . . 91
     B.2.  Address / Header Compression . . . . . . . . . . . . . . . 91
     B.3.  Managing Multiple Instances  . . . . . . . . . . . . . . . 92
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 92

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).  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 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
   [I-D.ietf-roll-building-routing-reqs], [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 [I-D.ietf-roll-building-routing-reqs], [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.

   RPL is a generic protocol that is

   In order to be deployed by instantiating the
   generic operation described useful in this document with a specific
   objective function (OF) (which ties together metrics, constraints, wide range of LLN application domains, RPL
   separates packet processing and an forwarding from the routing
   optimization objective) to realize a desired 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
   given environment. 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 but not limited to, low power wireless or PLC
   (Power Line Communication) technologies.

   Implementers may find RFC 3819 [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
         edges.  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.

   Rank: The rank of a node in a DAG identifies the nodes position with
         respect to a DODAG root.  The farther away a node is from a
         DODAG root, the higher is the rank of that node.  The rank of a
         node may be a simple topological distance, or may more commonly
         be calculated as a function of other properties as described
         later.

   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.  The DODAG parent of a node will have a lower rank than
         the node itself.  (See Section 3.6.2.1). 3.5.2.1).

   DODAG sibling:  A sibling of a node within a DODAG is defined in this
         specification to be any neighboring node which is located at
         the same rank within a DODAG.  Note that siblings defined in
         this manner do not necessarily share a common DODAG parent.
         (See Section 3.6.2.1). 3.5.2.1).

   Sub-DODAG  The sub-DODAG of a node is the set of other nodes in the
         DODAG that might use a path towards the DODAG root that
         contains that node.  Nodes in the sub-DODAG of a node have a
         greater rank than that node itself (although not all nodes of
         greater rank are necessarily in the sub-DODAG of that node).
         (See Section 3.6.2.1). 3.5.2.1).

   DODAGID:  The identifier of a DODAG root.  The DODAGID must be unique
         within the scope of a RPL Instance in the LLN.

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

   RPL Instance:  A set of possibly multiple DODAGs.  A network may have
         more than one RPL Instance, and a RPL node can participate in
         multiple RPL Instances.  Each RPL Instance operates
         independently of other RPL Instances.  This document describes
         operation within a single RPL Instance.  In RPL, a node can
         belong to at most one DODAG per RPL Instance.  The tuple
         (RPLInstanceID, DODAGID) uniquely identifies a DODAG.

   RPLInstanceID:  Unique identifier of a RPL Instance.

   DODAGSequenceNumber:

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

   Up:   Up refers to the direction from leaf nodes towards DODAG roots,
         following the orientation of the edges within the DODAG.  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."

   Down: Down refers to the direction from DODAG roots towards leaf
         nodes, going against the orientation of the edges within the
         DODAG.  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."

   Objective Code Point (OCP):  An identifier, used to indicate which
         Objective Function is in use for forming a DODAG.  The
         Objective Code Point is further described in
         [I-D.ietf-roll-routing-metrics].

   Objective Function (OF):  Defines which routing metrics, optimization
         objectives, and related functions are in use in a DODAG.  The
         Objective Function is further described in
         [I-D.ietf-roll-routing-metrics].

   Goal: The Goal is a host or set of hosts that satisfy a particular
         application objective / OF. (OF).  Whether or not a DODAG can provide
         connectivity to a goal is a property of the DODAG.  For
         example, a goal might be a host serving as a data collection
         point, or a gateway providing connectivity to an external
         infrastructure.

   Grounded:  A DODAG is said to be grounded, when the root can reach
         the Goal of the objective function.

   Floating:  A DODAG is floating if is not Grounded.  A floating DODAG
         is not expected to reach the Goal defined for the OF.
         Typically, a DAG that is only intended to provide inner
         connectivity is a Floating DAG.

   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, and the rules by
   which these are constructed, i.e. the rules governing DODAG
   formation.

3.1.1.  Topology Identifiers

   RPL uses four identifiers to track and control maintain the 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 OF.  A network may have multiple RPLInstanceIDs, each of
      which defines an independent set of DODAGs, which may be optimized
      for different OFs and/or applications.  The set of DODAGs
      identified by a RPLInstanceID is called a RPL Instance.

   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 DODAGSequenceNumber.  The scope of a
      DODAGSequenceNumber is a DODAG.  A DODAG is sometimes
      reconstructed from the DODAG root, by incrementing the
      DODAGSequenceNumber.  The combination of RPLInstanceID, DODAGID,
      and DODAGSequenceNumber uniquely identifies a DODAG Iteration.

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

3.1.2.  DODAG Information

   For each DODAG that a node is, or may become, a member of, the
   implementation should conceptually keep track of the following
   information.  The data structures described in this section are
   intended to illustrate a possible implementation to aid in the
   description of the protocol, but are not intended to be normative.

   o  RPLInstanceID

   o  DODAGID

   o  DODAGSequenceNumber

   o  DAG Metric Container, including DAGObjectiveCodePoint

   o  A set third is a DODAGVersionNumber.  The scope of Destination Prefixes offered by the a
      DODAGVersionNumber is a DODAG.  A DODAG root and
      available via paths upwards along is sometimes reconstructed
      from the DODAG

   o  A set root, by incrementing the DODAGVersionNumber.  The
      combination of RPLInstanceID, DODAGID, and DODAGVersionNumber
      uniquely identifies a DODAG parents Version.

   o  A set  The fourth is rank.  The scope of rank is a DODAG siblings

   o  A timer Version.  Rank
      establishes a partial order over a DODAG Version, defining
      individual node positions with respect to govern the sending of RPL control messages DODAG root.

3.2.  Instances, DODAGs, and DODAG Iterations Versions

   Each RPL Instance constructs a routing topology optimized for a
   certain Objective Function (OF). (OF) and routing metrics
   [I-D.ietf-roll-routing-metrics].  A RPL Instance may provide routes
   to certain destination prefixes, reachable via the DODAG roots. roots or
   alternate paths within the DODAG.  A single RPL Instance contains one
   or more Destination Oriented DAG (DODAG) roots.  These roots may
   operate independently, or may coordinate over a non-LLN backchannel.

   Each root has a unique identifier, the DODAGID.

   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 to coordinate to form a single DODAG, and further 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 LLN sinks
      (with the same DODAGID) over some non-LLN backbone

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

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

   Traffic is bound to a specific RPL Instance by a marking in meta-data that is
   carried with the flow
   label of packet and associates the IPv6 header.  Traffic originating in support of packet to a particular application may be tagged to follow an appropriate RPL
   instance which enables certain (path) properties, for example to
   follow paths optimized for low latency or low energy.
   RPLInstanceID (Section 8.2).  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.

   An example of a RPL Instance comprising a number of DODAGs is
   depicted in Figure 1.  A  Revision of a DODAG Iteration Version (two "versions" iterations of
   the same DODAG) is depicted in Figure 2.

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

                          Figure 1: RPL Instance

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

                          Figure 2: DODAG Iteration

3.3.  Traffic Flows

3.3.1.  Multipoint-to-Point Traffic

   Multipoint-to-Point (MP2P) is a dominant traffic flow in many LLN
   applications ([I-D.ietf-roll-building-routing-reqs],
   [I-D.ietf-roll-home-routing-reqs], [RFC5673], [RFC5548]).  The
   destinations of MP2P flows are designated nodes that have some
   application significance, such as providing connectivity to the
   larger Internet or core private IP network.  RPL supports MP2P
   traffic by allowing MP2P destinations to be reached via DODAG roots.

3.3.2.  Point-to-Multipoint Traffic

   Point-to-multipoint (P2MP) is a traffic pattern required by several
   LLN applications ([I-D.ietf-roll-building-routing-reqs],
   [I-D.ietf-roll-home-routing-reqs], [RFC5673], [RFC5548]).  RPL
   supports P2MP traffic by using a destination advertisement mechanism
   that provisions routes toward destination prefixes and away from
   roots.  Destination advertisements can update routing tables as the
   underlying 2: DODAG topology changes.

3.3.3.  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.

   RPL also supports the case where a P2P destination is a 'one-hop'
   neighbor.

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

3.4. Version

3.3.  Upward Routes and DODAG Construction

   RPL provisions routes up towards DODAG roots, forming a DODAG
   optimized according to the Objective Function (OF) in use.  RPL nodes
   construct and maintain these DODAGs through exchange of DODAG
   Information Object (DIO) messages.  Undirected links between siblings
   are also identified during this process, which can be used to provide
   additional diversity.

3.4.1.  DODAG Information Object (DIO)

   A DIO identifies the RPL Instance, the DODAGID, the values used to
   compute the RPL Instance's objective function, and the present DODAG
   Sequence Number.  It can also include additional routing and
   configuration information.  The DIO includes a measure derived from
   the position of the node within the DODAG, the rank, which is used
   for nodes to determine their positions relative to each other and to
   inform loop avoidance/detection procedures.  RPL exchanges DIO
   messages to establish and maintain routes.

   RPL adapts the rate at which nodes send DIO messages.  When a DODAG
   is detected to be inconsistent or needs repair, RPL sends DIO
   messages more frequently.  As the DODAG stabilizes, the DIO message
   rate tapers off, reducing the maintenance cost of DODAG roots, forming a steady DODAG
   optimized according to the Objective Function (OF) and well-
   working DODAG.

   This document defines an ICMPv6 Message Type "RPL Control Message",
   which is capable routing
   metrics/constraints in use.  RPL nodes construct and maintain these
   DODAGs through exchange of carrying a DIO.

3.4.2. DODAG Information Object (DIO) messages.
   Undirected links between siblings are also identified during this
   process, which can be used to provide additional diversity.

3.3.1.  DAG Repair

   RPL supports global repair over the DODAG.  A DODAG Root may
   increment the DODAG Sequence Version Number, thereby initiating a new DODAG
   iteration.
   version.  This institutes a global repair operation, revising the
   DODAG and allowing nodes to choose an arbitrary new position within
   the new DODAG iteration. version.  Global repair can be seen as a global
   reoptimization mechanism.

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

3.3.2.  Grounded and Floating DODAGs

   DODAGs can be grounded or floating.  A grounded DODAG offers
   connectivity to reach a goal.  A floating DODAG offers no such
   connectivity, and provides routes only to nodes within the DODAG.

   Floating DODAGs may be used, for example, to preserve inner
   connectivity during repair.

3.3.3.  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.

3.3.4.  Objective Function (OF)

   The Objective Function (OF) implements the optimization objectives of
   route selection within the RPL Instance.  The OF is identified by an
   Objective Code Point (OCP) within the DIO.  The OF also specifies the
   procedure used to select parents and compute rank within a DODAG
   version along with potentially other DODAG characteristics.  Further
   details may be found in Section 11, [I-D.ietf-roll-routing-metrics],
   [I-D.ietf-roll-of0], and related companion specifications.

3.3.5.  Distributed Algorithm Operation

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

   o  Some nodes are configured from the DODAG root.  Local repair options include the
   allowing a node, upon detecting a loss of connectivity to a be DODAG it
   is a member of, to: roots, with associated DODAG
      configuration.

   o  Poison its sub-DODAG  Nodes advertise their presence, affiliation with a DODAG, routing
      cost, and related metrics by advertising an effective rank of INFINITY sending link-local multicast DIO
      messages.

   o  Nodes may adjust the rate at which DIO messages are sent in
      response to its sub-DODAG, OR detach stability or detection of routing inconsistencies from
      both control or data packets (see Section 8.2 for more).

   o  Nodes listen for DIOs and form use their information to join a floating DODAG in order new
      DODAG, or to
      preserve inner connectivity within its sub-DODAG. maintain an existing DODAG, as according to the
      specified Objective Function and rank-based loop avoidance rules.

   o  Move down within  Nodes provision routing table entries, for the destinations
      specified by the DIO, via their DODAG iteration (i.e. increase its rank) parents in the DODAG
      version.  Nodes MUST provision a
      limited manner, no further than DODAG parent as a bound configured by default route
      for the DODAG
      root via associated instance.  It is up to the DIO so as not end-to-end
      application to count all select the way RPL instance to infinity.  Such
      a move may be undertaken after waiting an appropriate poisoning
      interval, associated to its
      traffic (should there be more than one instance) and thus the
      default route upwards when no longer-match exists.

   o  Nodes may identify DODAG siblings within the DODAG version to
      increase path diversity and decrease convergence time during
      repair.

3.4.  Downward Routes and Destination Advertisement

   RPL constructs and should allow the node maintains DODAGs with DIO messages to restore connectivity establish
   upward routes: it uses Destination Advertisement Object (DAO)
   messages to establish downward routes along the DODAG Iteration, if at all possible.

3.4.3.  Grounded and Floating DODAGs

   DODAGs can be grounded as well as
   other P2P routes.  DAO messages are an optional feature for
   applications that require P2MP or floating.  A grounded DODAG offers
   connectivity to P2P traffic, in either storing
   (fully stateful) or non-storing (fully source routed
   [I-D.hui-6man-rpl-routing-header]) mode.

3.5.  Routing Metrics and Constraints Used By RPL

   Routing metrics are used by routing protocols to a goal.  A floating DODAG offers no compute shortest
   paths.  Interior Gateway Protocols (IGPs) such
   connectivity, as IS-IS ([RFC5120])
   and provides routes only to nodes within OSPF ([RFC4915]) use static link metrics.  Such link metrics can
   simply reflect the DODAG.
   Floating DODAGs may bandwidth or can also be used, for example, computed according to preserve inner
   connectivity during repair.

3.4.4.  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
   polynomial function of several metrics defining different link
   characteristics.  Some routing protocols support application
   requirements or needs.

3.4.5.  Objective Function (OF)

   The Objective Function (OF) implements more than one
   metric: in the optimization objectives vast majority of
   route selection within the RPL Instance.  The OF cases, one metric is identified by an
   Objective Code Point (OCP) within the DIO, and its specification also
   indicates the metrics and constraints in use.  The OF also specifies
   the procedure used to compute rank within per
   (sub)topology.  Less often, a DODAG iteration.  Further
   details second metric may be found in [I-D.ietf-roll-routing-metrics],
   [I-D.ietf-roll-of0], and related companion specifications.

   By using defined OFs that are understood by all nodes in used as a particular
   deployment, tie-
   breaker in the presence of Equal Cost Multiple Paths (ECMP).  The
   optimization of multiple metrics is known as an NP complete problem
   and is sometimes supported by referencing these in some centralized path computation
   engine.

   In contrast, LLNs do require the DIO message, RPL nodes
   may work to build optimized LLN routes using a variety support of application both static and implementation specific metrics dynamic
   metrics.  Furthermore, both link and goals. node metrics are required.  In
   the case where a node of RPL, it is unable virtually impossible to encounter define one metric, or
   even a suitable composite metric, that will satisfy all use cases.

   In addition, RPL
   Instance using a known Objective Function, it supports constrained-based routing where constraints
   may be configured applied to
   join both link and nodes.  If a RPL Instance using an unknown Objective Function - but in that
   case only acting as link or a leaf node.

3.4.6.  Distributed Algorithm Operation

   A high level overview of the distributed algorithm which constructs node does not
   satisfy a required constraint, it is 'pruned' from the DODAG candidate
   list, thus leading to a constrained shortest path.

   The set of supported link/node constraints and metrics is as follows:

   o  Some nodes specified
   in [I-D.ietf-roll-routing-metrics].

   An Objective Function specifies constraints in use, and how these are configured
   used, in addition to be DODAG roots, with associated DODAG
      configuration.

   o  Nodes advertise their presence, affiliation with a DODAG, routing
      cost, the objectives used to compute the (constrained)
   path.  Upstream and related Downstream metrics by sending link-local multicast DIO
      messages.

   o  Nodes may adjust be merged or advertised
   separately depending on the OF and the metrics.  When they are
   advertised separately, it may happen that the rate at which set of DIO parents is
   different from the set of DAO parents (a DAO parent is a node to
   which unicast DAO messages are sent in
      response sent).  Yet, all are DODAG parents
   with regards to stability or detection of routing inconsistencies.

   o  Nodes listen the rules for DIOs Rank computation.

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

   Example 2: Constrained shortest path: the path that does not traverse
              any battery-operated node and use their information to join a new
      DODAG, or that optimizes the path
              reliability

3.5.1.  Loop Avoidance

   RPL guarantees neither loop free path selection nor tight delay
   convergence times.  In order to maintain an existing DODAG, reduce control overhead, however,
   such as according to the
      specified Objective Function and cost of the count-to-infinity problem, RPL avoids
   creating loops when undergoing topology changes.  Furthermore, RPL
   includes rank-based loop avoidance rules.

   o  Nodes provision routing table entries, datapath validation mechanisms for detecting
   loops when they do occur.  RPL uses this loop detection to ensure
   that packets make forward progress within the destinations
      specified by the DIO, via their DODAG parents version and
   trigger repairs when necessary.

3.5.1.1.  Greediness and Rank-based Instabilities

   A node is greedy if it attempts to move deeper in the DODAG
      iteration.  Nodes may provision version,
   in order to increase the size of the parent set or improve some other
   metric.  Moving deeper in within a DODAG parent as version in this manner could
   result in instability and be detrimental to other nodes.

   Once a node has joined a default
      gateway.

   o  Nodes may identify DODAG siblings within version, RPL disallows certain
   behaviors, including greediness, in order to prevent resulting
   instabilities in the DODAG iteration version.

   Suppose a node is willing to
      increase path diversity.

   o  Using DIOs, receive and possibly information process a DIO messages from
   a node in data packets, RPL nodes
      detect possible routing loops.  When its own sub-DODAG, and in general a RPL node detects deeper than
   itself.  In this case, a possible
      routing loop, it may adapt its DIO transmission rate to apply possibility exists that a
      local repair feedback loop is
   created, wherein two or more nodes continue to the topology.

3.5.  Downward Routes and Destination Advertisement

   RPL constructs try and maintains DODAGs with DIO messages to establish
   upward routes: it uses Destination Advertisement Object (DAO)
   messages to establish downward routes along move in the
   DODAG as well as
   other routes.  DAO messages are an optional feature version while attempting to optimize against each other.  In
   some cases, this will result in instability.  It is for applications this reason
   that require P2MP or P2P traffic. RPL limits the cases where a node may process DIO messages advertise whether
   destination advertisements are enabled within from
   deeper nodes to some forms of local repair.  This approach creates an
   'event horizon', whereby a given DODAG.

3.5.1.  Destination Advertisement Object (DAO)

   A Destination Advertisement Object (DAO) conveys destination
   information upwards along node cannot be influenced beyond some
   limit into an instability by the DODAG so action of nodes that a may be in its
   own sub-DODAG.

3.5.1.2.  DODAG root (and other
   intermediate nodes) can provision downward routes. Loops

   A DAO message
   includes prefix information to identify destinations, DODAG loop may occur when a capability to
   record routes in support of source routing, node detaches from the DODAG and information
   reattaches to
   determine the freshness of a particular advertisement.

   Nodes that are capable of maintaining routing state device in its prior sub-DODAG.  This may aggregate
   routes from DAO happen in
   particular when DIO messages that they receive before transmitting a DAO
   message.  Nodes that are not capable missed.  Strict use of maintaining routing state may
   attach a next-hop address to the Reverse Route Stack contained within the DAO message.  The Reverse Route Stack is subsequently used to
   generate piecewise source routes over regions DODAG
   Version Number can eliminate this type of the LLN that are
   incapable loop, but this type of storing downward routing state. loop
   may possibly be encountered when using some local repair mechanisms.

3.5.1.3.  DAO Loops

   A special case of DAO loop may occur when the parent has a route installed upon
   receiving and processing a DAO message, termed message from a no-DAO, is used to clear
   downward routing state that child, but the child
   has been provisioned through subsequently cleaned up the related DAO
   operation. state.  This document defines an ICMPv6 Message Type "RPL Control Message",
   which is capable of carrying a DAO.

3.5.1.1.  'One-Hop' Neighbors

   In addition to sending DAOs toward DODAG roots, RPL nodes may
   occasionally emit loop happens
   when a link-local multicast No-Path (a DAO message advertising
   available destination prefixes.  This mechanism allow provisioning that invalidates a
   trivial 'one-hop' route to local neighbors.

3.6.  Routing Metrics previously announced
   prefix) was missed and Constraints Used By persists until all state has been cleaned up.
   RPL

   Routing metrics are used by routing protocols includes an optional mechanism 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 acknowledge DAO messages, which
   may mitigate the bandwidth or can also be computed according to impact of a
   polynomial function single DAO message being missed.  RPL
   includes loop detection mechanisms that may mitigate the impact of several metrics defining different link
   characteristics; in all cases they are static metrics.  Some
   DAO loops and trigger their repair.

   In the case where stateless DAO operation is used, i.e. source
   routing
   protocols support more than one metric: in specifies the vast majority down routes, then DAO Loops should not occur on
   the stateless portions of the
   cases, one metric is used per (sub)topology.  Less often, path.

3.5.1.4.  Sibling Loops

   Sibling loops could occur if a second
   metric group of siblings kept choosing
   amongst themselves as successors such that a packet does not make
   forward progress.  This specification limits the number of times that
   sibling forwarding may be used as at a tie-breaker given rank, in order to prevent
   sibling loops.

3.5.2.  Rank Properties

   The rank of a node is a scalar representation of the presence location of Equal Cost
   Multiple Paths (ECMP). that
   node within a DODAG version.  The optimization of multiple metrics rank is known
   as an NP complete problem used to avoid and detect
   loops, and as such must demonstrate certain properties.  The exact
   calculation of the rank is sometimes supported by some
   centralized path computation engine.

   In contrast, LLNs do require left to the support of both static Objective Function, and dynamic
   metrics.  Furthermore, both may
   depend on parents, link metrics, and the node metrics 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 required.  In not necessarily those of all metrics:

   Type:   The rank is an abstract decimal value.

   Function:  The rank is the case expression 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 relative position within a
           DODAG version with regard to both link neighbors and nodes.  If is not necessarily
           a link good indication or a node does not
   satisfy proper expression of a required constraint, it is 'pruned' from the candidate
   list, thus leading to distance or a constrained shortest path.
           cost to the root.

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

   The role the rank determines the stability of the Objective Function is to specify which
           routing
   metrics and constraints are in use, and how these are used, in
   addition to the objectives used topology.  Some dampening or filtering might be
           applied to compute the (constrained) shortest
   path.

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

   Example 2: Constrained shortest path: topology stable, and thus 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 strong global
   convergence.  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 mechanisms for detecting loops when they do occur.  RPL uses
   this loop detection fast as some physical metrics
           would.  A new DODAG version would be a good opportunity to ensure that packets make forward progress
   within
           reconcile the DODAG iteration and trigger repairs when necessary.

3.6.1.1.  Greediness discrepancies that might form over time between
           metrics and Rank-based Instabilities

   Once a node has joined ranks within a DODAG iteration, RPL disallows certain
   behaviors, including greediness, in order to prevent resulting
   instabilities in version.

   Granularity:  The portion of the DODAG iteration.

   If a node rank that is allowed to be greedy and attempts used to move deeper define a node's
           position in the
   DODAG iteration, beyond its most preferred parent, in order to
   increase DAG, DAGRank(node), is coarse grained.  A
           fine granularity would make the size selection of siblings
           difficult, since siblings must have the parent set, then an instability can result.

   Suppose a node exact same rank
           value.

   Properties:  The rank is willing to receive strictly monotonic, and process can be used to
           validate a DIO messages progression from
   a node in its own sub-DODAG, and in general a node deeper than
   itself.  In or towards the root.  A metric,
           like bandwidth or jitter, does not necessarily exhibit this case,
           property.

   Abstract:  The rank does not have a possibility exists that physical unit, but rather a feedback loop range
           of increment per hop, where the assignment of each increment
           is
   created, wherein two or more nodes continue to try and move in be determined by the Objective Function.

   The rank value feeds into DODAG iteration while attempting parent selection, according to optimize against each other.  In
   some cases, this will result in instability.  It is for this reason
   that RPL limits the cases where
   RPL loop-avoidance strategy.  Once a node may process DIO messages from
   deeper nodes to some forms of local repair.  This approach creates an
   'event horizon', whereby parent has been added, and a
   rank value for the node cannot be influenced beyond some
   limit into an instability by within the DODAG has been advertised, the action of
   nodes that may be in its
   own sub-DODAG.

3.6.1.2. further options with regard to DODAG Loops

   A parent selection and
   movement within the DODAG are restricted in favor of loop avoidance.

3.5.2.1.  Rank Comparison (DAGRank())

   Rank may occur when be thought of as a node detaches from fixed point number, where the DODAG position of
   the decimal point between the integer part and
   reattaches to a device in its prior sub-DODAG.  This may happen the fractional part is
   determined by MinHopRankIncrease.  MinHopRankIncrease is the minimum
   increase in
   particular when DIO messages are missed.  Strict use rank between a node and any of its DODAG parents.  When
   an objective function computes rank, the DAG
   sequence number can eliminate this type of loop, but this type objective function operates
   on the entire (i.e. 16-bit) rank quantity.  When rank is compared,
   e.g. for determination of parent/sibling relationships or loop may possibly
   detection, the integer portion of the rank is to be encountered when using some local repair
   mechanisms.

3.6.1.3.  DAO Loops

   A DAO loop may occur when used.  The
   integer portion of the parent has a route installed upon
   receiving Rank is computed by the DAGRank() macro as
   follows:

              DAGRank(rank) = floor(rank/MinHopRankIncrease)

   MinHopRankIncrease is provisioned at the DODAG Root and processing a DAO message from a child, but propagated in
   the child
   has subsequently cleaned up DIO message.  For efficient implementation the related DAO state.  This loop happens
   when MinHopRankIncrease
   MUST be a no-DAO was missed and persists until all state has been
   cleaned up.  RPL includes loop detection mechanisms that power of 2.  An implementation may mitigate configure a value
   MinHopRankIncrease as appropriate to balance between the impact loop
   avoidance logic of DAO loops RPL (i.e. selection of eligible parents and
   siblings) and trigger their repair.

   In the case metrics in use.

   By convention in this document, using the macro DAGRank(node) may be
   interpreted as DAGRank(node.rank), where stateless DAO operation node.rank is used, i.e. source
   routing specifies the down routes, then DAO Loops should not occur on the stateless portions of the path.

3.6.1.4.  Sibling Loops

   Sibling loops could occur if a group of siblings kept choosing
   amongst themselves rank value
   as successors such that maintained by the node.

   A node A has a packet does not make
   forward progress.  This specification limits rank less than the number rank of times that
   sibling forwarding may be used at a given rank, in order node B if DAGRank(A) is
   less than DAGRank(B).

   A node A has a rank equal to prevent
   sibling loops.

3.6.2.  Rank Properties

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

   A node A has a scalar representation of rank greater than the location rank of that
   node within a DODAG iteration. node B if DAGRank(A)
   is greater than DAGRank(B).

3.5.2.2.  Rank Relationships

   The computation of the rank is used MUST be done in such a way so as to avoid and detect
   loops,
   maintain the following properties for any nodes M and as such 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 demonstrate certain properties.  The exact
   calculation be of the rank is left to the Objective Function, and may
   depend on parents, link metrics, and less than DAGRank(N).  In
           other words, the node configuration and
   policies.

   The rank is not presented by a cost metric, although its value can node N MUST be derived from
   and influenced greater
           than that presented by metrics.  The rank has properties any of its own that
   are not necessarily those parents.

   DAGRank(M) equals DAGRank(N):  In this case the positions of all metrics:

   Type:   Rank is an abstract scalar.  Some metrics are boolean (e.g.
           grounded), others are statistical M and better expressed as a
           tuple like an expected value N
           within the DODAG and with respect to the DODAG root are
           similar (identical).  In some cases, Node M may be used as a variance.  Some OCPs use
           not one but a set of metrics bound
           successor by Node N, which however entails the chance of
           creating a piece loop (which must be detected and resolved by some
           other means).

   DAGRank(M) is greater than DAGRank(N):  In this case, the position of logic.

   Function:  Rank
           M is farther from the expression 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 relative position within risk to
           create a
           DODAG iteration with regard loop.

   As an example, the rank could be computed in such a way so as to neighbors
   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 objective function is not
           necessarily a good indication to
   minimize ETX, or a proper expression of a
           distance latency when the objective function is to minimize
   latency, or in a cost more complicated way as appropriate to the root.

   Stability:  The stability of the rank determines objective
   function being used within the stability DODAG.

3.6.  Traffic Flows Supported by RPL

3.6.1.  Multipoint-to-Point Traffic

   Multipoint-to-Point (MP2P) is a dominant traffic flow in many LLN
   applications ([I-D.ietf-roll-building-routing-reqs], [RFC5826],
   [RFC5673], [RFC5548]).  The destinations of MP2P flows are designated
   nodes that have some application significance, such as providing
   connectivity to the
           routing topology.  Some dampening larger Internet or filtering might be
           applied core private IP network.  RPL
   supports MP2P traffic by allowing MP2P destinations to keep the topology stable, be reached via
   DODAG roots.

3.6.2.  Point-to-Multipoint Traffic

   Point-to-multipoint (P2MP) is a traffic pattern required by several
   LLN applications ([I-D.ietf-roll-building-routing-reqs], [RFC5826],
   [RFC5673], [RFC5548]).  RPL supports P2MP traffic by using a
   destination advertisement mechanism that provisions routes toward
   destination prefixes and thus the rank does
           not necessarily change as fast away from roots.  Destination advertisements
   can update routing tables as some physical metrics
           would.  A new the underlying DODAG iteration would be topology changes.

3.6.3.  Point-to-Point Traffic

   RPL DODAGs provide a good opportunity basic structure for point-to-point (P2P)
   traffic.  For a RPL network to
           reconcile the discrepancies that might form over time between
           metrics and ranks within support P2P traffic, a DODAG iteration.

   Granularity:  Rank is coarse grained.  A fine granularity would
           prevent the selection of siblings.

   Properties:  Rank is strictly monotonic, and can root must be used
   able to route packets to validate a progression from or towards destination.  Nodes within the root.  A metric, like
           bandwidth or jitter, does not necessarily exhibit this
           property.

   Abstract:  Rank does not network may
   also have routing tables to destinations.  A packet flows towards a physical unit, but rather
   root until it reaches an ancestor that has a range of
           increment per hop, where the assignment of each increment is 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 determined by the implementation.

   The rank value feeds into DODAG parent selection, according root.  In other cases it may be a node
   closer to both the source and destination.

   RPL loop-avoidance strategy.  Once also supports the case where a parent has been added, and P2P destination is a
   rank value 'one-hop'
   neighbor.

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

4.  RPL Instance

   Within a given LLN, there may be multiple, logically independent RPL
   instances.  This document describes how a single instance behaves.

   A node within may belong to multiple RPL Instances.

   An instance can be either local to a root or global.  When the DODAG has been advertised,
   instance is local, the
   nodes further options with regard to DAG is a single DODAG parent selection and
   movement within that is rooted at the DODAG are restricted
   node that owns the DODAGID.  This is used in favor of loop avoidance.

3.6.2.1.  Rank Comparison (DAGRank())

   Rank may be thought particular for the
   construction of as a fixed point number, where the position temporary DODAG in support of
   the decimal point P2P traffic
   optimization between the integer part root and the fractional part is
   determined by MinHopRankIncrease.  MinHopRankIncrease is the minimum
   increase some other nodes.

   Control and Data Packets that traverse a RPL network MUST be tagged
   in rank between such a node and any of its DODAG parents.  When
   an objective function computes rank, the objective function operates
   on fashion that the entire (i.e. 16-bit) rank quantity.  When rank instance is compared,
   e.g. for determination of parent/sibling relationships unambiguously identified (TBD
   flow label or loop
   detection, RPL Hop-by-hop option ([I-D.hui-6man-rpl-option])).
   The identifiers include the integer portion of RPLInstanceID and the rank is to DODAGID for local
   instances.

4.1.  RPL Instance ID

   A global RPLInstanceID MUST be used.  The
   integer portion unique to the whole LLN.  Mechanisms
   for allocating and provisioning global RPLInstanceID are out of scope
   for this document.  There can be up to 128 global instance in the Rank
   whole network, and up 64 local instances per DODAGID.

   A global RPLinstanceID is computed by the DAGRank() macro encoded in a RPLinstanceID field as
   follows:

              DAGRank(rank) = floor(rank/MinHopRankIncrease)

   MinHopRankIncrease

        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 provisioned at autoconfigured by the DODAG Root and propagated in node that owns the DIO message.  For efficient implementation
   DODAGID and it MUST be unique for that DODAGID.  In that case, the MinHopRankIncrease
   SHOULD
   DODAGID MUST be a power valid address of 2.  An implementation may configure the root that is used as an
   endpoint of all communications within that instance.

   A local RPLinstanceID is encoded in a value
   MinHopRankIncrease RPLinstanceID field as appropriate 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 is always set to 0 in RPL control
   messages.  It is used in data packets to balance between indicate whether the loop
   avoidance logic of RPL (i.e. selection DODAGID
   is the source or the destination of eligible parents and
   siblings) and the metrics in use.

   By convention in this document, using packet.  If the macro DAGRank(node) may D flag is set
   to 1 then the destination address of the IPv6 packet MUST be
   interpreted as DAGRank(node.rank), where node.rank the
   DODAGID.  If the D flag is clear then the rank value
   as maintained by source address of the node. IPv6
   packet MUST be the DODAGID.

5.  ICMPv6 RPL Control Message

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

   A RPL Control Message has a rank less than the rank scope of a node B if DAGRank(A) link.  The source address is
   less than DAGRank(B).

   A node A has
   a rank equal to link local address.  The destination address is either all routers
   multicast address (FF02::2) or a link local address.

   In accordance with [RFC4443], the rank RPL Control Message consists of an
   ICMPv6 header followed by a node B if DAGRank(A) message body.  The message body is
   comprised of a message base and possibly a number of options as
   illustrated 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |     Code      |          Checksum             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                             Base                              .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                           Option(s)                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 5: RPL Control Message

   The RPL Control message is
   equal to DAGRank(B).

   A node A has an ICMPv6 information message with a rank greater than the rank
   requested Type of a node B if DAGRank(A)
   is greater than DAGRank(B).

3.6.2.2.  Rank Relationships 155 (to be confirmed by IANA).

   The computation of Code field identifies the rank MUST be done in such a way so as to
   maintain type of RPL Control Message.  This
   document defines codes for the following properties for any nodes M and N that RPL Control Message types
   (all codes are
   neighbors in the LLN:

   DAGRank(M) is less than DAGRank(N):  In this case, the position of M
           is closer to be confirmed by the IANA Section 15.2):

   o  0x00: DODAG root than Information Solicitation (Section 5.2)

   o  0x01: 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 DODAG Information Solicitation (Section 5.2.2)

   o  0x81: Secure DODAG Information Object (Section 5.3.2)

   o  0x82: Secure Destination Advertisement Object (Section 5.4.2)

   o  0x83: Secure Destination Advertisement Object Acknowledgment
      (Section 5.5.2)

   The high order bit (0x80) of the position code denotes whether the RPL message
   has security enabled.  Secure versions of N. Node M
           may safely be RPL messages have a DODAG parent for Node N without risk
   modified format to support confidentiality and integrity, illustrated
   in Figure 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
           creating a loop.  Further, for 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 a node N, all parents secure version.  The secure versions provide
   integrity and confidentiality.  Because security covers the base
   message as well as options, in secured messages the
           DODAG parent set must be security
   information lies between the checksum and base, as shown in Figure
   Figure 6.

   The format of rank less than DAGRank(N).  In
           other words, the rank presented by 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0|0|C|KIM| LVL |                                               |
       +-+-+-+-+-+-+-+-+                                               +
       |                            Counter                            |
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                        Key Identifier                         .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Security

   All fields are considered as packet payload from a node N MUST be greater
           than that presented by any security
   processing perspective.  The exact placement and format of its parents.

   DAGRank(M) equals DAGRank(N):  In this case the positions message
   integrity/authentication codes has not yet been determined.

   Use of M and N
           within the DODAG Security section is further detailed in Section 14.

   Security Control Field:  The Security Control Field has one flag and with respect to
         two fields:

         Counter Compression (C):  If the DODAG root are
           similar (identical).  In some cases, Node M may be used as a
           successor by Node N, which however entails Counter Compression flag is
               set then the chance of
           creating a loop (which must be detected Counter field is compressed from 4 bytes
               into 1 byte.  If the Counter Compression flag is clear
               then the Counter field is 4 bytes and resolved by some
           other means).

   DAGRank(M) uncompressed.

         Key Identifier Mode (KIM):  The Key Identifier Mode field
               indicates whether the key used for packet protection is greater than DAGRank(N):  In this case,
               determined implicitly or explicitly and indicates the position
               particular representation of
           M the Key Identifier field.
               The Key Identifier Mode is farther from set one of the DODAG root than non-reserved
               values from the position table below:

               +------+-----+-----------------------------+------------+
               | Mode | KIM |           Meaning           |    Key     |
               |      |     |                             | Identifier |
               |      |     |                             |   Length   |
               |      |     |                             |  (octets)  |
               +------+-----+-----------------------------+------------+
               |  0   | 00  | Peer-to-peer key determined |     0      |
               |      |     | implicitly from originator  |            |
               |      |     | and recipient of N.
           Further, Node M packet.    |            |
               |      |     |                             |            |
               |      |     | Key Source is not present.  |            |
               |      |     | Key Index is not present.   |            |
               +------+-----+-----------------------------+------------+
               |  1   | 01  | Group key determined        |     1      |
               |      |     | implicitly from Key Index   |            |
               |      |     | and side information.       |            |
               |      |     |                             |            |
               |      |     | Key Source is not present.  |            |
               |      |     | Key Index is present.       |            |
               +------+-----+-----------------------------+------------+
               |  2   | 10  | Signature key used; group   |    0/9     |
               |      |     | key determined explicitly   |            |
               |      |     | if encryption used.         |            |
               |      |     |                             |            |
               |      |     | Key Source may in fact be in the sub-DODAG of Node N. If
           node N selects node M as DODAG parent there present.  |            |
               |      |     | Key Index may be present.   |            |
               +------+-----+-----------------------------+------------+
               |  3   | 11  | Group key determined        |     9      |
               |      |     | explicitly from Key Source  |            |
               |      |     | Identifier and Key Index.   |            |
               |      |     |                             |            |
               |      |     | Key Source is a risk to
           create a loop.

   As an example, present.      |            |
               |      |     | Key Index is present.       |            |
               +------+-----+-----------------------------+------------+

                          Key Identifier Mode (KIM) Encoding

         Security Level (LVL):  The Security Level field indicates the rank could
               provided packet protection.  This value can be computed in such adapted on
               a way so as to
   closely track ETX when the objective function per-packet basis and allows for varying levels of data
               authenticity and, optionally, for data confidentiality.
               When nontrivial protection is to minimize ETX, or
   latency when the objective function provided, replay protection
               is always provided.  The Security Level is set to minimize latency, or one of
               the non-reserved values in a
   more complicated way as appropriate to the objective function being table below:

                          +--------------------+-------------------+
                          | Without Signatures |  With Signatures  |
               +----+-----+-------------+------+-------------+-----+
               | ID | LVL | Attributes  | Auth | Attributes  | Sig |
               |    |     |             | Len  |             | Len |
               +----+-----+-------------+------+-------------+-----+
               |  0 | 000 |    None     |  0   |     None    | 37  |
               |  1 | 001 |   MIC-32    |  4   |   Sign-32   | 37  |
               |  2 | 010 |   MIC-64    |  8   |   Sign-64   | 45  |
               |  3 | 011 |    Rsvd     | N/A  |      Rsvd   | N/A |
               |  4 | 100 |     ENC     |  0   |     ENC     | 37  |
               |  5 | 101 | ENC-MIC-32  |  4   | ENC-Sign-32 | 41  |
               |  6 | 110 | ENC-MIC-64  |  8   | ENC-Sign-64 | 45  |
               |  7 | 111 |    Rsvd     | N/A  |   Reserved  | N/A |
               +----+-----+-------------+------+-------------+-----+

                           Security Level (LVL) Encoding

   Counter:  The Counter field indicates the non-repeating value (nonce)
         used within with the DODAG.

4.  ICMPv6 RPL Control Message cryptographic mechanism that implements packet
         protection and allows for the provision of semantic security.
         This document defines value is compressed from 4 octets to 1 octet if the RPL
         Counter Compression field of the Security Control Message, a new ICMPv6 message.

   In accordance with [RFC4443], Field is set
         to one.

   Key Identifier:  The Key Identifier field indicates which key was
         used to protect the RPL Control Message has 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
   following format: 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |     Code      |          Checksum                                                               |
       .                          Key Source                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                         Message Body                          +
       .                           Key Index                           .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Key Identifier

         Key Source:  The Key Source field, when present, indicates the
               logical identifier of the originator of a group key.
               When present this field is 8 bytes in length.

         Key Index:  The Key Index field, when present, allows unique
               identification of different keys with the same
               originator.  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 to 0x00.  When present this field is
               1 byte in length.

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

5.2.  DODAG Information Solicitation (DIS)

   The DODAG Information Solicitation (DIS) message may be used to
   solicit a DODAG Information Object from a RPL node.  Its use is
   analogous to that of a Router Solicitation as specified in IPv6
   Neighbor Discovery; a node may use DIS to probe its neighborhood for
   nearby DODAGs.  Section 6.3 describes how nodes respond to a DIS.

5.2.1.  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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Reserved            |   Option(s)...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 3: RPL Control Message 7: The RPL Control 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 message follows the format in Figure Figure 6, where the
   base format is an ICMPv6 information the DIS message with a
   requested Type of 155. shown in Figure Figure 7.

5.2.3.  DIS Options

   The Code field identifies the type of RPL Control Message. DIS message MAY carry valid options.

   This
   document defines three codes specification allows for the following RPL Control Message
   types:

   o  0x01: DODAG Information Solicitation (Section 5.2)

   o  0x02: DODAG Information Object (Section 5.1)

   o  0x04: Destination Advertisement Object (Section 6.1)

5.  Upward Routes

   This section describes how RPL discovers and maintains upward routes.
   It describes DODAG Information Objects (DIOs), the messages used DIS message to
   discover and maintain these routes.  It specifies how carry the following
   options:
      0x00 Pad1
      0x01 PadN
      0x05 RPL generates
   and responds to DIOs.  It also describes DODAG Target
      0x07 Solicited Information
   Solicitation (DIS) messages, which are used to trigger DIO
   transmissions.

5.1.

5.3.  DODAG Information Object (DIO)

   The DODAG Information Object carries information that allows a node
   to discover a RPL Instance, learn its configuration parameters,
   select a DODAG parent set, and maintain the upward routing topology.

5.1.1.  DIO Base

5.3.1.  Format of the DIO Base is an always-present container option in a DIO message.
   Every DIO MUST include a 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |G|A|T|S|0| Prf
       |   Sequence RPLInstanceID |    Version    |             Rank              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | RPLInstanceID
       |G|A|T|MOP| Prf |     DTSN      |           Reserved            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                            DODAGID                                                               |
       +                            DODAGID                            +
       |                                                               |
       +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                                                               +
       |                                                               |   sub-option(s)...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Option(s)...
       +-+-+-+-+-+-+-+-+

                       Figure 4: 8: The DIO Base Object

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

         Grounded (G):  The Grounded (G) flag indicates whether the
               upward routes this node advertises provide connectivity
               to the set of addresses which are application-defined
               goals.  If the flag is set, the DODAG is grounded and
               provides such connectivity.  If the flag is cleared, the
               DODAG is floating and may not provide such connectivity.

         Destination Advertisement Supported (A):  The Destination
               Advertisement Supported (A) flag indicates whether the
               root of this DODAG can collect and use downward route
               state.  If the flag is set, nodes in the network are
               enabled to exchange destination advertisements messages
               to build downward routes (Section 6). 7).  If the flag is
               cleared, destination advertisement messages are disabled
               and the DODAG maintains only upward routes.

         Destination Advertisement Trigger (T):  The Destination
               Advertisement Trigger (T) flag indicates a complete
               refresh of downward routes.  If the flag is set, then a
               refresh of downward route state is to take place over the
               entire DODAG.  If the flag is cleared, the downward route
               maintenance is in its normal mode of operation.  The
               further details of this process are described in
               Section 6.

         Destination Advertisements Stored (S): 7.

         Mode of Operation (MOP):  The Destination
               Advertisements Stored (S) flag is used to indicate that a
               non-root ancestor is storing routing table entries
               learned from DAO messaging.  If Mode of Operation (MOP) field
               identifies the flag is set, then a
               non-root ancestor is known to be storing routing table
               entries learned from DAO messages.  If mode of operation of the flag is
               cleared, only RPL Instance as
               administratively provisioned at and distributed by the
               DODAG Root.  All nodes who join the root node may DODAG must be storing routing table
               entries learned from DAO messaging.  This flag able to
               honor the MOP in order to fully participate as a router,
               or else they must only join as a leaf.  MOP is further
               described encoded as
               in Section 6. the table below:

               +-----+-------------------------------------------------+
               | MOP | Meaning                                         |
               +-----+-------------------------------------------------+
               |  00 | Non-storing                                     |
               |  01 | Storing                                         |
               |  10 | Reserved for future specification of mixed-mode |
               |  11 | Reserved                                        |
               +-----+-------------------------------------------------+

                           Mode of Operation (MOP) Encoding

         DODAGPreference (Prf):  A 3-bit unsigned integer that defines
               how preferable the root of this DODAG is compared to
               other DODAG roots within the instance.  DAGPreference
               ranges from 0x00 (least preferred) to 0x07 (most
               preferred).  The default is 0 (least preferred).
               Section 5.3 6.2 describes how DAGPreference affects DIO
               processing.

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

   Sequence

   Version Number:  8-bit unsigned integer set by the DODAG root.
         Section 5.3 6.2 describes the rules for sequence 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 5.3 6.2 describes how Rank is set
         and how it affects DIO processing.

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

   Destination Advertisement Trigger Sequence Number (DTSN):  8-bit
         unsigned integer set by the node issuing the DIO message.  The
         Destination Advertisement Trigger Sequence Number (DTSN) flag
         is used as part of the procedure to maintain downward routes.
         The details of this process are described in Section 6.

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

5.1.2.  DIO Base Rules

   1.  If the 'A' flag of a DIO Base is cleared, the 'T' flag MUST also
       be cleared.

   2.  For the following DIO Base fields, a node that is not a DODAG
       root MUST advertise the same values as its preferred DODAG parent
       (defined in Section 5.3.2).  Therefore, if a DODAG root does not
       change these values, every node in a route to that DODAG root
       eventually advertises the same values for these fields.  These
       fields are:
       1.  Grounded (G)
       2.  Destination Advertisement Supported (A)
       3.  Destination Advertisement Trigger (T)
       4.  DAGPreference (Prf)
       5.  Sequence
       6.  RPLInstanceID
       7.  DODAGID

   3.  A node MAY update issuing the following fields at each hop:
       1. DIO message.  The
         Destination Advertisements Stored (S)
       2.  DAGRank
       3.  DTSN

   4. Advertisement Trigger Sequence Number (DTSN) flag
         is used as part of the procedure to maintain downward routes.
         The DODAGID field each details of this process are described in Section 7.

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

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

5.3.2.  Secure DIO

   A Secure DIO message follows the RPL
       Instance.

5.1.3. format in Figure Figure 6, where the
   base format is the DIS message shown in Figure Figure 8.

5.3.3.  DIO Options

   The DIO Suboptions message MAY carry valid options.

   This section describes specification allows for the format of DIO suboptions and message to carry the five
   suboptions this document defines: Pad 1, Pad N, DAG following
   options:
      0x00 Pad1
      0x01 PadN
      0x02 Metric Container,
   DAG Container
      0x03 Routing Information
      0x04 DODAG Configuration
      0x09 Prefix Information

5.4.  Destination Prefix, and DAG Configuration.

5.1.3.1.  DIO Suboption Format Advertisement Object (DAO)

   The Pad N, DAG Metric Container, DAG Destination Prefix, and DAG
   Configuration suboptions all follow this format: Advertisement Object (DAO) is used to propagate
   destination information upwards along the DODAG.  The DAO message is
   unicast by the child to the selected parent(s).  The DAO message may
   optionally, upon explicit request or error, be acknowledged by the
   parent with a Destination Advertisement Acknowledgement (DAO-ACK)
   message back to the child.

5.4.1.  Format of the 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 |K|D|         Reserved          | DAOSequence   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            DODAGID*                           +
       |  Subopt. Type                                                               |       Suboption Length
       +                                                               +
       | Suboption Data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Option(s)...
       +-+-+-+-+-+-+-+-+

                       Figure 5: DIO Suboption Generic Format

   Suboption Type: 9: The DAO Base Object

   RPLInstanceID:  8-bit identifier of the type of suboption.

   Suboption Length:  16-bit unsigned integer, representing field indicating the length
         in octets of topology instance
         associated with the suboption, not including DODAG, as learned from the suboption Type
         and Length fields.

   Suboption Data:  A variable length field DIO.

   K:    The 'K' flag indicates that contains data specific
         to the option. parent is expected to send a
         DAO-ACK back.

   D:    The following subsections specify the DIO message suboptions which
   are currently defined for use in 'D' flag indicates that the DODAG Information Object.

   When processing a DIO message containing DODAGID field is present.  This
         would typically only be set when a suboption for which the
   Suboption Type value local RPLInstanceID is not recognized by the receiver, the receiver
   MUST silently ignore the unrecognized option and continue to process
   the following suboption, correctly handling any remaining options used.

   DAOSequence:  Incremented at each unique DAO message, echoed in the
         DAO-ACK message.

   DIO message suboptions may have alignment requirements.  Following

   DODAGID*:  128-bit unsigned integer set by a DODAG root which
         uniquely identifies a DODAG.  This field is only present when
         the convention 'D' flag is set.  This field is typically only present when
         a local RPLInstanceID is in IPv6, options with alignment requirements are
   aligned use, in a packet such order to identify the
         DODAGID that multi-octet values within is associated with the Option
   Data RPLInstanceID.  When a
         global RPLInstanceID is in use this field of each option fall on natural boundaries (i.e., fields of
   width n octets are placed at an integer multiple of n octets from the
   start need not be present.

   Unassigned bits of the header, for n = 1, 2, 4, or 8).

5.1.3.2.  Pad1

   The Pad1 suboption DAO Base are reserved.  They MUST be set to
   zero on transmission and MUST be ignored on reception.

5.4.2.  Secure DAO

   A Secure DAO message follows the format is as follows:

        0
        0 1 2 3 4 5 6 7
       +-+-+-+-+-+-+-+-+
       |   Type = 0    |
       +-+-+-+-+-+-+-+-+ in Figure 6: Pad 1

   NOTE! Figure 6, where the
   base format of the Pad1 option is a special case - it has
   neither Option Length nor Option Data fields.

   The Pad1 option is used to insert one or two octets of padding the DAO message shown in Figure Figure 9.

5.4.3.  DAO Options

   The DAO message MAY carry valid options.

   This specification allows for the
   DIO DAO message to enable suboptions alignment.  If more than two octets
   of padding is required, carry the PadN option, described next, should be
   used rather than multiple following
   options:
      0x00 Pad1 options.

5.1.3.3.  PadN

   The PadN suboption format 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    |       Suboption Length        | Suboption Data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -

                              Figure 7: Pad N

   The
      0x01 PadN suboption
      0x05 RPL Target
      0x06 Transit Information

   A special case of the DAO message, termed a No-Path, is used to insert three or more octets of padding
   in clear
   downward routing state that has been provisioned through DAO
   operation.  The No-Path carries a RPL Transit Information option,
   which identifies the DIO message destination to enable suboptions alignment.  For N (N > 2)
   octets of padding, the Suboption Length field contains the value N-3,
   and which the Option Data consists DAO is associated, with
   a lifetime of N-3 zero-valued octets.  PadN Option
   data MUST be ignored by the receiver.

5.1.3.4.  Metric Container 0x00000000 to indicate a loss of reachability.

5.5.  Destination Advertisement Object Acknowledgement (DAO-ACK)

   The Metric Container suboption format DAO-ACK message is sent as follows: a unicast packet by a DAO parent in
   response to a unicast DAO message from a child.

5.5.1.  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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Type = 2 RPLInstanceID |       Suboption Length    Reserved   | Metric Data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - DAOSequence   |   Status      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Option(s)...
       +-+-+-+-+-+-+-+-+
                    Figure 8: Metric Container 10: The Metric Container is used to report metrics along DAO ACK Base Object

   RPLInstanceID:  8-bit field indicating the DODAG.  The
   Metric Container may contain a number of discrete node, link, and
   aggregate path metrics topology instance
         associated with the DODAG, as chosen learned from the DIO.

   DAOSequence:  Incremented at each DAO message from a given child,
         echoed in the DAO-ACK by the implementer. parent.  The Suboption
   Length field contains the length DAOSequence serves in octets of
         the Metric Data.  The
   order, content, parent-child communication and coding of is not to be confused with
         the Metric Container data Transit Information option Sequence that is as
   specified in [I-D.ietf-roll-routing-metrics].

   The processing and propagation associated to a
         given target down the DODAG.

   Status:  Indicates the completion. 0 is unqualified acceptance, above
         128 are rejection code indicating that the node should select
         an alternate parent.

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

5.5.2.  Secure DAO-ACK

   A Secure DAO-ACK message follows the format in Figure Figure 6, where
   the base format is governed the DAO-ACK message shown in Figure Figure 10.

5.5.3.  DAO-ACK Options

   This specification does not define any options to be carried by
   implementation specific policy functions.

5.1.3.5.  Destination Prefix

   The Destination Prefix suboption format is as follows: the
   DAO-ACK message.

5.6.  RPL Control Message Options

5.6.1.  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    |      Suboption Length         |Resvd|Prf|Resvd|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Prefix Lifetime  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Prefix Option Length |                                               |
       +-+-+-+-+-+-+-+-+                                               |
       |             Destination Prefix (Variable Length)              |
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option Data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -

                   Figure 9: DAG Destination Prefix

   The Destination Prefix suboption is used to indicate that
   connectivity to the specified destination prefix is available from
   the DODAG root, or from another node located upwards along the DODAG
   on the path to the DODAG root.  This may be useful in cases where
   more than one LBR is operating within the LLN and offering
   connectivity to different administrative domains, e.g. a home network
   and a utility network.  In such cases, upon observing the Destination
   Prefixes offered by a particular DODAG, a node MAY decide to join
   multiple DODAGs in support 11: RPL Option Generic Format

   Option Type:  8-bit identifier of a particular application.

   The Suboption Length is coded as the length type of the suboption in
   octets, excluding the Type and Length fields.

   Prf is the Route Preference as in [RFC4191]. option.  The reserved fields
   MUST be set Option
         Type values are to zero on transmission and MUST be ignored on receipt.

   The Prefix Lifetime is a 32-bit confirmed by the IANA Section 15.4.

   Option Length:  8-bit unsigned integer integer, representing the length of time in seconds (relative to
         octets of the time option, not including the packet is sent) Option Type and Length
         fields.

   Option Data:  A variable length field that contains data specific to
         the Destination Prefix is valid option.

   When processing a RPL message containing an option for route determination.  The
   lifetime which the
   Option Type value is initially set not recognized by the node that owns receiver, the prefix and
   denotes receiver
   MUST silently ignore the valid lifetime for that prefix (similar unrecognized option and continue to
   AdvValidLifetime [RFC4861]).  The value might be reduced by process
   the
   originator and/or en-route nodes following option, correctly handling any remaining options in the
   message.

   RPL message options may have alignment requirements.  Following the
   convention in IPv6, options with alignment requirements are aligned
   in a packet such that will not provide connectivity
   for multi-octet values within the whole valid lifetime.  A value of all one bits (0xFFFFFFFF)
   represents infinity.  A value Option Data field
   of all zero bits (0x00000000) indicates
   a loss each option fall on natural boundaries (i.e., fields of reachability.

   The Prefix Length is width n
   octets are placed at an 8-bit unsigned integer that indicates the
   number multiple of leading bits in n octets from the destination prefix.

   The Destination Prefix contains Prefix Length significant bits start
   of the
   destination prefix. header, for n = 1, 2, 4, or 8).

5.6.2.  Pad1

   The remaining bits of the Destination Prefix, Pad1 option may be present in DIS, DIO, DAO, and DAO-ACK
   messages, and its format is as
   required to complete follows:

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

                   Figure 12: Format of the trailing octet, are set Pad 1 Option

   The Pad1 option is used to 0.

   In insert one or two octets of padding into
   the event that a DIO message may need to specify connectivity to enable options alignment.  If more than one destination, octet of
   padding is required, the Destination Prefix suboption may PadN option should be
   repeated.

5.1.3.6.  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.

5.6.3.  PadN

   The DODAG Configuration suboption PadN option may be present in 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 | DIOIntDoubl.  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  DIOIntMin.   |   DIORedun.   |  MaxRankInc   | MinHopRankInc |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 10: DODAG Configuration

   The DODAG Configuration suboption is used to distribute configuration
   information for DODAG Operation through the DODAG.  The information
   communicated in this suboption is generally static and unchanging
   within the DODAG, therefore it is not necessary to include in every
   DIO.  This suboption MAY be included occasionally by the DODAG Root,
   and MUST be included in response to a unicast request, e.g. a unicast
   DODAG Information Solicitation (DIS) message.

   The Length is coded as 5.

   DIOIntervalDoublings is an 8-bit unsigned integer, configured on the
   DODAG root and used to configure the trickle timer (see
   Section 5.3.5.1 for details on trickle timers) governing when DIO
   message should be sent within the DODAG.  DIOIntervalDoublings is the
   number of times that the DIOIntervalMin is allowed to be doubled
   during the trickle timer operation.

   DIOIntervalMin is an 8-bit unsigned integer, configured on the DODAG
   root and used to configure the trickle timer governing when DIO
   message should be sent within 0x00 Padding...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -

                   Figure 13: Format of the DODAG. Pad N Option

   The minimum configured
   interval for the DIO trickle timer in units of ms is
   2^DIOIntervalMin.  For example, a DIOIntervalMin value of 16ms is
   expressed as 4.

   DIORedundancyConstant PadN option is an 8-bit unsigned integer used to configure
   suppression insert two or more octets of DIO transmissions.  DIORedundancyConstant is padding into
   the
   minimum number of relevant incoming DIOs required message to suppress a DIO
   transmission.  If the value is 0xFF then enable options alignment.  PadN Option data MUST be
   ignored by the suppression mechanism is
   disabled.

   MaxRankInc, 8-bit unsigned integer, is receiver.

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

   Option Length:  For N (N > 1) octets of padding, the DAGMaxRankIncrease.  This
   is Option Length
         field contains the allowable increase in rank in support value N-2.

   Option Data:  For N (N > 1) octets of local repair.  If
   DAGMaxRankIncrease is 0 then this mechanism is disabled.

   MinHopRankInc, 8-bit unsigned integer, is padding, the MinHopRankIncrease as
   described in Section 3.6.2.1.

5.2.  DODAG Information Solicitation (DIS) Option Data
         consists of N-2 zero-valued octets.

5.6.4.  Metric Container

   The DODAG Information Solicitation (DIS) message Metric Container option may be used to
   solicit a DODAG Information Object from a RPL node.  Its use is
   analogous to that of a Router Solicitation; a node may use DIS to
   probe its neighborhood for nearby DODAGs.  The DODAG Information
   Solicitation carries no additional message body.  Section 5.3.5
   describes how nodes respond to a DIS.

5.3.  Upward Route Discovery present in DIO messages, and Maintenance

   Upward route discovery allows a node to join a DODAG by discovering
   neighbors that are members its
   format 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 = 2    | Option Length | Metric Data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -

             Figure 14: Format of the DODAG and identifying a set of
   parents. Metric Container Option

   The exact policies for selecting neighbors and parents Metric Container is
   implementation-dependent.  This section specifies the set of rules
   those policies must follow for interoperability.

5.3.1.  RPL Instance

      A RPLInstanceID MUST be unique across an LLN.

      A node MAY belong used to multiple RPL Instances.

   Within a given LLN, there report metrics along the DODAG.  The
   Metric Container may be multiple, logically independent RPL
   instances.  This document describes how contain a single instance behaves.

5.3.2.  Neighbors number of discrete node, link, and Parents within a DODAG Iteration

   RPL's upward route discovery algorithms
   aggregate path metrics and processing are constraints specified in terms
   of three logical sets of link-local nodes.  First,
   [I-D.ietf-roll-routing-metrics] as chosen by the candidate
   neighbor set is a subset implementer.

   The processing and propagation of the nodes that can Metric Container is governed by
   implementation specific policy functions.

   Option Type:  0x02 (to be reached via link-
   local multicast. confirmed by IANA)

   Option Length:  The selection of this set is implementation-
   dependent and OF-dependent.  Second, Option Length field contains the parent set is a restricted
   subset length in octets
         of the candidate neighbor set.  Finally, the preferred parent,
   a set of size one, is an element Metric Data.

   Metric Data:  The order, content, and coding of the parent set that Metric Container
         data is as specified in [I-D.ietf-roll-routing-metrics].

5.6.5.  Route Information

   The Route Information option may be present in DIO messages, and is
   equivalent in function to the
   preferred next hop IPv6 ND Route Information option as
   defined in upward routes.

   More precisely:

   1. [RFC4191].  The DODAG parent set MUST be a subset format of the candidate neighbor
       set.

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

   3.  A node that option is not a DODAG root MAY maintain a DODAG parent set
       of size greater than or equal modified slightly
   (Type, Length) in order to one.

   4.  A node's 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 a neighbor is no longer reachable, carried as a RPL node MUST NOT consider this node in 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 = 3    | Option Length | Prefix Length |Resvd|Prf|Resvd|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Route Lifetime                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                   Prefix (Variable Length)                    .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 15: Format of the candidate neighbor
       set when calculating and advertising routes until it determines
       that it Route Information Option

   The Route Information option is again reachable.  Routes through an unreachable
       neighbor MUST be eliminated from the routing table.

   These rules ensure used to indicate that there is a consistent partial order on nodes
   within connectivity to
   the specified destination prefix is available from the DODAG.  As long as node ranks do not change, following DODAG root.

   In the
   above rules ensures event that every node's route to a DODAG root is loop-
   free, RPL Control Message may need to specify
   connectivity to more than one destination, the Route Information
   option may be repeated.

   [RFC4191] should be consulted as rank decreases on each hop the authoritative reference with
   respect to the root. Route Information option.  The OF can guide
   candidate neighbor set and parent set selection, as discussed field descriptions are
   transcribed here for convenience:

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

   Option Length:  Variable, length of the option in
   [I-D.ietf-roll-routing-metrics].

5.3.3.  Neighbors octets excluding
         the Type and Parents across DODAG Iterations

   The above rules govern a single DODAG iteration.  The rules in Length fields.  Note that this
   section define how RPL operates when there are multiple DODAG
   iterations:

5.3.3.1.  DODAG Iteration

   1. length is expressed
         in units of single-octets, unlike in IPv6 ND.

   Prefix Length  8-bit unsigned integer.  The tuple (RPLInstanceID, DODAGID, DODAGSequenceNumber) uniquely
       defines a DODAG Iteration.  Every element number of a node's DODAG
       parent set, as conveyed by leading bits in
         the last heard DIO Prefix that are valid.  The value ranges from each DODAG
       parent, MUST belong to the same DODAG iteration.  Elements of a
       node's candidate neighbor set MAY belong 0 to different DODAG
       Iterations.

   2.  A node 128.
         The Prefix field is a member of a DODAG iteration if every element of its
       DODAG parent set belongs to that DODAG iteration, 0, 8, or if that node
       is 16 octets depending on Length.

   Prf:  2-bit signed integer.  The Route Preference indicates whether
         to prefer the root of router associated with this prefix over others,
         when multiple identical prefixes (for different routers) have
         been received.  If the Reserved (10) value is received, the corresponding DODAG.

   3.  A node
         Route Information Option MUST NOT send DIOs for DODAG iterations of which it is not
       a member.

   4.  DODAG roots MAY increment be ignored.

   Resvd:  Two 3-bit unused fields.  They MUST be initialized to zero by
         the DODAGSequenceNumber that they
       advertise sender and thus move to a new DODAG iteration.  When a DODAG
       root increments its DODAGSequenceNumber, it MUST follow be ignored by the
       conventions receiver.

   Route Lifetime  32-bit unsigned integer.  The length of Serial Number Arithmetic as described time in
       [RFC1982].

   5.  Within a given DODAG, a node
         seconds (relative to the time the packet is sent) that the
         prefix is valid for route determination.  A value of all one
         bits (0xffffffff) represents infinity.

   Prefix  Variable-length field containing an IP address or a not a root MUST NOT
       advertise a DODAGSequenceNumber higher than prefix of
         an IP address.  The Prefix Length field contains the highest
       DODAGSequenceNumber it has heard.  Higher is defined as number of
         valid leading bits in the
       greater-than operator prefix.  The bits in [RFC1982].

   6.  Once a node has advertised a DODAG iteration by sending a DIO, it the prefix after
         the prefix length (if any) are reserved and MUST NOT be member initialized
         to zero by the sender and ignored by the receiver.

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

5.6.6.  DODAG iteration Configuration

   The DODAG Configuration option may be present in 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 = 4    | Option Length |  Resvd  | PCS | DIOIntDoubl.  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  DIOIntMin.   |   DIORedun.   |        MaxRankIncrease        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      MinHopRankIncrease       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 16: Format of the same DODAG (i.e. with the same RPLInstanceID, the same DODAGID, and a
       lower DODAGSequenceNumber).  Lower is defined as the less-than
       operator in [RFC1982].

   Within a particular implementation, a Configuration Option

   The DODAG root may increment the
   DODAGSequenceNumber periodically, at a rate that depends on the
   deployment.  In other implementations, loop detection may be
   considered sufficient Configuration option is used to solve routing issues, and the distribute configuration
   information for DODAG root may
   increment Operation through the DODAGSequenceNumber only upon administrative
   intervention.  Another possibility DODAG.

   The information communicated in this option is that nodes generally static and
   unchanging within the LLN have
   some means by which they can signal detected routing inconsistencies
   or suboptimalities DODAG, therefore it is not necessary to the DODAG root, include
   in order to request an on-
   demand DODAGSequenceNumber increment (i.e. request a global repair of
   the DODAG).

   When the DODAG parent set becomes empty on a node that every DIO.  This information is not a root,
   (i.e. configured at the last parent has been removed, causing DODAG Root and
   distributed throughout the node to no longer
   be associated DODAG with that DODAG), then the DODAG information should not
   be suppressed until after the expiration of an implementation-
   specific local timer in order to observe if the DODAGSequenceNumber
   has been incremented, should any new parents appear for Configuration Option.

   Nodes other than the DODAG.

   As DODAG Root MUST NOT modify this information when
   propagating the DODAG Configuration option.  This option MAY be
   included occasionally by the DODAGSequenceNumber is incremented, a new DODAG Iteration
   spreads outward from Root (as determined by the DODAG root.  Thus
   Root), and MUST be included in response to a parent that advertises
   the new DODAGSequenceNumber can not possibly belong unicast request, e.g. a
   unicast DODAG Information Solicitation (DIS) message.

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

   Option Length:  8 bytes

   Path Control Size (PCS):  3-bit unsigned integer used to configure
         the sub-DODAG number of a node bits that still advertises an older DODAGSequenceNumber.  A node may safely add such a parent, without risk be allocated to the Path Control
         field (see Section 7.1.4.2).

   DIOIntervalDoublings:  8-bit unsigned integer used to configure Imax
         of forming a loop, without
   regard the DIO trickle timer (see Section 6.3.1).

   DIOIntervalMin:  8-bit unsigned integer used to its relative rank in configure Imin of the prior DODAG Iteration.  This is
   equivalent
         DIO trickle timer (see Section 6.3.1).

   DIORedundancyConstant:  8-bit unsigned integer used to jumping configure k of
         the DIO trickle timer (see Section 6.3.1).

   MaxRankIncrease:  16-bit unsigned integer used to a different DODAG.

   As a node transitions configure
         DAGMaxRankIncrease, the allowable increase in rank in support
         of local repair.  If DAGMaxRankIncrease is 0 then this
         mechanism is disabled.

   MinHopRankInc  16-bit unsigned integer used to new DODAG Iterations configure
         MinHopRankIncrease as a consequence described in Section 3.5.2.1.

5.6.7.  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 = 5    | Option Length |   Reserved    | Prefix Length |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                Target Prefix (Variable Length)                |
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 17: Format of
   following these rules, the node will be unable to advertise the
   previous DODAG Iteration (prior DODAGSequenceNumber) once it has
   committed to advertising the new DODAG Iteration.

   During transition RPL Target Option

   The RPL Target Option is used to indicate a new DODAG Iteration, a node may decide to
   forward packets via 'future parents' target IPv6 address,
   prefix, or multicast group that belong to is reachable or queried along the same DODAG
   (same RPLInstanceID and DODAGID), but are observed
   DODAG.  It is used in DIO to advertise identify a
   more recent (incremented) DODAGSequenceNumber.

5.3.3.2.  DODAG Roots

   1.  A DODAG root resource that does not have connectivity to the set of
       addresses described as application-level goals, MUST NOT set the
       Grounded bit.

   2.  A DODAG root MUST advertise is
   trying to reach, and in a rank of ROOT_RANK.

   3. DAO to indicate reachability.  It is used
   in a DAO message to indicate reachability.  A node whose DODAG parent set is empty of one or more
   Transit Information options MAY become directly follow the DODAG root
       of Target option in
   a floating DODAG.  It MAY also set its DAGPreference such that
       it is less preferred.

   An LLN node that is DAO message in support of constructing source routes in a goal for the Objective Function is non-
   storing mode of operation [I-D.hui-6man-rpl-routing-header].  When
   the root same set of
   its own grounded DODAG, at rank ROOT_RANK.

   In a deployment that uses a backbone link Transit Information options apply equally to federate a number set of LLN
   roots, it is possible
   DODAG Target options, the group of Target options MUST appear first,
   followed by the Transit Information options which apply to run those
   Targets.

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

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

   Option Length:  Variable, length of the option in octets excluding
         the Type and use one
   router as a "backbone root". 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 backbone root is Prefix Length field
         contains the virtual root number of valid leading bits in the DODAG, and exposes a rank of BASE_RANK over prefix.  The
         bits in the backbone.  All prefix after the LLN roots that prefix length (if any) are parented to that backbone root, including the
   backbone root if it also serves as LLN root itself, expose a rank of
   ROOT_RANK
         reserved and MUST be set to the LLN, zero on transmission and are part of the same DODAG, coordinating
   DODAGSequenceNumber MUST be
         ignored on receipt.

5.6.8.  Transit Information

   The Transit Information option may be present in DAO messages, and other DODAG root determined parameters with
   the virtual root over
   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 | Path Sequence | Path Control  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Path Lifetime                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                        Parent Address*                        +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 18: Format of the backbone.

5.3.3.3.  DODAG Selection Transit Information option

   The DODAGPreference (Prf) provides an administrative mechanism Transit Information option is used for a node to
   engineer the self-organization of 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 LLN, Transit Information option(s).

   The Transit Information option can used for example indicating the
   most preferred LBR.  If a node has the option to join a more
   preferred indicate its
   DODAG while still meeting other optimization objectives,
   then parents to an ancestor that is collecting DODAG routing
   information, typically for the node purpose of constructing source routes.
   In the non-storing mode of operation this ancestor will generally seek to join be the more preferred DODAG as
   determined
   Root, and this option is carried by the OF.  All else being equal, it DAO message.  The option
   length is left to the
   implementation used to determine which DODAG is most preferred, possibly
   based on additional criteria beyond Prf and whether the OF.

5.3.3.4.  Rank and Movement within a DODAG Iteration
   1. Parent Address is present or
   not.

   A non-storing node MUST NOT advertise a rank less that has more than or equal to any member
       of its one DAO parent set within the DODAG Iteration.

   2.  A node MAY advertise include a rank lower than its prior advertisement
       within the DODAG Iteration.

   3.  Let L be
   Transit Information option for each DAO parent as part of the lowest rank within a DODAG iteration that a given non-
   storing Destination Advertisement operation.  The node has advertised.  Within may code the same DODAG Iteration, that node
       MUST NOT advertise an effective rank higher than L +
       DAGMaxRankIncrease.  INFINITE_RANK is an exception to this rule:
       a node MAY advertise an INFINITE_RANK at any time.  (This
       corresponds
   Path Control field in order to signal a limited rank increase for preference among parents.

   One or more Transit Information options MUST be preceded by one or
   more RPL Target options.  In this manner the RPL Target option
   indicates the purpose of local
       repair within child node, and the Transit Information option(s)
   enumerate the DODAG Iteration.)

   4. parents.

   A typical non-storing node MAY, at any time, choose will use multiple Transit Information
   options, and it will send the DAO thus formed to join a different DODAG within
       a RPL Instance.  Such a join has no rank restrictions, unless
       that different DODAG is a DODAG Iteration of which only one parent that node has
       previously been a member, in which case
   will forward it to the rule of root.  A typical storing node with use one
   Transit Information option with no parent field, and will send the previous
       bullet (3) must
   DAO thus formed to multiple parents.

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

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

   Path-Sequence:  8-bit unsigned integer.  When a RPL Target option is
         issued by the node transmits a DIO
       indicating its new DODAG membership, it MUST forward packets
       along that owns the previous DODAG.

   5.  A Target Prefix (i.e. in a DAO
         message), that node MAY, at any sets the Path-Sequence and increments the
         Path-Sequence each time after hearing it issues a RPL Target option.

   Path Control:  8-bit bitfield.  The Path Control field limits the next
       DODAGSequenceNumber Iteration advertised from suitable DODAG
       parents, choose
         number of DAO-Parents to migrate which a DAO message advertising
         connectivity to a specific destination may be sent, as well as
         providing some indication of relative preference.  The limit
         provides some bound on overall DAO fan-out in the next DODAG Iteration within the
       DODAG.

   Conceptually, an implementation LLN.  The
         leftmost bit is maintaining associated with a DODAG parent set
   within path that contains a most-
         preferred link, and the DODAG Iteration.  Movement entails changes subsequent bits are ordered down to the
         rightmost bit which is least preferred.

   Path Lifetime:  32-bit unsigned integer.  The length of time in
         seconds (relative to the DODAG
   parent set.  Moving up does not present time the risk to create a loop but
   moving down might, so packet is sent) that operation the
         prefix is subject to additional
   constraints.

   When valid for route determination.  A value of all one
         bits (0xFFFFFFFF) represents infinity.  A value of all zero
         bits (0x00000000) indicates a node migrates to loss of reachability.  This is
         referred as a No-Path in this document.

   Parent Address (optional):  IPv6 Address of the next DODAG Iteration, Parent of the
         node originally issuing the Transit Information Option.  This
         field may not be present, as according to the DODAG parent Mode of
         Operation and sibling sets need to be rebuilt for indicated by the new iteration.  An
   implementation could defer to migrate for some reasonable amount Transit Information option
         length.

   Unassigned bits 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 the Transit Information option are reserved.  They
   MUST be set to construct new DODAG parent/sibling sets zero on transmission and MUST be ignored on reception.

5.6.9.  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    | Option Length | RPLInstanceID |V|I|D|  Rsvd   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            DODAGID                            +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Version    |
       +-+-+-+-+-+-+-+-+

           Figure 19: Format of the Solicited Information Option

   The Solicited Information option is used for this new DODAG.

   When a node moves to improve its position, it must conceptually
   abandon all DODAG parents and siblings with a rank larger than
   itself.  As request a consequence
   subset of neighboring nodes that meet the movement it may also add new
   siblings.  Such specified criteria to
   respond to a movement DIS message.

   The Solicited Information option may occur at any time specify a number of predicate
   criteria to decrease the
   rank, as per the calculation indicated be matched by the OF.  Maintenance of the
   parent and sibling sets occurs as the rank of candidate neighbors is
   observed as reported in their DIOs. a receiving node.  If a node needs to move down receiving a DODAG that it is attached to, causing
   multicast DIS message containing a Solicited Information option
   matches ALL of the rank to increase, predicates, then it MAY poison MUST reset its routes and delay before
   moving as described in Section 5.3.3.5.

5.3.3.5.  Poisoning a Broken Path

   1.  A node MAY poison, trickle timer
   in order to avoid being used as an ancestor by trigger a DIO response to the nodes in its sub-DODAG, by advertising an effective rank of
       INFINITE_RANK DIS message.  When a node
   receives a DIS message containing a Solicited information option, and resetting
   the associated DIO DIS message is unicast OR the node does not match ALL the
   predicates, then the node MUST NOT reset the trickle timer to
       cause this INFINITE_RANK to timer.

   Option Type:  0x07 (to be announced promptly.

   2. confirmed by IANA)

   Option Length:  19 bytes

   Control Field:  The node MAY advertise an effective rank of INFINITE_RANK for an
       arbitrary number of DIO timer events, before announcing a new
       rank.

   3.  As per Section 5.3.3.4, Solicited Information option Control Field has
         three flags:

         V:    If the node MUST advertise INFINITE_RANK
       within V flag is set then the DODAG iteration in which it participates, Version field is valid and
               a node should only respond if its
       revision in rank would exceed DODAGVersionNumber
               matches the maximum rank increase.

   An implementation may choose requested version.  If the V flag is clear
               then the Version field is not valid and the Version field
               MUST be set to employ this poisoning mechanism when
   a node loses all of its current parents, i.e. zero on transmission and ignored upon
               receipt.

         I:    If the I flag is set of DODAG
   parents becomes depleted, then the RPLInstanceID field is
               valid and a node should only respond if it can not jump to an alternate DODAG.
   An alternate mechanism matches the
               requested RPLInstanceID.  If the I flag is to form a floating DODAG.

   The motivation for delaying announcement of clear then the revised route through
   multiple DIO events
               RPLInstanceID field is to (i) increase tolerance to DIO loss, (ii)
   allow time for not valid and the poisoning action RPLInstanceID
               field MUST be set to propagate, zero on transmission and (iii) to
   develop an accurate assessment of its new rank.  Such gains are
   obtained at ignored
               upon receipt.

         D:    If the expense of potentially increasing D flag is set then the delay before
   portions of DODAGID field is valid and
               a node should only respond if it matches the network are able requested
               DODAGID.  If the D flag is clear then the DODAGID field
               is not valid and the DODAGID field MUST be set to re-establish upwards routes.
   Path redundancy in zero on
               transmission and ignored upon receipt.

   Version:  8-bit unsigned integer containing the DODAG reduces Version number
         that is being solicited when valid.

   RPLInstanceID:  8-bit unsigned integer containing the significance RPLInstanceID
         that is being solicited when valid.

   DODAGID:  128-bit unsigned integer containing the DODAGID that is
         being solicited when valid.

   Unassigned bits of either
   effect, since children with alternate parents should the Solicited Information option are reserved.
   They MUST be able set to
   utilize those alternates zero on transmission and retain their rank while the detached
   parent re-establishes its rank.

   Although an implementation MUST be ignored on
   reception.

5.6.10.  Prefix Information

   The Prefix Information option may advertise INFINITE_RANK for the
   purposes of poisoning, it is not expected to be equivalent to setting
   the rank to INFINITE_RANK, present in DIO messages, and an implementation would likely retain
   its rank value prior is
   equivalent in function to the poisoning IPv6 ND Prefix Information option as
   defined in some form, for purpose of
   maintaining its effective position within (L + DAGMaxRankIncrease).

5.3.3.6.  Detaching

   1.  A node unable to stay connected to a DODAG within a given DODAG
       iteration MAY detach from this DODAG iteration.  A node that
       detaches becomes root [RFC4861].  The format of its own floating DODAG and SHOULD
       immediately advertise this new situation the option is modified slightly
   (Type, Length) in a DIO as an alternate order to poisoning.

5.3.3.7.  Following a Parent

   1.  If a node receives be carried as a DIO from one 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    | Option Length | Prefix Length |L|A| Reserved1 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Valid Lifetime                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Preferred Lifetime                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Reserved2                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            Prefix                             +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 20: Format of its DODAG parents,
       indicating that the parent has left the DODAG, that node SHOULD
       stay in its current DODAG through an alternative DODAG parent, if
       possible.  It MAY follow the leaving parent.

   A DODAG parent Prefix Information Option

   The Prefix Information option may have moved, migrated be used to distribute the next DODAG Iteration,
   or jumped to a different DODAG.  A node should give some preference
   to remaining prefix in
   use inside the current DODAG, if possible, but ought e.g. for address autoconfiguration.

   [RFC4861] should be consulted as the authoritative reference with
   respect to follow the parent if there Prefix Information option.  The field descriptions are no other options.

5.3.4.  DIO Message Communication

   When an DIO message is received, the receiving node must first
   determine whether or not the DIO message should be accepted
   transcribed here for
   further processing, and subsequently present 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 DIO message Prefix that are valid.  The value ranges from 0 to 128.
         The prefix length field provides necessary information for
   further processing if eligible.

   1.  If on-
         link determination (when combined with the DIO message is malformed, then L flag in the DIO message is not
       eligible prefix
         information option).  It also assists with address
         autoconfiguration as specified in [RFC4862], for further processing and is silently discarded.  A RPL
       implementation MAY log 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 reception
         advertisement makes no statement about on-link or off-link
         properties of a malformed DIO message.

   2.  If the sender of prefix.  In other words, if the DIO message L flag is not
         set a member of the candidate
       neighbor set, then host MUST NOT conclude that an address derived from the DIO
         prefix is eligible for further processing.

5.3.4.1.  DIO Message Processing

   As DIO messages are received from candidate neighbors, off-link.  That is, it MUST NOT update a previous
         indication that the neighbors
   may address is on-link.

   A     1-bit autonomous address-configuration flag.  When set
         indicates that this prefix can be promoted to DODAG parents by following the rules of DODAG
   discovery used for stateless address
         configuration as described specified in Section 5.3.  When a node 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 [RFC4862].

   Reserved1  6-bit unused field.  It MUST be used initialized to restrict which other
   nodes may become DODAG parents.  Some nodes in zero by the DODAG parent set
   may
         sender and MUST be ignored by the receiver.

   Valid Lifetime  32-bit unsigned integer.  The length of a rank less than or equal time in
         seconds (relative to the most preferred DODAG
   parent.  (This case may occur, for example, if an energy constrained
   device time the packet is at a lesser rank but should be avoided as per an
   optimization objective, resulting in a more preferred parent at a
   greater rank).

5.3.5.  DIO Transmission

   Each node maintains a timer, sent) that governs when to multicast DIO
   messages.  This timer the
         prefix is valid for the purpose of on-link determination.  A
         value of all one bits (0xffffffff) represents infinity.  The
         Valid Lifetime is a trickle timer, as detailed in
   Section 5.3.5.1. also used by [RFC4862].

   Preferred Lifetime  32-bit unsigned integer.  The DIO Configuration Option includes length of time in
         seconds (relative to the
   configuration time the packet is sent) that
         addresses generated from the prefix via stateless address
         autoconfiguration remain preferred [RFC4862].  A value of a RPL Instance's trickle timer.

   o  When a node detects or causes an inconsistency, it all
         one bits (0xffffffff) represents infinity.  See [RFC4862].
         Note that the value of this field MUST reset NOT exceed the
      trickle timer.

   o  When a node migrates Valid
         Lifetime field to a new DODAG Iteration it avoid preferring addresses that are no longer
         valid.

   Reserved2  This field is unused.  It MUST reset the
      trickle timer be initialized to its minimum value

   o  When zero by
         the sender and MUST be ignored by the receiver.

   Prefix  An IP address or a node detects prefix of an inconsistency when forwarding a packet, as
      detailed IP address.  The Prefix
         Length field contains the number of valid leading bits in Section 7.2, the node
         prefix.  The bits in the prefix after the prefix length are
         reserved and MUST reset be initialized to zero by the trickle timer.

   o  When a node receives sender and
         ignored by the receiver.  A router SHOULD NOT send a multicast DIS message, it MUST reset prefix
         option for the
      trickle timer to its minimum value.

   o  When link-local prefix and a node receives host SHOULD ignore such
         a unicast DIS message, it prefix option.

   Unassigned bits of the Prefix Information option are reserved.  They
   MUST unicast a DIO
      message in response, be set to zero on transmission and the response MUST include be ignored on reception.

6.  Upward Routes

   This section describes how RPL discovers and maintains upward routes.
   It describes the use of DODAG
      Configuration Object.  This provides a means that an interrogating
      node may be guaranteed to receive 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 Configuration Object,
   Information Solicitation (DIS) messages, which otherwise might not be included at are used to trigger
   DIO transmissions.

6.1.  DIO Base Rules

   1.  If the option 'A' flag of the sender.
      In this case the node SHOULD NOT reset the trickle timer.

   o  If a node DIO Base is not a member of a DODAG, it cleared, the 'T' flag MUST suppress
      transmission of also
       be cleared.

   2.  For the following DIO messages.

   o  When Base fields, a node that is initialized, it MAY be configured to remain silent
      and not multicast any DIO messages until it has encountered and
      joined a DODAG (perhaps initially probing for a nearby DODAG with
      an DIS message).  Alternately, it MAY choose to
       root MUST advertise the same values as its own
      floating preferred DODAG and begin multicasting DIO messages using a default
      trickle configuration.  The second case may be advantageous parent
       (defined in Section 6.2.1).  Therefore, if it
      is desired for independent nodes to begin aggregating into
      scattered floating DODAGs, a DODAG root does not
       change these values, every node in a route to that DODAG root
       eventually advertises the same values for these fields.  These
       fields are:
       1.  Grounded (G)
       2.  Destination Advertisement Supported (A)
       3.  Destination Advertisement Trigger (T)
       4.  DAGPreference (Prf)
       5.  Version
       6.  RPLInstanceID
       7.  DODAGID

   3.  A node MAY update the following fields at each hop:
       1.  Destination Advertisements Stored (S)
       2.  DAGRank
       3.  DTSN

   4.  The DODAGID field each root sets MUST be unique within the absence of a grounded node, for
      example in support of LLN installation and commissioning.

5.3.5.1.  Trickle Timer for DIO Transmission RPL treats the construction of a DODAG as a consistency problem,
       Instance.

6.2.  Upward Route Discovery and
   uses Maintenance

   Upward route discovery allows a trickle timer [Levis08] node to control the rate of control
   broadcasts.

   For each join a DODAG by discovering
   neighbors that a node is part are members of (i.e. one DODAG per RPL
   Instance), the node must maintain a single trickle timer.  The
   required state contains the following conceptual items:

   I:    The current length DODAG of the communication interval

   T:    A timer with interest and identifying a duration
   set to a random value in the range
         [I/2, I]

   C:    Redundancy Counter

   I_min: of parents.  The smallest communication interval in milliseconds.  This
         value exact policies for selecting neighbors and
   parents is learned from implementation-dependent and driven by the DIO message as (2^DIOIntervalMin)ms.
         The default value is DEFAULT_DIO_INTERVAL_MIN.

   I_doublings:  The number of times I_min should be doubled before
         maintaining a constant rate, i.e.  I_max = I_min *
         2^I_doublings. OF.  This value is learned from the DIO message as
         DIOIntervalDoublings.  The default value is
         DEFAULT_DIO_INTERVAL_DOUBLINGS.

5.3.5.1.1.  Resetting
   section specifies the Trickle Timer

   The trickle timer set of rules those policies must follow for
   interoperability.

6.2.1.  Neighbors and Parents within a DODAG is reset by:

   1.  Setting I_min Version

   RPL's upward route discovery algorithms and I_doublings to the values learned from processing are in terms
   of three logical sets of link-local nodes.  First, the
       DODAG root via a received DIO message.

   2.  Setting C to zero.

   3.  If I candidate
   neighbor set is not equal to I_min:

       1.  Setting I to I_min.

       2.  Setting T to a random value as described above.

       3.  Restarting the trickle timer to expire after a duration T

   When a node learns about a DODAG through a DIO message, and makes subset of the
   decision to join nodes that can be reached via link-
   local multicast.  The selection of this DODAG, it initializes set is implementation-
   dependent and OF-dependent.  Second, the state parent set is a restricted
   subset of the trickle
   timer by resetting candidate neighbor set.  Finally, the trickle timer and listening.  Each time it
   hears preferred parent,
   a redundant DIO message for this DODAG, it MAY increment C. The
   exact determination set of what constitutes a redundant DIO message size one, is
   left to an implementation; it could for example include DIOs that
   advertise element of the same rank.

   When parent set that is the timer fires at time T,
   preferred next hop 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 compares C to the redundancy
   constant, DIORedundancyConstant.  If C that is less not a DODAG root MAY maintain a DODAG parent set
       of size greater than that value, or if
   the DIORedundancyConstant value is 0xFF, the node generates equal to one.

   4.  A node's preferred DODAG parent MUST be a new DIO
   message and multicasts it. member of its DODAG
       parent set.

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

   6.  When the communication interval I
   expires, the Neighbor Unreachability Detection (NUD), or an equivalent
       mechanism, determines that a neighbor is no longer reachable, a
       RPL node MUST NOT consider this node doubles in the interval I so long as it has previously
   doubled it fewer than I_doubling times, resets C, candidate neighbor
       set when calculating and chooses a new T
   value.

5.3.5.1.2.  Determination of Inconsistency

   The trickle timer is reset whenever an inconsistency advertising routes until it determines
       that it is detected
   within again reachable.  Routes through an unreachable
       neighbor MUST be removed from the DODAG, for example:

   o  The node joins routing table.

   These rules ensure that there is a new DODAG

   o  The node moves consistent partial order on nodes
   within a DODAG

   o  The the DODAG.  As long as node receives a DIO message from a DODAG parent that updates ranks do not change, following the information learned from a prior DIO message for
   above rules ensures that DODAG
      Parent

   o  A DODAG parent forwards a packet intended every node's route to move up, indicating
      an inconsistency and possible loop.

   o  A metric communicated in the DIO message a DODAG root is determined to be
      inconsistent, loop-
   free, as according rank decreases on each hop to a implementation specific path
      metric selection engine.

   o the root.  The rank of a DODAG OF can guide
   candidate neighbor set and parent has changed.

5.3.6. set selection, as discussed in
   [I-D.ietf-roll-routing-metrics] and [I-D.ietf-roll-of0].

6.2.2.  Neighbors and Parents across DODAG Selection Versions

   The above rules govern a single DODAG selection is implementation and algorithm dependent.  Nodes
   SHOULD prefer to join DODAGs 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 version.  The rules in this
   section define how RPL operates when there are multiple DODAG
   versions:

6.2.2.1.  DODAG Version

   1.  The tuple (RPLInstanceID, DODAGID, DODAGVersionNumber) uniquely
       defines a means to filter out DODAG Version.  Every element of a node's DODAG parent whose availability is
   detected
       set, as fluctuating, at least when more stable choices are
   available.

   When connection conveyed by the last heard DIO message from each DODAG
       parent, MUST belong to the same DODAG version.  Elements of a fixed network is not possible or preferable for
   security or other reasons, scattered DODAGs
       node's candidate neighbor set MAY aggregate as much as
   possible into larger DODAGs in order belong to allow connectivity within the
   LLN. different DODAG
       Versions.

   2.  A node SHOULD verify that bidirectional connectivity and adequate
   link quality is available with a candidate neighbor before it
   considers that candidate as member of a DODAG parent.

5.4.  Operation as a Leaf Node

   In some cases a RPL node may attach version if every element of its
       DODAG parent set belongs to a that DODAG as a leaf version, or if that node only.
   One example of such a case
       is when a node does not understand the RPL
   Instance's OF.  A leaf node does not extend DODAG connectivity but
   still needs to advertise its presence using DIOs. root of the corresponding DODAG.

   3.  A node operating
   as a leaf node must obey the following rules:

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

   2.  Its send DIOs must advertise a DAGRank for DODAG versions of INFINITE_RANK.

   3.  It MAY transmit unicast DAOs as described in Section 6.2. which it is not a
       member.

   4.  It  DODAG roots MAY transmit multicast DAOs increment the DODAGVersionNumber that they
       advertise and thus move to a new DODAG version.  When a DODAG
       root increments its DODAGVersionNumber, it MUST follow the '1 hop' neighborhood
       conventions of Serial Number Arithmetic as described in Section 6.2.9.

5.5.  Administrative Rank

   In some cases it might be beneficial to adjust the rank advertised by
       [RFC1982].

   5.  Within a given DODAG, a node beyond that computed by is a not a root MUST NOT
       advertise a DODAGVersionNumber higher than the OF based on some implementation
   specific policy and properties of highest
       DODAGVersionNumber it has heard.  Higher is defined as the node.  For example,
       greater-than operator in [RFC1982].

   6.  Once a node that has limited battery should advertised a DODAG version by sending a DIO, it
       MUST NOT be member of a leaf unless there is no other choice,
   and may then augment previous DODAG version of the rank computation specified by same DODAG
       (i.e. with the OF in
   order to expose an exaggerated rank.

5.6.  Collision

   A race condition occurs if 2 nodes send DIO messages at same RPLInstanceID, the same time DODAGID, and then attempt to join each other.  This might happen, for example,
   between nodes which act a lower
       DODAGVersionNumber).  Lower is defined as the less-than operator
       in [RFC1982].

   Within a particular implementation, a DODAG root of their own DODAGs.  In order
   to detect the situation, LLN Nodes time stamp may increment the sending of DIO
   message.  Any DIO message received within a short link-layer-
   dependent period introduces
   DODAGVersionNumber periodically, at a risk.  It left to rate that depends on the implementation
   deployment, in order to
   define the duration trigger a global reoptimization of the risk window.

   There is risk of a collision when a node receives DODAG.
   In other implementations, loop detection may be considered sufficient
   to solve routing issues by triggering local repair mechanisms, and processes a DIO
   within
   the risk window.  For example, it DODAG root may occur increment the DODAGVersionNumber only upon
   administrative intervention.  Another possibility is that two nodes are
   associated with different DODAGs and near-simultaneously send DIO
   messages, which are received and processed
   within the LLN have some means by both, and possibly
   result in both nodes simultaneously deciding which they can signal detected
   routing inconsistencies or suboptimalities to attach the DODAG root, in
   order to each other.
   As request an on-demand DODAGVersionNumber increment (i.e.
   request a remedy, in the face global repair of the DODAG).  Note that such a potential collision, as determined by
   receiving a DIO within mechanism is
   for further study and out of the risk window, scope of this document.

   When the DIO message is not
   processed.  It is expected DODAG parent set becomes empty on a node that subsequent DIOs would is not cross.

6.  Downward Routes

   This section describes how RPL discovers and maintains downward
   routes.  Messages containing a root,
   (i.e. the Destination Advertisement Object
   (DAO), used last parent has been removed, causing the node to construct downward routes, are described.  The
   downward routes are necessary in support of P2MP flows, from no longer
   be associated with that DODAG), then the DODAG roots toward information should not
   be suppressed until after the leaves.  It specifies non-storing and storing
   behavior expiration of nodes with respect to DAO messaging and DAO routing table
   entries.  Nodes, as according an implementation-
   specific local timer in order to their resources and observe if the
   implementation, may selectively store routing table entries learned
   from DAO messages, or DODAGVersionNumber
   has been incremented, should any new parents appear for the DODAG.
   This will help protect against the possibility of loops that may instead propagate
   occur of that node were to inadvertently rejoin the DAO information
   upwards while adding source routing information.  A further
   optimization old DODAG version
   in its own prior sub-DODAG.

   As the DODAGVersionNumber is described whereby DAO messages may be used incremented, a new DODAG Version spreads
   outward from the DODAG root.  Thus a parent that advertises the new
   DODAGVersionNumber cannot possibly belong to
   populate routing table entries for the '1-hop' neighbors, which sub-DODAG of a node
   that still advertises an older DODAGVersionNumber.  A node may
   be useful safely
   add such a parent, without risk of forming a loop, without regard to
   its relative rank in some cases the prior DODAG Version.  This is equivalent to
   jumping to a different DODAG.

   As a node transitions to new DODAG Versions as a shortcut for P2P flows.

6.1.  Destination Advertisement Object (DAO)

   The Destination Advertisement Object (DAO) is used consequence of
   following these rules, the node will be unable to propagate
   destination information upwards along advertise the DODAG.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         DAO Sequence          |           DAO Rank            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | RPLInstanceID |   Route Tag   | Prefix Length |    RRCount    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          DAO Lifetime                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             Destination Prefix (Variable Length)              |
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             Reverse Route Stack (Variable Length)             |
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   sub-option(s)...
       +-+-+-+-+-+-+-+-+

           Figure 11: The Destination Advertisement Object (DAO)

   DAO Sequence:  16-bit unsigned integer.  Incremented by
   previous DODAG Version (prior DODAGVersionNumber) once it has
   committed to advertising the new DODAG Version.

   During transition to a new DODAG Version, a node may decide to
   forward packets via 'future parents' that
         owns belong to the prefix for each new DAO message for same DODAG
   (same RPLInstanceID and DODAGID), but are observed to advertise a
   more recent (incremented) DODAGVersionNumber.  In that prefix.

   DAO Rank:  16-bit unsigned integer indicating case, the DAO Rank associated node
   MUST act as a leaf with the advertised Destination Prefix.  The DAO Rank is
         analogous regard to the Rank in new version for the DIO message purpose of
   loop detection as specified in Section 8.2.

6.2.2.2.  DODAG Roots

   1.  A DODAG root that it may be used
         to convey a relative distance does not have connectivity to the Destination Prefix set of
       addresses described as
         computed by application-level goals, MUST NOT set the Objective Function in use over
       Grounded bit.

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

   3.  A node whose DODAG parent set is empty MAY become the DODAG root
       of a floating DODAG.  It
         serves as a mechanism by which an ancestor MAY also set its DAGPreference such that
       it is less preferred.

   An LLN node may order
         alternate DAO paths.

   RPLInstanceID:  8-bit field indicating that is a goal for the topology instance
         associated with Objective Function is the root of
   its own grounded DODAG, as learned from the DIO.

   Route Tag:  8-bit unsigned integer.  The Route Tag may be used at rank ROOT_RANK.

   In a deployment that uses a backbone link to
         give federate a priority number of LLN
   roots, it is possible to prefixes run RPL over that should be stored.  This may be
         useful in cases where intermediate nodes are capable of storing backbone and use one
   router as a limited amount of routing state. "backbone root".  The further specification backbone root is the virtual root
   of this field the DODAG, and its use is under investigation.

   Prefix Length:  8-bit unsigned integer.  Number exposes a rank of valid leading bits
         in BASE_RANK over the IPv6 Prefix.

   RRCount:  8-bit unsigned integer.  This counter is used backbone.  All
   the LLN roots that are parented to that backbone root, including the
   backbone root if it also serves as LLN root itself, expose a rank of
   ROOT_RANK to count the
         number LLN, and are part of entries in the Reverse Route Stack.  A value of '0'
         indicates that no Reverse Route Stack is present.

   DAO Lifetime:  32-bit unsigned integer. same DODAG, coordinating
   DODAGVersionNumber and other DODAG root determined parameters with
   the virtual root over the backbone.

6.2.2.3.  DODAG Selection

   The length of time in
         seconds (relative DODAGPreference (Prf) provides an administrative mechanism to
   engineer the time the packet is sent) that self-organization of the
         prefix is valid LLN, for route determination.  A value of all one
         bits (0xFFFFFFFF) represents infinity.  A value of all zero
         bits (0x00000000) indicates example indicating the
   most preferred LBR.  If a loss of reachability.

   Destination Prefix:  Variable-length field identifying an IPv6
         destination address, prefix, or multicast group.  The Prefix
         Length field contains node has the number of valid leading bits in option to join a more
   preferred DODAG while still meeting other optimization objectives,
   then the
         prefix.  The bits in node will generally seek to join the prefix after more preferred DODAG as
   determined by the prefix length (if
         any) are reserved and MUST be set OF.  All else being equal, it is left to zero the
   implementation to determine which DODAG is most preferred, possibly
   based on transmission additional criteria beyond Prf and the OF.

6.2.2.4.  Rank and Movement within a DODAG Version

   1.  A node MUST be ignored on receipt.

   Reverse Route Stack:  Variable-length field containing NOT advertise a sequence rank less than or equal to any member
       of
         RRCount (possibly compressed) IPv6 addresses. its parent set within the DODAG Version.

   2.  A node MAY advertise a rank lower than its prior advertisement
       within the DODAG Version.

   3.  Let L be the lowest rank within a DODAG version that a given node
       has advertised.  Within the same DODAG Version, that adds
         on node MUST
       NOT advertise an effective rank higher than L +
       DAGMaxRankIncrease.  INFINITE_RANK is an exception to the Reverse Route Stack will append this rule:
       a node MAY advertise an INFINITE_RANK at any time.  (This rule
       corresponds to a limited rank increase for the list and
         increment purpose of local
       repair within the RRCount.

6.1.1.  DAO Suboptions

   The DAO message may optionally include DODAG Version.)

   4.  A node MAY, at any time, choose to join a number different DODAG within
       a RPL Instance.  Such a join has no rank restrictions, unless
       that different DODAG is a DODAG Version of suboptions.

   The DAO suboptions are which this node has
       previously been a member, in which case the same format as rule of the DIO Suboptions
   described in Section 6.1.1.

   In particular, previous
       bullet (3) must be observed.  Until a DAO message may include node transmits a DAG Metric Container
   suboption as described in Section 5.1.3.4.  This suboption may be
   present in implementations where DIO
       indicating its new DODAG membership, it MUST forward packets
       along the DAO Rank is insufficient previous DODAG.

   5.  A node MAY, at any time after hearing the next DODAGVersionNumber
       Version advertised from suitable DODAG parents, choose to
   optimize a path migrate
       to the DAO Destination Prefix.

6.2.  Downward Route Discovery and Maintenance

6.2.1.  Overview

   Destination Advertisement operation produces DAO messages that flow
   up the DODAG, provisioning downward routing state for destination
   prefixes available in the sub-DODAG of the next DODAG root, and possibly
   other nodes.  The routing state provisioned with this mechanism Version within the DODAG.

   Conceptually, an implementation is in maintaining a DODAG parent set
   within the form of soft-state routing table entries.  DAO messages are able DODAG Version.  Movement entails changes to record loose source routing information as by propagate the DODAG
   parent set.  Moving up does not present the
   DODAG.  This mechanism risk to create a loop but
   moving down might, so that operation is flexible subject to support the provisioning of
   paths which consist of fully specified source routes, piecewise
   source routes, or hop-by-hop routes as according additional
   constraints.

   When a node migrates to the
   implementation next DODAG Version, the DODAG parent and
   sibling sets need to be rebuilt for the capabilities new version.  An
   implementation could defer to migrate for some reasonable amount of the nodes.

   Destination Advertisement may or may not be enabled over
   time, to see if some other neighbors with potentially better metrics
   but higher rank announce themselves.  Similarly, when a DODAG
   rooted at node jumps
   into a new DODAG root.  This is an it needs to construct new DODAG parent/sibling sets
   for this new DODAG.

   When a priori configuration determined
   by the implementation/deployment node moves to improve its position, it must conceptually
   abandon all DODAG parents and not generally changed during the
   operation of the RPL LLN.

   When Destination Advertisement is enabled:

   1.  Some nodes in the LLN MAY store at least one routing table entry
       for siblings with a particular destination learned from rank larger than
   itself.  As a DAO. consequence of the movement it may also add new
   siblings.  Such a node is
       termed a 'storing node', with respect to that particular
       destination.

   2.  Some nodes are capable to store movement may occur at least one routing table entry
       for every unique destination any time to decrease the
   rank, as per the calculation indicated by the OF.  Maintenance of the
   parent and sibling sets occurs as the rank of candidate neighbors is
   observed from all DAOs that pass
       through.  Such as reported in their DIOs.

   If a node is termed needs to move down a 'fully storing node'.

   3. DODAG roots nodes SHOULD be fully-storing nodes.

   4.  Other nodes in that it is attached to, causing
   the DODAG are not required rank to store routing table
       entries for any particular destinations observed increase, then it MAY poison its routes and delay before
   moving as described in DAOs.  Nodes
       that do not store routing table entries from DAOs are termed
       'non-storing nodes', with respect to Section 6.2.2.5.

6.2.2.5.  Poisoning a particular destination.

   5.  Non-storing nodes MUST participate Broken Path

   1.  A node MAY poison, in the construction of
       piecewise source routes order to avoid being used as they propagate an ancestor by
       the DAO message, as
       described nodes in its sub-DODAG, by advertising an effective rank of
       INFINITE_RANK and resetting the associated DIO trickle timer to
       cause this INFINITE_RANK to be announced promptly.

   2.  The node MAY advertise an effective rank of INFINITE_RANK for an
       arbitrary number of DIO timer events, before announcing a new
       rank.

   3.  As per Section 6.2.5.

   6.  Storing nodes 6.2.2.4, the node MUST store any source route information received
       from advertise INFINITE_RANK
       within the DAO (RRStack) DODAG version in which it participates, if its
       revision in rank would exceed the routing table entry entry.  If maximum rank increase.

   An implementation may choose to employ this poisoning mechanism when
   a node loses all of its current parents, i.e. the set of DODAG
   parents becomes depleted, and it can not jump to an alternate DODAG.
   An alternate mechanism is to form a floating DODAG.

   The motivation for delaying announcement of the revised route through
   multiple DIO events is not capable to do this then it must act as a non-storing
       node with respect (i) increase tolerance to that particular destination.

   7.  Storing nodes MUST use piecewise source routes in order DIO loss, (ii)
   allow time for the poisoning action to
       forward data across a non-storing region propagate, and (iii) to
   develop an accurate assessment of its new rank.  Such gains are
   obtained at the expense of potentially increasing the LLN.  The source
       routing mechanism is delay before
   portions of the network are able to be described re-establish upwards routes.
   Path redundancy in a companion
       specification.  (If a node is not capable to do this, then that
       node MUST NOT operate as a storing node).

6.2.2.  Mode the DODAG reduces the significance of Operation

   o  DAO Operation may not either
   effect, since children with alternate parents should be required for all use cases.

   o  Some applications able to
   utilize those alternates and retain their rank while the detached
   parent re-establishes its rank.

   Although an implementation may only need support advertise INFINITE_RANK for collection/upward/MP2P
      flow with no acknowledgement/reciprocal traffic.

   o  Some DODAGs may not support DAO Operation, which could mean that
      DAO Operation the
   purposes of poisoning, it is wasteful overhead.

   o  As a special case, multicast DAO operation may not expected to be used equivalent to populate
      'one-hop' neighborhood routing table entries, and is distinct from setting
   the unicast DAO operation used rank to INFINITE_RANK, and an implementation would likely retain
   its rank value prior to establish downward routes along the DODAG.

   1.  The 'A' flag poisoning in the DIO as conveyed from the DODAG root serves some form, for purpose of
   maintaining its effective position within (L + DAGMaxRankIncrease).

6.2.2.6.  Detaching

   1.  A node unable to stay connected to
       enable/disable DAO operation over the entire DODAG.  This flag
       should be administratively provisioned a priori at the DODAG root
       as within a function given DODAG
       version MAY detach from this DODAG version.  A node that detaches
       becomes root of the implementation/deployment its own floating DODAG and not tend SHOULD immediately
       advertise this new situation in a DIO as an alternate to
       change.

   2.  When DAO Operation is disabled,
       poisoning.

6.2.2.7.  Following a node SHOULD NOT emit DAOs.

   3.  When DAO Operation is disabled, Parent

   1.  If a node MAY ignore received DAOs.

6.2.3.  Destination Advertisement Parents

   o  Nodes will select receives a subset DIO from one of their its DODAG Parents to whom DAOs
      will be sent

      *  This subset is parents,
       indicating that the set of 'DAO Parents'

      *  Each DAO parent MUST be a has left the DODAG, that node SHOULD
       stay in its current DODAG Parent.  (Not all through an alternative DODAG parents
         need to be DAO parents).

      *  Operation with more than DAO Parent requires consideration of
         such issues as DAO fan-out and path diversity, to be elaborated
         in a future version of this specification.

   o  The selection of DAO parents is implementation specific and may be
      based on selecting parent, if
       possible.  It MAY follow the leaving parent.

   A DODAG Parents that offer the best upwards
      cost (as opposed parent may have moved, migrated to downwards or mixed), as determined by the
      metrics in use and the Objective Function.

   o  When DAO messages are unicast next DODAG Version, or
   jumped to a different DODAG.  A node should give some preference to
   remaining in the DAO Parent, the identity of current DODAG, if possible via an alternate parent,
   but ought to follow the DAO Parent (DODAGID x DAGSequenceNumber) combined with parent if there are no other options.

6.2.3.  DIO Message Communication

   When an DIO message is received, the
      RPLInstanceID in receiving node must first
   determine whether or not the DAO DIO message unambiguously associates the DAO
      message, should be accepted for
   further processing, and thus subsequently present the particular destination prefix, with a DODAG
      Iteration.

   o  When DAO messages are unicast to DIO message for
   further processing if eligible.

   1.  If the DAO Parent, DIO message is malformed, then the DAO Rank may DIO message is not
       eligible for further processing and MUST be updated as according to the silently discarded.
       A RPL implementation and Objective
      Function in use to reflect MAY log the relative (aggregated) cost reception of
      reaching the Destination Prefix through that DAO parent.  As a
      further extension, a DAO Suboption for malformed DIO
       message.

   2.  If the Metric Container may be
      included.

6.2.4.  Operation sender of DAO Storing Nodes

6.2.4.1.  DAO Routing Table Entry

   A DAO Routing Table Entry conceptually contains the following
   elements:

   o  Advertising Neighbor Information
      *  IPv6 Addr
      *  Interface ID
   o  To which DAO Parents has this entry been reported
   o  Retry Counter
   o  Logical equivalent DIO message is a member of DAO Content:
      *  DAO Sequence
      *  DAO Rank
      *  DAO Lifetime
      *  Route tag (used to prioritize which destination entries should
         be stored)
      *  Destination Prefix (or Address or Mcast Group)
      *  RR Stack*

   The DAO Routing Table Entry the candidate
       neighbor set, then the DIO is logically associated with eligible for further processing.

6.2.3.1.  DIO Message Processing

   As DIO messages are received from candidate neighbors, the
   following states:

   CONNECTED   This entry is 'owned' neighbors
   may be promoted to DODAG parents by following the node - it is manually
               configured and is considered rules of DODAG
   discovery as described in Section 6.2.  When a 'self' entry for DAO
               Operation

   REACHABLE   This entry has been reported from node places a neighbor of
   into the DODAG parent set, the node becomes attached to the DODAG
   through the new DODAG parent node.
               This state includes

   The most preferred parent should be used to restrict which other
   nodes may become DODAG parents.  Some nodes in the following substates:

               CONFIRMED This entry is active, newly validated, and
                         usable

               PENDING   This entry is active, awaiting validation, and
                         usable.  A Retry Counter is associated with
                         this substate

   UNREACHABLE This entry is being cleaned up.  This entry DODAG parent set
   may be
               suppressed when of a rank less than or equal to the cleanup process is complete.

   When most preferred DODAG
   parent.  (This case may occur, for example, if an attempt energy constrained
   device is to at a lesser rank but should be made to report the DAO entry avoided as per an
   optimization objective, resulting in a more preferred parent at a
   greater rank).

6.3.  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 DAO Parents, the DAO Entry record is logically marked recipient's parent set, preferred
   parent, or Rank SHOULD be considered consistent with respect to indicate that an attempt
   has not yet been made for each parent.  As the unicast attempts are
   completed for each parent, this mark may
   Trickle timer.

   The following packets and events MUST be cleared.  This mechanism
   may serve considered inconsistencies
   with respect to limit DAO entry updates for each parent the Trickle timer, and cause the Trickle timer to
   reset:

   o  When a subset node detects an inconsistency when forwarding a packet, as
      detailed in Section 8.2.

   o  When a node receives a multicast DIS message whose constraints
      (Solicited Information) it satisfies.

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

   Note that
   needs this list is not exhaustive, and an implementation MAY
   consider other messages or events to be reported.

6.2.4.1.1.  DAO Routing Table Entry Management

           +---------------------------------+
           |                                 |
           |            REACHABLE            |    +-------------+
           |                                 |    |             |
           |        +-----------+            |    |  CONNECTED  |
     (*)----------->|           |-------+    |    |             |
           |        | Confirmed |       |    |    +-------------+
           |    +-->|           |---+   |    |
           |    |   +-----------+   |   |    |
           |    |                   |   |    |
           |    |                   |   |    |
           |    |                   |   |    |
           |    |   +-----------+   |   |    |    +-------------+
           |    |   |           |<--+   +-------->|             |
           |    +---|  Pending  |            |    | UNREACHABLE |
           |        |           |---------------->|             |--->(*)
           |        +-----------+            |    +-------------+
           |                                 |
           +---------------------------------+

                        DAO Routing Table Entry FSM

6.2.4.1.1.1.  Operation inconsistencies.

   If a node receives a unicast DIS message whose constraints (Solicited
   Information) it satisfies, it MUST unicast a DIO in response, and
   this DIO MUST include the CONNECTED state

   1.  CONNECTED DAO entries RPL instance's DODAG Configuration object.

6.3.1.  Trickle Parameters

   The configuration parameters of the trickle timer are to be provisioned outside specified as
   follows:

   Imin: learned from the DIO message as (2^DIOIntervalMin)ms.  The
         default value of DIOIntervalMin is DEFAULT_DIO_INTERVAL_MIN.

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

   k:    learned from the
       context DIO message as DIORedundancyConstant.  The
         default value of DIORedundancyConstant is
         DEFAULT_DIO_REDUNDANCY_CONSTANT.  In RPL, e.g. through when k has the value
         of 0x00 this is to be treated as a management API.  An redundancy constant of
         infinity in RPL, i.e.  Trickle never suppresses messages.

6.4.  DODAG Selection

   The DODAG selection is implementation and OF dependent.  Nodes SHOULD
   prefer to join DODAGs 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 a means to provision/manage CONNECTED DAO entries,
       including whether they filter out a parent whose availability is
   detected as fluctuating, at least when more stable choices are to be redistributed in RPL.

6.2.4.1.1.2.  Operation in the REACHABLE state

   1.
   available.

   When connection to a REACHABLE(*) entry times out, i.e. the DAO Lifetime has
       elapsed, the entry MUST be placed grounded DODAG is not possible or preferable for
   security or other reasons, scattered DODAGs MAY aggregate as much as
   possible into the UNREACHABLE state and
       no-DAO SHOULD be scheduled to send larger DODAGs in order to allow connectivity within the node's DAO Parents.

   2.  When a no-DAO for a REACHABLE(*) entry
   LLN.

   A node SHOULD verify that bidirectional connectivity and adequate
   link quality is received available with a newer
       DAO Sequence Number, the entry MUST be placed into the
       UNREACHABLE state and no-DAO SHOULD be scheduled to send candidate neighbor before it
   considers that candidate as a DODAG parent.

6.5.  Operation as a Leaf Node

   In some cases a RPL node may attach to the
       node's DAO Parents.

   3.  When a REACHABLE(*) entry DODAG as a leaf node only.
   One example of such a case is to be removed because NUD or
       equivalent has determined that when a node does not understand the next-hop neighbor is no longer
       reachable, RPL
   Instance's OF or advertised path metric.  A leaf node does not extend
   DODAG connectivity but still needs to advertise its presence using
   DIOs.  A node operating as a leaf node must obey the entry following rules:

   1.  It MUST be placed into the UNREACHABLE state
       and no-DAO SHOULD be scheduled to send to NOT transmit DIOs containing the node's DAO Parents.

   4.  When DAG Metric Container.

   2.  Its DIOs must advertise a REACHABLE(*) entry is DAGRank of INFINITE_RANK.

   3.  It MAY transmit unicast DAOs as described in Section 7.1.

   4.  It MAY transmit multicast DAOs to be removed because an associated
       Forwarding Error has been returned by the next-hop neighbor, the
       entry MUST be placed into the UNREACHABLE state and no-DAO SHOULD '1 hop' neighborhood as
       described in Section 7.1.9.

6.6.  Administrative Rank

   In some cases it might be scheduled to send beneficial to adjust the node's DAO Parents.

   5.  When a DAO (or no-DAO) for rank advertised by
   a REACHABLE(*) entry is received with
       an older or unchanged DAO Sequence Number, then node beyond that computed by the DAO (or no-
       DAO) SHOULD be ignored OF based on some implementation
   specific policy and properties of the associated entry MUST NOT be
       updated with the stale information.

6.2.4.1.1.2.1.  REACHABLE(Confirmed)

   1.  When node.  For example, a DAO for node that
   has limited battery should be a previously unknown (or UNREACHABLE) destination leaf unless there is received no other choice,
   and is to be stored, it MUST be entered into may then augment the
       routing table in rank computation specified by the REACHABLE(Confirmed) state, and a DAO SHOULD
       be scheduled OF in
   order to send expose an exaggerated rank.

7.  Downward Routes

   This section describes how RPL discovers and maintains downward
   routes.  The use of messages containing the Destination Advertisement
   Object (DAO), used to construct downward routes, are described.  The
   downward routes are necessary in support of P2MP flows, from the node's DAO Parents.  Alternately
   DODAG roots toward the
       node may behave as a leaves.  It specifies non-storing node and storing
   behavior of nodes with respect to this
       destination.

   2.  When a DAO for a REACHABLE(Confirmed) entry is received with a
       newer DAO Sequence Number, the entry MUST be updated with the
       logical equivalent of the DAO contents messaging and a DAO SHOULD be
       scheduled to send routing table
   entries.  Nodes, as according to their resources and the node's
   implementation, may selectively store routing table entries learned
   from DAO Parents.

   3.  When a messages, or may instead propagate the DAO for a REACHABLE(Confirmed) entry is expected, e.g.
       because a DIO to request information
   upwards and independently source local topology information in a new
   DAO refresh message. information.  A further optimization is sent, then the described
   whereby DAO
       entry MUST messages may be placed in the REACHABLE(Pending) state and used to populate routing table entries
   for the
       associated Retry Counter MUST '1-hop' neighbors, which may be set to 0.

6.2.4.1.1.2.2.  REACHABLE(Pending)

   1.  When useful in some cases as a DAO
   shortcut for a REACHABLE(Pending) entry is received with a
       newer P2P flows.

7.1.  Downward Route Discovery and Maintenance

7.1.1.  Overview

   Destination Advertisement operation produces DAO Sequence Number, messages that flow
   up the entry MUST be updated with DODAG, provisioning downward routing state for destination
   prefixes available in the
       logical equivalent sub-DODAG of the DAO contents DODAG root, and the entry MUST be
       placed possibly
   other nodes.  The routing state provisioned with this mechanism is in
   the REACHABLE(Confirmed) state.

   2.  When a form of soft-state routing table entries.  DAO for a REACHABLE(Pending) entry operation is expected, e.g.
       because DAO has (again) been triggered with respect to that
       neighbor, then the associated Retry Counter MUST be incremented.

   3.  When the associated Retry Counter
   presently defined in two distinct modes of operation, non-storing and
   storing, and allowance is made for future expansion.

   Destination Advertisement may or may not be enabled over a REACHABLE(Pending) entry
       reaches DODAG
   rooted at a maximum threshold, the entry MUST be placed into DODAG root.  This is an a priori configuration determined
   by the
       UNREACHABLE state implementation/deployment and no-DAO SHOULD not generally changed during the
   operation of the RPL LLN.

   Destination Advertisement may be scheduled to send configured to operate in either a
   storing or non-storing mode, as reported in the
       node's DAO Parents.

6.2.4.1.1.3.  Operation MOP in the UNREACHABLE state

   1.  An implementation SHOULD bound DIO
   message.  Every node in the time network participating in Destination
   Advertisement must behave consistently with that the entry configured mode of
   operation, or alternately behave only as a leaf node.  Hybrid or
   mixed-mode operation is
       allocated in the UNREACHABLE state.  Upon not currently specified.

   When Destination Advertisement is enabled:

   1.  The RPL Instance will be configured a priori as appropriate to
       satisfy the equivalent expiry
       of application to operate in either non-storing or
       storing mode.

   2.  All nodes who join the related timer (RemoveTimer), DODAG MUST abide with the entry SHOULD be
       suppressed.

   2.  While MOP setting from
       the entry is in root.  Nodes that would not have the UNREACHABLE state a node SHOULD make capability to fully
       participate as a
       reasonable attempt router (e.g. to report operate as a storing node) can
       still join as a no-DAO leaf (i.e. host).

   3.  In storing mode operation, all non-root nodes are expected to each of the
       either store routing table entries for ALL destinations learned
       from DAO parents.

   3.  When operation, or to act as a leaf node only.

   4.  In non-storing mode operation, no node other than the DODAG Root
       is expected to store routing table entries learned from DAO
       messages.  Each node has completed an attempt is only responsible to report a no-DAO to each its own set of
       parents to the DAO parents, the entry DODAG Root.

   5.  DODAG roots nodes SHOULD be suppressed.

6.2.5.  Operation of DAO Non-storing Nodes

   1.  When a DAO is received from a child by a node who will not capable to store
       a routing table entry for the DAO,
       entries learned from DAO operation when the node MUST schedule to pass RPL Instance is
       operated in a non-storing mode.

   6.  The mode of operation in the DAO contents along to its DAO parents.  Prior to passing RPL Instance is signaled from the
       DAO along,
       DODAG Root in the node MUST process MOP control field of the DIO message.

7.1.2.  Mode of Operation

   o  DAO as follows, in order Operation may not be required for all use cases.

   o  Some applications may only need support for collection/upward/MP2P
      flow with no acknowledgement/reciprocal traffic.

   o  Some DODAGs may not support DAO Operation, which could mean that information necessary to construct
      DAO Operation is wasteful overhead.

   o  As a loose source route special case, multicast DAO operation may be accumulated within used to populate
      'one-hop' neighborhood routing table entries, and is distinct from
      the unicast DAO payload as it moves up the DODAG:

       1.  The most recent addition operation used to establish downward routes along
      the RRStack (the 'next waypoint') DODAG.  This special case is investigated an exception to determine if the node already has a route
           provisioned RPL Instance
      mode of operation as well.

   1.  The 'A' flag in the DIO as conveyed from the DODAG root serves to
       enable/disable DAO operation over the waypoint.  If entire DODAG.  This flag
       should be administratively provisioned a priori at the node already has such DODAG root
       as a
           route, then it is function of the implementation/deployment and not necessary to add additional information tend to the RRStack.  The
       change.

   2.  When DAO Operation is disabled, a node SHOULD MUST NOT modify the RRStack
           further.

       2.  If emit DAO
       messages.

   3.  When DAO Operation is disabled, a node MAY ignore the MOP field.

   4.  When DAO Operation is disabled, a node does not have MAY ignore received DAO
       messages.

7.1.3.  Destination Advertisement Parents

   o  Nodes will select a route provisioned subset of their DODAG Parents to whom DAO
      messages will be sent

      *  This subset is the next
           waypoint, then the node set of 'DAO Parents'

      *  Each DAO parent MUST append the address be a DODAG Parent.  (Not all DODAG parents
         need to be DAO parents).

   o  The selection of DAO parents is implementation specific and may be
      based on selecting the child DODAG Parents that offer the best upwards
      cost (as opposed to downwards or mixed), as determined by the RRStack,
      metrics in use and increment RRCount.

6.2.6.  Scheduling to Send DAO (or no-DAO)

   1.  An implementation SHOULD arrange to rate-limit the sending of
       DAOs.

   2. Objective Function.

   o  When scheduling to send a DAO, an implementation SHOULD
       equivalently start a timer (DelayDAO) DAO messages are unicast to delay sending the DAO.
       If DAO Parent, the DelayDAO timer is already running then identity of
      the DAO may be
       considered as already scheduled, Parent (DODAGID and implementation SHOULD leave DODAGVersionNumber) combined with the timer running at its present duration.

   o  When computing
      RPLInstanceID in the delay before sending DAO message unambiguously associates the DAO
      message, and thus the particular destination prefix, with a DAO, in order to
      increase DODAG
      Version.

7.1.4.  DAO Operation on Storing Nodes

7.1.4.1.  DAO Routing Table Entry

   A DAO Routing Table Entry conceptually contains the effectiveness following
   elements:

   o  Advertising Neighbor Information
      *  IPv6 Address
      *  Interface ID
   o  To which DAO Parents has this entry been reported
   o  Retry Counter
   o  Logical equivalent of aggregation, an implementation MAY
      allow time to receive DAOs from its sub-DODAG prior to emitting
      DAOs to its DAO Parents. Content:
      *  DAO Sequence
      *  DAO Lifetime
      *  DAO Path Control (as learned from each child)
      *  Destination Prefix (or Address or Mcast Group)

   The scheduled delay in such cases may be, for example, such
         that DAO_LATENCY/DAGRank(self_rank) <= DelayDAO < DAO_LATENCY/
         DAGRank(parent_rank), where DAGRank() DAO Routing Table Entry is defined as in
         Section 3.6.2, such that nodes deeper in logically associated with the DODAG may tend to
         report DAO messages first before their parent nodes will report
   following states:

   CONNECTED   This entry is 'owned' by the node - it is manually
               configured and is considered as a 'self' entry for DAO messages.  Note that
               Operation

   REACHABLE   This entry has been reported from a neighbor of the node.
               This state includes the following substates:

               CONFIRMED This entry is active, newly validated, and
                         usable

               PENDING   This entry is active, awaiting validation, and
                         usable.  A Retry Counter is associated with
                         this suggestion substate

   UNREACHABLE This entry is intended as being cleaned up.  This entry may be
               suppressed when the cleanup process is complete.

   When an
         optimization to allow efficient aggregation -- it attempt is not
         required for correct operation in to be made to report the general case.

6.2.7.  Triggering DAO Message from the Sub-DODAG

   Triggering entry to DAO messages from the Sub-DODAG occurs by using the
   following control fields with the rules described below:

   The DTSN field from Parents,
   the DIO DAO Entry record is a sequence number logically marked to indicate that is part of an attempt
   has not yet been made for each parent.  As the unicast attempts are
   completed for each parent, this mark may be cleared.  This mechanism
   may serve to trigger limit DAO messages.  The motivation to use a sequence
   number is to provide some means of reliable signaling entry updates for each parent to the sub-
   DODAG-- whereas a control flag subset that is activated for a short time may
   needs to be unobserved by the sub-DODAG if reported.

7.1.4.1.1.  DAO Routing Table Entry Management

           +---------------------------------+
           |                                 |
           |            REACHABLE            |    +-------------+
           |                                 |    |             |
           |        +-----------+            |    |  CONNECTED  |
     (*)----------->|           |-------+    |    |             |
           |        | Confirmed |       |    |    +-------------+
           |    +-->|           |---+   |    |
           |    |   +-----------+   |   |    |
           |    |                   |   |    |
           |    |                   |   |    |
           |    |                   |   |    |
           |    |   +-----------+   |   |    |    +-------------+
           |    |   |           |<--+   +-------->|             |
           |    +---|  Pending  |            |    | UNREACHABLE |
           |        |           |---------------->|             |--->(*)
           |        +-----------+            |    +-------------+
           |                                 |
           +---------------------------------+
                        DAO Routing Table Entry FSM

7.1.4.1.1.1.  Operation in the triggering DIO messages CONNECTED state

   1.  CONNECTED DAO entries are
   lost, the DTSN increment may be observed later even if some DIO
   messages have been lost since the sequence number increment.

   The 'T' flag provides a way to signal the refresh be provisioned outside of DAO information
   over the entire DODAG iteration.  Whereas
       context of RPL, e.g. through a DTSN increment may only
   trigger management API.  An implementation
       SHOULD provide a means to provision/manage CONNECTED DAO refresh as far as the nearest storing node (because a
   storing node will not increment its own DTSN entries,
       including whether they are to be redistributed in response, as
   described RPL.

7.1.4.1.1.2.  Operation in the rules below), the assertion of the 'T' flag in
   conjunction with an incremented DTSN will 'punch through' storing
   nodes to elicit REACHABLE state

   1.  When a REACHABLE(*) entry times out, i.e. the DAO refresh from Lifetime has
       elapsed, the entire DODAG Iteration.

   The 'S' flag provides a way entry MUST be placed into the UNREACHABLE state and
       No-Path SHOULD be scheduled to signal send to a sub-DODAG that there is at
   least one non-root node somewhere in the set of DODAG ancestors,
   where that non-root node is node's DAO Parents.

   2.  When a storing node.  This allows No-Path for an
   optimization-- when it is clear to a non-storing node that the root
   node can be the only storing ancestor, then that node does not
   necessarily need to trigger updates from its sub-DODAG when it
   modifies its DAO parent set.  The motivation here REACHABLE(*) entry is that the root
   node should be able to update its stored source routing information
   for the affected sub-DODAG based only on receiving received with a newer
       DAO information
   concerning the link that changed.  In the other case, when Sequence Number, the 'S'
   flag is set, entry MUST be placed into the non-storing node does not have a means
       UNREACHABLE state and No-Path SHOULD be scheduled to determine
   which DAO information may (or may not) need send to be updated in the
   intermediate storing node so it must trigger
       node's DAO messages in order Parents.

   3.  When a REACHABLE(*) entry is to
   update the intermediate storing node.  Please note be removed because NUD or
       equivalent has determined that some aspects
   of the proper use of next-hop neighbor is no longer
       reachable, the 'S' flag remain under investigation.

   Further examples of triggering DAO messages are contained in
   Appendix B.

   The control fields are used to trigger DAO messages as follows:

   1.   The DODAG root entry MUST clear be placed into the 'S' flag when it emits DIO
        messages.

   2.   Non-root nodes that store routing table entries learned from
        DAOs MUST set UNREACHABLE state
       and No-Path SHOULD be scheduled to send to the 'S' flag when they emit DIO messages.

   3.   A node that has any node's DAO Parent with
       Parents.

   4.  When a REACHABLE(*) entry is to be removed because an associated
       Forwarding Error has been returned by the 'S' flag set next-hop neighbor, the
       entry MUST also
        set be placed into the 'S' flag when it emits DIO messages.

   4.   A node that has all DAO Parents with cleared 'S' flags, UNREACHABLE state and does
        not store routing table entries learned from DAOs, MUST clear No-Path
       SHOULD be scheduled to send to the 'S' flag when it emits DIO messages. node's DAO Parents.

   5.   A  When a DAO (or No-Path) for a REACHABLE(*) entry is received with
       an older or unchanged DAO Trigger Sequence Number (DTSN) Number, then the DAO (or No-
       Path) SHOULD be ignored and the associated entry MUST NOT be maintained by each
        node per RPL Instance.  The DTSN, in conjunction
       updated with the 'T'
        flag from the DIO message, provides stale information.

7.1.4.1.1.2.1.  REACHABLE(Confirmed)

   1.  When a means by which DAO
        messages may for a previously unknown (or UNREACHABLE) destination
       is received and is to be reliably triggered in the event of topology
        change.

   6.   The DTSN stored, it MUST be advertised by entered into the node
       routing table in the DIO message.

   7.   A node keeps track of the DTSN that it has heard from REACHABLE(Confirmed) state, and a DAO SHOULD
       be scheduled to send to the last
        DIO from each of its node's DAO Parents.  Note that there

   2.  When a DAO for a REACHABLE(Confirmed) entry is one DTSN
        maintained per received with a
       newer DAO Parent- each Sequence Number, the entry MUST be updated with the
       logical equivalent of the DAO Parent may independently
        increment it at will.

   8.   A node that is not contents and a fully-storing node DAO SHOULD increment its own
        DTSN when it adds a new parent, that parent having the 'S' flag
        set, be
       scheduled to send to its DAO Parent set.  It MAY defer advertising the
        increment as long as it has node's DAO Parents.

   3.  When a DAO parent that already provides
        adequate connectivity.

   9.   A node that is not for a fully-storing node MUST increment its own
        DTSN when it receives REACHABLE(Confirmed) entry is expected, e.g.
       because a DIO from to request a DAO refresh is sent, then the DAO
       entry MUST be placed in the REACHABLE(Pending) state and the
       associated Retry Counter MUST be set to 0.

7.1.4.1.1.2.2.  REACHABLE(Pending)

   1.  When a DAO Parent that contains for a
        newly incremented DTSN.  (The newly incremented DTSN REACHABLE(Pending) entry is detected
        by comparing the value received in with a
       newer DAO Sequence Number, the DIO entry MUST be updated with the value last
        recorded for that
       logical equivalent of the DAO parent).

   10.  A fully-storing node contents and the entry MUST increment its own DTSN when it
        receives be
       placed in the REACHABLE(Confirmed) state.

   2.  When a DIO from DAO for a REACHABLE(Pending) entry is expected, e.g.
       because DAO Parent has (again) been triggered with respect to that contains a newly
        incremented DTSN and a set 'T' flag.

   11.
       neighbor, then the associated Retry Counter MUST be incremented.

   3.  When the associated Retry Counter for a storing or non-storing node joins REACHABLE(Pending) entry
       reaches a new DODAG iteration,
        it SHOULD increment its DTSN as if maximum threshold, the 'T' flag has been set.

   12.  DAO Transmission entry MUST be placed into the
       UNREACHABLE state and No-Path SHOULD be scheduled when a new parent is added to send to the
       node's DAO Parent set.

   13.  A node that receives a newly incremented DTSN from a DAO Parent
        MUST schedule a DAO transmission.

   o  When a node Parents.

7.1.4.1.1.3.  Operation in the UNREACHABLE state

   1.  An implementation SHOULD bound the time that the entry is not fully-storing sees a DTSN increment, it
      will increment its own DTSN.  This will cause
       allocated in the DTSN increment
      to extend down UNREACHABLE state.  Upon the DODAG to equivalent expiry
       of the first fully-storing node, which
      will send its DAOs back up, rebuilding source routes information
      along related timer (RemoveTimer), the way entry SHOULD be
       suppressed.

   2.  While the entry is in the UNREACHABLE state a node SHOULD make a
       reasonable attempt to the first node that incremented the DTSN, who
      then may report a No-Path to each of the new DAO information to its new parent.

   o
       parents.

   3.  When a fully-storing the node sees has completed an attempt to report a DTSN increment, it is caused No-Path to
      reissue its entire set
       each of routing table entries learned the DAO parents, the entry SHOULD be suppressed.

7.1.4.2.  Storing Mode DAO Message and Path Control

   In the storing mode of operation, a DAO message from DAOs
      (or an aggregated subset thereof), but will not need to increment
      its own DTSN.  The 'DTSN increment wave' stops when it encounters
      fully-storing nodes.

   o  When a fully-storing node sees will
   contain one or more Target Options, each Target Option specifying
   either a DTSN increment AND the 'T' flag
      is set, it does increment its own DTSN as well.  The 'T' flag
      'punches through' all nodes, causing all routing tables CONNECTED destination or a destination in the
      entire sub-DODAG of
   the node.

   For each attempt made to be refreshed.

6.2.8.  Sending report the DAO Messages entry to a set of DAO Parents
   parents, the Path Control field will be constructed as follows:

   1.  When storing nodes send DAO messages for stored entries  The size of the
       RRStack SHOULD path control field will be cleared in specified by the DAO message. PCS
       control field of the DODAG Configuration Option.  The default
       value is DEFAULT_PATH_CONTROL_SIZE.

   2.  DAO Messages sent  For each unique destination to DAO Parents MUST be unicast.

       *  The IPv6 Source Address reported that is CONNECTED, the node sending the DAO message.

       *  The IPv6 Destination Address
       logical equivalent of a path control bitmap that is DAO parent.

   3.  When the appointed time arrives (DelayDAO) for the transmission size of DAO messages (with jitter as appropriate) for
       the requested
       entries, path control field shall be initialized with the implementation MAY aggregate leftmost
       bits set, where the number of leftmost bits corresponds to the entries into a
       reduced numbers
       size of DAOs the path control field as specified by PCS.

   3.  For each unique destination to be reported to each parent, and
       perform compression if possible.

   4.  Note: it that is NOT RECOMMENDED not CONNECTED,
       i.e. that destination is contained in the node's sub-DODAG, the
       logical equivalent of a DAO Transmission (No-DAO) be
       scheduled when a DAO Parent path control bitmap that is removed from the DAO Parent set.

6.2.9.  Multicast Destination Advertisement Messages

   A special case size of
       the path control field shall be initialized by ORing the content
       of all of the Path Control fields received in DAO operation, distinct messages from unicast DAO operation,
   is multicast
       the node's children for that destination.

   4.  For each DAO operation which may be used to populate '1-hop'
   routing table entries.

   1.  A Parent that the node MAY multicast a DAO message to shall attempt an update to, the link-local scope all-
       nodes multicast address FF02::1.

   2.  A multicast
       node shall exclusively allocate 1 or more set bits from the path
       control bitmap to that DAO message MUST Parent.  The path control bits SHOULD
       be used only to advertise
       information about self, i.e. prefixes directly connected to or
       owned by this node, allocated in order of preference, such as a multicast group that the node is
       subscribed to most
       significant bits, or a global address owned by groupings of bits, are allocated to the node.

   3.  A multicast most
       preferred DAO message MUST NOT be used to relay connectivity
       information learned (e.g. through unicast DAO) from another parents as determined by the node.

   4.  Information obtained  Once a bit from
       the path control bitmap has been allocated to a multicast DAO MAY Parent for
       this attempt, the corresponding bit MUST be installed set in the
       routing table and MAY be propagated by a node Path
       Control field in unicast DAOs.

   5.  A node the DAO message sent to that DAO Parent, and
       that bit MUST NOT perform be allocated to any other DAO related processing on Parent.

   5.  A unicast DAO message may be sent for DAO Parents that have a
       received multicast DAO,
       non-zero Path Control field.

   6.  If any DAO Parent is left without any bits set in particular its Path
       Control field, then that a node unicast DAO message MUST NOT perform the
       actions of a be sent
       to that DAO parent upon receipt for this attempt.

7.1.5.  Operation of DAO Non-storing Nodes

   1.  In the non-storing mode of operation, each node sending a multicast DAO.

   o  The multicast DAO may be used
       message to enable direct P2P communication,
      without needing the its DODAG Parents will include a RPL routing structure Target option to relay
       describe itself, followed by RPL Transit Information option(s) to
       describe its parents.  This information is sufficient for the packets.

   o  The multicast DAO does not presume any
       DODAG relationship between Root to collect the emitter DODAG topology and construct source
       routes in the receiver.

7.  Packet Forwarding and Loop Avoidance/Detection
7.1.  Suggestions for Packet Forwarding

   When forwarding downward direction.

   2.  In the non-storing mode of operation, each node receiving a packet DAO
       message will arrange to pass the content of the DAO message along
       to the DODAG Root.  When possible the content of DAO messages may
       be aggregated.

   3.  When a destination, precedence DAO is given received from a child by a node who will not store
       a routing table entry for the DAO, the node MUST schedule to pass
       the DAO contents along to its DAO parents.

7.1.6.  Scheduling to
   selection of a next-hop successor as follows: Send DAO (or No-Path)

   1.  In the scope of this specification, it is preferred  An implementation SHOULD arrange to select a
       successor from a DODAG iteration that matches the RPLInstanceID
       marked in rate-limit the IPv6 header sending of the packet being forwarded.
       DAOs.

   2.  If a local administrative preference favors  When scheduling to send a route that has been
       learned from DAO, an implementation SHOULD
       equivalently start a different routing protocol than RPL, then use that
       successor.

   3. timer (DelayDAO) to delay sending the DAO.
       If there the DelayDAO timer is an entry in already running then the routing table matching DAO may be
       considered as already scheduled, and implementation SHOULD leave
       the
       destination that has been learned from a multicast destination
       advertisement (e.g. timer running at its present duration.

   o  When computing the destination is delay before sending a one-hop neighbor), then
       use that successor.

   4.  If DAO, in order to
      increase the effectiveness of aggregation, an implementation MAY
      allow time to receive DAOs from its sub-DODAG prior to emitting
      DAOs to its DAO Parents.

      *  Suppose there is an entry in the routing table matching implementation parameter DAO_LATENCY which
         represents the
       destination that has been learned from maximum expected time for a unicast destination
       advertisement (e.g. DAO operation to
         traverse the destination is located down LLN from the sub-
       DODAG), then use that successor.

   5.  If there is a DODAG iteration offering a route farthest node to a prefix
       matching the destination, then select one of those DODAG parents
       as a successor.

   6.  If there root.  The
         scheduled delay in such cases may be, for example, such that
         DAO_LATENCY/DAGRank(self_rank) <= DelayDAO < DAO_LATENCY/
         DAGRank(parent_rank), where DAGRank() is a DODAG parent offering a default route then select defined as in
         Section 3.5.2, such that nodes deeper in the DODAG may tend to
         report DAO messages first before their parent as a successor.

   7.  If there nodes will report
         DAO messages.  Note that this suggestion is a DODAG iteration offering a route intended as an
         optimization to a prefix
       matching allow efficient aggregation -- it is not
         required for correct operation in the destination, but all DODAG parents have been tried
       and are temporarily unavailable (as determined general case.

7.1.7.  Triggering DAO Message from the Sub-DODAG

   Triggering DAO messages from the Sub-DODAG occurs by using the forwarding
       procedure), then select a DODAG sibling as a successor.

   8.  Finally, if no DODAG siblings are available,
   following control fields with the packet is
       dropped.  ICMP Destination Unreachable may be invoked.  An
       inconsistency is detected.

   TTL MUST be decremented when forwarding.  If rules described below:

   The DTSN field from the packet DIO is being
   forwarded via a sibling, then sequence number that is part of the TTL MAY be decremented more
   aggressively (by more than one)
   mechanism to limit the impact trigger DAO messages.  The motivation to use a sequence
   number is to provide some means of possible
   loops.

   Note that the chosen successor MUST NOT be reliable signaling to the neighbor sub-
   DODAG.  Whereas a control flag that was the
   predecessor of the packet (split horizon), except in the case where
   it is intended activated for a short time may
   be unobserved by the packet to change from an up to an down flow,
   such as switching from DIO routes to DAO routes as sub-DODAG if the destination is
   neared.

7.2.  Loop Avoidance and Detection

   RPL loop avoidance mechanisms triggering DIO messages are kept simple and designed to
   minimize churn and states.  Loops
   lost, the DTSN increment may form for be observed later even if some
   intervening DIO messages have been lost.

   The 'T' flag provides a number of reasons,
   from control packet loss way to sibling forwarding.  RPL includes a
   reactive loop detection technique that protects from meltdown and
   triggers repair signal the refresh of broken paths.

   RPL loop detection uses DAO information that is placed into
   over the packet in entire DODAG version.  Whereas a DTSN increment may only
   trigger a DAO refresh as far as the IPv6 flow label.  The IPv6 flow label is defined in [RFC2460] and next storing node (because a
   storing node will not increment its operation is further specified own DTSN in response, as
   described in [RFC3697].  For the purpose rules below), the assertion of
   RPL operations, the flow label is constructed 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               |O|S|R|F|  SenderRank   | RPLInstanceID |
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 12: RPL Flow Label

   Down 'O' bit:  1-bit 'T' flag indicating whether in
   conjunction with an incremented DTSN will result in a DAO refresh
   from the packet is expected entire DODAG.

   The control fields are used to progress up or down. trigger DAO messages as follows:

   1.  A router sets DAO Trigger Sequence Number (DTSN) MUST be maintained by each
       node per RPL Instance.  The DTSN, in conjunction with the 'O' bit when 'T'
       flag from the
         packet is expect to progress down (using DIO message, provides a means by which DAO routes), and
         resets it when forwarding towards messages
       may be reliably triggered in the root event of the DODAG
         iteration.  A host topology change.

   2.  The DTSN MUST set be advertised by the bit to 0.

   Sibling 'S' bit:  1-bit flag indicating whether node in the packet DIO message.

   3.  A node keeps track of the DTSN that it has been
         forwarded via a sibling at heard from the present rank, and denotes a risk last
       DIO from each of a sibling loop.  A host sets the bit to 0.

   Rank-Error 'R' bit:  1-bit flag indicating whether a rank error was
         detected.  A rank error is detected when its DAO Parents.  Note that there is one DTSN
       maintained per DAO Parent- each DAO Parent may independently
       increment it at will.

   4.  DAO Transmission SHOULD be scheduled when a mismatch in
         the relative ranks and the direction as indicated in new parent is added
       to the 'O'
         bit. DAO Parent set.

   5.  A host node that receives a newly incremented DTSN from a DAO Parent
       MUST schedule a DAO transmission.

   o  In storing mode operation, when a node sees a DTSN increment, it
      is caused to reissue its entire set the bit of routing table entries
      learned from DAO messages (or an aggregated subset thereof), but
      will not need to 0.

   Forwarding-Error 'F' bit:  1-bit flag indicating that this increment its own DTSN.

   o  In either storing or non-storing modes of operation, when a node can
         not forward the packet further towards
      sees a DTSN increment AND the destination. 'T' flag is set, it does increment
      its own DTSN as well.  The
         'F' bit might 'T' flag 'punches through' all nodes,
      causing all routing state from the entire sub-DODAG to be set by sibling that can not forward
      refreshed.

7.1.8.  Sending DAO Messages to DAO Parents

   1.  DAO Messages sent to DAO Parents MUST be unicast.

       *  The IPv6 Source Address is a
         parent a packet with link local address of the Sibling 'S' bit set, or by a child node that does not have a route to destination for
          sending the DAO message.

       *  The IPv6 Destination Address is a packet
         with link local address of the down 'O' bit set.
          DAO parent.

   2.  A host node MUST set send the bit DAO with the same sequence to 0.

   SenderRank:  8-bit field set all its DAO
       parents that are to zero by be used on the source and way back to
         DAGRank(rank) by a router that forwards inside the RPL network.
         (Note DAO target.

   3.  When using source routing, a Destination that builds the case where DAGRank(rank) does not fit into 8
         bits is under investigation.)

   RPLInstanceID:  8-bit field indicating the DODAG instance along which DAO also
       indicates its parent in the packet is sent.

7.2.1.  Source Node Operation

   A packet that is sourced at DAO as a Transit Information option.
       If the node connected has multiple DAO parents, it MAY include one Transit
       Information Option per parent and pass the DAO to a RPL network one or
   destined to a node connected to a RPL network MUST be issued with more
       parent.  The Transit Information option indicates the
   flow label zeroed out, but preference
       for that parent encoded in the RPLInstanceID field.

   If Path Control bitfield.

   4.  When the source is aware of appointed time arrives (DelayDAO) for the RPLInstanceID that is preferred transmission
       of DAO messages (with jitter as appropriate) for the
   flow, then it MUST set requested
       entries, the RPLInstanceID field in implementation MAY aggregate the flow label
   accordingly, otherwise it MUST set it to the RPL_DEFAULT_INSTANCE.

   If entries into a compression mechanism such as 6LoWPAN is applied
       reduced numbers of DAOs to the packet,
   the flow label MUST NOT be compressed even reported to each parent, and
       perform compression if possible.

   5.  Note: it is set to all
   zeroes.

7.2.2.  Router Operation

7.2.2.1.  Conformance to RFC 3697

   [RFC3697] mandates NOT RECOMMENDED that a DAO Transmission (No-Path) be
       scheduled when a DAO Parent is removed from the Flow Label value DAO Parent set.

   6.  A node MAY set by the source MUST
   be delivered unchanged K flag in a unicast DAO message to the destination node(s).

   In solicit a
       unicast DAO-ACK in response in order to restore confirm the flow label to its original value, an RPL
   router that delivers a packet to attempt.  A
       node receiving a destination connected to unicast DAO message with the K flag set SHOULD
       respond with a RPL
   network or that routes DAO-ACK.  A node receiving a packet outside the RPL network MUST zero out
   all the fields but the RPLInstanceID field that must be delivered DAO message without
       the K flag set MAY respond with a change.

7.2.2.2.  Instance Forwarding

   Instance IDs are used DAO-ACK, especially to avoid loops between DODAGs report
       an error condition.

7.1.9.  Multicast Destination Advertisement Messages

   A special case of DAO operation, distinct from different
   origins.  DODAGs that 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 unicast DAO operation,
   is
   associated multicast DAO operation which may be used to populate '1-hop'
   routing table entries.

   1.  A node MAY multicast a given instance.

   The RPLInstanceID is placed by the source in DAO message to the flow label.  This
   RPLInstanceID link-local scope all-
       nodes multicast address FF02::1.

   2.  A multicast DAO message MUST match the RPL Instance onto which the packet is
   placed by any node, be it a host used only to advertise
       information about self, i.e. prefixes directly connected to or router.

   When a router receives
       owned by this node, such as a packet multicast group that specifies a given RPLInstanceID
   and the node can forward the packet along the DODAG associated is
       subscribed to
   that instance, then the router MUST do so and leave the RPLInstanceID
   flag unchanged.

   If any node can not forward or a packet along global address owned by the DODAG associated node.

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

   4.  Information obtained from a multicast DAO MAY be installed in the flow label, then the node SHOULD discard the
   packet.

7.2.2.3.  DAG Inconsistency Loop Detection

   The DODAG is inconsistent if the direction of
       routing table and MAY be propagated by a packet does not match
   the rank relationship. node in unicast DAOs.

   5.  A receiver detects an inconsistency if it
   receives a packet with either:

      the 'O' bit set (to down) from a node of MUST NOT perform any other DAO related processing on a higher rank.

      the 'O' bit reset (for up) from
       received multicast DAO, in particular a node of a lesser rank. MUST NOT perform the 'S' bit set (to sibling) from
       actions of a node DAO parent upon receipt of a different rank.

   When multicast DAO.

   o  The multicast DAO may be used to enable direct P2P communication,
      without needing the DODAG root increments RPL routing structure to relay the DODAGSequenceNumber a temporary
   rank discontinuity may form packets.

   o  The multicast DAO does not presume any DODAG relationship between
      the next iteration emitter and the prior
   iteration, in particular if nodes are adjusting their rank in the
   next iteration receiver.

8.  Packet Forwarding and deferring their migration into the next iteration.
   A router that is still Loop Avoidance/Detection

8.1.  Suggestions for Packet Forwarding

   When forwarding a member of the prior iteration may choose packet to
   forward a packet destination, precedence is given to
   selection of a (future) parent that next-hop successor as follows:

   1.  This specification only covers how a successor is in the next iteration.
   In some cases this could cause selected from
       the parent to detect an inconsistency
   because DODAG version that matches the rank-ordering RPLInstanceID marked in the prior iteration is not necessarily
       IPv6 header of the same packet being forwarded.  Routing outside the
       instance can be done as long as additional rules are put in the next iteration place
       such as strict ordering of instances and the packet may be judged routing protocols to not
   be making forward progress.
       protect against loops.

   2.  If the sending router is aware a local administrative preference favors a route that the
   chosen successor has already joined the next iteration, then the
   sending router MUST update the SenderRank to INFINITE_RANK as it
   forwards the packets across the discontinuity into the next DODAG
   iteration in order to avoid been
       learned from a false detection of rank inconsistency.

   One inconsistency along the path different routing protocol than RPL, then use that
       successor.

   3.  If there is not considered as a critical
   error and an entry in the packet may continue.  But a second detection along routing table matching the
   path of
       destination that has been learned from a same packet should not occur and multicast destination
       advertisement (e.g. the packet destination is dropped.

   This process a one-hop neighbor), then
       use that successor.

   4.  If there is controlled by the Rank-Error bit an entry in the Flow Label.
   When an inconsistency, is detected on a packet, if routing table matching the Rank-Error bit
   was not set then
       destination that has been learned from a unicast destination
       advertisement (e.g. the Rank-Error bit destination is set. located down the sub-
       DODAG), then use that successor.  If it was set there are DAO Path Control
       bits associated with multiple successors, then consult the packet
   is discarded and Path
       Control bits to order the trickle timer successors by preference when choosing.

   5.  If there is reset.

7.2.2.4.  Sibling Loop Avoidance

   When a packet is forwarded along siblings, it cannot be checked for
   forward progress DODAG version offering a route to a prefix matching
       the destination, then select one of those DODAG parents as a
       successor according to the OF and routing metrics.

   6.  Any other as-yet-unattempted DODAG parent may loop between siblings.  Experimental
   evidence has shown that one sibling hop can be very useful but is
   generally sufficient to avoid loops.  Based on that evidence, this
   specification enforces chosen for the simple rule that
       next attempt to forward a unicast packet may not make 2
   sibling hops in a row.

   When when no better match
       exists.

   7.  If there is a host issues DODAG version offering a packet or when route to a router forwards prefix matching
       the destination, but all DODAG parents have been tried and are
       temporarily unavailable (as determined by the forwarding
       procedure), then select a packet to DODAG sibling as a
   non-sibling, the Sibling bit successor (after
       appropriate packet marking for loop detection as described in
       Section 8.2.

   8.  Finally, if no DODAG siblings are available, the packet is
       dropped.  ICMP Destination Unreachable may be invoked (an
       inconsistency is detected).

   TTL must be reset.  When decremented when forwarding.  If the packet is being
   forwarded via a
   router forwards sibling, then the TTL may be decremented more
   aggressively (by more than one) to a sibling: if limit the Sibling bit was not set then impact of possible
   loops.

   Note that the
   Sibling bit is set.  If chosen successor MUST NOT be the Sibling bit neighbor that was set then then the router
   SHOULD return
   predecessor of the packet to (split horizon), except in the sibling that that passed case where
   it with is intended for the
   Forwarding-Error 'F' bit set.

7.2.2.5.  DAO Inconsistency Loop Detection and Recovery

   A DAO inconsistency happens when router that has packet to change from an up to an down DAO route
   via a child that is a remnant flow,
   such as switching from an obsolete state that is not
   matched in the child.  With DIO routes to DAO inconsistency routes as the destination is
   neared.

8.2.  Loop Avoidance and Detection

   RPL loop recovery, a packet
   can be used avoidance mechanisms are kept simple and designed to recursively explore
   minimize churn and cleanup the obsolete DAO
   states along a sub-DODAG.

   In a general manner, states.  Loops may form for a number of reasons,
   from control packet loss to sibling forwarding.  RPL includes a
   reactive loop detection technique that goes down should never go up
   again.  If DAO inconsistency protects from meltdown and
   triggers repair of broken paths.

   RPL loop recovery detection uses information that is applied, then placed into the
   router SHOULD send packet.
   A future version of this specification will detail how this
   information is carried with the packet to the parent that passed it with (e.g. a hop-by-hop option
   ([I-D.hui-6man-rpl-option]) or summarized somehow into the
   Forwarding-Error 'F' bit set.  Otherwise flow
   label).  For the router MUST silently
   discard purpose of RPL operations, the packet.

7.2.2.6.  Forward Path Recovery

   Upon receiving a packet information carried
   with a Forwarding-Error bit set, the node
   MUST remove 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|S|R|F|0|0|0|0| RPLInstanceID |          SenderRank           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          RPL Packet Information

   Down 'O' bit:  1-bit flag indicating whether the routing states that caused forwarding packet is expected
         to that
   neighbor, clear progress up or down.  A router sets the Forwarding-Error 'O' bit and attempt to send when the
         packet again.  The packet may its way is expect to an alternate neighbor.  If
   that alternate neighbor still has an inconsistent progress down (using DAO state via this
   node, the process will recurse, this node will set the Forwarding-
   Error 'F' bit routes), and
         resets it when forwarding towards the routing state in the alternate neighbor will be
   cleaned up as well.

8.  Multicast Operation

   This section describes further root of the multicast routing operations over
   an IPv6 DODAG
         version.  A host or RPL network, and specifically how unicast DAOs can be used to
   relay group registrations up.  Wherever leaf node MUST set the following text mentions
   Multicast Listener Discovery (MLD), one can read MLDv2 ([RFC3810]) or
   v3.

   As is traditional, bit to 0.

   Sibling 'S' bit:  1-bit flag indicating whether the packet has been
         forwarded via a listener uses sibling at the present rank, and denotes a protocol such as MLD with risk
         of a
   router to register sibling loop.  A host or RPL leaf node MUST set the bit to
         0.

   Rank-Error 'R' bit:  1-bit flag indicating whether a multicast group.

   Along the path between rank error was
         detected.  A rank error is detected when there is a mismatch in
         the router relative ranks and the DODAG root, MLD requests
   are mapped and transported direction as DAO messages within indicated in the 'O'
         bit.  A host or RPL protocol;
   each hop coalesces leaf node MUST set the multiple requests for a same group as a single
   DAO message bit to 0.

   Forwarding-Error 'F' bit:  1-bit flag indicating that this node can
         not forward the parent(s), in a fashion similar to proxy IGMP, but
   recursively between child router and parent up to packet further towards the root.

   A router destination.  The
         'F' bit might select be set by sibling that can not forward 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 a packet with the transmission fails
   over Sibling 'S' bit set, or by a child
         node that link.  Alternatively the router might select does not have a route to copy
   additional parents as it would do destination for DAO messages advertising
   unicast destinations, in 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 case there might be duplicates that
         the router will need packet is sent.

   SenderRank:  16-bit field set to prune.

   As zero by the source and to
         DAGRank(rank) by a result, multicast routing states are installed in each router on that forwards inside the way from RPL network.

8.2.1.  Source Node Operation

   If the listeners to source is aware of the root, enabling RPLInstanceID that is preferred for the
   packet, then it MUST set the RPLInstanceID field associated with the root to copy a
   multicast
   packet accordingly, otherwise it MUST set it to all its children routers the
   RPL_DEFAULT_INSTANCE.

8.2.2.  Router Operation

8.2.2.1.  Instance Forwarding

   Instance IDs are used to avoid loops between DODAGs from different
   origins.  DODAGs that had issued a DAO
   message including a DAO constructed for that multicast group, as well as all antagonistic constraints might
   contain paths that, if mixed together, would yield loops.  Those
   loops are avoided by forwarding a packet along the
   attached nodes DODAG that registered over MLD.

   For unicast traffic, it is expected that
   associated to a given instance.

   The RPLInstanceID is associated by the grounded root of an
   DODAG terminates RPL and MAY redistribute source with the packet.  This
   RPLInstanceID MUST match the RPL routes over Instance onto which the
   external infrastructure using whatever routing protocol packet is used
   there.
   placed by any node, be it a host or router.  For multicast traffic, the root MAY proxy MLD for all the
   nodes attached to traffic originating
   outside of the RPL routers (this would domain there may be needed if the
   multicast source is located in the external infrastructure).  For
   such a source, mapping occurring at the packet will be replicated as it flows down
   gateway into the
   DODAG RPL domain, possibly based on an encoding within the multicast routing table entries installed from the
   DAO message.

   For
   flow label.  This aspect of RPL operation is to be clarified in a source inside
   future version of this specification.

   When a router receives a packet that specifies a given RPLInstanceID
   and the DODAG, node can forward the packet is passed to along the preferred
   parents, and if DODAG associated to
   that fails instance, then to the alternates in router MUST do so and leave the DODAG.  The RPLInstanceID
   value unchanged.

   If any node can not forward a packet is also copied to all the registered children, except for the
   one that passed along the packet.  Finally, if there is a listener in DODAG associated to
   the
   external infrastructure RPLInstanceID, then the DODAG root has to further propagate node SHOULD discard the packet into and send
   an ICMP error message.

8.2.2.2.  DAG Inconsistency Loop Detection

   The DODAG is inconsistent if the external infrastructure.

   As direction of a result, packet does not match
   the DODAG Root acts as rank relationship.  A receiver detects an automatic proxy Rendezvous
   Point for the RPL network, and as source towards the Internet for all
   multicast flows started in inconsistency if it
   receives a packet with either:

      the RPL LLN.  So regardless 'O' bit set (to down) from a node of whether a higher rank.

      the
   root is actually attached to 'O' bit reset (for up) from a node of a lesser rank.

      the Internet, and regardless 'S' bit set (to sibling) from a node of whether a different rank.

   When the DODAG is grounded or floating, the root can serve inner multicast
   streams at all times.

9.  Maintenance of Routing Adjacency

   The selection of successors, along root increments the default paths up along DODAGVersionNumber a temporary
   rank discontinuity may form between the
   DODAG, or along next version and the paths learned from destination advertisements
   down along prior
   version, in particular if nodes are adjusting their rank in the DODAG, leads to next
   version and deferring their migration into the formation of routing adjacencies next version.  A
   router that require maintenance.

   In IGPs such as OSPF [RFC4915] or IS-IS [RFC5120], the maintenance is still a member of the prior version may choose to
   forward a routing adjacency involves packet to a (future) parent that is in the use of Keepalive mechanisms (Hellos)
   or other protocols such as BFD ([I-D.ietf-bfd-base]) and MANET
   Neighborhood Discovery Protocol (NHDP [I-D.ietf-manet-nhdp]).
   Unfortunately, such next version.
   In some cases this could cause the parent to detect an approach inconsistency
   because the rank-ordering in the prior version is not desirable in constrained
   environments such necessarily the
   same as LLN and would lead to excessive control traffic in light of the data traffic with a negative impact on both link
   loads next version and nodes resources.  Overhead to maintain the routing
   adjacency should packet may be minimized.  Furthermore, it is not always
   possible judged to rely on not be
   making forward progress.  If the link or transport layer sending router is aware that the
   chosen successor has already joined the next version, then the
   sending router MUST update the SenderRank to provide
   information of INFINITE_RANK as it
   forwards the associated link state.  The network layer needs packets across the discontinuity into the next DODAG
   version in order to
   fall back on its own mechanism.

   Thus RPL makes use avoid a false detection of rank inconsistency.

   One inconsistency along the path is not considered as a different approach consisting of probing critical
   error and the
   neighbor using packet may continue.  But a Neighbor Solicitation message (see [RFC4861]).  The
   reception second detection along the
   path of a Neighbor Advertisement (NA) message with same packet should not occur and the
   "Solicited Flag" set packet is used to verify dropped.

   This process is controlled by the validity of Rank-Error bit associated with the routing
   adjacency.  Such mechanism MAY be used prior to sending a data
   packet.  This allows for detecting whether or  When an inconsistency is detected on a packet, if the Rank-
   Error bit was not set then the routing
   adjacency Rank-Error bit is still valid, and should set.  If it not be the case, select
   another feasible successor to forward was set
   the packet.

10.  Guidelines for Objective Functions

   An Objective Function (OF) allows for packet is discarded and the selection of trickle timer is reset.

8.2.2.3.  Sibling Loop Avoidance

   When a DODAG to
   join, packet is forwarded along siblings, it cannot be checked for
   forward progress and a number of peers in may loop between siblings.  Experimental
   evidence has shown that DODAG as parents.  The OF is used
   to compute an ordered list of parents.  The OF one sibling hop can be very useful and is also responsible
   generally sufficient to
   compute the rank of the device within avoid loops.  Based on that evidence, this
   specification enforces the DODAG iteration.

   The Objective Function is indicated simple rule that a packet may not make 2
   sibling hops in the DIO message using an
   Objective Code Point (OCP), as specified a row.

   When a host issues a packet or when a router forwards a packet to a
   non-sibling, the Sibling bit in
   [I-D.ietf-roll-routing-metrics], and indicates the method that packet must be used reset.  When a
   router forwards to construct a sibling: if the DODAG (e.g. "minimize Sibling bit was not set then the path cost using
   Sibling bit is set.  If the ETX metric and avoid 'Blue' links").  The Objective Code Points
   are specified in [I-D.ietf-roll-routing-metrics],
   [I-D.ietf-roll-of0], and related companion specifications.

   Most Objective Functions are expected Sibling bit was set then then the router
   SHOULD return the packet to follow the same abstract
   behavior:

   o  The parent selection is triggered each time sibling that that passed it with the
   Forwarding-Error 'F' bit set and the 'S' bit left untouched.

8.2.2.4.  DAO Inconsistency Loop Detection and Recovery

   A DAO inconsistency happens when router that has an event indicates down DAO route
   via a child that is a potential next hop information remnant from an obsolete state that is updated.  This might
      happen upon not
   matched in the reception of child.  With DAO inconsistency loop recovery, a DIO message, packet
   can be used to recursively explore and cleanup the obsolete DAO
   states along a timer elapse, or sub-DODAG.

   In a
      trigger indicating that the state of general manner, a candidate neighbor has
      changed.

   o  An OF scans all packet that goes down should never go up
   again.  If DAO inconsistency loop recovery is applied, then the interfaces on
   router SHOULD send 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 packet back to be usable or not for RPL operation.  An interface
      can also be configured the parent that passed it with
   the Forwarding-Error 'F' bit set and the 'O' bit left untouched.
   Otherwise the router MUST silently discard the packet.

8.2.2.5.  Forward Path Recovery

   Upon receiving a packet with a preference or dynamically learned Forwarding-Error bit set, the node
   MUST remove the routing states that caused forwarding to
      be better than another by some heuristics that might be link-layer
      dependent
   neighbor, clear the Forwarding-Error bit and are out of scope.  Finally attempt to send the
   packet again.  The packet may be sent to an interface might or not
      match a required criterion for alternate neighbor.  If
   that alternate neighbor still has an Objective Function, for instance
      a degree of security.  As a result some interfaces might be
      completely excluded from inconsistent DAO state via this
   node, the computation, while others might be
      more or less preferred.

   o  An OF scans all process will recurse, this node will set the candidate neighbors on Forwarding-
   Error 'F' bit and the possible interfaces
      to check whether they can act as a router for a DODAG.  There
      might routing state in the alternate neighbor will be multiple of them
   cleaned up as well.

9.  Multicast Operation

   This section describes further the multicast routing operations over
   an IPv6 RPL network, and a candidate neighbor might need to
      pass some validation tests before it specifically how unicast DAOs can be used.  In particular,
      some link layers require experience on the activity with a router used to enable
   relay group registrations up.  Wherever the router as following text mentions
   Multicast Listener Discovery (MLD), one can read MLDv1 ([RFC2710]) or
   MLDv2 ([RFC3810]).

   As is traditional, a next hop.

   o  An OF computes self's rank by adding listener uses a protocol such as MLD with a
   router to register to the rank of the candidate a value representing multicast group.

   Along the relative locations of self and path between the
      candidate in router and the DODAG iteration.

      *  The increase in rank must be at least MinHopRankIncrease.
         (This prevents the creation of a path of sibling links
         connecting a child with its parent.)

      *  To keep loop avoidance root, MLD requests
   are mapped and metric optimization in alignment, transported as DAO messages within the increase in rank should reflect any increase in RPL protocol;
   each hop coalesces the metric
         value.  For example, with multiple requests for a purely additive metric such same group as ETX, a single
   DAO message to the increase parent(s), in rank can be made proportional a fashion similar to proxy IGMP, but
   recursively between child router and parent up to the increase 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 metric.

      *  Candidate neighbors transmission fails
   over that would cause self's rank link.  Alternatively the router might select to increase
         are not considered copy
   additional parents as it would do for parent selection

   o  Candidate neighbors DAO messages advertising
   unicast destinations, in which case there might be duplicates that advertise an OF incompatible with the set
      of OF specified by
   the policy functions are ignored.

   o router will need to prune.

   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 result, multicast routing states are
      critical to reach installed in each router on
   the objective.  A test between way from the routers
      determines an order relation.

      *  If listeners to the root, enabling the root to copy a
   multicast packet to all its children routers are roughly equal that had issued a DAO
   message including a DAO for that relation then multicast group, as well as all the
         next test
   attached nodes that registered over MLD.

   For unicast traffic, it is attempted between the routers,

      *  Else expected that the best grounded root of the 2 becomes the current best parent an
   DODAG terminates RPL and MAY redistribute 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 RPL routes over the scan
   external infrastructure using whatever routing protocol is complete, used in
   the preferred parent is elected and
      self's rank is computed as other routing domain.  For multicast traffic, the preferred parent rank plus root MAY proxy
   MLD for all the step
      in rank with that parent.

   o  Other rounds of scans might be necessary nodes attached to elect alternate
      parents and siblings.  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 (siblings) are
         ignored for parent selection

      *  Candidate neighbors of a lesser rank than self (non-siblings)
         are preferred

11.  RPL Constants and Variables

   Following is a summary of RPL constants and variables.

   BASE_RANK  This domain (this would be
   needed if the multicast source is located in the rank for external
   infrastructure).  For such a virtual root that might source, the packet will be used to
         coordinate multiple roots.  BASE_RANK has replicated as
   it flows down the DODAG based on the multicast routing table entries
   installed from the DAO message.

   For a value of 0.

   ROOT_RANK  This source inside the DODAG, the packet is passed to the rank 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.  ROOT_RANK root has to further propagate
   the packet into the external infrastructure.

   As a value
         of 1.

   INFINITE_RANK  This is result, the constant maximum DODAG Root acts as an automatic proxy Rendezvous
   Point for the rank.
         INFINITE_RANK has a value RPL network, and as source towards the Internet for all
   multicast flows started in the RPL LLN.  So regardless of 0xFFFF.

   RPL_DEFAULT_INSTANCE  This is whether the RPLInstanceID that
   root is used by this
         protocol by a node without any overriding policy.
         RPL_DEFAULT_INSTANCE has a value actually attached to the Internet, and regardless of 0.

   DEFAULT_DIO_INTERVAL_MIN  TBD (To be determined)

   DEFAULT_DIO_INTERVAL_DOUBLINGS  TBD (To be determined)

   DEFAULT_DIO_REDUNDANCY_CONSTANT  TBD (To be determined)

   DIO Timer  One instance per whether
   the 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 5.3.5.1

   DAG Sequence Number Increment Timer  Up grounded or floating, the root can serve inner multicast
   streams at all times.

10.  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 one instance per DODAG the formation of routing adjacencies
   that require maintenance.

   In IGPs such as OSPF [RFC4915] or IS-IS [RFC5120], the node is acting maintenance of
   a routing adjacency involves the use of Keepalive mechanisms (Hellos)
   or other protocols such as DODAG root of.  May BFD ([I-D.ietf-bfd-base]) and MANET
   Neighborhood Discovery Protocol (NHDP [I-D.ietf-manet-nhdp]).
   Unfortunately, such an approach is not be supported desirable in all implementations.  Expiry triggers revision constrained
   environments such as LLN and would lead to excessive control traffic
   in light of
         DODAGSequenceNumber, causing the data traffic with a new series of updated DIO
         message negative impact on both link
   loads and nodes resources.  Overhead to be sent.  Interval maintain the routing
   adjacency should be chosen appropriate to
         propagation time of DODAG and as appropriate minimized.  Furthermore, it is not always
   possible to application
         requirements (e.g. response time vs. overhead).

   DelayDAO Timer  Up rely on the link or transport layer to one instance per DAO parent (the subset provide
   information of
         DODAG parents chosen the associated link state.  The network layer needs to receive destination advertisements) per
         DODAG.  Expiry triggers sending
   fall back on its own mechanism.

   Thus RPL makes use of DAO a different approach consisting of probing the
   neighbor using a Neighbor Solicitation message to (see [RFC4861]).  The
   reception of a Neighbor Advertisement (NA) message with the DAO
         parent.  See Section 6.2.6

   RemoveTimer  Up
   "Solicited Flag" set is used to one instance per DAO entry per neighbor (i.e.
         those neighbors that have given DAO messages verify the validity of the routing
   adjacency.  Such mechanism MAY be used prior to this node as a
         DODAG parent) Expiry triggers sending a change in state data
   packet.  This allows for detecting whether or not the DAO
         entry, setting up routing
   adjacency is still valid, and should it not be the case, select
   another feasible successor to do unreachable (No-DAO) advertisements or
         immediately deallocating forward the DAO entry if there are no DAO packet.

11.  Guidelines for Objective Functions

   An Objective Function (OF) allows for the selection of a DODAG to
   join, and a number of peers in that DODAG as parents.  See Section 6.2.4.1.1.3

12.  Manageability Considerations  The aim of this section OF is used
   to give consideration compute an ordered list of parents.  The OF is also responsible to
   compute the manageability rank of RPL, and how RPL will be operated in LLN beyond the use of a MIB
   module. device within the DODAG version.

   The scope of this section Objective Function is indicated in the DIO message using an
   Objective Code Point (OCP), as specified in
   [I-D.ietf-roll-routing-metrics], and indicates the method that must
   be used to consider construct the following
   aspects of manageability: fault management, configuration, accounting DODAG.  The Objective Code Points are
   specified in [I-D.ietf-roll-routing-metrics], [I-D.ietf-roll-of0],
   and performance.

12.1.  Control of related companion specifications.

11.1.  Objective Function and Policy

12.1.1.  Initialization Mode

   When 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 node potential next hop information is first powered up, it may either choose to stay silent
   and not send any multicast DIO message until it has joined updated.  This might
      happen upon the reception of a DIO message, a DODAG, timer elapse, all
      DODAG parents are unavailable, or to immediately root a transient DODAG and start sending multicast
   DIO messages.  A RPL implementation SHOULD allow configuring whether trigger indicating that the node should stay silent or should start advertising DIO messages.

   Furthermore,
      state of a candidate neighbor has changed.

   o  An OF scans all the implementation SHOULD 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 allow configuring whether be usable or not the node should start sending an DIS message as an initial
   probe for nearby DODAGs, RPL operation.  An interface
      can also be configured with a preference or should simply wait until it received DIO
   messages from other nodes dynamically learned to
      be better than another by some heuristics that might be link-layer
      dependent and are part of existing DODAGs.

12.1.2.  DIO Base option

   RPL specifies a number out of protocol parameters.

   A RPL implementation SHOULD allow configuring the following routing
   protocol parameters, which are further described in Section 5.1.1:

   DAGPreference
   RPLInstanceID
   DAGObjectiveCodePoint
   DODAGID
   Destination Prefixes
   DIOIntervalDoublings
   DIOIntervalMin
   DIORedundancyConstant

   DAG Root behavior:  In some cases, a node may scope.  Finally an interface might or not want to permanently
         act as
      match a DODAG root if it cannot join required criterion for an Objective Function, for instance
      a grounded DODAG.  For
         example degree of security.  As a battery-operated node may not want result some interfaces might be
      completely excluded from the computation, 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 DODAG
         root router for a long period DODAG.  There
      might be multiple of time.  Thus them and a RPL implementation MAY
         support the ability candidate neighbor might need to configure whether or not
      pass some validation tests before it can be used.  In particular,
      some link layers require experience on the activity with a node could
         act router
      to enable the router as a DODAG root for next hop.

   o  An OF computes self's rank by adding to the rank of the candidate
      a configured period value representing the relative locations of time. self and the
      candidate in the DODAG Table Entry Suppression  A RPL implementation SHOULD provide version.

      *  The increase in rank must be at least MinHopRankIncrease.

      *  To keep loop avoidance and metric optimization in alignment,
         the ability 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 configure 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 timer after 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 expiration of which
         logical equivalent routers,

      *  Else the best of the DODAG table that contains all two routers becomes the
         records about current best
         parent and the scan continues with the next candidate neighbor

      *  Some OFs may include a DODAG is suppressed, test to be invoked compare the ranks that would
         result if the DODAG node joined either router

   o  When the scan is complete, the preferred parent set becomes empty.

12.1.3.  Trickle Timers

   A RPL implementation makes use 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 trickle timer scans might be necessary to govern elect alternate
      parents and siblings.  In the sending
   of DIO message.  Such an algorithm is determined a by a set of
   configurable parameters next rounds:

      *  Candidate neighbors that are then advertised by the DODAG root
   along not in the same DODAG in DIO messages.

   For each DODAG, a RPL implementation MUST allow are ignored

      *  Candidate neighbors that are of greater rank than self are
         ignored

      *  Candidate neighbors of an equal rank to self (siblings) are
         ignored for the monitoring parent selection

      *  Candidate neighbors of
   the following parameters, further described in Section 5.3.5.1:

   I
   T
   C
   I_min
   I_doublings

   A a lesser rank than self (non-siblings)
         are preferred

12.  RPL implementation SHOULD provide Constants and Variables

   Following is a command (for example via API,
   CLI, or SNMP MIB) whereby any procedure that detects an inconsistency
   may cause the trickle timer to reset.

12.1.4.  DAG Sequence Number Increment

   A summary of RPL implementation may allow by configuration at constants and variables.

   BASE_RANK  This is the DODAG rank for a virtual root that might be used to
   refresh
         coordinate multiple roots.  BASE_RANK has a value of 0.

   ROOT_RANK  This is the rank for a DODAG states by updating the DODAGSequenceNumber.  A RPL
   implementation SHOULD allow configuring whether or not periodic or
   event triggered mechanism are used root.  ROOT_RANK has a value
         of MinHopRankIncrease (as advertised by the DODAG root to control
   DODAGSequenceNumber change.

12.1.5.  Destination Advertisement Timers

   The following set of parameters of root), such
         that DAGRank(ROOT_RANK) is 1.

   INFINITE_RANK  This is the DAO messages SHOULD be
   configurable:

   o  The DelayDAO timer

   o  The Remove timer

12.1.6.  Policy Control

   DAG discovery enables nodes to implement different policies constant maximum for
   selecting their DODAG parents.

   A RPL implementation SHOULD allow configuring the set rank.
         INFINITE_RANK has a value of acceptable
   or preferred Objective Functions (OF) referenced 0xFFFF.

   RPL_DEFAULT_INSTANCE  This is the RPLInstanceID that is used by this
         protocol by their Objective
   Codepoints (OCPs) for a node to join without any overriding policy.
         RPL_DEFAULT_INSTANCE has a DODAG, and what action should value of 0.

   DEFAULT_PATH_CONTROL_SIZE  TBD (To be taken if none determined)

   DEFAULT_DIO_INTERVAL_MIN  TBD (To be determined)

   DEFAULT_DIO_INTERVAL_DOUBLINGS  TBD (To be determined)
   DEFAULT_DIO_REDUNDANCY_CONSTANT  TBD (To be determined)

   DEFAULT_MIN_HOP_RANK_INCREASE  TBD a power of two (To be determined)

   DIO Timer  One instance per DODAG that a node's candidate neighbors advertise node is a member of.  Expiry
         triggers DIO message transmission.  Trickle timer with variable
         interval in [0, DIOIntervalMin..2^DIOIntervalDoublings].  See
         Section 6.3.1

   DAG Version Increment Timer  Up to one of instance per DODAG that the
   configured allowable Objective Functions.

   A
         node in an LLN may learn routing information from different routing
   protocols including RPL.  It is in this case desirable 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 control via
   administrative preference which route be sent.  Interval should be favored.  An
   implementation SHOULD allow for specifying an administrative
   preference for the routing protocol from which the route was learned.

   A RPL implementation SHOULD allow for the configuration of the "Route
   Tag" field chosen appropriate to
         propagation time of the DAO messages according DODAG and as appropriate to a set application
         requirements (e.g. response time vs. overhead).

   DelayDAO Timer  Up to one instance per DAO parent (the subset of rules defined by
   policy.

12.1.7.  Data Structures

   Some RPL implementation may limit the size
         DODAG parents chosen to receive destination advertisements) per
         DODAG.  Expiry triggers sending of DAO message to the candidate DAO
         parent.  See Section 7.1.6

   RemoveTimer  Up to one instance per DAO entry per neighbor
   list in order (i.e.
         those neighbors that have given DAO messages to bound the memory usage, this node as a
         DODAG parent) Expiry triggers a change 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 state for the size of DAO
         entry, setting up to do unreachable (No-Path) advertisements or
         immediately deallocating the
   candidate neighbor list.

12.2.  Information and Data Models DAO entry if there are no DAO
         parents.  See Section 7.1.4.1.1.3

13.  Manageability Considerations

   The information and data models necessary for aim of this section is to give consideration to the operation manageability
   of RPL, and how RPL will be defined operated in a separate document specifying LLN beyond the RPL SNMP MIB.

12.3.  Liveness Detection and Monitoring use of a MIB
   module.  The aim scope of this section is to describe the various RPL mechanisms
   specified to monitor consider the protocol.

   As specified in Section 3.1, an implementation is expected to
   maintain a set of data structures in support following
   aspects of DODAG discovery:

   o  The candidate neighbors data structure

   o  For each DODAG:

      *  A set manageability: fault management, configuration, accounting
   and performance.

13.1.  Control of DODAG parents

12.3.1.  Candidate Neighbor Data Structure

   A node in the candidate neighbor list is Function and Policy

13.1.1.  Initialization Mode

   When a node discovered by the
   some means and qualified is first powered up, it may either choose to potentially become of neighbor stay silent
   and not send any multicast DIO message until it has joined a DODAG,
   or to immediately root a
   sibling (with high enough local confidence). transient DODAG and start sending multicast
   DIO messages.  A RPL implementation SHOULD provide a way monitor the candidate neighbors list with some
   metric reflecting local confidence (the degree of stability of the
   neighbors) measured by some metrics.

   A RPL implementation MAY provide a counter reporting allow configuring whether
   the number of
   times a candidate neighbor has been ignored, node should stay silent or should start advertising DIO messages.

   Furthermore, the number of
   candidate neighbors exceeds the maximum authorized value.

12.3.2.  Directed Acyclic Graph (DAG) Table

   For each DAG, a RPL implementation is expected to keep track of the
   following DODAG table values:

   o  DODAGID

   o  DAGObjectiveCodePoint

   o  A set of Destination Prefixes offered upwards along the DODAG

   o  A set of DODAG Parents

   o  timer SHOULD to govern allow configuring whether
   or not the node should start sending of an DIS message as an initial
   probe for nearby DODAGs, or should simply wait until it received DIO
   messages for the DODAG

   o  DODAGSequenceNumber

   The set from other nodes that are part of DODAG parents structure is itself existing DODAGs.

13.1.2.  DIO Base option

   RPL specifies a table with the
   following entries:

   o  A reference to the neighboring device which is the DAG parent

   o  A record number of most recent information taken from the DAG Information
      Object last processed from the DODAG Parent

   o protocol parameters.

   A flag reporting if RPL implementation SHOULD allow configuring the Parent is a DAO Parent as following routing
   protocol parameters, which are further described in Section 6

12.3.3. 5.3:

   DAGPreference
   RPLInstanceID
   DAGObjectiveCodePoint
   DODAGID
   Routing Table Information
   Prefix Information
   DIOIntervalDoublings
   DIOIntervalMin
   DIORedundancyConstant

   DAG Root behavior:  In some cases, a node may not want to permanently
         act as a DODAG root if it cannot join a grounded DODAG.  For each route provisioned by RPL operation,
         example a battery-operated node may not want to act as a DODAG
         root for a long period of time.  Thus a RPL implementation
   MUST keep track of the following:

   o  Destination Prefix

   o  Destination Prefix Length

   o  Lifetime Timer

   o  Next Hop

   o  Next Hop Interface

   o  Flag indicating that MAY
         support the route was provisioned from one of:

      *  Unicast DAO message

      *  DIO message

      *  Multicast DAO message

12.3.4.  Other RPL Monitoring Parameters ability to configure whether or not a node could
         act as a DODAG root for a configured period of time.

   DODAG Table Entry Suppression  A RPL implementation SHOULD provide
         the ability to configure a counter reporting timer after the number expiration of which
         logical equivalent of
   a times the node has detected an inconsistency with respect to DODAG table that contains all the
         records about a DODAG parent, e.g. is suppressed, to be invoked if the DODAGID has changed. DODAG
         parent set becomes empty.

13.1.3.  Trickle Timers

   A RPL implementation MAY log makes use of trickle timer to govern the reception sending
   of a malformed DIO message message.  Such an algorithm is determined a by a set of
   configurable parameters that are then advertised by the DODAG root
   along with the neighbor identification if avialable.

12.3.5.  RPL Trickle Timers

   A DODAG in DIO messages.

   For each DODAG, a RPL implementation operating on a DODAG root MUST allow for the
   configuration monitoring of
   the following trickle parameters:

   o  The DIOIntervalMin expressed parameters, further described in ms

   o  The DIOIntervalDoublings

   o  The DIORedundancyConstant Section 6.3.1:

   I
   T
   C
   I_min
   I_doublings

   A RPL implementation MAY SHOULD provide a counter reporting the number of
   times command (for example via API,
   CLI, or SNMP MIB) whereby any procedure that detects an inconsistency (and thus
   may cause the trickle timer has been reset).

12.4.  Verifying Correct Operation

   This section has to be completed in further revision of this document reset.

13.1.4.  DAG Version Number Increment

   A RPL implementation may allow by configuration at the DODAG root to list potential Operations and Management (OAM) tools that could be
   used for verifying
   refresh the correct operation of RPL.

12.5.  Requirements on Other Protocols and Functional Components

   RPL does not have any impact on DODAG states by updating the operation of existing protocols.

12.6.  Impact on Network Operation

   To be completed.

13.  Security Considerations

   Security Considerations for DODAGVersionNumber.  A RPL
   implementation SHOULD allow configuring whether or not periodic or
   event triggered mechanism are to be developed in accordance
   with recommendations laid out in, for example,
   [I-D.tsao-roll-security-framework].

14.  IANA Considerations
14.1.  RPL Control Message

   The RPL Control Message is an ICMP information message type that is
   to be used carry DODAG Information Objects, by the DODAG Information
   Solicitations, and root to control
   DODAGVersionNumber change.

13.1.5.  Destination Advertisement Objects in support of
   RPL operation.

   IANA has defined a ICMPv6 Type Number Registry. Timers

   The suggested type
   value for following set of parameters of the RPL DAO messages SHOULD be
   configurable:

   o  The DelayDAO timer

   o  The Remove timer

13.1.6.  Policy Control Message is 155,

   DAG discovery enables nodes to be confirmed by IANA.

14.2.  New Registry implement different policies for
   selecting their DODAG parents.

   A RPL Control Codes

   IANA is requested implementation SHOULD allow configuring the set of acceptable
   or preferred Objective Functions (OF) referenced by their Objective
   Codepoints (OCPs) for a node to create join a registry, RPL Control Codes, for the
   Code field DODAG, and what action should
   be taken if none of a node's candidate neighbors advertise one of the ICMPv6 RPL Control Message.

   New codes may be allocated only by
   configured allowable Objective Functions.

   A node in an IETF Consensus action.  Each
   code 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 tracked with the following qualities:

   o  Code

   o  Description

   o  Defining RFC

   Three codes are currently defined:

        +------+----------------------------------+---------------+
        | Code | Description                      | Reference     |
        +------+----------------------------------+---------------+
        | 0x01 | DODAG Information Solicitation   | This document |
        | 0x02 | DODAG Information Object         | This document |
        | 0x04 | Destination Advertisement Object | This document |
        +------+----------------------------------+---------------+

                             RPL Control Codes

14.3.  New Registry favored.  An
   implementation SHOULD allow for specifying an administrative
   preference for the Control Field routing protocol from which the route was learned.

13.1.7.  Data Structures

   Some RPL implementation may limit the size of the DIO Base

   IANA is requested candidate neighbor
   list in order to create a registry for the Control field of bound the
   DIO Base.

   New fields memory usage, in which case some otherwise
   viable candidate neighbors may not be allocated only by considered and simply dropped
   from the candidate neighbor list.

   A RPL implementation MAY provide an IETF Consensus action.  Each
   field should be tracked with indicator on the following qualities:

   o  Bit number (counting from bit 0 as size of the most significant bit)

   o  Capability description
   o  Defining RFC

   Four groups are currently defined:

    +-------+-----------------------------------------+---------------+
    |  Bit  | Description                             | Reference     |
    +-------+-----------------------------------------+---------------+
    |   0   | Grounded DODAG (G)                      | This document |
    |   1   | Destination Advertisement Supported (A) | This document |
    |   2   | Destination Advertisement Trigger (T)   | This document |
    |   3   | Destination Advertisements Stored (S)   | This document |
    | 5,6,7 | DODAG Preference (Prf)                  | This document |
    +-------+-----------------------------------------+---------------+

                              DIO Base Flags

14.4.  DODAG
   candidate neighbor list.

13.2.  Information Object (DIO) Suboption

   IANA is requested to create a registry and Data Models

   The information and data models necessary for the DIO Base Suboptions

         +-------+------------------------------+---------------+
         | Value | Meaning                      | Reference     |
         +-------+------------------------------+---------------+
         |   0   | Pad1 - DIO Padding           | This document |
         |   1   | PadN - DIO suboption padding | This document |
         |   2   | DAG Metric Container         | This Document |
         |   3   | Destination Prefix           | This Document |
         |   4   | DAG Timer Configuration      | This Document |
         +-------+------------------------------+---------------+

              DODAG Information Option (DIO) Base Suboptions

15.  Acknowledgements

   The authors would like to acknowledge operation of RPL
   will be defined in a separate document specifying the review, feedback, and
   comments from Emmanuel Baccelli, Dominique Barthel, Yusuf Bashir,
   Phoebus Chen, Mathilde Durvy, Manhar Goindi, Mukul Goyal, Anders
   Jagd, Quentin Lampin, Jerry Martocci, Alexandru Petrescu, RPL SNMP MIB.

13.3.  Liveness Detection and Don
   Sturek. Monitoring

   The authors would like aim of this section is to acknowledge describe the guidance and input provided various RPL mechanisms
   specified to monitor the protocol.

   As specified in Section 3.1, an implementation is expected to
   maintain a set of data structures in support of DODAG discovery:

   o  The candidate neighbors data structure

   o  For each DODAG:

      *  A set of DODAG parents

13.3.1.  Candidate Neighbor Data Structure

   A node in the candidate neighbor list is a node discovered by the ROLL Chairs, David Culler
   some means and JP Vasseur.

   The authors would like qualified to acknowledge prior contributions potentially become 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,
   and Arsalan Tavakoli, which have provided useful design
   considerations neighbor or a
   sibling (with high enough local confidence).  A RPL implementation
   SHOULD provide a way monitor the candidate neighbors list with some
   metric reflecting local confidence (the degree of stability of the
   neighbors) 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.

13.3.2.  Directed Acyclic Graph (DAG) Table

   For each DAG, a RPL implementation is expected to keep track of the
   following DODAG table values:

   o  DODAGID

   o  DAGObjectiveCodePoint
   o  A set of prefixes offered upwards along the DODAG

   o  A set of DODAG Parents

   o  timer to RPL.

16.  Contributors

   RPL is govern the result sending of DIO messages for the contribution DODAG

   o  DODAGVersionNumber

   The set of DODAG parents structure is itself a table with the
   following members of entries:

   o  A reference to the
   ROLL Design Team, including neighboring device which is the editors, and additional contributors
   as listed below:

   JP Vasseur
   Cisco Systems, Inc
   11, Rue Camille Desmoulins
   Issy Les Moulineaux,   92782
   France

   Email: jpv@cisco.com

   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 Hall, Stanford University
   Stanford, CA  94305-9030
   USA

   Email: pal@cs.stanford.edu

   Richard Kelsey
   Ember Corporation
   Boston, MA
   USA

   Phone: +1 617 951 1225
   Email: kelsey@ember.com

   Jonathan W. Hui
   Arch Rock Corporation
   501 2nd St. Ste. 410
   San Francisco, CA  94107
   USA

   Email: jhui@archrock.com

   Kris Pister
   Dust Networks
   30695 Huntwood Ave.
   Hayward,   94544
   USA

   Email: kpister@dustnetworks.com

   Anders Brandt
   Zensys, Inc.
   Emdrupvej 26
   Copenhagen, DK-2100
   Denmark

   Email: abr@zen-sys.com

   Stephen Dawson-Haggerty
   UC Berkeley
   Soda Hall, UC Berkeley
   Berkeley, CA  94720
   USA

   Email: stevedh@cs.berkeley.edu

17.  References

17.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

17.2.  Informative References

   [I-D.ietf-bfd-base]
              Katz, D. and D. Ward, "Bidirectional Forwarding
              Detection", draft-ietf-bfd-base-11 (work in progress),
              January 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-11 (work DAG parent

   o  A record of most recent information taken from the DAG Information
      Object last processed from the DODAG Parent

   o  A flag reporting if the Parent is a DAO Parent as described in progress), October 2009.

   [I-D.ietf-roll-building-routing-reqs]
              Martocci, J., Riou, N., Mil, P., and W. Vermeylen,
              "Building Automation
      Section 7

13.3.3.  Routing Requirements in Low Power and
              Lossy Networks", draft-ietf-roll-building-routing-reqs-09
              (work in progress), January 2010.

   [I-D.ietf-roll-home-routing-reqs]
              Brandt, A. and J. Buron, "Home Automation Table

   For each route provisioned by RPL operation, a RPL implementation
   MUST keep track of the following:

   o  Routing
              Requirements in Low Power and Lossy Networks",
              draft-ietf-roll-home-routing-reqs-11 (work in progress),
              January 2010.

   [I-D.ietf-roll-of0]
              Thubert, P., "RPL Objective Function 0",
              draft-ietf-roll-of0-01 (work Information (prefix, prefix length, ...)

   o  Lifetime Timer

   o  Next Hop

   o  Next Hop Interface

   o  Flag indicating that the route was provisioned from one of:

      *  Unicast DAO message

      *  DIO message

      *  Multicast DAO message

13.3.4.  Other RPL Monitoring Parameters

   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.

   A RPL implementation MAY log the reception of a malformed DIO message
   along with the neighbor identification if avialable.

13.3.5.  RPL Trickle Timers

   A RPL implementation operating on a DODAG root MUST allow for the
   configuration of the following trickle parameters:

   o  The DIOIntervalMin expressed in progress), February 2010.

   [I-D.ietf-roll-routing-metrics]
              Vasseur, J. ms

   o  The DIOIntervalDoublings

   o  The DIORedundancyConstant

   A RPL implementation MAY provide a counter reporting the number of
   times an inconsistency (and thus the trickle timer has been reset).

13.4.  Verifying Correct Operation

   This section has to be completed in further revision of this document
   to list potential Operations and D. Networks, "Routing Metrics Management (OAM) tools that could be
   used for
              Path Calculation in Low Power and Lossy Networks",
              draft-ietf-roll-routing-metrics-04 (work in progress),
              December 2009.

   [I-D.ietf-roll-terminology]
              Vasseur, J., "Terminology in Low power And Lossy
              Networks", draft-ietf-roll-terminology-02 (work in
              progress), October 2009.

   [I-D.tsao-roll-security-framework]
              Tsao, T., Alexander, R., Dohler, M., Daza, V., verifying the correct operation of RPL.

13.5.  Requirements on Other Protocols and A.
              Lozano, "A Functional Components

   RPL does not have any impact on the operation of existing protocols.

13.6.  Impact on Network Operation

   To be completed.

14.  Security Framework for Routing over Low Power
              and Lossy Networks", draft-tsao-roll-security-framework-01
              (work in progress), September 2009.

   [Levis08]  Levis, P., Brewer, E., Culler, D., Gay, D., Madden, S.,
              Patel, N., Polastre, J., Shenker, S., Szewczyk, R., Considerations

      +----------------------------------------------------------------+
      |                                                                |
      |                             TBD                                |
      |                     Under Construction                         |
      |            Deference given to Security Design Team             |
      |                                                                |
      +----------------------------------------------------------------+

14.1.  Overview

   From a security perspective, RPL networks are no different from any
   other network.  They are vulnerable to passive eavesdropping attacks
   and A.
              Woo, "The Emergence of potentially even active tampering when physical access to a Networking Primitive wire
   is not required to participate in Wireless
              Sensor Networks", Communications communications.  The very nature of the ACM, v.51 n.7,
              July 2008,
              <http://portal.acm.org/citation.cfm?id=1364804>.

   [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
              August 1996.

   [RFC3697]  Rajahalme, J., Conta, A., Carpenter, B., and S. Deering,
              "IPv6 Flow Label Specification", RFC 3697, March 2004.

   [RFC3810]  Vida, R.
   ad hoc networks 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., their cost objectives impose additional security
   constraints, which perhaps make these networks the most difficult
   environments to secure.  Devices are low-cost and L.
              Wood, "Advice for Internet Subnetwork Designers", BCP 89,
              RFC 3819, July 2004.

   [RFC4101]  Rescorla, E. have limited
   capabilities in terms of computing power, available storage, and IAB, "Writing Protocol Models", RFC 4101,
              June 2005.

   [RFC4191]  Draves, R.
   power drain; and D. Thaler, "Default Router Preferences 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
              More-Specific Routes", RFC 4191, November 2005.

   [RFC4443]  Conta, A., Deering, S., might involve short-term relationships
   between devices that may never have communicated before.  These
   constraints might severely limit the choice of cryptographic
   algorithms and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for protocols and influence the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., design of the security
   architecture because the establishment and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., maintenance of trust
   relationships between devices need to be addressed with care.  In
   addition, battery lifetime and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, June 2007.

   [RFC5120]  Przygienda, T., Shen, N., 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 N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System may, therefore, be considered to
              Intermediate Systems (IS-ISs)", RFC 5120, February 2008.

   [RFC5548]  Dohler, M., Watteyne, T., Winter, T., 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 D. Barthel,
              "Routing Requirements for Urban Low-Power public-key cryptography and use keys that are to be provided by
   higher layer processes.  The establishment and Lossy
              Networks", RFC 5548, May 2009.

   [RFC5673]  Pister, K., Thubert, P., Dwars, S., maintenance of these
   keys are outside the scope of this standard.  The mechanisms assume a
   secure implementation of cryptographic operations and T. Phinney,
              "Industrial Routing Requirements in Low-Power secure and Lossy
              Networks", RFC 5673, October 2009.

Appendix A.  Requirements

A.1.  Protocol Properties Overview

   RPL demonstrates
   authentic storage of keying material.

   The security mechanisms specified provide particular combinations of
   the following properties, consistent with the
   requirements specified by security services:

   Data confidentiality:  Assurance that transmitted information is only
               disclosed to parties for which it is intended.

   Data authenticity:  Assurance of the application-specific requirements
   documents.

A.1.1.  IPv6 Architecture

   RPL source of transmitted
               information (and, hereby, that information was not
               modified in transit).

   Replay protection:  Assurance that a duplicate of transmitted
               information is strictly compliant with layered IPv6 architecture.

   Further, RPL 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 designed with consideration to
   required, replay protection is always provided.

   Replay protection is provided via the practical support use of a non-repeating value
   (nonce) in the packet protection process and implementation storage of IPv6 architecture some status
   information for each originating device on devices the receiving device,
   which may operate
   under severe resource constraints, including but not limited to
   memory, processing power, energy, and communication. 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 RPL design
   does not presume high quality reliable links, 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 operates over lossy
   links (usually low bandwidth with low packet delivery success rate).

A.1.2.  Typical LLN Traffic Patterns

   Multipoint-to-Point (MP2P) application-specific
   tradeoffs between key storage and Point-to-multipoint (P2MP) traffic
   flows from nodes within key maintenance costs versus the LLN from
   cryptographic protection provided.  If a group key is used for peer-
   to-peer communication, protection is provided only against outsider
   devices and to egress points are very
   common not against potential malicious devices in LLNs.  Low power and lossy network Border Router (LBR)
   nodes the key-
   sharing group.

   Data authenticity may typically be at provided using symmetric-key based or
   public-key based techniques.  With public-key based techniques (via
   signatures), one corroborates evidence as to the root unique originator of such flows, although such flows
   are not exclusively rooted at LBRs as determined on an application-
   specific basis.  In particular, several applications
   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 building with group communications (broadcast, multicast), or home automation do in
   scenarios that require P2P (Point-to-Point) communication.

   As required by the aforementioned routing requirements documents, RPL
   supports the installation of multiple paths.  The use non-repudiation.

14.2.  Functional Description of multiple
   paths include sending duplicated traffic along diverse paths, as well
   as to support advanced features such as Class Packet Protection

14.2.1.  Transmission of Service (CoS) based
   routing, or simple load balancing among a set Outgoing Packets

   This section describes the transmission of paths (which could
   be useful for secured RPL control
   packets.  Give an outgoing RPL control packet and required security
   protection, this section describes how RPL generates the LLN secured
   packet to spread traffic load and avoid fast energy
   depletion on some, e.g. battery powered, nodes).  Conceptually,
   multiple instances transmit.  It describes the order of cryptographic
   operations to provide the required protection.

   A RPL can be used node MUST set the security section in the RPL packet to send traffic along different
   topology instances,
   describes the construction required protection level.

   The Counter field of which is governed by
   different Objective Functions (OF).  Details the security header MUST be an increment of the
   last Counter field transmitted.

   If the RPL operation in
   support packet is not a response to a Consistency Check message,
   the node MAY set the Counter Compression field of multiple instances are beyond the scope security
   option.  If the packet is a response to a Consistency Check message,
   the node MUST clear the Counter Compression field.

   A node sets the Key Identifier Mode (KIM) of the present
   specification.

A.1.3.  Constraint Based Routing

   The RPL design supports constraint based routing, packet based on a set its
   understanding of
   routing metrics and constraints.  The routing metrics and constraints
   for links and nodes what keys destinations have.

   A node MUST replaced the original packet payload with capabilities supported by RPL are that payload
   encrypted using the security protection, key, and nonce specified in
   the security section.

14.2.2.  Reception of Incoming Packets

   This section describes the reception of a companion document to secured RPL packet.  Given
   an incoming RPL packet, this specification,

   [I-D.ietf-roll-routing-metrics]. section describes now RPL signals generates an
   unencrypted version of the metrics,
   constraints, packet and related Objective Functions (OFs) in use in a
   particular implementation by means validates its integrity.

   The receiver uses the security control field of an Objective Code Point (OCP).
   Both the routing metrics, constraints, security section
   to determine what processing to do.  If the described level of
   security does not meet locally maintained security policies, a node
   MAY discard the packet without further processing.  These policies
   can include security levels, keys used, or source identifiers.

   Using a nonce derived from the Counter field and other information
   (as described in Section Figure 21), the OF help determine receiver checks the
   construction
   integrity of the Directed Acyclic Graphs (DAG) using packet by comparing the received MAC with the
   computed MAC.  If this integrity check does not pass, a distributed
   path computation algorithm.

A.2.  Deferred Requirements

   NOTE: node MUST
   discard the packet.

   RPL is still a work uses the key information described in progress.  At this time there remain
   several unsatisfied application requirements, but these are a RPL message to be
   addressed decrypt
   its contents as RPL is further specified.

Appendix B.  Examples

B.1.  DAO Operation When Only necessary.  Once a message has passed its integrity
   checks and been successfully decrypted, the Root Node Stores DAO Information

   Consider node can update its local
   security information, such as the example source's expected counter value for
   counter compression.  A node MUST NOT update security information on
   receipt of Figure 13.  In this example only the root
   node, (LBR*), will store DAO information.  This is not known, nor is
   it required to be known, to all nodes a priori.  Rather, each node message that fails security policy checks, integrity
   checks, or decryption.

14.2.3.  Cryptographic Mode of Operation

   The cryptographic mode of operation used is
   able to observe from based on the state CCM mode of the 'S' flag that no ancestor,
   operation specified with [TBDREF] and the exception block-cipher AES-128
   [TBDREF].  This mode of operation is widely supported by existing
   implementations and coincides with the root node, stores DAO information.

                                  (LBR*)
                                   /  \
                                  /    \
                                 /      \
                             (11)        (12) CCM* mode of operation
   specified with [TBDREF].

14.2.3.1.  Nonce

   The so-called nonce is constructed 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                            |
                             (21)        (22)
                                 \
                                  \
                                   \
                                   (31)
                                   /  \
                                  /    \
                                 /      \
                             (41)        (42)
                               :          :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Reserved | LVL |
       +-+-+-+-+-+-+-+-+

                           Figure 13: Only Root Node Stores DAOs

   In this example:

   o  The 'S' flag is cleared in DIO messages emitted by (LBR*), because
      (LBR*) 21: CCM* Nonce

   Source Identifier:  8 bytes.  Source Identifier is set to the DODAG root.

   o  The 'S' flag logical
         identifier of the originator of the protected packet.

   Counter:  4 bytes.  Counter is cleared in all DIO messages emitted by all other
      nodes, because no other node stores DAO information.

   o  (LBR*) has learned from DAO messages how to reach node (31) with a
      source route via {(11) (21)}.

   o  All source routes set to nodes in the sub-DODAG (uncompressed) value of node (31),
      including nodes (41), (42), and others will include the prefix
      {(11) (21) (31)}

   o  Node (31) maintains a DTSN, (31).DTSN, that it will advertise
         corresponding field in
      DIO messages.

   Suppose now that there is a topology change within the same DODAG
   iteration, causing node (31) to evict node (21) as a DAO parent and
   add node (22) as a DAO parent:

   1.  Node (31) will schedule a DAO transmission because it has added a
       new node (22) Security option of the RPL control
         message.

   Security Level (LVL):  3 bits.  Security Level is set to its DAO parent set.

   2.  Node (31) need not increment (31).DTSN at this event, because the value of
         the corresponding field in
       this example no DAO parents have the 'S' flag set.  Specifically
       this indicates to Node (31) that there Security option of the RPL
         control message.

   Unassigned bits of the nonce are no intermediate
       storing nodes that may need to reserved.  They MUST be explicitly updated with DAO
       information from it's sub-DODAG.  Hence nodes (41), (42), and by
       extension set to zero
   when constructing the sub-DODAG nonce.

   All fields of node (31) will not subsequently
       observe an incremented (31).DTSN and the sub-DODAG will not emit
       DAOs.

   3.  A new flow of DAOs for node (31) reaches nonce shall be represented is most-significant-
   octet and most-significant-bit first order.

14.3.  Protecting RPL ICMPv6 messages

   For a RPL ICMPv6 message, the (LBR*), updating entire packet is within the
       source route information for node (31) to include scope of
   RPL security.  The message authentication code is calculated over the new path
       {(12) (22)}.

   4.  (LBR*) may implicitly update all source routes
   entire IPv6 packet.  This calculation is done before any compression
   that must transit
       node (31), i.e. the sub-DODAG lower layers may apply.  The IPv6 and ICMPv6 headers are never
   encrypted.  The body of node (31), to use the updated
       source route prefix {(12) (22)} instead of {(11) (21)}.

   Thus RPL ICMPv6 message MAY be encrypted,
   starting from the use of first byte after the 'S' flag in security information and
   continuing to the case where only end of the packet.

14.4.  Security State Machine

   A DAG root node
   stores DAO information has allowed an optimization whereby only starting a DAO
   update DODAG sets the RPL routing security policy for
   the node that changed its DAO parent set, (31), needs to
   be sent entire DODAG.

   A member of a secure DODAG MUST conform to the DODAG policy set by the DAG
   root.

B.2.  DAO Operation  When All Nodes Fully Store DAO Information

   Consider starting a secure DODAG, the example of Figure 14.  In this example all nodes DAG root will
   fully store DAO information.

                                  (LBR*)
                                   /  \
                                  /    \
                                 /      \
                            (11*)        (12*)
                               |          |
                               |          |
                               |          |
                            (21*)        (22*)
                                 \
                                  \
                                   \
                                  (31*)
                                   /  \
                                  /    \
                                 /      \
                            (41*)        (42*)
                               :          :

                      Figure 14: All Nodes Store DAOs

   In this example:

   o  The 'S' flag is cleared in DIO messages emitted by (LBR*), because
      (LBR*) is the DODAG root.

   o  The 'S' flag is set in send secure
   DIO messages emitted by all non-root nodes
      because each non-root node stores DAO information.

   o  Source routing state is effectively not provisioned in this
      example, because each node has been able to store hop-by-hop
      routing state for each destination, possibly aggregated, as
      learned from DAOs.  For example, messages.  A node (11*) attempting to join the DODAG will have learned and
      stored information from send a DAO secure
   Authentication Request (AREQ) to the effect DAG root.  Nodes that node (41*) is
      routable through are not
   authenticated in a next hop secure DODAG will be unable to generate properly
   constructed secured RPL packets.  These nodes are in state
   "unauthenticated".  A member of node (21*).  Node (12*) on a secure DODAG MUST forward an AREQ
   packet to the DAG root, and MUST NOT forward any other hand does not necessarily have a route provisioned type of packet
   from an unauthenticated node.

   The DAG root may choose to respond to the AREQ with an ARSP packet.
   This packet will provide the authenticating node
      (41*).

   Suppose now that there with the
   cryptographic materials necessary to participate in RPL routing.
   Some authentication flows may involve the exchange of more than one
   AREQ or ARSP packets.

   The simplest authentication flow will involve the use of a single
   pre-installed network-wide authentication key.  The installation of
   this key is out of scope of this document.  The authenticating node
   will use the pre-installed key to calculate a topology change within MIC for the same AREQ
   packet.  The DODAG
   iteration, causing node (31*) to evict root will verify the authenticity of the
   authenticating node (21*) as using the same key.  The DODAG root, having
   previously chosen a DAO parent single random instance-wide shared key, will send
   this key, encrypted and
   add node (22*) as a DAO parent:

   1.  Node (31*) authenticated with the pre-installed key, in
   the ARSP packet.  The authenticating node, decoding this packet with
   the pre-installed key, will schedule a DAO transmission because it has added
       a new node (22*) to its DAO parent set.

   2.  Node (31) need not increment (31).DTSN, because it verify the authenticity of the DODAG
   root.

   It is assumed that additional authentication and key exchange
   mechanisms will be included in future drafts of the document.

   Periodic key updates will use the secure KU packet code.  The
   responsibility for initiating key update will reside with the DODAG
   root, and is out of scope of this document.

15.  IANA Considerations

15.1.  RPL Control Message

   The RPL Control Message is a fully
       storing node and does not need to trigger DAO an ICMP information from
       its sub-DODAG.

   3.  Node (31) gives a DAO Update to node (22*).  Presuming message type that node
       (22*) is
   to be used carry DODAG Information Objects, DODAG Information
   Solicitations, and Destination Advertisement Objects in support of
   RPL operation.

   IANA has received the update, node (22*) will store defined an ICMPv6 Type Number Registry.  The suggested type
   value for the new
       entries RPL Control Message is 155, to be confirmed by IANA.

15.2.  New Registry for RPL Control Codes

   IANA is requested to create a registry, RPL Control Codes, for routes including the sub-DODAG
   Code field of node (31*),
       including nodes (41*) and (42*).  Node (22*) will schedule a DAO
       transmission 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    |
   | 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

15.3.  New Registry for the new entries.

   4.  Similarly, node (22*) updates node (12*) and node (12*) updates
       (LBR*).  Hop-by-hop routing state Mode of Operation (MOP) DIO Control Field

   IANA is requested to create a registry for the sub-DODAG Mode of node (31*) Operation
   (MOP) DIO Control Field, which is now provisioned at nodes (12*) and (22*).

   Thus contained in the addition 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

   Two values are currently defined:

          +-----+-------------------------------+---------------+
          | MOP | Description                   | Reference     |
          +-----+-------------------------------+---------------+
          |  00 | Non-Storing mode of operation | This document |
          |  01 | Storing mode of operation     | This document |
          +-----+-------------------------------+---------------+

                              DIO Base Flags

15.4.  RPL Control Message Option

   IANA is requested to create a registry for the DAO Parent set at 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   | DAG Timer Configuration | This Document |
            |   5   | RPL Target              | This Document |
            |   6   | Transit Information     | This Document |
            |   7   | Solicited Information   | This Document |
            |   8   | Prefix Information      | This Document |
            +-------+-------------------------+---------------+

                        RPL Control Message Options

16.  Acknowledgements

   The authors would like to acknowledge the fully storing node
   (31*) does not elicit additional DAO-related traffic review, feedback, and
   comments from its sub-
   DODAG. Roger Alexander, Emmanuel Baccelli, Dominique Barthel,
   Yusuf Bashir, Phoebus Chen, Mathilde Durvy, Manhar Goindi, Mukul
   Goyal, Anders Jagd, JeongGil (John) Ko, Quentin Lampin, Jerry
   Martocci, Matteo Paris, Alexandru Petrescu, Joseph Reddy, and Don
   Sturek.

   The intermediate nodes along authors would like to acknowledge the 'new' downward path are
   updated guidance and input provided
   by DAO messages along the new path.

   Suppose next that 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,
   and Arsalan Tavakoli, which have provided useful design
   considerations to RPL.

17.  Contributors

   RPL is the DODAG root triggers a refresh result of DAO
   information over the same DODAG Iteration.  (Note that contribution of the DODAG root
   might also trigger a DAO refresh but allow other topology changes at following members of the same time by incrementing
   RPL Author Team, including the DODAG Sequence Number to cause a
   move editors, and additional contributors
   as listed below:

   JP Vasseur
   Cisco Systems, Inc
   11, Rue Camille Desmoulins
   Issy Les Moulineaux,   92782
   France

   Email: jpv@cisco.com

   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 Hall, Stanford University
   Stanford, CA  94305-9030
   USA

   Email: pal@cs.stanford.edu

   Richard Kelsey
   Ember Corporation
   Boston, MA
   USA

   Phone: +1 617 951 1225
   Email: kelsey@ember.com

   Jonathan W. Hui
   Arch Rock Corporation
   501 2nd St. Ste. 410
   San Francisco, CA  94107
   USA

   Email: jhui@archrock.com

   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

   Stephen Dawson-Haggerty
   UC Berkeley
   Soda Hall, UC Berkeley
   Berkeley, CA  94720
   USA

   Email: stevedh@cs.berkeley.edu

18.  References
18.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to the next DODAG Iteration).:

   1.  (LBR*) will increment its DTSN Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

18.2.  Informative References

   [I-D.hui-6man-rpl-option]
              Hui, J. and issue a DIO with the 'T' flag
       set.

   2.  Nodes (11*) J. Vasseur, "RPL Option for Carrying RPL
              Information in Data-Plane Datagrams",
              draft-hui-6man-rpl-option-00 (work in progress),
              March 2010.

   [I-D.hui-6man-rpl-routing-header]
              Hui, J., Vasseur, J., and (12*) will increment their own DTSNs D. Culler, "A Source Routing
              Header for RPL", draft-hui-6man-rpl-routing-header-00
              (work in response
       to observing progress), May 2010.

   [I-D.ietf-bfd-base]
              Katz, D. and D. Ward, "Bidirectional Forwarding
              Detection", draft-ietf-bfd-base-11 (work in the DIO from LBR a new DTSN progress),
              January 2010.

   [I-D.ietf-manet-nhdp]
              Clausen, T., Dearlove, C., and the 'T' flag
       being set.  They will reset their trickle timers to cause the
       issue of new DIOs with the 'T' flag set.  These nodes will also
       schedule a DAO transmission J. Dean, "Mobile Ad Hoc
              Network (MANET) Neighborhood Discovery Protocol (NHDP)",
              draft-ietf-manet-nhdp-12 (work in response to observing a new DTSN
       from their DAO Parent, (LBR*).  (This DAO transmission may be
       scheduled with a sufficient delay computed based on rank to allow
       a chance progress), March 2010.

   [I-D.ietf-roll-building-routing-reqs]
              Martocci, J., Riou, N., Mil, P., and W. Vermeylen,
              "Building Automation Routing Requirements in Low Power and
              Lossy Networks", draft-ietf-roll-building-routing-reqs-09
              (work in progress), January 2010.

   [I-D.ietf-roll-of0]
              Thubert, P., "RPL Objective Function 0",
              draft-ietf-roll-of0-01 (work in progress), February 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-06 (work in
              progress), April 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.

   [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
              August 1996.

   [RFC2710]  Deering, S., Fenner, W., and B. Haberman, "Multicast
              Listener Discovery (MLD) for the sub-DODAGs of the nodes to report DAO messages
       prior to the nodes reporting their own DAO information to (LBR*).
       This is implementation specific IPv6", RFC 2710,
              October 1999.

   [RFC3810]  Vida, R. and may allow a chance L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for DAO
       aggregation.).

   3.  Node (21*) receives a DIO from node (11*) IPv6", RFC 3810, June 2004.

   [RFC3819]  Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
              Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and observes the new
       (11*).DTSN as well as the set 'T' flag.  Node (21*) increments
       its own DTSN, resets the trickle timer, L.
              Wood, "Advice for Internet Subnetwork Designers", BCP 89,
              RFC 3819, July 2004.

   [RFC4101]  Rescorla, E. and schedules a DAO
       transmission.

   4.  Similarly, as each node observes the incremented DTSN with the
       'T' flag set from each of its parents, each node will increment
       its own DTSN, reset the DIO trickle timer, IAB, "Writing Protocol Models", RFC 4101,
              June 2005.

   [RFC4191]  Draves, R. and schedule a DAO
       transmission.

   Thus the entire DODAG iteration has been re-armed to send DAO
   messages based on the (LBR*)'s assertion of 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 'T' flag.  Note that
   normally a DTSN increment would cause no further action 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 a sub-
   DODAG beyond the first fully storing node that is encountered, but
   that OSPF",
              RFC 4915, June 2007.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in this case the 'T' flag effectively provides a means Intermediate System to 'punch
   through' all fully storing nodes.

B.3.  DAO Operation When Nodes Have Mixed Capabilities

   Consider the example of Figure 15.  In this example some nodes are
   capable of storing DAO information
              Intermediate Systems (IS-ISs)", RFC 5120, February 2008.

   [RFC5548]  Dohler, M., Watteyne, T., Winter, T., and some are not.

                                  (LBR*)
                                   /  \
                                  /    \
                                 /      \
                             (11)        (12*)
                               |          |
                               |          |
                               |          |
                             (21)        (22)
                                 \
                                  \
                                   \
                                   (31)
                                   /  \
                                  /    \
                                 /      \
                             (41)        (42*)
                               :          :

                 Figure 15: Mixed Capability DAO Operation

   In this example:

   o  The 'S' flag is cleared in DIO messages emitted by (LBR*), because
      (LBR*) is the DODAG root.

   o  The 'S' flag is set 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 DIO messages emitted by (12*), because it
      is a storing node.

   o  The 'S' flag will be set Low-Power and Lossy
              Networks", RFC 5673, October 2009.

   [RFC5826]  Brandt, A., Buron, J., and G. Porcu, "Home Automation
              Routing Requirements in DIO messages emitted by nodes that
      contain node (12*) (or more generally any non-root storing node)
      as a DAO parent/ancestor.  This indicates that somewhere along Low-Power and Lossy Networks",
              RFC 5826, April 2010.

Appendix A.  Requirements

A.1.  Protocol Properties Overview

   RPL demonstrates the
      DAO path there following properties, consistent with the
   requirements specified by the application-specific requirements
   documents.

A.1.1.  IPv6 Architecture

   RPL is a non-root storing node that may need to have
      its state updated (by a DAO refresh) in certain conditions.

   Suppose that there strictly compliant with layered IPv6 architecture.

   Further, RPL is a topology change within the same DODAG
   iteration, causing node (31) to add node (22) as a DAO parent:

   1.  Node (31) will schedule a DAO transmission because it has added a
       new node (22) designed with consideration to its DAO parent set.  Node (31) will increment
       (31).DTSN because node (22) has set the 'S' flag in its DIO
       messages.  Node (31) will reset its DIO trickle timer.

   2.  Node (31)'s trickle timer will then expire practical support
   and a DIO is issued implementation of IPv6 architecture on devices which may operate
   under severe resource constraints, including but not limited to
   memory, processing power, energy, and received by node's (41) communication.  The RPL design
   does not presume high quality reliable links, and (42*).

   3.  Node (41) is a non-storing node.  It will increment (41).DTSN in
       response to observing the increment in (31).DTSN, operates over lossy
   links (usually low bandwidth with low packet delivery success rate).

A.1.2.  Typical LLN Traffic Patterns

   Multipoint-to-Point (MP2P) and reset its
       trickle timer.  This results finally in Point-to-multipoint (P2MP) traffic
   flows from nodes within the reliable (thanks LLN from and to egress points are very
   common in LLNs.  Low power and lossy network Border Router (LBR)
   nodes may typically be at the DTSN) triggering root of a DAO update from node (41)'s sub-DODAG.

   4. such flows, although such flows
   are not exclusively rooted at LBRs as determined on an application-
   specific basis.  In particular, several applications such as building
   or home automation do require P2P (Point-to-Point) communication.

   As node (41) receives DAO updates from its sub-DODAG it updates required by the DAOs with source aforementioned routing information requirements documents, RPL
   supports the installation of multiple paths.  The use of multiple
   paths include sending duplicated traffic along diverse paths, as well
   as necessary and passes
       them on to node (31), along with its own (node (41)) DAO update.

   5.  Meanwhile, node (42*) is support advanced features such as Class of Service (CoS) based
   routing, or simple load balancing among a fully storing node.  It observes set of paths (which could
   be useful for the
       increment LLN to (31).DTSN spread traffic load and schedules a DAO update.  Node (42*)
       does not need avoid fast energy
   depletion on some, e.g. battery powered, nodes).  Conceptually,
   multiple instances of RPL can be used to increment (42*).DTSN, since it send traffic along different
   topology instances, the construction of which is a fully
       storing node it does not need to solicit DAO updates from its
       sub-DODAG governed by
   different Objective Functions (OF).  Details of RPL operation in this case.  At
   support of multiple instances are beyond the scheduled time Node (42*)
       reissues its DAO information to node (31).

   6.  Node (31) receives scope of the DAO messages from its sub-DODAG, adds
       source present
   specification.

A.1.3.  Constraint Based Routing

   The RPL design supports constraint based routing, based on a set of
   routing information as necessary, metrics and issues DAO updates
       to node (22).

   7.  Node (22) similarly receives DAO messages from node (31), updates
       source constraints.  The routing information as necessary, metrics and issues DAO updates
       to node (12*).

   8.  The intermediate storing node (12*) has now received from DAO
       messages the information necessary constraints
   for links and nodes with capabilities supported by RPL are specified
   in a companion document to provision routing state for
       node (31) this specification,
   [I-D.ietf-roll-routing-metrics].  RPL signals the metrics,
   constraints, and its sub-DODAG.  As downwards traffic is routed
       through node (12*) it is able to consult source related Objective Functions (OFs) in use in a
   particular implementation by means of an Objective Code Point (OCP).
   Both the routing
       information that was learned from metrics, constraints, and the DAO messages as needed to
       specify routes down OF help determine the DAG across
   construction of the non-storing nodes (22),
       (31), ... Directed Acyclic Graphs (DAG) using a distributed
   path computation algorithm.

A.2.  Deferred Requirements

   NOTE: RPL is still a work in progress.  At this time there remain
   several unsatisfied application requirements, but these are to be
   addressed as RPL is further specified.

Appendix C. B.  Outstanding Issues

   This section enumerates some outstanding issues that are to be
   addressed in future revisions of the RPL specification.

C.1.

B.1.  Additional Support for P2P Routing

   In some situations the baseline mechanism to support arbitrary P2P
   traffic, by flowing upwards along the DODAG until a common ancestor
   is reached and then flowing down, may not be suitable for all
   application scenarios.  A related scenario may occur when the down
   paths setup along the DODAG by the destination advertisement
   mechanism are not the most desirable downward paths for the specific
   application scenario (in part because the DODAG links may not be
   symmetric).  It may be desired to support within RPL the discovery
   and installation of more direct routes 'across' the DAG.  Such
   mechanisms need to be investigated.

C.2.  Destination Advertisement / DAO Fan-out

   When DAO messages are relayed to more than one DODAG parent, in some
   cases a situation may be created where a large number of DAO messages
   conveying information about the same destination flow upwards along
   the DAG.  It is desirable to bound/limit the multiplication/fan-out
   of DAO messages in this manner.  Some aspects of the Destination
   Advertisement mechanism remain under investigation, such as behavior
   in the face of links that may not be symmetric.

   In general, the utility of providing redundancy along downwards
   routes by sending DAO messages to more than one parent is under
   investigation.

C.3.  Source Routing

   In support of nodes that maintain minimal routing state, and to make
   use of the collection of piecewise source routes from the destination
   advertisement mechanism, there needs to be some investigation of a
   mechanism to specify, attach, and follow source routes for packets
   traversing the LLN.

C.4.

B.2.  Address / Header Compression

   In order to minimize overhead within the LLN it is desirable to
   perform some sort of address and/or header compression, perhaps via
   labels, addresses aggregation, or some other means.  This is still
   under investigation.

C.5.

B.3.  Managing Multiple Instances

   A network may run multiple instances of RPL concurrently.  Such a
   network will require methods for assigning and otherwise managing
   RPLInstanceIDs.  This will likely be addressed in a separate
   document.

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

   ROLL Design

   RPL Author Team
   IETF ROLL WG

   Email: rpl-authors@external.cisco.com