draft-ietf-roll-rpl-19.txt   rfc6550.txt 
ROLL T. Winter, Ed. Internet Engineering Task Force (IETF) T. Winter, Ed.
Internet-Draft Request for Comments: 6550
Intended status: Standards Track P. Thubert, Ed. Category: Standards Track P. Thubert, Ed.
Expires: September 14, 2011 Cisco Systems ISSN: 2070-1721 Cisco Systems
A. Brandt A. Brandt
Sigma Designs Sigma Designs
T. Clausen
LIX, Ecole Polytechnique
J. Hui J. Hui
Arch Rock Corporation Arch Rock Corporation
R. Kelsey R. Kelsey
Ember Corporation Ember Corporation
P. Levis P. Levis
Stanford University Stanford University
K. Pister K. Pister
Dust Networks Dust Networks
R. Struik R. Struik
Struik Security Consultancy
JP. Vasseur JP. Vasseur
Cisco Systems Cisco Systems
March 13, 2011 R. Alexander
Cooper Power Systems
March 2012
RPL: IPv6 Routing Protocol for Low power and Lossy Networks RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks
draft-ietf-roll-rpl-19
Abstract Abstract
Low power and Lossy Networks (LLNs) are a class of network in which Low-Power and Lossy Networks (LLNs) are a class of network in which
both the routers and their interconnect are constrained. LLN routers both the routers and their interconnect are constrained. LLN routers
typically operate with constraints on processing power, memory, and typically operate with constraints on processing power, memory, and
energy (battery power). Their interconnects are characterized by energy (battery power). Their interconnects are characterized by
high loss rates, low data rates, and instability. LLNs are comprised high loss rates, low data rates, and instability. LLNs are comprised
of anything from a few dozen and up to thousands of routers. of anything from a few dozen to thousands of routers. Supported
Supported traffic flows include point-to-point (between devices traffic flows include point-to-point (between devices inside the
inside the LLN), point-to-multipoint (from a central control point to LLN), point-to-multipoint (from a central control point to a subset
a subset of devices inside the LLN), and multipoint-to-point (from of devices inside the LLN), and multipoint-to-point (from devices
devices inside the LLN towards a central control point). This inside the LLN towards a central control point). This document
document specifies the IPv6 Routing Protocol for LLNs (RPL), which specifies the IPv6 Routing Protocol for Low-Power and Lossy Networks
provides a mechanism whereby multipoint-to-point traffic from devices (RPL), which provides a mechanism whereby multipoint-to-point traffic
inside the LLN towards a central control point, as well as point-to- from devices inside the LLN towards a central control point as well
multipoint traffic from the central control point to the devices as point-to-multipoint traffic from the central control point to the
inside the LLN, is supported. Support for point-to-point traffic is devices inside the LLN are supported. Support for point-to-point
also available. traffic is also available.
Status of this Memo
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Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on September 14, 2011. Information about the current status of this document, any errata,
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http://www.rfc-editor.org/info/rfc6550.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction ....................................................8
1.1. Design Principles . . . . . . . . . . . . . . . . . . . 8 1.1. Design Principles ..........................................8
1.2. Expectations of Link Layer Type . . . . . . . . . . . . 10 1.2. Expectations of Link-Layer Type ...........................10
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 11 2. Terminology ....................................................10
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 14 3. Protocol Overview ..............................................13
3.1. Topology . . . . . . . . . . . . . . . . . . . . . . . . 14 3.1. Topologies ................................................13
3.1.1. Constructing Topologies . . . . . . . . . . . . . . . 14 3.1.1. Constructing Topologies ............................13
3.1.2. RPL Identifiers . . . . . . . . . . . . . . . . . . . 14 3.1.2. RPL Identifiers ....................................14
3.1.3. Instances, DODAGs, and DODAG Versions . . . . . . . . 15 3.1.3. Instances, DODAGs, and DODAG Versions ..............14
3.2. Upward Routes and DODAG Construction . . . . . . . . . . 17 3.2. Upward Routes and DODAG Construction ......................16
3.2.1. Objective Function (OF) . . . . . . . . . . . . . . . 17 3.2.1. Objective Function (OF) ............................17
3.2.2. DODAG Repair . . . . . . . . . . . . . . . . . . . . 17 3.2.2. DODAG Repair .......................................17
3.2.3. Security . . . . . . . . . . . . . . . . . . . . . . 18 3.2.3. Security ...........................................17
3.2.4. Grounded and Floating DODAGs . . . . . . . . . . . . 18 3.2.4. Grounded and Floating DODAGs .......................18
3.2.5. Local DODAGs . . . . . . . . . . . . . . . . . . . . 18 3.2.5. Local DODAGs .......................................18
3.2.6. Administrative Preference . . . . . . . . . . . . . . 19 3.2.6. Administrative Preference ..........................18
3.2.7. Datapath Validation and Loop Detection . . . . . . . 19 3.2.7. Data-Path Validation and Loop Detection ............18
3.2.8. Distributed Algorithm Operation . . . . . . . . . . . 19 3.2.8. Distributed Algorithm Operation ....................19
3.3. Downward Routes and Destination Advertisement . . . . . 20 3.3. Downward Routes and Destination Advertisement .............19
3.4. Local DODAGs Route Discovery . . . . . . . . . . . . . . 20 3.4. Local DODAGs Route Discovery ..............................20
3.5. Rank Properties . . . . . . . . . . . . . . . . . . . . 21 3.5. Rank Properties ...........................................20
3.5.1. Rank Comparison (DAGRank()) . . . . . . . . . . . . . 22 3.5.1. Rank Comparison (DAGRank()) ........................21
3.5.2. Rank Relationships . . . . . . . . . . . . . . . . . 23 3.5.2. Rank Relationships .................................22
3.6. Routing Metrics and Constraints Used By RPL . . . . . . 23 3.6. Routing Metrics and Constraints Used by RPL ...............23
3.7. Loop Avoidance . . . . . . . . . . . . . . . . . . . . . 24 3.7. Loop Avoidance ............................................24
3.7.1. Greediness and Instability . . . . . . . . . . . . . 25 3.7.1. Greediness and Instability .........................24
3.7.2. DODAG Loops . . . . . . . . . . . . . . . . . . . . . 27 3.7.2. DODAG Loops ........................................26
3.7.3. DAO Loops . . . . . . . . . . . . . . . . . . . . . . 27 3.7.3. DAO Loops ..........................................27
4. Traffic Flows Supported by RPL . . . . . . . . . . . . . . . 28 4. Traffic Flows Supported by RPL .................................27
4.1. Multipoint-to-Point Traffic . . . . . . . . . . . . . . 28 4.1. Multipoint-to-Point Traffic ...............................27
4.2. Point-to-Multipoint Traffic . . . . . . . . . . . . . . 28 4.2. Point-to-Multipoint Traffic ...............................27
4.3. Point-to-Point Traffic . . . . . . . . . . . . . . . . . 28 4.3. Point-to-Point Traffic ....................................27
5. RPL Instance . . . . . . . . . . . . . . . . . . . . . . . . 29 5. RPL Instance ...................................................28
5.1. RPL Instance ID . . . . . . . . . . . . . . . . . . . . 29 5.1. RPL Instance ID ...........................................29
6. ICMPv6 RPL Control Message . . . . . . . . . . . . . . . . . 31 6. ICMPv6 RPL Control Message .....................................30
6.1. RPL Security Fields . . . . . . . . . . . . . . . . . . 33 6.1. RPL Security Fields .......................................32
6.2. DODAG Information Solicitation (DIS) . . . . . . . . . . 38 6.2. DODAG Information Solicitation (DIS) ......................38
6.2.1. Format of the DIS Base Object . . . . . . . . . . . . 38 6.2.1. Format of the DIS Base Object ......................38
6.2.2. Secure DIS . . . . . . . . . . . . . . . . . . . . . 38 6.2.2. Secure DIS .........................................38
6.2.3. DIS Options . . . . . . . . . . . . . . . . . . . . . 38 6.2.3. DIS Options ........................................38
6.3. DODAG Information Object (DIO) . . . . . . . . . . . . . 38 6.3. DODAG Information Object (DIO) ............................38
6.3.1. Format of the DIO Base Object . . . . . . . . . . . . 39 6.3.1. Format of the DIO Base Object ......................39
6.3.2. Secure DIO . . . . . . . . . . . . . . . . . . . . . 41 6.3.2. Secure DIO .........................................41
6.3.3. DIO Options . . . . . . . . . . . . . . . . . . . . . 41 6.3.3. DIO Options ........................................41
6.4. Destination Advertisement Object (DAO) . . . . . . . . . 41 6.4. Destination Advertisement Object (DAO) ....................41
6.4.1. Format of the DAO Base Object . . . . . . . . . . . . 41 6.4.1. Format of the DAO Base Object ......................42
6.4.2. Secure DAO . . . . . . . . . . . . . . . . . . . . . 43 6.4.2. Secure DAO .........................................43
6.4.3. DAO Options . . . . . . . . . . . . . . . . . . . . . 43 6.4.3. DAO Options ........................................43
6.5. Destination Advertisement Object Acknowledgement 6.5. Destination Advertisement Object Acknowledgement
(DAO-ACK) . . . . . . . . . . . . . . . . . . . . . . . 43 (DAO-ACK) .................................................43
6.5.1. Format of the DAO-ACK Base Object . . . . . . . . . . 43 6.5.1. Format of the DAO-ACK Base Object ..................44
6.5.2. Secure DAO-ACK . . . . . . . . . . . . . . . . . . . 45 6.5.2. Secure DAO-ACK .....................................45
6.5.3. DAO-ACK Options . . . . . . . . . . . . . . . . . . . 45 6.5.3. DAO-ACK Options ....................................45
6.6. Consistency Check (CC) . . . . . . . . . . . . . . . . . 45 6.6. Consistency Check (CC) ....................................45
6.6.1. Format of the CC Base Object . . . . . . . . . . . . 45 6.6.1. Format of the CC Base Object .......................46
6.6.2. CC Options . . . . . . . . . . . . . . . . . . . . . 47 6.6.2. CC Options .........................................47
6.7. RPL Control Message Options . . . . . . . . . . . . . . 47 6.7. RPL Control Message Options ...............................47
6.7.1. RPL Control Message Option Generic Format . . . . . . 47 6.7.1. RPL Control Message Option Generic Format ..........47
6.7.2. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 48 6.7.2. Pad1 ...............................................48
6.7.3. PadN . . . . . . . . . . . . . . . . . . . . . . . . 48 6.7.3. PadN ...............................................48
6.7.4. Metric Container . . . . . . . . . . . . . . . . . . 49 6.7.4. DAG Metric Container ...............................49
6.7.5. Route Information . . . . . . . . . . . . . . . . . . 50 6.7.5. Route Information ..................................50
6.7.6. DODAG Configuration . . . . . . . . . . . . . . . . . 51 6.7.6. DODAG Configuration ................................52
6.7.7. RPL Target . . . . . . . . . . . . . . . . . . . . . 53 6.7.7. RPL Target .........................................54
6.7.8. Transit Information . . . . . . . . . . . . . . . . . 55 6.7.8. Transit Information ................................55
6.7.9. Solicited Information . . . . . . . . . . . . . . . . 58 6.7.9. Solicited Information ..............................58
6.7.10. Prefix Information . . . . . . . . . . . . . . . . . 59 6.7.10. Prefix Information ................................59
6.7.11. RPL Target Descriptor . . . . . . . . . . . . . . . . 62 6.7.11. RPL Target Descriptor .............................63
7. Sequence Counters . . . . . . . . . . . . . . . . . . . . . . 64 7. Sequence Counters ..............................................63
7.1. Sequence Counter Overview . . . . . . . . . . . . . . . 64 7.1. Sequence Counter Overview .................................63
7.2. Sequence Counter Operation . . . . . . . . . . . . . . . 65 7.2. Sequence Counter Operation ................................64
8. Upward Routes . . . . . . . . . . . . . . . . . . . . . . . . 67 8. Upward Routes ..................................................66
8.1. DIO Base Rules . . . . . . . . . . . . . . . . . . . . . 67 8.1. DIO Base Rules ............................................67
8.2. Upward Route Discovery and Maintenance . . . . . . . . . 68 8.2. Upward Route Discovery and Maintenance ....................67
8.2.1. Neighbors and Parents within a DODAG Version . . . . 68 8.2.1. Neighbors and Parents within a DODAG Version .......67
8.2.2. Neighbors and Parents across DODAG Versions . . . . . 69 8.2.2. Neighbors and Parents across DODAG Versions ........68
8.2.3. DIO Message Communication . . . . . . . . . . . . . . 74 8.2.3. DIO Message Communication ..........................73
8.3. DIO Transmission . . . . . . . . . . . . . . . . . . . . 74 8.3. DIO Transmission ..........................................74
8.3.1. Trickle Parameters . . . . . . . . . . . . . . . . . 75 8.3.1. Trickle Parameters .................................75
8.4. DODAG Selection . . . . . . . . . . . . . . . . . . . . 75 8.4. DODAG Selection ...........................................75
8.5. Operation as a Leaf Node . . . . . . . . . . . . . . . . 76 8.5. Operation as a Leaf Node ..................................75
8.6. Administrative Rank . . . . . . . . . . . . . . . . . . 77 8.6. Administrative Rank .......................................76
9. Downward Routes . . . . . . . . . . . . . . . . . . . . . . . 78 9. Downward Routes ................................................77
9.1. Destination Advertisement Parents . . . . . . . . . . . 78 9.1. Destination Advertisement Parents .........................77
9.2. Downward Route Discovery and Maintenance . . . . . . . . 79 9.2. Downward Route Discovery and Maintenance ..................78
9.2.1. Maintenance of Path Sequence . . . . . . . . . . . . 80 9.2.1. Maintenance of Path Sequence .......................79
9.2.2. Generation of DAO Messages . . . . . . . . . . . . . 80 9.2.2. Generation of DAO Messages .........................79
9.3. DAO Base Rules . . . . . . . . . . . . . . . . . . . . . 81 9.3. DAO Base Rules ............................................80
9.4. Structure of DAO Messages . . . . . . . . . . . . . . . 81 9.4. Structure of DAO Messages .................................80
9.5. DAO Transmission Scheduling . . . . . . . . . . . . . . 84 9.5. DAO Transmission Scheduling ...............................83
9.6. Triggering DAO Messages . . . . . . . . . . . . . . . . 84 9.6. Triggering DAO Messages ...................................83
9.7. Non-storing Mode . . . . . . . . . . . . . . . . . . . . 85 9.7. Non-Storing Mode ..........................................84
9.8. Storing Mode . . . . . . . . . . . . . . . . . . . . . . 86 9.8. Storing Mode ..............................................85
9.9. Path Control . . . . . . . . . . . . . . . . . . . . . . 87 9.9. Path Control ..............................................86
9.9.1. Path Control Example . . . . . . . . . . . . . . . . 88 9.9.1. Path Control Example ...............................88
9.10. Multicast Destination Advertisement Messages . . . . . . 90 9.10. Multicast Destination Advertisement Messages .............89
10. Security Mechanisms . . . . . . . . . . . . . . . . . . . . . 91 10. Security Mechanisms ...........................................90
10.1. Security Overview . . . . . . . . . . . . . . . . . . . 91 10.1. Security Overview ........................................90
10.2. Joining a Secure Network . . . . . . . . . . . . . . . . 92 10.2. Joining a Secure Network .................................91
10.3. Installing Keys . . . . . . . . . . . . . . . . . . . . 93 10.3. Installing Keys ..........................................92
10.4. Consistency Checks . . . . . . . . . . . . . . . . . . . 93 10.4. Consistency Checks .......................................93
10.5. Counters . . . . . . . . . . . . . . . . . . . . . . . . 94 10.5. Counters .................................................93
10.6. Transmission of Outgoing Packets . . . . . . . . . . . . 95 10.6. Transmission of Outgoing Packets .........................94
10.7. Reception of Incoming Packets . . . . . . . . . . . . . 96 10.7. Reception of Incoming Packets ............................95
10.7.1. Timestamp Key Checks . . . . . . . . . . . . . . . . 97 10.7.1. Timestamp Key Checks ..............................97
10.8. Coverage of Integrity and Confidentiality . . . . . . . 98 10.8. Coverage of Integrity and Confidentiality ................97
10.9. Cryptographic Mode of Operation . . . . . . . . . . . . 98 10.9. Cryptographic Mode of Operation ..........................98
10.9.1. CCM Nonce . . . . . . . . . . . . . . . . . . . . . . 98 10.9.1. CCM Nonce .........................................98
10.9.2. Signatures . . . . . . . . . . . . . . . . . . . . . 99 10.9.2. Signatures ........................................99
11. Packet Forwarding and Loop Avoidance/Detection . . . . . . . 101 11. Packet Forwarding and Loop Avoidance/Detection ................99
11.1. Suggestions for Packet Forwarding . . . . . . . . . . . 101 11.1. Suggestions for Packet Forwarding ........................99
11.2. Loop Avoidance and Detection . . . . . . . . . . . . . . 102 11.2. Loop Avoidance and Detection ............................101
11.2.1. Source Node Operation . . . . . . . . . . . . . . . . 103 11.2.1. Source Node Operation ............................102
11.2.2. Router Operation . . . . . . . . . . . . . . . . . . 103 11.2.2. Router Operation .................................102
12. Multicast Operation . . . . . . . . . . . . . . . . . . . . . 106 12. Multicast Operation ..........................................104
13. Maintenance of Routing Adjacency . . . . . . . . . . . . . . 108 13. Maintenance of Routing Adjacency .............................105
14. Guidelines for Objective Functions . . . . . . . . . . . . . 109 14. Guidelines for Objective Functions ...........................106
14.1. Objective Function Behavior . . . . . . . . . . . . . . 109 14.1. Objective Function Behavior .............................106
15. Suggestions for Interoperation with Neighbor Discovery . . . 111 15. Suggestions for Interoperation with Neighbor Discovery .......108
16. Summary of Requirements for Interoperable Implementations . . 112 16. Summary of Requirements for Interoperable Implementations ....109
16.1. Common Requirements . . . . . . . . . . . . . . . . . . 112 16.1. Common Requirements .....................................109
16.2. Operation as a RPL Leaf Node (only) . . . . . . . . . . 112 16.2. Operation as a RPL Leaf Node (Only) .....................110
16.3. Operation as a RPL Router . . . . . . . . . . . . . . . 113 16.3. Operation as a RPL Router ...............................110
16.3.1. Support for Upward Routes only . . . . . . . . . . . 113 16.3.1. Support for Upward Routes (Only) .................110
16.3.2. Support for Upward Routes and Downward Routes in 16.3.2. Support for Upward Routes and Downward
Non-Storing mode . . . . . . . . . . . . . . . . . . 113 Routes in Non-Storing ............................110
16.3.3. Support for Upward Routes and Downward Routes in 16.3.3. Support for Upward Routes and Downward
Storing mode . . . . . . . . . . . . . . . . . . . . 114 Routes in Storing Mode ...........................111
16.4. Items for Future Specification . . . . . . . . . . . . . 114 16.4. Items for Future Specification ..........................111
17. RPL Constants and Variables . . . . . . . . . . . . . . . . . 115 17. RPL Constants and Variables ..................................112
18. Manageability Considerations . . . . . . . . . . . . . . . . 117 18. Manageability Considerations .................................113
18.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 117 18.1. Introduction ............................................114
18.2. Configuration Management . . . . . . . . . . . . . . . . 118 18.2. Configuration Management ................................115
18.2.1. Initialization Mode . . . . . . . . . . . . . . . . . 118 18.2.1. Initialization Mode ..............................115
18.2.2. DIO and DAO Base Message and Options Configuration . 119 18.2.2. DIO and DAO Base Message and Options
18.2.3. Protocol Parameters to be configured on every Configuration ....................................115
router in the LLN . . . . . . . . . . . . . . . . . . 119 18.2.3. Protocol Parameters to Be Configured on
18.2.4. Protocol Parameters to be configured on every Every Router in the LLN ..........................116
non-DODAG-root router in the LLN . . . . . . . . . . 120 18.2.4. Protocol Parameters to Be Configured on
18.2.5. Parameters to be configured on the DODAG root . . . . 120 Every Non-DODAG-Root .............................117
18.2.6. Configuration of RPL Parameters related to 18.2.5. Parameters to Be Configured on the DODAG Root ....117
DAO-based mechanisms . . . . . . . . . . . . . . . . 121 18.2.6. Configuration of RPL Parameters Related
to DAO-Based Mechanisms ..........................118
18.2.7. Configuration of RPL Parameters related to 18.2.7. Configuration of RPL Parameters Related
Security mechanisms . . . . . . . . . . . . . . . . . 122 to Security Mechanisms ...........................119
18.2.8. Default Values . . . . . . . . . . . . . . . . . . . 123 18.2.8. Default Values ...................................119
18.3. Monitoring of RPL Operation . . . . . . . . . . . . . . 123 18.3. Monitoring of RPL Operation .............................120
18.3.1. Monitoring a DODAG parameters . . . . . . . . . . . . 123 18.3.1. Monitoring a DODAG Parameters ....................120
18.3.2. Monitoring a DODAG inconsistencies and loop 18.3.2. Monitoring a DODAG Inconsistencies and
detection . . . . . . . . . . . . . . . . . . . . . . 124 Loop Detection ...................................121
18.4. Monitoring of the RPL data structures . . . . . . . . . 125 18.4. Monitoring of the RPL Data Structures ...................121
18.4.1. Candidate Neighbor Data Structure . . . . . . . . . . 125 18.4.1. Candidate Neighbor Data Structure ................121
18.4.2. Destination Oriented Directed Acyclic Graph (DAG) 18.4.2. Destination-Oriented Directed Acyclic
Table . . . . . . . . . . . . . . . . . . . . . . . . 125 Graph (DODAG) Table ..............................122
18.4.3. Routing Table and DAO Routing Entries . . . . . . . . 126 18.4.3. Routing Table and DAO Routing Entries ............122
18.5. Fault Management . . . . . . . . . . . . . . . . . . . . 127 18.5. Fault Management ........................................123
18.6. Policy . . . . . . . . . . . . . . . . . . . . . . . . . 127 18.6. Policy ..................................................124
18.7. Fault Isolation . . . . . . . . . . . . . . . . . . . . 128 18.7. Fault Isolation .........................................125
18.8. Impact on Other Protocols . . . . . . . . . . . . . . . 129 18.8. Impact on Other Protocols ...............................125
18.9. Performance Management . . . . . . . . . . . . . . . . . 129 18.9. Performance Management ..................................126
18.10. Diagnostics . . . . . . . . . . . . . . . . . . . . . . 129 18.10. Diagnostics ............................................126
19. Security Considerations . . . . . . . . . . . . . . . . . . . 130 19. Security Considerations ......................................126
19.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 130 19.1. Overview ................................................126
20. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 132 20. IANA Considerations ..........................................128
20.1. RPL Control Message . . . . . . . . . . . . . . . . . . 132 20.1. RPL Control Message .....................................128
20.2. New Registry for RPL Control Codes . . . . . . . . . . . 132 20.2. New Registry for RPL Control Codes ......................128
20.3. New Registry for the Mode of Operation (MOP) . . . . . . 133 20.3. New Registry for the Mode of Operation (MOP) ............129
20.4. RPL Control Message Option . . . . . . . . . . . . . . . 134 20.4. RPL Control Message Option ..............................130
20.5. Objective Code Point (OCP) Registry . . . . . . . . . . 134 20.5. Objective Code Point (OCP) Registry .....................131
20.6. New Registry for the Security Section Algorithm . . . . 135 20.6. New Registry for the Security Section Algorithm .........131
20.7. New Registry for the Security Section Flags . . . . . . 135 20.7. New Registry for the Security Section Flags .............132
20.8. New Registry for Per-KIM Security Levels . . . . . . . . 136 20.8. New Registry for Per-KIM Security Levels ................132
20.9. New Registry for the DIS (DODAG Informational 20.9. New Registry for DODAG Informational
Solicitation) Flags . . . . . . . . . . . . . . . . . . 137 Solicitation (DIS) Flags ................................133
20.10. New Registry for the DODAG Information Object (DIO) 20.10. New Registry for the DODAG Information Object
Flags . . . . . . . . . . . . . . . . . . . . . . . . . 138 (DIO) Flags ............................................134
20.11. New Registry for the Destination Advertisement Object 20.11. New Registry for the Destination Advertisement
(DAO) Flags . . . . . . . . . . . . . . . . . . . . . . 138 Object (DAO) Flags .....................................134
20.12. New Registry for the Destination Advertisement Object 20.12. New Registry for the Destination Advertisement
(DAO) Acknowledgement Flags . . . . . . . . . . . . . . 139 Object (DAO) Flags .....................................135
20.13. New Registry for the Consistency Check (CC) Flags . . . 139 20.13. New Registry for the Consistency Check (CC) Flags ......135
20.14. New Registry for the DODAG Configuration Option Flags . 140 20.14. New Registry for the DODAG Configuration Option Flags ..136
20.15. New Registry for the RPL Target Option Flags . . . . . . 140 20.15. New Registry for the RPL Target Option Flags ...........136
20.16. New Registry for the Transit Information Option Flags . 141 20.16. New Registry for the Transit Information Option Flags ..137
20.17. New Registry for the Solicited Information Option 20.17. New Registry for the Solicited Information
Flags . . . . . . . . . . . . . . . . . . . . . . . . . 141 Option Flags ...........................................137
20.18. ICMPv6: Error in Source Routing Header . . . . . . . . . 142 20.18. ICMPv6: Error in Source Routing Header .................138
20.19. Link-Local Scope multicast address . . . . . . . . . . . 142 20.19. Link-Local Scope Multicast Address .....................138
21. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 143 21. Acknowledgements .............................................138
22. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 144 22. Contributors .................................................139
23. References . . . . . . . . . . . . . . . . . . . . . . . . . 145 23. References ...................................................139
23.1. Normative References . . . . . . . . . . . . . . . . . . 145 23.1. Normative References ....................................139
23.2. Informative References . . . . . . . . . . . . . . . . . 146 23.2. Informative References ..................................140
Appendix A. Example Operation . . . . . . . . . . . . . . . . . 149 Appendix A. Example Operation ....................................143
A.1. Example Operation in Storing Mode With Node-owned A.1. Example Operation in Storing Mode with Node-Owned
Prefixes . . . . . . . . . . . . . . . . . . . . . . . . 149 Prefixes .................................................143
A.1.1. DIO messages and PIO . . . . . . . . . . . . . . . . 150 A.1.1. DIO Messages and PIO ..............................144
A.1.2. DAO messages . . . . . . . . . . . . . . . . . . . . 151 A.1.2. DAO Messages ......................................145
A.1.3. Routing Information Base . . . . . . . . . . . . . . 151 A.1.3. Routing Information Base ..........................145
A.2. Example Operation in Storing Mode With Subnet-wide A.2. Example Operation in Storing Mode with Subnet-Wide
Prefix . . . . . . . . . . . . . . . . . . . . . . . . . 152 Prefix ...................................................146
A.2.1. DIO messages and PIO . . . . . . . . . . . . . . . . 153 A.2.1. DIO Messages and PIO ..............................147
A.2.2. DAO messages . . . . . . . . . . . . . . . . . . . . 154 A.2.2. DAO Messages ......................................148
A.2.3. Routing Information Base . . . . . . . . . . . . . . 154 A.2.3. Routing Information Base ..........................148
A.3. Example Operation in Non-Storing Mode With Node-owned A.3. Example Operation in Non-Storing Mode with Node-Owned
Prefixes . . . . . . . . . . . . . . . . . . . . . . . . 155 Prefixes .................................................149
A.3.1. DIO messages and PIO . . . . . . . . . . . . . . . . 156 A.3.1. DIO Messages and PIO ..............................150
A.3.2. DAO messages . . . . . . . . . . . . . . . . . . . . 156 A.3.2. DAO Messages ......................................150
A.3.3. Routing Information Base . . . . . . . . . . . . . . 157 A.3.3. Routing Information Base ..........................151
A.4. Example Operation in Non-Storing Mode With A.4. Example Operation in Non-Storing Mode with
Subnet-wide Prefix . . . . . . . . . . . . . . . . . . . 157 Subnet-Wide Prefix .......................................151
A.4.1. DIO messages and PIO . . . . . . . . . . . . . . . . 158 A.4.1. DIO Messages and PIO ..............................152
A.4.2. DAO messages . . . . . . . . . . . . . . . . . . . . 159 A.4.2. DAO Messages ......................................153
A.4.3. Routing Information Base . . . . . . . . . . . . . . 159 A.4.3. Routing Information Base ..........................153
A.5. Example with External Prefixes . . . . . . . . . . . . . 160 A.5. Example with External Prefixes ...........................154
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 162
1. Introduction 1. Introduction
Low power and Lossy Networks (LLNs) consist of largely of constrained Low-power and Lossy Networks (LLNs) consist largely of constrained
nodes (with limited processing power, memory, and sometimes energy nodes (with limited processing power, memory, and sometimes energy
when they are battery operated or energy scavenging). These routers when they are battery operated or energy scavenging). These routers
are interconnected by lossy links, typically supporting only low data are interconnected by lossy links, typically supporting only low data
rates, that are usually unstable with relatively low packet delivery rates, that are usually unstable with relatively low packet delivery
rates. Another characteristic of such networks is that the traffic rates. Another characteristic of such networks is that the traffic
patterns are not simply point-to-point, but in many cases point-to- patterns are not simply point-to-point, but in many cases point-to-
multipoint or multipoint-to-point. Furthermore such networks may multipoint or multipoint-to-point. Furthermore, such networks may
potentially comprise up to thousands of nodes. These characteristics potentially comprise up to thousands of nodes. These characteristics
offer unique challenges to a routing solution: the IETF ROLL Working offer unique challenges to a routing solution: the IETF ROLL working
Group has defined application-specific routing requirements for a Low group has defined application-specific routing requirements for a
power and Lossy Network (LLN) routing protocol, specified in Low-power and Lossy Network (LLN) routing protocol, specified in
[RFC5867], [RFC5826], [RFC5673], and [RFC5548]. [RFC5867], [RFC5826], [RFC5673], and [RFC5548].
This document specifies the IPv6 Routing Protocol for Low power and This document specifies the IPv6 Routing Protocol for LLNs (RPL).
lossy networks (RPL). Note that although RPL was specified according Note that although RPL was specified according to the requirements
to the requirements set forth in the aforementioned requirement set forth in the aforementioned requirement documents, its use is in
documents, its use is in no way limited to these applications. no way limited to these applications.
1.1. Design Principles 1.1. Design Principles
RPL was designed with the objective to meet the requirements spelled RPL was designed with the objective to meet the requirements spelled
out in [RFC5867], [RFC5826], [RFC5673], and [RFC5548]. out in [RFC5867], [RFC5826], [RFC5673], and [RFC5548].
A network may run multiple instances of RPL concurrently. Each such A network may run multiple instances of RPL concurrently. Each such
instance may serve different and potentially antagonistic constraints instance may serve different and potentially antagonistic constraints
or performance criteria. This document defines how a single instance or performance criteria. This document defines how a single instance
operates. operates.
In order to be useful in a wide range of LLN application domains, RPL In order to be useful in a wide range of LLN application domains, RPL
separates packet processing and forwarding from the routing separates packet processing and forwarding from the routing
optimization objective. Examples of such objectives include optimization objective. Examples of such objectives include
minimizing energy, minimizing latency, or satisfying constraints. minimizing energy, minimizing latency, or satisfying constraints.
This document describes the mode of operation of RPL. Other This document describes the mode of operation of RPL. Other
companion documents specify routing objective functions. A RPL companion documents specify routing Objective Functions. A RPL
implementation, in support of a particular LLN application, will implementation, in support of a particular LLN application, will
include the necessary objective function(s) as required by the include the necessary Objective Function(s) as required by the
application. application.
RPL operations require bidirectional links. In some LLN scenarios RPL operations require bidirectional links. In some LLN scenarios,
those links may exhibit asymmetric properties. It is required that those links may exhibit asymmetric properties. It is required that
the reachability of a router is verified before the router can be the reachability of a router be verified before the router can be
used as a parent. RPL expects an external mechanism to be triggered used as a parent. RPL expects an external mechanism to be triggered
during the parent selection phase in order to verify link properties during the parent selection phase in order to verify link properties
and neighbor reachability. Neighbor Unreachability Detection (NUD) and neighbor reachability. Neighbor Unreachability Detection (NUD)
is such a mechanism, but alternates are possible, including is such a mechanism, but alternates are possible, including
Bidirectional Forwarding Detection [RFC5881] and hints from lower Bidirectional Forwarding Detection (BFD) [RFC5881] and hints from
layers via L2 triggers like [RFC5184]. In a general fashion, a lower layers via Layer 2 (L2) triggers like [RFC5184]. In a general
detection mechanism that is reactive to traffic is favored in order fashion, a detection mechanism that is reactive to traffic is favored
to minimize the cost of monitoring links that are not being used. in order to minimize the cost of monitoring links that are not being
used.
RPL also expects an external mechanism to access and transport some RPL also expects an external mechanism to access and transport some
control information, referred to as the "RPL Packet Information", in control information, referred to as the "RPL Packet Information", in
data packets. The RPL Packet Information is defined in Section 11.2 data packets. The RPL Packet Information is defined in Section 11.2
and enables the association of a data packet with a RPL instance and and enables the association of a data packet with a RPL Instance and
the validation of RPL routing states. The IPv6 Hop-by-Hop RPL Option the validation of RPL routing states. The RPL option [RFC6553] is an
[I-D.ietf-6man-rpl-option] is an example of such mechanism. The example of such mechanism. The mechanism is required for all packets
mechanism is required for all packets except when strict source except when strict source routing is used (that is for packets going
routing is used (that is for packets going downward in non-storing Downward in Non-Storing mode as detailed further in Section 9), which
mode as detailed further in Section 9), which by nature prevents by nature prevents endless loops and alleviates the need for the RPL
endless loops and alleviates the need for the RPL Packet Information. Packet Information. Future companion specifications may propose
Future companion specifications may propose alternate ways to carry alternate ways to carry the RPL Packet Information in the IPv6
the RPL Packet Information in the IPv6 packets and may extend the RPL packets and may extend the RPL Packet Information to support
Packet Information to support additional features. additional features.
RPL provides a mechanism to disseminate information over the RPL provides a mechanism to disseminate information over the
dynamically-formed network topology. The dissemination enables dynamically formed network topology. This dissemination enables
minimal configuration in the nodes, allowing nodes to operate mostly minimal configuration in the nodes, allowing nodes to operate mostly
autonomously. This mechanism uses trickle [I-D.ietf-roll-trickle] to autonomously. This mechanism uses Trickle [RFC6206] to optimize the
optimize the dissemination as described in Section 8.3. dissemination as described in Section 8.3.
In some applications, RPL assembles topologies of routers that own In some applications, RPL assembles topologies of routers that own
independent prefixes. Those prefixes may or may not be aggregatable independent prefixes. Those prefixes may or may not be aggregatable
depending on the origin of the routers. A prefix that is owned by a depending on the origin of the routers. A prefix that is owned by a
router is advertised as on-link. router is advertised as on-link.
RPL also introduces the capability to bind a subnet together with a RPL also introduces the capability to bind a subnet together with a
common prefix and to route within that subnet. A source can inject common prefix and to route within that subnet. A source can inject
information about the subnet to be disseminated by RPL, and that information about the subnet to be disseminated by RPL, and that
source is authoritative for that subnet. Because many LLN links have source is authoritative for that subnet. Because many LLN links have
non-transitive properties, a common prefix that RPL disseminates over non-transitive properties, a common prefix that RPL disseminates over
the subnet must not be advertised as on-link. the subnet must not be advertised as on-link.
RPL may in particular disseminate IPv6 Neighbor Discovery (ND) In particular, RPL may disseminate IPv6 Neighbor Discovery (ND)
information such as the [RFC4861] Prefix Information Option (PIO) and information such as the [RFC4861] Prefix Information Option (PIO) and
the [RFC4191] Route Information Option (RIO). ND information that is the [RFC4191] Route Information Option (RIO). ND information that is
disseminated by RPL conserves all its original semantics for router disseminated by RPL conserves all its original semantics for router
to host, with limited extensions for router to router, though it is to host, with limited extensions for router to router, though it is
not to be confused with routing advertisements and it is never to be not to be confused with routing advertisements and it is never to be
directly redistributed in another routing protocol. A RPL node often directly redistributed in another routing protocol. A RPL node often
combines host and router behaviors. As a host, it will process the combines host and router behaviors. As a host, it will process the
options as specified in [RFC4191], [RFC4861], [RFC4862] and options as specified in [RFC4191], [RFC4861], [RFC4862], and
[RFC3775]. As a router, the RPL node may advertise the information [RFC6275]. As a router, the RPL node may advertise the information
from the options as required for the specific link, for instance in a from the options as required for the specific link, for instance, in
ND RA message, though the exact operation is out of scope. an ND Router Advertisement (RA) message, though the exact operation
is out of scope.
A set of companion documents to this specification will provide A set of companion documents to this specification will provide
further guidance in the form of applicability statements specifying a further guidance in the form of applicability statements specifying a
set of operating points appropriate to the Building Automation, Home set of operating points appropriate to the Building Automation, Home
Automation, Industrial, and Urban application scenarios. Automation, Industrial, and Urban application scenarios.
1.2. Expectations of Link Layer Type 1.2. Expectations of Link-Layer Type
In compliance with the layered architecture of IP, RPL does not rely In compliance with the layered architecture of IP, RPL does not rely
on any particular features of a specific link layer technology. RPL on any particular features of a specific link-layer technology. RPL
is designed to be able to operate over a variety of different link is designed to be able to operate over a variety of different link
layers, including ones that are constrained, potentially lossy, or layers, including ones that are constrained, potentially lossy, or
typically utilized in conjunction with highly constrained host or typically utilized in conjunction with highly constrained host or
router devices, such as but not limited to, low power wireless or PLC router devices, such as but not limited to, low-power wireless or PLC
(Power Line Communication) technologies. (Power Line Communication) technologies.
Implementers may find [RFC3819] a useful reference when designing a Implementers may find [RFC3819] a useful reference when designing a
link layer interface between RPL and a particular link layer link-layer interface between RPL and a particular link-layer
technology. technology.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC "OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119]. 2119 [RFC2119].
Additionally, this document uses terminology from Additionally, this document uses terminology from [ROLL-TERMS], and
[I-D.ietf-roll-terminology], and introduces the following introduces the following terminology:
terminology:
DAG: Directed Acyclic Graph. A directed graph having the property DAG: Directed Acyclic Graph. A directed graph having the property
that all edges are oriented in such a way that no cycles exist. that all edges are oriented in such a way that no cycles exist.
All edges are contained in paths oriented toward and All edges are contained in paths oriented toward and
terminating at one or more root nodes. terminating at one or more root nodes.
DAG root: A DAG root is a node within the DAG that has no outgoing DAG root: A DAG root is a node within the DAG that has no outgoing
edge. Because the graph is acyclic, by definition all DAGs edge. Because the graph is acyclic, by definition, all DAGs
must have at least one DAG root and all paths terminate at a must have at least one DAG root and all paths terminate at a
DAG root. DAG root.
Destination Oriented DAG (DODAG): A DAG rooted at a single Destination-Oriented DAG (DODAG): A DAG rooted at a single
destination, i.e. at a single DAG root (the DODAG root) with no destination, i.e., at a single DAG root (the DODAG root) with
outgoing edges. no outgoing edges.
DODAG root: A DODAG root is the DAG root of a DODAG. The DODAG root DODAG root: A DODAG root is the DAG root of a DODAG. The DODAG root
may act as a border router for the DODAG, and in particular it may act as a border router for the DODAG; in particular, it may
may aggregate routes in the DODAG, and may redistribute DODAG aggregate routes in the DODAG and may redistribute DODAG routes
routes into other routing protocols. into other routing protocols.
Virtual DODAG root: A Virtual DODAG root is the result of two or Virtual DODAG root: A Virtual DODAG root is the result of two or more
more RPL routers, for instance 6LoWPAN Border Routers (6LBRs), RPL routers, for instance, 6LoWPAN Border Routers (6LBRs),
coordinating to synchronize DODAG state and act in concert as coordinating to synchronize DODAG state and act in concert as
if they are a single DODAG root (with multiple interfaces), if they are a single DODAG root (with multiple interfaces),
with respect to the LLN. The coordination most likely occurs with respect to the LLN. The coordination most likely occurs
between powered devices over a reliable transit link, and the between powered devices over a reliable transit link, and the
details of that scheme are out of scope for this specification details of that scheme are out of scope for this specification
(to be defined in future companion specifications). (to be defined in future companion specifications).
Up: Up refers to the direction from leaf nodes towards DODAG roots, Up: Up refers to the direction from leaf nodes towards DODAG roots,
following DODAG edges. This follows the common terminology following DODAG edges. This follows the common terminology
used in graphs and depth-first-search, where vertices further used in graphs and depth-first-search, where vertices further
from the root are "deeper," or "down," and vertices closer to from the root are "deeper" or "down" and vertices closer to the
the root are "shallower," or "up". root are "shallower" or "up".
Down: Down refers to the direction from DODAG roots towards leaf Down: Down refers to the direction from DODAG roots towards leaf
nodes, in the reverse direction of DODAG edges. This follows nodes, in the reverse direction of DODAG edges. This follows
the common terminology used in graphs and depth-first-search, the common terminology used in graphs and depth-first-search,
where vertices further from the root are "deeper," or "down," where vertices further from the root are "deeper" or "down" and
and vertices closer to the root are "shallower," or "up". vertices closer to the root are "shallower" or "up".
Rank: A node's Rank defines the node's individual position relative Rank: A node's Rank defines the node's individual position relative
to other nodes with respect to a DODAG root. Rank strictly to other nodes with respect to a DODAG root. Rank strictly
increases in the Down direction and strictly decreases in the increases in the Down direction and strictly decreases in the
Up direction. The exact way Rank is computed depends on the Up direction. The exact way Rank is computed depends on the
DAG's Objective Function (OF). The Rank may analogously track DAG's Objective Function (OF). The Rank may analogously track
a simple topological distance, may be calculated as a function a simple topological distance, may be calculated as a function
of link metrics, and may consider other properties such as of link metrics, and may consider other properties such as
constraints. constraints.
Objective Function (OF): Defines how routing metrics, optimization Objective Function (OF): An OF defines how routing metrics,
objectives, and related functions are used to compute Rank. optimization objectives, and related functions are used to
Furthermore, the OF dictates how parents in the DODAG are compute Rank. Furthermore, the OF dictates how parents in the
selected and thus the DODAG formation. DODAG are selected and, thus, the DODAG formation.
Objective Code Point (OCP): An identifier that indicates which Objective Code Point (OCP): An OCP is an identifier that indicates
Objective Function the DODAG uses. which Objective Function the DODAG uses.
RPLInstanceID: A unique identifier within a network. DODAGs with RPLInstanceID: A RPLInstanceID is a unique identifier within a
the same RPLInstanceID share the same Objective Function. network. DODAGs with the same RPLInstanceID share the same
Objective Function.
RPL Instance: A set of one or more DODAGs that share a RPL Instance: A RPL Instance is a set of one or more DODAGs that
RPLInstanceID. A RPL node can belong to at most one DODAG in a share a RPLInstanceID. At most, a RPL node can belong to one
RPL Instance. Each RPL Instance operates independently of DODAG in a RPL Instance. Each RPL Instance operates
other RPL Instances. This document describes operation within independently of other RPL Instances. This document describes
a single RPL Instance. operation within a single RPL Instance.
DODAGID: The identifier of a DODAG root. The DODAGID is unique DODAGID: A DODAGID is the identifier of a DODAG root. The DODAGID is
within the scope of a RPL Instance in the LLN. The tuple unique within the scope of a RPL Instance in the LLN. The
(RPLInstanceID, DODAGID) uniquely identifies a DODAG. tuple (RPLInstanceID, DODAGID) uniquely identifies a DODAG.
DODAG Version: A specific iteration ("Version") of a DODAG with a DODAG Version: A DODAG Version is a specific iteration ("Version") of
given DODAGID. a DODAG with a given DODAGID.
DODAGVersionNumber: A sequential counter that is incremented by the DODAGVersionNumber: A DODAGVersionNumber is a sequential counter that
root to form a new Version of a DODAG. A DODAG Version is is incremented by the root to form a new Version of a DODAG. A
identified uniquely by the (RPLInstanceID, DODAGID, DODAG Version is identified uniquely by the (RPLInstanceID,
DODAGVersionNumber) tuple. DODAGID, DODAGVersionNumber) tuple.
Goal: The Goal is an application specific goal that is defined Goal: The Goal is an application-specific goal that is defined
outside the scope of RPL. Any node that roots a DODAG will outside the scope of RPL. Any node that roots a DODAG will
need to know about this Goal to decide if the Goal can be need to know about this Goal to decide whether or not the Goal
satisfied or not. A typical Goal is to construct the DODAG can be satisfied. A typical Goal is to construct the DODAG
according to a specific objective function and to keep according to a specific Objective Function and to keep
connectivity to a set of hosts (e.g. to use an objective connectivity to a set of hosts (e.g., to use an Objective
function that minimizes a metric and to be connected to a Function that minimizes a metric and is connected to a specific
specific database host to store the collected data). database host to store the collected data).
Grounded: A DODAG is grounded when the DODAG root can satisfy the Grounded: A DODAG is grounded when the DODAG root can satisfy the
Goal. Goal.
Floating: A DODAG is floating if it is not Grounded. A floating Floating: A DODAG is floating if it is not grounded. A floating
DODAG is not expected to have the properties required to DODAG is not expected to have the properties required to
satisfy the goal. It may, however, provide connectivity to satisfy the goal. It may, however, provide connectivity to
other nodes within the DODAG. other nodes within the DODAG.
DODAG parent: A parent of a node within a DODAG is one of the 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 immediate successors of the node on a path towards the DODAG
root. A DODAG parent's Rank is lower than the node's. (See root. A DODAG parent's Rank is lower than the node's. (See
Section 3.5.1). Section 3.5.1).
Sub-DODAG The sub-DODAG of a node is the set of other nodes whose Sub-DODAG: The sub-DODAG of a node is the set of other nodes whose
paths to the DODAG root pass through that node. Nodes in the paths to the DODAG root pass through that node. Nodes in the
sub-DODAG of a node have a greater Rank than that node. (See sub-DODAG of a node have a greater Rank than that node. (See
Section 3.5.1). Section 3.5.1).
Local DODAG: Local DODAGs contain one and only one root node, and Local DODAG: Local DODAGs contain one and only one root node, and
allows that single root node to allocate and manage a RPL they allow that single root node to allocate and manage a RPL
Instance, identified by a local RPLInstanceID, without Instance, identified by a local RPLInstanceID, without
coordination with other nodes. This is typically done in order coordination with other nodes. Typically, this is done in
to optimize routes to a destination within the LLN. (See order to optimize routes to a destination within the LLN. (See
Section 5). Section 5).
Global DODAG: A Global DODAG uses a global RPLInstanceID that may be Global DODAG: A Global DODAG uses a global RPLInstanceID that may be
coordinated among several other nodes. (See Section 5). coordinated among several other nodes. (See Section 5).
DIO: DODAG Information Object (See Section 6.3) DIO: DODAG Information Object (see Section 6.3)
DAO: Destination Advertisement Object (See Section 6.4) DAO: Destination Advertisement Object (see Section 6.4)
DIS: DODAG Information Solicitation (See Section 6.2) DIS: DODAG Information Solicitation (see Section 6.2)
CC: Consistency Check (See Section 6.6) CC: Consistency Check (see Section 6.6)
As they form networks, LLN devices often mix the roles of 'host' and As they form networks, LLN devices often mix the roles of host and
'router' when compared to traditional IP networks. In this document, router when compared to traditional IP networks. In this document,
'host' refers to an LLN device that can generate but does not forward "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 RPL traffic; "router" refers to an LLN device that can forward as
well as generate RPL traffic, and 'node' refers to any RPL device, well as generate RPL traffic; and "node" refers to any RPL device,
either a host or a router. either a host or a router.
3. Protocol Overview 3. Protocol Overview
The aim of this section is to describe RPL in the spirit of The aim of this section is to describe RPL in the spirit of
[RFC4101]. Protocol details can be found in further sections. [RFC4101]. Protocol details can be found in further sections.
3.1. Topology 3.1. Topologies
This section describes the basic RPL topologies that may be formed, This section describes the basic RPL topologies that may be formed,
and the rules by which these are constructed, i.e. the rules and the rules by which these are constructed, i.e., the rules
governing DODAG formation. governing DODAG formation.
3.1.1. Constructing Topologies 3.1.1. Constructing Topologies
LLNs, such as Radio Networks, do not typically have a predefined LLNs, such as Radio Networks, do not typically have predefined
topologies, for example those imposed by point to point wires, so RPL topologies, for example, those imposed by point-to-point wires, so
has to discover links and then select peers sparingly. RPL has to discover links and then select peers sparingly.
Because in many cases layer 2 ranges overlap only partially, RPL In many cases, because Layer 2 ranges overlap only partially, RPL
forms non-transitive/NBMA network topologies upon which it computes forms non-transitive / Non-Broadcast Multi-Access (NBMA) network
routes. topologies upon which it computes routes.
RPL routes are optimized for traffic to or from one or more roots RPL routes are optimized for traffic to or from one or more roots
that act as sinks for the topology. As a result, RPL organizes a that act as sinks for the topology. As a result, RPL organizes a
topology as a Directed Acyclic Graph (DAG) that is partitioned into topology as a Directed Acyclic Graph (DAG) that is partitioned into
one or more Destination Oriented DAGS (DODAGs), one DODAG per sink. one or more Destination Oriented DAGs (DODAGs), one DODAG per sink.
If the DAG has multiple roots, then it is expected that the roots are If the DAG has multiple roots, then it is expected that the roots are
federated by a common backbone such as a transit link. federated by a common backbone, such as a transit link.
3.1.2. RPL Identifiers 3.1.2. RPL Identifiers
RPL uses four values to identify and maintain a topology: RPL uses four values to identify and maintain a topology:
o The first is a RPLInstanceID. A RPLInstanceID identifies a set of o The first is a RPLInstanceID. A RPLInstanceID identifies a set of
one or more Destination Oriented DAGs (DODAGs). A network may one or more Destination Oriented DAGs (DODAGs). A network may
have multiple RPLInstanceIDs, each of which defines an independent have multiple RPLInstanceIDs, each of which defines an independent
set of DODAGs, which may be optimized for different Objective set of DODAGs, which may be optimized for different Objective
Functions (OFs) and/or applications. The set of DODAGs identified Functions (OFs) and/or applications. The set of DODAGs identified
skipping to change at page 15, line 16 skipping to change at page 14, line 40
o The fourth is Rank. The scope of Rank is a DODAG Version. Rank o The fourth is Rank. The scope of Rank is a DODAG Version. Rank
establishes a partial order over a DODAG Version, defining establishes a partial order over a DODAG Version, defining
individual node positions with respect to the DODAG root. individual node positions with respect to the DODAG root.
3.1.3. Instances, DODAGs, and DODAG Versions 3.1.3. Instances, DODAGs, and DODAG Versions
A RPL Instance contains one or more DODAG roots. A RPL Instance may A RPL Instance contains one or more DODAG roots. A RPL Instance may
provide routes to certain destination prefixes, reachable via the provide routes to certain destination prefixes, reachable via the
DODAG roots or alternate paths within the DODAG. These roots may DODAG roots or alternate paths within the DODAG. These roots may
operate independently, or may coordinate over a network that is not operate independently, or they may coordinate over a network that is
necessarily as constrained as a LLN. not necessarily as constrained as an LLN.
A RPL Instance may comprise: A RPL Instance may comprise:
o a single DODAG with a single root o a single DODAG with a single root
* For example, a DODAG optimized to minimize latency rooted at a * For example, a DODAG optimized to minimize latency rooted at a
single centralized lighting controller in a home automation single centralized lighting controller in a Home Automation
application. application.
o multiple uncoordinated DODAGs with independent roots (differing o multiple uncoordinated DODAGs with independent roots (differing
DODAGIDs) DODAGIDs)
* For example, multiple data collection points in an urban data * For example, multiple data collection points in an urban data
collection application that do not have suitable connectivity collection application that do not have suitable connectivity
to coordinate with each other, or that use the formation of to coordinate with each other or that use the formation of
multiple DODAGs as a means to dynamically and autonomously multiple DODAGs as a means to dynamically and autonomously
partition the network. partition the network.
o a single DODAG with a virtual root that coordinates LLN sinks o a single DODAG with a virtual root that coordinates LLN sinks
(with the same DODAGID) over a backbone network. (with the same DODAGID) over a backbone network.
* For example, multiple border routers operating with a reliable * For example, multiple border routers operating with a reliable
transit link, e.g. in support of a 6LowPAN application, that transit link, e.g., in support of an IPv6 Low-Power Wireless
are capable to act as logically equivalent interfaces to the Personal Area Network (6LoWPAN) application, that are capable
sink of the same DODAG. of acting as logically equivalent interfaces to the sink of the
same DODAG.
o a combination of the above as suited to some application scenario. o a combination of the above as suited to some application scenario.
Each RPL packet is associated with a particular RPLInstanceID (see Each RPL packet is associated with a particular RPLInstanceID (see
Section 11.2) and therefore RPL Instance (Section 5). The Section 11.2) and, therefore, RPL Instance (Section 5). The
provisioning or automated discovery of a mapping between a provisioning or automated discovery of a mapping between a
RPLInstanceID and a type or service of application traffic is out of RPLInstanceID and a type or service of application traffic is out of
scope for this specification (to be defined in future companion scope for this specification (to be defined in future companion
specifications). specifications).
Figure 1 depicts an example of a RPL Instance comprising three DODAGs Figure 1 depicts an example of a RPL Instance comprising three DODAGs
with DODAG Roots R1, R2, and R3. Each of these DODAG Roots with DODAG roots R1, R2, and R3. Each of these DODAG roots
advertises the same RPLInstanceID. The lines depict connectivity advertises the same RPLInstanceID. The lines depict connectivity
between parents and children. between parents and children.
Figure 2 depicts how a DODAG Version number increment leads to a new Figure 2 depicts how a DODAGVersionNumber increment leads to a new
DODAG Version. This depiction illustrates a DODAG Version number DODAG Version. This depiction illustrates a DODAGVersionNumber
increment that results in a different DODAG topology. Note that a increment that results in a different DODAG topology. Note that a
new DODAG Version does not always imply a different DODAG topology. new DODAG Version does not always imply a different DODAG topology.
To accommodate certain topology changes requires a new DODAG Version, To accommodate certain topology changes requires a new DODAG Version,
as described later in this specification. as described later in this specification.
Please note that in the following examples tree-like structures are In the following examples, please note that tree-like structures are
depicted for simplicity, although the DODAG structure allows for each depicted for simplicity, although the DODAG structure allows for each
node to have multiple parents when the connectivity supports it. node to have multiple parents when the connectivity supports it.
+----------------------------------------------------------------+ +----------------------------------------------------------------+
| | | |
| +--------------+ | | +--------------+ |
| | | | | | | |
| | (R1) | (R2) (R3) | | | (R1) | (R2) (R3) |
| | / \ | /| \ / | \ | | | / \ | /| \ / | \ |
| | / \ | / | \ / | \ | | | / \ | / | \ / | \ |
skipping to change at page 17, line 37 skipping to change at page 17, line 11
optimized according to an Objective Function (OF). RPL nodes optimized according to an Objective Function (OF). RPL nodes
construct and maintain these DODAGs through DODAG Information Object construct and maintain these DODAGs through DODAG Information Object
(DIO) messages. (DIO) messages.
3.2.1. Objective Function (OF) 3.2.1. Objective Function (OF)
The Objective Function (OF) defines how RPL nodes select and optimize The Objective Function (OF) defines how RPL nodes select and optimize
routes within a RPL Instance. The OF is identified by an Objective routes within a RPL Instance. The OF is identified by an Objective
Code Point (OCP) within the DIO Configuration option. An OF defines Code Point (OCP) within the DIO Configuration option. An OF defines
how nodes translate one or more metrics and constraints, which are how nodes translate one or more metrics and constraints, which are
themselves defined in [I-D.ietf-roll-routing-metrics], into a value themselves defined in [RFC6551], into a value called Rank, which
called Rank, which approximates the node's distance from a DODAG approximates the node's distance from a DODAG root. An OF also
root. An OF also defines how nodes select parents. Further details defines how nodes select parents. Further details may be found in
may be found in Section 14, [I-D.ietf-roll-routing-metrics], Section 14, [RFC6551], [RFC6552], and related companion
[I-D.ietf-roll-of0], and related companion specifications. specifications.
3.2.2. DODAG Repair 3.2.2. DODAG Repair
A DODAG Root institutes a global repair operation by incrementing the A DODAG root institutes a global repair operation by incrementing the
DODAG Version Number. This initiates a new DODAG Version. Nodes in DODAGVersionNumber. This initiates a new DODAG Version. Nodes in
the new DODAG Version can choose a new position whose Rank is not the new DODAG Version can choose a new position whose Rank is not
constrained by their Rank within the old DODAG Version. constrained by their Rank within the old DODAG Version.
RPL also supports mechanisms which may be used for local repair RPL also supports mechanisms that may be used for local repair within
within the DODAG Version. The DIO message specifies the necessary the DODAG Version. The DIO message specifies the necessary
parameters as configured from and controlled by policy at the DODAG parameters as configured from and controlled by policy at the DODAG
root. root.
3.2.3. Security 3.2.3. Security
RPL supports message confidentiality and integrity. It is designed RPL supports message confidentiality and integrity. It is designed
such that link-layer mechanisms can be used when available and such that link-layer mechanisms can be used when available and
appropriate, yet in their absence RPL can use its own mechanisms. appropriate; yet, in their absence, RPL can use its own mechanisms.
RPL has three basic security modes. RPL has three basic security modes.
In the first, called "unsecured," RPL control messages are sent In the first, called "unsecured", RPL control messages are sent
without any additional security mechanisms. Unsecured mode does not without any additional security mechanisms. Unsecured mode does not
imply that the RPL network is unsecure: it could be using other imply that the RPL network is unsecure: it could be using other
present security primitives (e.g. link-layer security) to meet present security primitives (e.g., link-layer security) to meet
application security requirements. application security requirements.
In the second, called "pre-installed," nodes joining a RPL Instance In the second, called "preinstalled", nodes joining a RPL Instance
have pre-installed keys that enable them to process and generate have preinstalled keys that enable them to process and generate
secured RPL messages. secured RPL messages.
The third mode is called "authenticated." In authenticated mode, The third mode is called "authenticated". In authenticated mode,
nodes have pre-installed keys as in pre-installed mode, but the pre- nodes have preinstalled keys as in preinstalled mode, but the
installed key may only be used to join a RPL Instance as a leaf. preinstalled key may only be used to join a RPL Instance as a leaf.
Joining an authenticated RPL Instance as a router requires obtaining Joining an authenticated RPL Instance as a router requires obtaining
a key from an authentication authority. The process by which this a key from an authentication authority. The process by which this
key is obtained is out of scope for this specification. Note that key is obtained is out of scope for this specification. Note that
this specification alone does not provide sufficient detail for a RPL this specification alone does not provide sufficient detail for a RPL
implementation to securely operate in authenticated mode. For a RPL implementation to securely operate in authenticated mode. For a RPL
implementation to operate securely in authenticated mode it is implementation to operate securely in authenticated mode, it is
necessary for a future companion specification to detail the necessary for a future companion specification to detail the
mechanisms by which a node obtains/requests the authentication mechanisms by which a node obtains/requests the authentication
material (e.g. key, certificate), and to determine from where that material (e.g., key, certificate) and to determine from where that
material should be obtained. See also Section 10.3. material should be obtained. See also Section 10.3.
3.2.4. Grounded and Floating DODAGs 3.2.4. Grounded and Floating DODAGs
DODAGs can be grounded or floating: the DODAG root advertises which DODAGs can be grounded or floating: the DODAG root advertises which
is the case. A grounded DODAG offers connectivity to hosts that are is the case. A grounded DODAG offers connectivity to hosts that are
required for satisfying the application-defined goal. A floating required for satisfying the application-defined goal. A floating
DODAG is not expected to satisfy the goal and in most cases only DODAG is not expected to satisfy the goal; in most cases, it only
provides routes to nodes within the DODAG. Floating DODAGs may be provides routes to nodes within the DODAG. Floating DODAGs may be
used, for example, to preserve inner connectivity during repair. used, for example, to preserve interconnectivity during repair.
3.2.5. Local DODAGs 3.2.5. Local DODAGs
RPL nodes can optimize routes to a destination within an LLN by RPL nodes can optimize routes to a destination within an LLN by
forming a local DODAG whose DODAG Root is the desired destination. forming a Local DODAG whose DODAG root is the desired destination.
Unlike global DAGs, which can consist of multiple DODAGs, local DAGs Unlike global DAGs, which can consist of multiple DODAGs, local DAGs
have one and only one DODAG and therefore one DODAG Root. Local have one and only one DODAG and therefore one DODAG root. Local
DODAGs can be constructed on-demand. DODAGs can be constructed on demand.
3.2.6. Administrative Preference 3.2.6. Administrative Preference
An implementation/deployment may specify that some DODAG roots should An implementation/deployment may specify that some DODAG roots should
be used over others through an administrative preference. be used over others through an administrative preference.
Administrative preference offers a way to control traffic and Administrative preference offers a way to control traffic and
engineer DODAG formation in order to better support application engineer DODAG formation in order to better support application
requirements or needs. requirements or needs.
3.2.7. Datapath Validation and Loop Detection 3.2.7. Data-Path Validation and Loop Detection
The low-power and lossy nature of LLNs motivates RPL's use of on- The low-power and lossy nature of LLNs motivates RPL's use of on-
demand loop detection using data packets. Because data traffic can demand loop detection using data packets. Because data traffic can
be infrequent, maintaining a routing topology that is constantly up be infrequent, maintaining a routing topology that is constantly up
to date with the physical topology can waste energy. Typical LLNs to date with the physical topology can waste energy. Typical LLNs
exhibit variations in physical connectivity that are transient and exhibit variations in physical connectivity that are transient and
innocuous to traffic, but that would be costly to track closely from innocuous to traffic, but that would be costly to track closely from
the control plane. Transient and infrequent changes in connectivity the control plane. Transient and infrequent changes in connectivity
need not be addressed by RPL until there is data to send. This need not be addressed by RPL until there is data to send. This
aspect of RPL's design draws from existing, highly used LLN protocols aspect of RPL's design draws from existing, highly used LLN protocols
as well as extensive experimental and deployment evidence on its as well as extensive experimental and deployment evidence on its
efficacy. efficacy.
The RPL Packet Information that is transported with data packets The RPL Packet Information that is transported with data packets
includes the Rank of the transmitter. An inconsistency between the includes the Rank of the transmitter. An inconsistency between the
routing decision for a packet (upward or downward) and the Rank routing decision for a packet (Upward or Downward) and the Rank
relationship between the two nodes indicates a possible loop. On relationship between the two nodes indicates a possible loop. On
receiving such a packet, a node institutes a local repair operation. receiving such a packet, a node institutes a local repair operation.
For example, if a node receives a packet flagged as moving in the For example, if a node receives a packet flagged as moving in the
upward direction, and if that packet records that the transmitter is Upward direction, and if that packet records that the transmitter is
of a lower (lesser) Rank than the receiving node, then the receiving of a lower (lesser) Rank than the receiving node, then the receiving
node is able to conclude that the packet has not progressed in the node is able to conclude that the packet has not progressed in the
upward direction and that the DODAG is inconsistent. Upward direction and that the DODAG is inconsistent.
3.2.8. Distributed Algorithm Operation 3.2.8. Distributed Algorithm Operation
A high level overview of the distributed algorithm, which constructs A high-level overview of the distributed algorithm, which constructs
the DODAG, is as follows: the DODAG, is as follows:
o Some nodes are configured to be DODAG roots, with associated DODAG o Some nodes are configured to be DODAG roots, with associated DODAG
configurations. configurations.
o Nodes advertise their presence, affiliation with a DODAG, routing o Nodes advertise their presence, affiliation with a DODAG, routing
cost, and related metrics by sending link-local multicast DIO cost, and related metrics by sending link-local multicast DIO
messages to all-RPL-nodes. messages to all-RPL-nodes.
o Nodes listen for DIOs and use their information to join a new o Nodes listen for DIOs and use their information to join a new
DODAG (thus selecting DODAG parents), or to maintain an existing DODAG (thus, selecting DODAG parents), or to maintain an existing
DODAG, according to the specified Objective Function and Rank of DODAG, according to the specified Objective Function and Rank of
their neighbors. their neighbors.
o Nodes provision routing table entries, for the destinations o Nodes provision routing table entries, for the destinations
specified by the DIO message, via their DODAG parents in the DODAG specified by the DIO message, via their DODAG parents in the DODAG
Version. Nodes that decide to join a DODAG can provision one or Version. Nodes that decide to join a DODAG can provision one or
more DODAG parents as the next-hop for the default route and a more DODAG parents as the next hop for the default route and a
number of other external routes for the associated instance. number of other external routes for the associated instance.
3.3. Downward Routes and Destination Advertisement 3.3. Downward Routes and Destination Advertisement
RPL uses Destination Advertisement Object (DAO) messages to establish RPL uses Destination Advertisement Object (DAO) messages to establish
downward routes. DAO messages are an optional feature for Downward routes. DAO messages are an optional feature for
applications that require P2MP or P2P traffic. RPL supports two applications that require point-to-multipoint (P2MP) or point-to-
modes of downward traffic: storing (fully stateful) or non-storing point (P2P) traffic. RPL supports two modes of Downward traffic:
(fully source routed). Any given RPL Instance is either storing or Storing (fully stateful) or Non-Storing (fully source routed); see
non-storing. In both cases, P2P packets travel Up toward a DODAG Section 9. Any given RPL Instance is either storing or non-storing.
Root then Down to the final destination (unless the destination is on In both cases, P2P packets travel Up toward a DODAG root then Down to
the upward route). In the non-storing case the packet will travel the final destination (unless the destination is on the Upward
all the way to a DODAG root before traveling Down. In the storing route). In the Non-Storing case, the packet will travel all the way
case the packet may be directed Down towards the destination by a to a DODAG root before traveling Down. In the Storing case, the
common ancestor of the source and the destination prior to reaching a packet may be directed Down towards the destination by a common
DODAG Root. ancestor of the source and the destination prior to reaching a DODAG
root.
As of this specification no implementation is expected to support As of the writing of this specification, no implementation is
both storing and non-storing modes of operation. Most expected to support both Storing and Non-Storing modes of operation.
implementations are expected to support either no downward routes, Most implementations are expected to support either no Downward
non-storing mode only, or storing mode only. Other modes of routes, Non-Storing mode only, or Storing mode only. Other modes of
operation, such as a hybrid mix of storing and non-storing mode, are operation, such as a hybrid mix of Storing and Non-Storing mode, are
out of scope for this specification and may be described in other out of scope for this specification and may be described in other
companion specifications. companion specifications.
This specification describes a basic mode of operation in support of This specification describes a basic mode of operation in support of
P2P traffic. Note that more optimized P2P solutions may be described P2P traffic. Note that more optimized P2P solutions may be described
in companion specifications. in companion specifications.
3.4. Local DODAGs Route Discovery 3.4. Local DODAGs Route Discovery
A RPL network can optionally support on-demand discovery of DODAGs to Optionally, a RPL network can support on-demand discovery of DODAGs
specific destinations within an LLN. Such local DODAGs behave to specific destinations within an LLN. Such Local DODAGs behave
slightly differently than global DODAGs: they are uniquely defined by slightly differently than Global DODAGs: they are uniquely defined by
the combination of DODAGID and RPLInstanceID. The RPLInstanceID the combination of DODAGID and RPLInstanceID. The RPLInstanceID
denotes whether a DODAG is a local DODAG. denotes whether a DODAG is a Local DODAG.
3.5. Rank Properties 3.5. Rank Properties
The rank of a node is a scalar representation of the location of that The Rank of a node is a scalar representation of the location of that
node within a DODAG Version. The rank is used to avoid and detect node within a DODAG Version. The Rank is used to avoid and detect
loops, and as such must demonstrate certain properties. The exact loops and, as such, must demonstrate certain properties. The exact
calculation of the rank is left to the Objective Function. Even calculation of the Rank is left to the Objective Function. Even
though the specific computation of the rank is left to the Objective though the specific computation of the Rank is left to the Objective
Function, the rank must implement generic properties regardless of Function, the Rank must implement generic properties regardless of
the Objective Function. the Objective Function.
In particular, the rank of the nodes must monotonically decrease as In particular, the Rank of the nodes must monotonically decrease as
the DODAG version is followed towards the DODAG destination. In that the DODAG Version is followed towards the DODAG destination. In that
regard, the rank can be regarded as a scalar representation of the regard, the Rank can be considered a scalar representation of the
location or radius of a node within a DODAG Version. location or radius of a node within a DODAG Version.
The details of how the Objective Function computes rank are out of The details of how the Objective Function computes Rank are out of
scope for this specification, although that computation may depend, scope for this specification, although that computation may depend,
for example, on parents, link metrics, node metrics, and the node for example, on parents, link metrics, node metrics, and the node
configuration and policies. See Section 14 for more information. configuration and policies. See Section 14 for more information.
The rank is not a path cost, although its value can be derived from The Rank is not a path cost, although its value can be derived from
and influenced by path metrics. The rank has properties of its own and influenced by path metrics. The Rank has properties of its own
that are not necessarily those of all metrics: that are not necessarily those of all metrics:
Type: The rank is an abstract numeric value. Type: The Rank is an abstract numeric value.
Function: The rank is the expression of a relative position within a Function: The Rank is the expression of a relative position within a
DODAG Version with regard to neighbors and is not necessarily DODAG Version with regard to neighbors, and it is not
a good indication or a proper expression of a distance or a necessarily a good indication or a proper expression of a
path cost to the root. distance or a path cost to the root.
Stability: The stability of the rank determines the stability of the Stability: The stability of the Rank determines the stability of the
routing topology. Some dampening or filtering is RECOMMENDED routing topology. Some dampening or filtering is RECOMMENDED
to keep the topology stable, and thus the rank does not to keep the topology stable; thus, the Rank does not
necessarily change as fast as some link or node metrics necessarily change as fast as some link or node metrics would.
would. A new DODAG Version would be a good opportunity to A new DODAG Version would be a good opportunity to reconcile
reconcile the discrepancies that might form over time between the discrepancies that might form over time between metrics and
metrics and ranks within a DODAG Version. Ranks within a DODAG Version.
Properties: The rank is incremented in a strictly monotonic fashion, Properties: The Rank is incremented in a strictly monotonic fashion,
and can be used to validate a progression from or towards the and it can be used to validate a progression from or towards
root. A metric, like bandwidth or jitter, does not the root. A metric, like bandwidth or jitter, does not
necessarily exhibit this property. necessarily exhibit this property.
Abstract: The rank does not have a physical unit, but rather a range Abstract: The Rank does not have a physical unit, but rather a range
of increment per hop, where the assignment of each increment of increment per hop, where the assignment of each increment is
is to be determined by the Objective Function. to be determined by the Objective Function.
The rank value feeds into DODAG parent selection, according to the The Rank value feeds into DODAG parent selection, according to the
RPL loop-avoidance strategy. Once a parent has been added, and a RPL loop-avoidance strategy. Once a parent has been added, and a
rank value for the node within the DODAG has been advertised, the Rank value for the node within the DODAG has been advertised, the
node's further options with regard to DODAG parent selection and node's further options with regard to DODAG parent selection and
movement within the DODAG are restricted in favor of loop avoidance. movement within the DODAG are restricted in favor of loop avoidance.
3.5.1. Rank Comparison (DAGRank()) 3.5.1. Rank Comparison (DAGRank())
Rank may be thought of as a fixed point number, where the position of Rank may be thought of as a fixed-point number, where the position of
the radix point between the integer part and the fractional part is the radix point between the integer part and the fractional part is
determined by MinHopRankIncrease. MinHopRankIncrease is the minimum determined by MinHopRankIncrease. MinHopRankIncrease is the minimum
increase in rank between a node and any of its DODAG parents. A increase in Rank between a node and any of its DODAG parents. A
DODAG Root provisions MinHopRankIncrease. MinHopRankIncrease creates DODAG root provisions MinHopRankIncrease. MinHopRankIncrease creates
a tradeoff between hop cost precision and the maximum number of hops a trade-off between hop cost precision and the maximum number of hops
a network can support. A very large MinHopRankIncrease, for example, a network can support. A very large MinHopRankIncrease, for example,
allows precise characterization of a given hop's affect on Rank but allows precise characterization of a given hop's effect on Rank but
cannot support many hops. cannot support many hops.
When an objective function computes rank, the objective function When an Objective Function computes Rank, the Objective Function
operates on the entire (i.e. 16-bit) rank quantity. When rank is operates on the entire (i.e., 16-bit) Rank quantity. When Rank is
compared, e.g. for determination of parent relationships or loop compared, e.g., for determination of parent relationships or loop
detection, the integer portion of the rank is to be used. The detection, the integer portion of the Rank is to be used. The
integer portion of the Rank is computed by the DAGRank() macro as integer portion of the Rank is computed by the DAGRank() macro as
follows, where floor(x) is the function that evaluates to the follows, where floor(x) is the function that evaluates to the
greatest integer less than or equal to x: greatest integer less than or equal to x:
DAGRank(rank) = floor(rank/MinHopRankIncrease) DAGRank(rank) = floor(rank/MinHopRankIncrease)
For example, if a 16-bit rank quantity is decimal 27, and the For example, if a 16-bit Rank quantity is decimal 27, and the
MinHopRankIncrease is decimal 16, then DAGRank(27) = floor(1.6875) = MinHopRankIncrease is decimal 16, then DAGRank(27) = floor(1.6875) =
1. The integer part of the rank is 1 and the fractional part is 1. The integer part of the Rank is 1 and the fractional part is
11/16. 11/16.
By convention in this document, using the macro DAGRank(node) may be Following the conventions in this document, using the macro
interpreted as DAGRank(node.rank), where node.rank is the rank value DAGRank(node) may be interpreted as DAGRank(node.rank), where
as maintained by the node. node.rank is the Rank value as maintained by the node.
A node A has a rank less than the rank of a node B if DAGRank(A) is A Node A has a Rank less than the Rank of a Node B if DAGRank(A) is
less than DAGRank(B). less than DAGRank(B).
A node A has a rank equal to the rank of a node B if DAGRank(A) is A Node A has a Rank equal to the Rank of a Node B if DAGRank(A) is
equal to DAGRank(B). equal to DAGRank(B).
A node A has a rank greater than the rank of a node B if DAGRank(A) A Node A has a Rank greater than the Rank of a Node B if DAGRank(A)
is greater than DAGRank(B). is greater than DAGRank(B).
3.5.2. Rank Relationships 3.5.2. Rank Relationships
Rank computations maintain the following properties for any nodes M Rank computations maintain the following properties for any nodes M
and N that are neighbors in the LLN: and N that are neighbors in the LLN:
DAGRank(M) is less than DAGRank(N): In this case, the position of M DAGRank(M) is less than DAGRank(N):
is closer to the DODAG root than the position of N. Node M
may safely be a DODAG parent for Node N without risk of
creating a loop. Further, for a node N, all parents in the
DODAG parent set must be of rank less than DAGRank(N). In
other words, the rank presented by a node N MUST be greater
than that presented by any of its parents.
DAGRank(M) equals DAGRank(N): In this case the positions of M and N In this case, the position of M is closer to the DODAG root than
within the DODAG and with respect to the DODAG root are the position of N. Node M may safely be a DODAG parent for Node N
similar (identical). Routing through a node with equal Rank without risk of creating a loop. Further, for a Node N, all
may cause a routing loop (i.e., if that node chooses to route parents in the DODAG parent set must be of a Rank less than
through a node with equal Rank as well). DAGRank(N). In other words, the Rank presented by a Node N MUST
be greater than that presented by any of its parents.
DAGRank(M) is greater than DAGRank(N): In this case, the position of DAGRank(M) equals DAGRank(N):
M is farther from the DODAG root than the position of N.
Further, Node M may in fact be in the sub-DODAG of Node N. If
node N selects node M as DODAG parent there is a risk to
create a loop.
As an example, the rank could be computed in such a way so as to In this case, the positions of M and N within the DODAG and with
closely track ETX (Expected Transmission Count, a fairly common respect to the DODAG root are similar or identical. Routing
routing metric used in LLN and defined in through a node with equal Rank may cause a routing loop (i.e., if
[I-D.ietf-roll-routing-metrics]) when the metric that an objective that node chooses to route through a node with equal Rank as
function minimizes is ETX, or latency, or in a more complicated way well).
as appropriate to the objective function being used within the DODAG.
3.6. Routing Metrics and Constraints Used By RPL DAGRank(M) is greater than DAGRank(N):
In this case, the position of M is farther from the DODAG root
than the position of N. Further, Node M may in fact be in the
sub-DODAG of Node N. If Node N selects Node M as DODAG parent,
there is a risk of creating a loop.
As an example, the Rank could be computed in such a way so as to
closely track ETX (expected transmission count, a fairly common
routing metric used in LLN and defined in [RFC6551]) when the metric
that an Objective Function minimizes is ETX, or latency, or in a more
complicated way as appropriate to the Objective Function being used
within the DODAG.
3.6. Routing Metrics and Constraints Used by RPL
Routing metrics are used by routing protocols to compute shortest Routing metrics are used by routing protocols to compute shortest
paths. Interior Gateway Protocols (IGPs) such as IS-IS ([RFC5120]) paths. Interior Gateway Protocols (IGPs) such as IS-IS ([RFC5120])
and OSPF ([RFC4915]) use static link metrics. Such link metrics can and OSPF ([RFC4915]) use static link metrics. Such link metrics can
simply reflect the bandwidth or can also be computed according to a simply reflect the bandwidth or can also be computed according to a
polynomial function of several metrics defining different link polynomial function of several metrics defining different link
characteristics. Some routing protocols support more than one characteristics. Some routing protocols support more than one
metric: in the vast majority of the cases, one metric is used per metric: in the vast majority of the cases, one metric is used per
(sub)topology. Less often, a second metric may be used as a tie- (sub-)topology. Less often, a second metric may be used as a
breaker in the presence of Equal Cost Multiple Paths (ECMP). The tiebreaker in the presence of Equal Cost Multiple Paths (ECMPs). The
optimization of multiple metrics is known as an NP complete problem optimization of multiple metrics is known as an NP-complete problem
and is sometimes supported by some centralized path computation and is sometimes supported by some centralized path computation
engine. engine.
In contrast, LLNs do require the support of both static and dynamic In contrast, LLNs do require the support of both static and dynamic
metrics. Furthermore, both link and node metrics are required. In metrics. Furthermore, both link and node metrics are required. In
the case of RPL, it is virtually impossible to define one metric, or the case of RPL, it is virtually impossible to define one metric, or
even a composite metric, that will satisfy all use cases. even a composite metric, that will satisfy all use cases.
In addition, RPL supports constrained-based routing where constraints In addition, RPL supports constraint-based routing where constraints
may be applied to both link and nodes. If a link or a node does not may be applied to both link and nodes. If a link or a node does not
satisfy a required constraint, it is 'pruned' from the candidate satisfy a required constraint, it is "pruned" from the candidate
neighbor set, thus leading to a constrained shortest path. neighbor set, thus leading to a constrained shortest path.
An Objective Function specifies the objectives used to compute the An Objective Function specifies the objectives used to compute the
(constrained) path. Furthermore, nodes are configured to support a (constrained) path. Furthermore, nodes are configured to support a
set of metrics and constraints, and select their parents in the DODAG set of metrics and constraints and select their parents in the DODAG
according to the metrics and constraints advertised in the DIO according to the metrics and constraints advertised in the DIO
messages. Upstream and Downstream metrics may be merged or messages. Upstream and Downstream metrics may be merged or
advertised separately depending on the OF and the metrics. When they advertised separately depending on the OF and the metrics. When they
are advertised separately, it may happen that the set of DIO parents are advertised separately, it may happen that the set of DIO parents
is different from the set of DAO parents (a DAO parent is a node to is different from the set of DAO parents (a DAO parent is a node to
which unicast DAO messages are sent). Yet, all are DODAG parents which unicast DAO messages are sent). Yet, all are DODAG parents
with regards to the rules for Rank computation. with regard to the rules for Rank computation.
The Objective Function is decoupled from the routing metrics and The Objective Function is decoupled from the routing metrics and
constraints used by RPL. Indeed, whereas the OF dictates rules such constraints used by RPL. Whereas the OF dictates rules such as DODAG
as DODAG parents selection, load balancing and so on, the set of parent selection, load balancing, and so on, the set of metrics
metrics and/or constraints used, and thus determine the preferred and/or constraints used, and thus those that determine the preferred
path, are based on the information carried within the DAG container path, are based on the information carried within the DAG container
option in DIO messages. option in DIO messages.
The set of supported link/node constraints and metrics is specified The set of supported link/node constraints and metrics is specified
in [I-D.ietf-roll-routing-metrics]. in [RFC6551].
Example 1: Shortest path: path offering the shortest end-to-end Example 1: Shortest path: path offering the shortest end-to-end
delay. delay.
Example 2: Shortest Constrained path: the path that does not traverse Example 2: Shortest Constrained path: the path that does not traverse
any battery-operated node and that optimizes the path any battery-operated node and that optimizes the path
reliability. reliability.
3.7. Loop Avoidance 3.7. Loop Avoidance
RPL tries to avoid creating loops when undergoing topology changes RPL tries to avoid creating loops when undergoing topology changes
and includes rank-based datapath validation mechanisms for detecting and includes Rank-based data-path validation mechanisms for detecting
loops when they do occur (see Section 11 for more details). In loops when they do occur (see Section 11 for more details). In
practice, this means that RPL guarantees neither loop free path practice, this means that RPL guarantees neither loop-free path
selection nor tight delay convergence times, but can detect and selection nor tight delay convergence times, but it can detect and
repair a loop as soon as it is used. RPL uses this loop detection to repair a loop as soon as it is used. RPL uses this loop detection to
ensure that packets make forward progress within the DODAG Version ensure that packets make forward progress within the DODAG Version
and trigger repairs when necessary. and trigger repairs when necessary.
3.7.1. Greediness and Instability 3.7.1. Greediness and Instability
A node is greedy if it attempts to move deeper (increase Rank) in the A node is greedy if it attempts to move deeper (increase Rank) in the
DODAG Version in order to increase the size of the parent set or DODAG Version in order to increase the size of the parent set or
improve some other metric. Once a node has joined a DODAG Version, improve some other metric. Once a node has joined a DODAG Version,
RPL disallows certain behaviors, including greediness, in order to RPL disallows certain behaviors, including greediness, in order to
prevent resulting instabilities in the DODAG Version. prevent resulting instabilities in the DODAG Version.
Suppose a node is willing to receive and process a DIO message from a Suppose a node is willing to receive and process a DIO message from a
node in its own sub-DODAG, and in general a node deeper than itself. node in its own sub-DODAG and, in general, a node deeper than itself.
In this case, a possibility exists that a feedback loop is created, In this case, a possibility exists that a feedback loop is created,
wherein two or more nodes continue to try and move in the DODAG wherein two or more nodes continue to try and move in the DODAG
Version while attempting to optimize against each other. In some Version while attempting to optimize against each other. In some
cases, this will result in instability. It is for this reason that cases, this will result in instability. It is for this reason that
RPL limits the cases where a node may process DIO messages from RPL limits the cases where a node may process DIO messages from
deeper nodes to some forms of local repair. This approach creates an deeper nodes to some form of local repair. This approach creates an
'event horizon', whereby a node cannot be influenced beyond some "event horizon", whereby a node cannot be influenced beyond some
limit into an instability by the action of nodes that may be in its limit into an instability by the action of nodes that may be in its
own sub-DODAG. own sub-DODAG.
3.7.1.1. Example: Greedy Parent Selection and Instability 3.7.1.1. Example: Greedy Parent Selection and Instability
(A) (A) (A) (A) (A) (A)
|\ |\ |\ |\ |\ |\
| `-----. | `-----. | `-----. | `-----. | `-----. | `-----.
| \ | \ | \ | \ | \ | \
(B) (C) (B) \ | (C) (B) (C) (B) \ | (C)
\ | | / \ | | /
`-----. | | .-----' `-----. | | .-----'
\| |/ \| |/
(C) (B) (C) (B)
-1- -2- -3- -1- -2- -3-
Figure 3: Greedy DODAG Parent Selection Figure 3: Greedy DODAG Parent Selection
Figure 3 depicts a DODAG in 3 different configurations. A usable Figure 3 depicts a DODAG in three different configurations. A usable
link between (B) and (C) exists in all 3 configurations. In link between (B) and (C) exists in all three configurations. In
Figure 3-1, Node (A) is a DODAG parent for Nodes (B) and (C). In Figure 3-1, Node (A) is a DODAG parent for Nodes (B) and (C). In
Figure 3-2, Node (A) is a DODAG parent for Nodes (B) and (C), and Figure 3-2, Node (A) is a DODAG parent for Nodes (B) and (C), and
Node (B) is also a DODAG parent for Node (C). In Figure 3-3, Node Node (B) is also a DODAG parent for Node (C). In Figure 3-3, Node
(A) is a DODAG parent for Nodes (B) and (C), and Node (C) is also a (A) is a DODAG parent for Nodes (B) and (C), and Node (C) is also a
DODAG parent for Node (B). DODAG parent for Node (B).
If a RPL node is too greedy, in that it attempts to optimize for an If a RPL node is too greedy, in that it attempts to optimize for an
additional number of parents beyond its most preferred parents, then additional number of parents beyond its most preferred parents, then
an instability can result. Consider the DODAG illustrated in an instability can result. Consider the DODAG illustrated in
Figure 3-1. In this example, Nodes (B) and (C) may most prefer Node Figure 3-1. In this example, Nodes (B) and (C) may most prefer Node
(A) as a DODAG parent, but we will consider the case when they are (A) as a DODAG parent, but we will consider the case when they are
operating under the greedy condition that will try to optimize for 2 operating under the greedy condition that will try to optimize for
parents. two parents.
o Let Figure 3-1 be the initial condition. o Let Figure 3-1 be the initial condition.
o Suppose Node (C) first is able to leave the DODAG and rejoin at a o Suppose Node (C) first is able to leave the DODAG and rejoin at a
lower rank, taking both Nodes (A) and (B) as DODAG parents as lower Rank, taking both Nodes (A) and (B) as DODAG parents as
depicted in Figure 3-2. Now Node (C) is deeper than both Nodes depicted in Figure 3-2. Now Node (C) is deeper than both Nodes
(A) and (B), and Node (C) is satisfied to have 2 DODAG parents. (A) and (B), and Node (C) is satisfied to have two DODAG parents.
o Suppose Node (B), in its greediness, is willing to receive and o Suppose Node (B), in its greediness, is willing to receive and
process a DIO message from Node (C) (against the rules of RPL), process a DIO message from Node (C) (against the rules of RPL),
and then Node (B) leaves the DODAG and rejoins at a lower rank, and then Node (B) leaves the DODAG and rejoins at a lower Rank,
taking both Nodes (A) and (C) as DODAG parents. Now Node (B) is taking both Nodes (A) and (C) as DODAG parents. Now Node (B) is
deeper than both Nodes (A) and (C) and is satisfied with 2 DAG deeper than both Nodes (A) and (C) and is satisfied with two DAG
parents. parents.
o Then Node (C), because it is also greedy, will leave and rejoin o Then, Node (C), because it is also greedy, will leave and rejoin
deeper, to again get 2 parents and have a lower rank then both of deeper, to again get two parents and have a lower Rank then both
them. of them.
o Next Node (B) will again leave and rejoin deeper, to again get 2 o Next, Node (B) will again leave and rejoin deeper, to again get
parents two parents.
o And again Node (C) leaves and rejoins deeper... o Again, Node (C) leaves and rejoins deeper.
o The process will repeat, and the DODAG will oscillate between o The process will repeat, and the DODAG will oscillate between
Figure 3-2 and Figure 3-3 until the nodes count to infinity and Figure 3-2 and Figure 3-3 until the nodes count to infinity and
restart the cycle again. restart the cycle again.
o This cycle can be averted through mechanisms in RPL: o This cycle can be averted through mechanisms in RPL:
* Nodes (B) and (C) stay at a rank sufficient to attach to their * Nodes (B) and (C) stay at a Rank sufficient to attach to their
most preferred parent (A) and don't go for any deeper (worse) most preferred parent (A) and don't go for any deeper (worse)
alternate parents (Nodes are not greedy) alternate parents (Nodes are not greedy).
* Nodes (B) and (C) do not process DIO messages from nodes deeper * Nodes (B) and (C) do not process DIO messages from nodes deeper
than themselves (because such nodes are possibly in their own than themselves (because such nodes are possibly in their own
sub-DODAGs) sub-DODAGs).
These mechanisms are further described in Section 8.2.2.4 These mechanisms are further described in Section 8.2.2.4.
3.7.2. DODAG Loops 3.7.2. DODAG Loops
A DODAG loop may occur when a node detaches from the DODAG and A DODAG loop may occur when a node detaches from the DODAG and
reattaches to a device in its prior sub-DODAG. This may happen in reattaches to a device in its prior sub-DODAG. In particular, this
particular when DIO messages are missed. Strict use of the DODAG may happen when DIO messages are missed. Strict use of the
Version Number can eliminate this type of loop, but this type of loop DODAGVersionNumber can eliminate this type of loop, but this type of
may possibly be encountered when using some local repair mechanisms. loop may possibly be encountered when using some local repair
mechanisms.
For example, consider the local repair mechanism that allows a node For example, consider the local repair mechanism that allows a node
to detach from the DODAG, advertise a rank of INFINITE_RANK (in order to detach from the DODAG, advertise a Rank of INFINITE_RANK (in order
to poison its routes / inform its sub-DODAG), and then to re-attach to poison its routes / inform its sub-DODAG), and then reattach to
to the DODAG. In that case the node may in some cases re-attach to the DODAG. In some of these cases, the node may reattach to its own
its own prior-sub-DODAG, causing a DODAG loop, because the poisoning prior-sub-DODAG, causing a DODAG loop, because the poisoning may fail
may fail if the INFINITE_RANK advertisements are lost in the LLN if the INFINITE_RANK advertisements are lost in the LLN environment.
environment. (In this case the rank-based datapath validation (In this case, the Rank-based data-path validation mechanisms would
mechanisms would eventually detect and trigger correction of the eventually detect and trigger correction of the loop).
loop).
3.7.3. DAO Loops 3.7.3. DAO Loops
A DAO loop may occur when the parent has a route installed upon A DAO loop may occur when the parent has a route installed upon
receiving and processing a DAO message from a child, but the child receiving and processing a DAO message from a child, but the child
has subsequently cleaned up the related DAO state. This loop happens has subsequently cleaned up the related DAO state. This loop happens
when a No-Path (a DAO message that invalidates a previously announced when a No-Path (a DAO message that invalidates a previously announced
prefix) was missed and persists until all state has been cleaned up. prefix, see Section 6.4.3) was missed and persists until all state
RPL includes an optional mechanism to acknowledge DAO messages, which has been cleaned up. RPL includes an optional mechanism to
may mitigate the impact of a single DAO message being missed. RPL acknowledge DAO messages, which may mitigate the impact of a single
includes loop detection mechanisms that mitigate the impact of DAO DAO message being missed. RPL includes loop detection mechanisms
loops and trigger their repair. (See Section 11.2.2.3). that mitigate the impact of DAO loops and trigger their repair. (See
Section 11.2.2.3.)
4. Traffic Flows Supported by RPL 4. Traffic Flows Supported by RPL
RPL supports three basic traffic flows: Multipoint-to-Point (MP2P), RPL supports three basic traffic flows: multipoint-to-point (MP2P),
Point-to-Multipoint (P2MP), and Point-to-Point (P2P). point-to-multipoint (P2MP), and point-to-point (P2P).
4.1. Multipoint-to-Point Traffic 4.1. Multipoint-to-Point Traffic
Multipoint-to-Point (MP2P) is a dominant traffic flow in many LLN Multipoint-to-point (MP2P) is a dominant traffic flow in many LLN
applications ([RFC5867], [RFC5826], [RFC5673], [RFC5548]). The applications ([RFC5867], [RFC5826], [RFC5673], and [RFC5548]). The
destinations of MP2P flows are designated nodes that have some destinations of MP2P flows are designated nodes that have some
application significance, such as providing connectivity to the application significance, such as providing connectivity to the
larger Internet or core private IP network. RPL supports MP2P larger Internet or core private IP network. RPL supports MP2P
traffic by allowing MP2P destinations to be reached via DODAG roots. traffic by allowing MP2P destinations to be reached via DODAG roots.
4.2. Point-to-Multipoint Traffic 4.2. Point-to-Multipoint Traffic
Point-to-multipoint (P2MP) is a traffic pattern required by several Point-to-multipoint (P2MP) is a traffic pattern required by several
LLN applications ([RFC5867], [RFC5826], [RFC5673], [RFC5548]). RPL LLN applications ([RFC5867], [RFC5826], [RFC5673], and [RFC5548]).
supports P2MP traffic by using a destination advertisement mechanism RPL supports P2MP traffic by using a destination advertisement
that provisions Down routes toward destinations (prefixes, addresses, mechanism that provisions Down routes toward destinations (prefixes,
or multicast groups), and away from roots. Destination addresses, or multicast groups), and away from roots. Destination
advertisements can update routing tables as the underlying DODAG advertisements can update routing tables as the underlying DODAG
topology changes. topology changes.
4.3. Point-to-Point Traffic 4.3. Point-to-Point Traffic
RPL DODAGs provide a basic structure for point-to-point (P2P) RPL DODAGs provide a basic structure for point-to-point (P2P)
traffic. For a RPL network to support P2P traffic, a root must be 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 able to route packets to a destination. Nodes within the network may
also have routing tables to destinations. A packet flows towards a also have routing tables to destinations. A packet flows towards a
root until it reaches an ancestor that has a known route to the root until it reaches an ancestor that has a known route to the
destination. As pointed out later in this document, in the most destination. As pointed out later in this document, in the most
constrained case (when nodes cannot store routes), that common constrained case (when nodes cannot store routes), that common
ancestor may be the DODAG root. In other cases it may be a node ancestor may be the DODAG root. In other cases, it may be a node
closer to both the source and destination. closer to both the source and destination.
RPL also supports the case where a P2P destination is a 'one-hop' RPL also supports the case where a P2P destination is a 'one-hop'
neighbor. neighbor.
RPL neither specifies nor precludes additional mechanisms for RPL neither specifies nor precludes additional mechanisms for
computing and installing potentially more optimal routes to support computing and installing potentially more optimal routes to support
arbitrary P2P traffic. arbitrary P2P traffic.
5. RPL Instance 5. RPL Instance
Within a given LLN, there may be multiple, logically independent RPL Within a given LLN, there may be multiple, logically independent RPL
instances. A RPL node may belong to multiple RPL instances, and may Instances. A RPL node may belong to multiple RPL Instances, and it
act as a router in some and as a leaf in others. This document may act as a router in some and as a leaf in others. This document
describes how a single instance behaves. describes how a single instance behaves.
There are two types of RPL Instances: local and global. RPL divides There are two types of RPL Instances: Local and Global. RPL divides
the RPLInstanceID space between Global and Local instances to allow the RPLInstanceID space between Global and Local instances to allow
for both coordinated and unilateral allocation of RPLInstanceIDs. for both coordinated and unilateral allocation of RPLInstanceIDs.
Global RPL Instances are coordinated, have one or more DODAGs, and Global RPL Instances are coordinated, have one or more DODAGs, and
are typically long-lived. Local RPL Instances are always a single are typically long-lived. Local RPL Instances are always a single
DODAG whose singular root owns the corresponding DODAGID and DODAG whose singular root owns the corresponding DODAGID and
allocates the Local RPLInstanceID in a unilateral manner. Local RPL allocates the local RPLInstanceID in a unilateral manner. Local RPL
Instances can be used, for example, for constructing DODAGs in Instances can be used, for example, for constructing DODAGs in
support of a future on-demand routing solution. The mode of support of a future on-demand routing solution. The mode of
operation of Local RPL Instances is out of scope for this operation of Local RPL Instances is out of scope for this
specification and may be described in other companion specifications. specification and may be described in other companion specifications.
The definition and provisioning of RPL instances are out of scope for The definition and provisioning of RPL Instances are out of scope for
this specification. Guidelines may be application and implementation this specification. Guidelines may be application and implementation
specific, and are expected to be elaborated in future companion specific, and they are expected to be elaborated in future companion
specifications. Those operations are expected to be such that data specifications. Those operations are expected to be such that data
packets coming from the outside of the RPL network can unambiguously packets coming from the outside of the RPL network can unambiguously
be associated to at least one RPL instance, and be safely routed over be associated to at least one RPL Instance and be safely routed over
any instance that would match the packet. any instance that would match the packet.
Control and data packets within RPL network are tagged to Control and data packets within RPL network are tagged to
unambiguously identify what RPL Instance they are part of. unambiguously identify of which RPL Instance they are a part.
Every RPL control message has a RPLInstanceID field. Some RPL Every RPL control message has a RPLInstanceID field. Some RPL
control messages, when referring to a local RPLInstanceID as defined control messages, when referring to a local RPLInstanceID as defined
below, may also include a DODAGID. below, may also include a DODAGID.
Data packets that flow within the RPL network expose the Data packets that flow within the RPL network expose the
RPLInstanceID as part of the RPL Packet Information that RPL RPLInstanceID as part of the RPL Packet Information that RPL
requires, as further described in Section 11.2. For data packets requires, as further described in Section 11.2. For data packets
coming from outside the RPL network, the ingress router determines coming from outside the RPL network, the ingress router determines
the RPLInstanceID and places it into the resulting packet that it the RPLInstanceID and places it into the resulting packet that it
injects into the RPL network. injects into the RPL network.
5.1. RPL Instance ID 5.1. RPL Instance ID
A global RPLInstanceID MUST be unique to the whole LLN. Mechanisms A global RPLInstanceID MUST be unique to the whole LLN. Mechanisms
for allocating and provisioning global RPLInstanceID are out of scope for allocating and provisioning global RPLInstanceID are out of scope
for this specification. There can be up to 128 global instance in for this specification. There can be up to 128 Global instance in
the whole network. Local instances are always used in conjunction the whole network. Local instances are always used in conjunction
with a DODAGID (which is either given explicitly or implicitly in with a DODAGID (which is either given explicitly or implicitly in
some cases), and up 64 local instances per DODAGID can be supported. some cases), and up 64 Local instances per DODAGID can be supported.
Local instances are allocated and managed by the node that owns the Local instances are allocated and managed by the node that owns the
DODAGID, without any explicit coordination with other nodes, as DODAGID, without any explicit coordination with other nodes, as
further detailed below. further detailed below.
A global RPLinstanceID is encoded in a RPLinstanceID field as A global RPLInstanceID is encoded in a RPLInstanceID field as
follows: follows:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|0| ID | Global RPLinstanceID in 0..127 |0| ID | Global RPLInstanceID in 0..127
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 4: RPL Instance ID field format for global instances Figure 4: RPLInstanceID Field Format for Global Instances
A local RPLInstanceID is autoconfigured by the node that owns the A local RPLInstanceID is autoconfigured by the node that owns the
DODAGID and it MUST be unique for that DODAGID. The DODAGID used to DODAGID and it MUST be unique for that DODAGID. The DODAGID used to
configure the local RPLInstanceID MUST be a reachable IPv6 address of configure the local RPLInstanceID MUST be a reachable IPv6 address of
the node, and MUST be used as an endpoint of all communications the node, and it MUST be used as an endpoint of all communications
within that local instance. within that Local instance.
A local RPLinstanceID is encoded in a RPLinstanceID field as follows: A local RPLInstanceID is encoded in a RPLInstanceID field as follows:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|1|D| ID | Local RPLInstanceID in 0..63 |1|D| ID | Local RPLInstanceID in 0..63
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 5: RPL Instance ID field format for local instances Figure 5: RPLInstanceID Field Format for Local Instances
The D flag in a Local RPLInstanceID is always set to 0 in RPL control The 'D' flag in a local RPLInstanceID is always set to 0 in RPL
messages. It is used in data packets to indicate whether the DODAGID control messages. It is used in data packets to indicate whether the
is the source or the destination of the packet. If the D flag is set DODAGID is the source or the destination of the packet. If the 'D'
to 1 then the destination address of the IPv6 packet MUST be the flag is set to 1, then the destination address of the IPv6 packet
DODAGID. If the D flag is cleared then the source address of the MUST be the DODAGID. If the 'D' flag is cleared, then the source
IPv6 packet MUST be the DODAGID. address of the IPv6 packet MUST be the DODAGID.
For example, consider a node A that is the DODAG Root of a local RPL For example, consider a Node A that is the DODAG root of a Local RPL
Instance, and has allocated a local RPLInstanceID. By definition, Instance, and has allocated a local RPLInstanceID. By definition,
all traffic traversing that local RPL Instance will either originate all traffic traversing that Local RPL Instance will either originate
or terminate at node A. The DODAGID in this case will be the or terminate at Node A. In this case, the DODAGID will be the
reachable IPv6 address of node A, and all traffic will contain the reachable IPv6 address of Node A. All traffic will contain the
address of node A, thus the DODAGID, in either the source or address of Node A, and thus the DODAGID, in either the source or
destination address. Thus the Local RPLInstanceID may indicate that destination address. Thus, the local RPLInstanceID may indicate that
the DODAGID is equivalent to either the source address or the the DODAGID is equivalent to either the source address or the
destination address by setting the D flag appropriately. destination address by setting the 'D' flag appropriately.
6. ICMPv6 RPL Control Message 6. ICMPv6 RPL Control Message
This document defines the RPL Control Message, a new ICMPv6 [RFC4443] This document defines the RPL control message, a new ICMPv6 [RFC4443]
message. A RPL Control Message is identified by a code, and composed message. A RPL control message is identified by a code and composed
of a base that depends on the code, and a series of options. of a base that depends on the code (and a series of options).
Most RPL Control Message have the scope of a link. The only Most RPL control messages have the scope of a link. The only
exception is for the DAO / DAO-ACK messages in non-storing mode, exception is for the DAO / DAO-ACK messages in Non-Storing mode,
which are exchanged using a unicast address over multiple hops and which are exchanged using a unicast address over multiple hops and
thus uses global or unique-local addresses for both the source and thus uses global or unique-local addresses for both the source and
destination addresses. For all other RPL Control messages, the destination addresses. For all other RPL control messages, the
source address is a link-local address, and the destination address source address is a link-local address, and the destination address
is either the all-RPL-nodes multicast address or a link-local unicast is either the all-RPL-nodes multicast address or a link-local unicast
address of the destination. The all-RPL-nodes multicast address is a address of the destination. The all-RPL-nodes multicast address is a
new address with a requested value of FF02::1A (to be confirmed by new address with a value of ff02::1a.
IANA).
In accordance with [RFC4443], the RPL Control Message consists of an In accordance with [RFC4443], the RPL Control Message consists of an
ICMPv6 header followed by a message body. The message body is ICMPv6 header followed by a message body. The message body is
comprised of a message base and possibly a number of options as comprised of a message base and possibly a number of options as
illustrated in Figure 6. illustrated in Figure 6.
0 1 2 3 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 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 | | Type | Code | Checksum |
skipping to change at page 31, line 43 skipping to change at page 30, line 47
. Base . . Base .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Option(s) . . Option(s) .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: RPL Control Message Figure 6: RPL Control Message
The RPL Control message is an ICMPv6 information message with a The RPL control message is an ICMPv6 information message with a Type
requested Type of 155 (to be confirmed by IANA). of 155.
The Code field identifies the type of RPL Control Message. This The Code field identifies the type of RPL control message. This
document defines codes for the following RPL Control Message types document defines codes for the following RPL control message types
(all codes are to be confirmed by IANA Section 20.2): (see Section 20.2)):
o 0x00: DODAG Information Solicitation (Section 6.2) o 0x00: DODAG Information Solicitation (Section 6.2)
o 0x01: DODAG Information Object (Section 6.3) o 0x01: DODAG Information Object (Section 6.3)
o 0x02: Destination Advertisement Object (Section 6.4) o 0x02: Destination Advertisement Object (Section 6.4)
o 0x03: Destination Advertisement Object Acknowledgment o 0x03: Destination Advertisement Object Acknowledgment
(Section 6.5) (Section 6.5)
skipping to change at page 32, line 30 skipping to change at page 31, line 34
o 0x83: Secure Destination Advertisement Object Acknowledgment o 0x83: Secure Destination Advertisement Object Acknowledgment
(Section 6.5.2) (Section 6.5.2)
o 0x8A: Consistency Check (Section 6.6) o 0x8A: Consistency Check (Section 6.6)
If a node receives a RPL control message with an unknown Code field, If a node receives a RPL control message with an unknown Code field,
the node MUST discard the message without any further processing, MAY the node MUST discard the message without any further processing, MAY
raise a management alert, and MUST NOT send any messages in response. raise a management alert, and MUST NOT send any messages in response.
The checksum is computed as specified in [RFC4443]. It is set to The checksum is computed as specified in [RFC4443]. It is set to
zero for the RPL security operations specified below, and computed zero for the RPL security operations specified below and computed
once the rest of the content of the RPL message including the once the rest of the content of the RPL message including the
security fields is all set. security fields is all set.
The high order bit (0x80) of the code denotes whether the RPL message The high order bit (0x80) of the code denotes whether the RPL message
has security enabled. Secure RPL messages have a format to support has security enabled. Secure RPL messages have a format to support
confidentiality and integrity, illustrated in Figure 7. confidentiality and integrity, illustrated in Figure 7.
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 33, line 26 skipping to change at page 32, line 26
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Option(s) . . Option(s) .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Secure RPL Control Message Figure 7: Secure RPL Control Message
The remainder of this section describes the currently defined RPL The remainder of this section describes the currently defined RPL
Control Message Base formats followed by the currently defined RPL control message Base formats followed by the currently defined RPL
Control Message Options. Control Message options.
6.1. RPL Security Fields 6.1. RPL Security Fields
Each RPL message has a secure variant. The secure variants provide Each RPL message has a secure variant. The secure variants provide
integrity and replay protection as well as optional confidentiality integrity and replay protection as well as optional confidentiality
and delay protection. Because security covers the base message as and delay protection. Because security covers the base message as
well as options, in secured messages the security information lies well as options, in secured messages the security information lies
between the checksum and base, as shown in Figure 7. between the checksum and base, as shown in Figure 7.
The level of security and the algorithms in use are indicated in the The level of security and the algorithms in use are indicated in the
skipping to change at page 34, line 4 skipping to change at page 33, line 16
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 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T| Reserved | Algorithm |KIM|Resvd| LVL | Flags | |T| Reserved | Algorithm |KIM|Resvd| LVL | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Counter | | Counter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Key Identifier . . Key Identifier .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Security Section Figure 8: Security Section
Message authentication codes (MACs) and signatures provide Message Authentication Codes (MACs) and signatures provide
authentication over the entire unsecured ICMPv6 RPL control message, authentication over the entire unsecured ICMPv6 RPL control message,
including the Security section with all fields defined, but with the including the Security section with all fields defined, but with the
ICMPv6 checksum temporarily set to zero. Encryption provides ICMPv6 checksum temporarily set to zero. Encryption provides
confidentiality of the secured RPL ICMPv6 message starting at the confidentiality of the secured RPL ICMPv6 message starting at the
first byte after the Security section and continuing to the last byte first byte after the Security section and continuing to the last byte
of the packet. The security transformation yields a secured ICMPv6 of the packet. The security transformation yields a secured ICMPv6
RPL message with the inclusion of the cryptographic fields (MAC, RPL message with the inclusion of the cryptographic fields (MAC,
signature, etc.). In other words, the security transformation itself signature, etc.). In other words, the security transformation itself
(e.g. the Signature and/or Algorithm in use) will detail how to (e.g., the Signature and/or Algorithm in use) will detail how to
incorporate the cryptographic fields into the secured packet. The incorporate the cryptographic fields into the secured packet. The
Security section itself does not explicitly carry those cryptographic Security section itself does not explicitly carry those cryptographic
fields. Use of the Security section is further detailed in fields. Use of the Security section is further detailed in Sections
Section 19 and Section 10. 19 and 10.
Counter is Time (T): If the Counter is Time flag is set then the Counter is Time (T): If the counter's Time flag is set, then the
Counter field is a timestamp. If the flag is cleared then the Counter field is a timestamp. If the flag is cleared, then the
Counter is an incrementing counter. Section 10.5 describes the counter is an incrementing counter. Section 10.5 describes the
details of the 'T' flag and Counter field. details of the 'T' flag and Counter field.
Reserved: 7-bit unused field. The field MUST be initialized to zero Reserved: 7-bit unused field. The field MUST be initialized to zero
by the sender and MUST be ignored by the receiver. by the sender and MUST be ignored by the receiver.
Security Algorithm (Algorithm): The Security Algorithm field Security Algorithm (Algorithm): The Security Algorithm field
specifies the encryption, MAC, and signature scheme the network specifies the encryption, MAC, and signature scheme the network
uses. Supported values of this field are as follows: uses. Supported values of this field are as follows:
+-----------+-------------------+------------------------+ +-----------+-------------------+------------------------+
| Algorithm | Encryption/MAC | Signature | | Algorithm | Encryption/MAC | Signature |
+-----------+-------------------+------------------------+ +-----------+-------------------+------------------------+
| 0 | CCM with AES-128 | RSA with SHA-256 | | 0 | CCM with AES-128 | RSA with SHA-256 |
| 1-255 | Unassigned | Unassigned | | 1-255 | Unassigned | Unassigned |
+-----------+-------------------+------------------------+ +-----------+-------------------+------------------------+
Figure 9: Security Algorithm (Algorithm) Encoding Figure 9: Security Algorithm (Algorithm) Encoding
Section 10.9 describes the algorithms in greater detail. Section 10.9 describes the algorithms in greater detail.
Key Identifier Mode (KIM): The Key Identifier Mode is a 2-bit field Key Identifier Mode (KIM): The Key Identifier Mode is a 2-bit field
that indicates whether the key used for packet protection is that indicates whether the key used for packet protection is
determined implicitly or explicitly and indicates the determined implicitly or explicitly and indicates the
particular representation of the Key Identifier field. The Key particular representation of the Key Identifier field. The Key
Identifier Mode is set one of the values from the table below: Identifier Mode is set one of the values from the table below:
+------+-----+-----------------------------+------------+ +------+-----+-----------------------------+------------+
| Mode | KIM | Meaning | Key | | Mode | KIM | Meaning | Key |
| | | | Identifier | | | | | Identifier |
| | | | Length | | | | | Length |
| | | | (octets) | | | | | (octets) |
skipping to change at page 35, line 42 skipping to change at page 35, line 42
| 3 | 11 | Node's signature key used. | 0/9 | | 3 | 11 | Node's signature key used. | 0/9 |
| | | If packet is encrypted, | | | | If packet is encrypted, |
| | | it uses a group key, Key | | | | | it uses a group key, Key | |
| | | Index and Key Source | | | | | Index and Key Source | |
| | | specify key. | | | | | specify key. | |
| | | | | | | | | |
| | | Key Source may be present. | | | | | Key Source may be present. | |
| | | Key Index may be present. | | | | | Key Index may be present. | |
+------+-----+-----------------------------+------------+ +------+-----+-----------------------------+------------+
Figure 10: Key Identifier Mode (KIM) Encoding Figure 10: Key Identifier Mode (KIM) Encoding
In Mode 3 (KIM=11), the presence or absence of the Key Source In Mode 3 (KIM=11), the presence or absence of the Key Source and Key
and Key Identifier depends on the Security Level (LVL) Identifier depends on the Security Level (LVL) described below. If
described below. If the Security Level indicates there is the Security Level indicates there is encryption, then the fields are
encryption, then the fields are present; if it indicates there present; if it indicates there is no encryption, then the fields are
is no encryption, then the fields are not present. not present.
Resvd: 3-bit unused field. The field MUST be initialized to zero by Resvd: 3-bit unused field. The field MUST be initialized to zero by
the sender and MUST be ignored by the receiver. the sender and MUST be ignored by the receiver.
Security Level (LVL): The Security Level is a 3-bit field that Security Level (LVL): The Security Level is a 3-bit field that
indicates the provided packet protection. This value can be indicates the provided packet protection. This value can be
adapted on a per-packet basis and allows for varying levels of adapted on a per-packet basis and allows for varying levels of
data authenticity and, optionally, for data confidentiality. data authenticity and, optionally, for data confidentiality.
The KIM field indicates whether signatures are used and the The KIM field indicates whether signatures are used and the
meaning of the Level field. Note that the assigned values of meaning of the Level field. Note that the assigned values of
Security Level are not necessarily ordered-- a higher value of Security Level are not necessarily ordered -- a higher value of
LVL does not necessarily equate to increased security. The LVL does not necessarily equate to increased security. The
Security Level is set to one of the values in the tables below: Security Level is set to one of the values in the tables below:
+---------------------------+ +---------------------------+
| KIM=0,1,2 | | KIM=0,1,2 |
+-------+--------------------+------+ +-------+--------------------+------+
| LVL | Attributes | MAC | | LVL | Attributes | MAC |
| | | Len | | | | Len |
+-------+--------------------+------+ +-------+--------------------+------+
| 0 | MAC-32 | 4 | | 0 | MAC-32 | 4 |
skipping to change at page 36, line 44 skipping to change at page 36, line 41
| LVL | Attributes | Sig | | LVL | Attributes | Sig |
| | | Len | | | | Len |
+-------+---------------+-----+ +-------+---------------+-----+
| 0 | Sign-3072 | 384 | | 0 | Sign-3072 | 384 |
| 1 | ENC-Sign-3072 | 384 | | 1 | ENC-Sign-3072 | 384 |
| 2 | Sign-2048 | 256 | | 2 | Sign-2048 | 256 |
| 3 | ENC-Sign-2048 | 256 | | 3 | ENC-Sign-2048 | 256 |
| 4-7 | Unassigned | N/A | | 4-7 | Unassigned | N/A |
+-------+---------------+-----+ +-------+---------------+-----+
Figure 11: Security Level (LVL) Encoding Figure 11: Security Level (LVL) Encoding
The MAC attribute indicates that the message has a Message The MAC attribute indicates that the message has a MAC of the
Authentication Code of the specified length. The ENC attribute specified length. The ENC attribute indicates that the message is
indicates that the message is encrypted. The Sign attribute encrypted. The Sign attribute indicates that the message has a
indicates that the message has a signature of the specified signature of the specified length.
length.
Flags: 8-bit unused field reserved for flags. The field MUST be Flags: 8-bit unused field reserved for flags. The field MUST be
initialized to zero by the sender and MUST be ignored by the initialized to zero by the sender and MUST be ignored by the
receiver. receiver.
Counter: The Counter field indicates the non-repeating 4-octet value Counter: The Counter field indicates the non-repeating 4-octet value
used to construct the cryptographic mechanism that implements used to construct the cryptographic mechanism that implements
packet protection and allows for the provision of semantic packet protection and allows for the provision of semantic
security. See Section 10.9.1. security. See Section 10.9.1.
Key Identifier: The Key Identifier field indicates which key was Key Identifier: The Key Identifier field indicates which key was used
used to protect the packet. This field provides various levels to protect the packet. This field provides various levels of
of granularity of packet protection, including peer-to-peer granularity of packet protection, including peer-to-peer keys,
keys, group keys, and signature keys. This field is group keys, and signature keys. This field is represented as
represented as indicated by the Key Identifier Mode field and indicated by the Key Identifier Mode field and is formatted as
is formatted as follows: follows:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Key Source . . Key Source .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Key Index . . Key Index .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Key Identifier Figure 12: Key Identifier
Key Source: The Key Source field, when present, indicates the Key Source: The Key Source field, when present, indicates the logical
logical identifier of the originator of a group key. identifier of the originator of a group key. When present,
When present this field is 8 bytes in length. this field is 8 bytes in length.
Key Index: The Key Index field, when present, allows unique Key Index: The Key Index field, when present, allows unique
identification of different keys with the same identification of different keys with the same originator. It
originator. It is the responsibility of each key is the responsibility of each key originator to make sure that
originator to make sure that actively used keys that it actively used keys that it issues have distinct key indices and
issues have distinct key indices and that all key indices that all key indices have a value unequal to 0x00. Value 0x00
have a value unequal to 0x00. Value 0x00 is reserved for is reserved for a preinstalled, shared key. When present this
a pre-installed, shared key. When present this field is field is 1 byte in length.
1 byte in length.
Unassigned bits of the Security section are reserved. They MUST be Unassigned bits of the Security section are reserved. They MUST be
set to zero on transmission and MUST be ignored on reception. set to zero on transmission and MUST be ignored on reception.
6.2. DODAG Information Solicitation (DIS) 6.2. DODAG Information Solicitation (DIS)
The DODAG Information Solicitation (DIS) message may be used to The DODAG Information Solicitation (DIS) message may be used to
solicit a DODAG Information Object from a RPL node. Its use is solicit a DODAG Information Object from a RPL node. Its use is
analogous to that of a Router Solicitation as specified in IPv6 analogous to that of a Router Solicitation as specified in IPv6
Neighbor Discovery; a node may use DIS to probe its neighborhood for Neighbor Discovery; a node may use DIS to probe its neighborhood for
skipping to change at page 38, line 23 skipping to change at page 38, line 23
6.2.1. Format of the DIS Base Object 6.2.1. Format of the DIS Base Object
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | Option(s)... | Flags | Reserved | Option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: The DIS Base Object Figure 13: The DIS Base Object
Flags: 8-bit unused field reserved for flags. The field MUST be Flags: 8-bit unused field reserved for flags. The field MUST be
initialized to zero by the sender and MUST be ignored by the initialized to zero by the sender and MUST be ignored by the
receiver. receiver.
Reserved: 8-bit unused field. The field MUST be initialized to zero Reserved: 8-bit unused field. The field MUST be initialized to zero
by the sender and MUST be ignored by the receiver. by the sender and MUST be ignored by the receiver.
Unassigned bits of the DIS Base are reserved. They MUST be set to Unassigned bits of the DIS Base are reserved. They MUST be set to
zero on transmission and MUST be ignored on reception. zero on transmission and MUST be ignored on reception.
6.2.2. Secure DIS 6.2.2. Secure DIS
A Secure DIS message follows the format in Figure 7, where the base A Secure DIS message follows the format in Figure 7, where the base
format is the DIS message shown in Figure 13. format is the DIS message shown in Figure 13.
skipping to change at page 39, line 28 skipping to change at page 39, line 28
+ DODAGID + + DODAGID +
| | | |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)... | Option(s)...
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 14: The DIO Base Object Figure 14: The DIO Base Object
Grounded (G): The Grounded (G) flag indicates whether the DODAG Grounded (G): The Grounded 'G' flag indicates whether the DODAG
advertised can satisfy the application-defined goal. If the advertised can satisfy the application-defined goal. If the
flag is set, the DODAG is grounded. If the flag is cleared, flag is set, the DODAG is grounded. If the flag is cleared,
the DODAG is floating. the DODAG is floating.
Mode of Operation (MOP): The Mode of Operation (MOP) field Mode of Operation (MOP): The Mode of Operation (MOP) field identifies
identifies the mode of operation of the RPL Instance as the mode of operation of the RPL Instance as administratively
administratively provisioned at and distributed by the DODAG provisioned at and distributed by the DODAG root. All nodes
Root. All nodes who join the DODAG must be able to honor the who join the DODAG must be able to honor the MOP in order to
MOP in order to fully participate as a router, or else they fully participate as a router, or else they must only join as a
must only join as a leaf. MOP is encoded as in the figure leaf. MOP is encoded as in the figure below:
below:
+-----+-------------------------------------------------+ +-----+-----------------------------------------------------+
| MOP | Meaning | | MOP | Description |
+-----+-------------------------------------------------+ +-----+-----------------------------------------------------+
| 0 | No downward routes maintained by RPL | | 0 | No Downward routes maintained by RPL |
| 1 | Non storing mode | | 1 | Non-Storing Mode of Operation |
| 2 | Storing without multicast support | | 2 | Storing Mode of Operation with no multicast support |
| 3 | Storing with multicast support | | 3 | Storing Mode of Operation with multicast support |
| | | | | |
| | All other values are unassigned | | | All other values are unassigned |
+-----+-------------------------------------------------+ +-----+-----------------------------------------------------+
A value of 0 indicates that destination advertisement messages A value of 0 indicates that destination advertisement messages are
are disabled and the DODAG maintains only upward routes disabled and the DODAG maintains only Upward routes.
Figure 15: Mode of Operation (MOP) Encoding Figure 15: Mode of Operation (MOP) Encoding
DODAGPreference (Prf): A 3-bit unsigned integer that defines how DODAGPreference (Prf): A 3-bit unsigned integer that defines how
preferable the root of this DODAG is compared to other DODAG preferable the root of this DODAG is compared to other DODAG
roots within the instance. DAGPreference ranges from 0x00 roots within the instance. DAGPreference ranges from 0x00
(least preferred) to 0x07 (most preferred). The default is 0 (least preferred) to 0x07 (most preferred). The default is 0
(least preferred). Section 8.2 describes how DAGPreference (least preferred). Section 8.2 describes how DAGPreference
affects DIO processing. affects DIO processing.
Version Number: 8-bit unsigned integer set by the DODAG root to the Version Number: 8-bit unsigned integer set by the DODAG root to the
DODAGVersionNumber. Section 8.2 describes the rules for DODAG DODAGVersionNumber. Section 8.2 describes the rules for
Version numbers and how they affect DIO processing. DODAGVersionNumbers and how they affect DIO processing.
Rank: 16-bit unsigned integer indicating the DODAG rank of the node Rank: 16-bit unsigned integer indicating the DODAG Rank of the node
sending the DIO message. Section 8.2 describes how Rank is set sending the DIO message. Section 8.2 describes how Rank is set
and how it affects DIO processing. and how it affects DIO processing.
RPLInstanceID: 8-bit field set by the DODAG root that indicates RPLInstanceID: 8-bit field set by the DODAG root that indicates of
which RPL Instance the DODAG is part of. which RPL Instance the DODAG is a part.
Destination Advertisement Trigger Sequence Number (DTSN): 8-bit Destination Advertisement Trigger Sequence Number (DTSN): 8-bit
unsigned integer set by the node issuing the DIO message. The unsigned integer set by the node issuing the DIO message. The
Destination Advertisement Trigger Sequence Number (DTSN) flag Destination Advertisement Trigger Sequence Number (DTSN) flag
is used as part of the procedure to maintain downward routes. is used as part of the procedure to maintain Downward routes.
The details of this process are described in Section 9. The details of this process are described in Section 9.
Flags: 8-bit unused field reserved for flags. The field MUST be Flags: 8-bit unused field reserved for flags. The field MUST be
initialized to zero by the sender and MUST be ignored by the initialized to zero by the sender and MUST be ignored by the
receiver. receiver.
Reserved: 8-bit unused field. The field MUST be initialized to zero Reserved: 8-bit unused field. The field MUST be initialized to zero
by the sender and MUST be ignored by the receiver. by the sender and MUST be ignored by the receiver.
DODAGID: 128-bit IPv6 address set by a DODAG root which uniquely DODAGID: 128-bit IPv6 address set by a DODAG root that uniquely
identifies a DODAG. The DODAGID MUST be a routable IPv6 identifies a DODAG. The DODAGID MUST be a routable IPv6
address belonging to the DODAG root. address belonging to the DODAG root.
Unassigned bits of the DIO Base are reserved. They MUST be set to Unassigned bits of the DIO Base are reserved. They MUST be set to
zero on transmission and MUST be ignored on reception. zero on transmission and MUST be ignored on reception.
6.3.2. Secure DIO 6.3.2. Secure DIO
A Secure DIO message follows the format in Figure 7, where the base A Secure DIO message follows the format in Figure 7, where the base
format is the DIO message shown in Figure 14. format is the DIO message shown in Figure 14.
skipping to change at page 41, line 23 skipping to change at page 41, line 23
A Secure DIO message follows the format in Figure 7, where the base A Secure DIO message follows the format in Figure 7, where the base
format is the DIO message shown in Figure 14. format is the DIO message shown in Figure 14.
6.3.3. DIO Options 6.3.3. DIO Options
The DIO message MAY carry valid options. The DIO message MAY carry valid options.
This specification allows for the DIO message to carry the following This specification allows for the DIO message to carry the following
options: options:
0x00 Pad1 0x00 Pad1
0x01 PadN 0x01 PadN
0x02 Metric Container 0x02 DAG Metric Container
0x03 Routing Information 0x03 Routing Information
0x04 DODAG Configuration 0x04 DODAG Configuration
0x08 Prefix Information 0x08 Prefix Information
6.4. Destination Advertisement Object (DAO) 6.4. Destination Advertisement Object (DAO)
The Destination Advertisement Object (DAO) is used to propagate The Destination Advertisement Object (DAO) is used to propagate
destination information upwards along the DODAG. In storing mode the destination information Upward along the DODAG. In Storing mode, the
DAO message is unicast by the child to the selected parent(s). In DAO message is unicast by the child to the selected parent(s). In
non-storing mode the DAO message is unicast to the DODAG root. The Non-Storing mode, the DAO message is unicast to the DODAG root. The
DAO message may optionally, upon explicit request or error, be DAO message may optionally, upon explicit request or error, be
acknowledged by its destination with a Destination Advertisement acknowledged by its destination with a Destination Advertisement
Acknowledgement (DAO-ACK) message back to the sender of the DAO. Acknowledgement (DAO-ACK) message back to the sender of the DAO.
6.4.1. Format of the DAO Base Object 6.4.1. Format of the DAO Base Object
0 1 2 3 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 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| Flags | Reserved | DAOSequence | | RPLInstanceID |K|D| Flags | Reserved | DAOSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ DODAGID* + + DODAGID* +
| | | |
skipping to change at page 42, line 25 skipping to change at page 42, line 28
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)... | Option(s)...
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
The '*' denotes that the DODAGID is not always present, as described The '*' denotes that the DODAGID is not always present, as described
below. below.
Figure 16: The DAO Base Object Figure 16: The DAO Base Object
RPLInstanceID: 8-bit field indicating the topology instance RPLInstanceID: 8-bit field indicating the topology instance
associated with the DODAG, as learned from the DIO. associated with the DODAG, as learned from the DIO.
K: The 'K' flag indicates that the recipient is expected to send a K: The 'K' flag indicates that the recipient is expected to send a
DAO-ACK back. (See Section 9.3 DAO-ACK back. (See Section 9.3.)
D: The 'D' flag indicates that the DODAGID field is present. This D: The 'D' flag indicates that the DODAGID field is present. This
flag MUST be set when a local RPLInstanceID is used. flag MUST be set when a local RPLInstanceID is used.
Flags: The 6-bits remaining unused in the Flags field are reserved Flags: The 6 bits remaining unused in the Flags field are reserved
for flags. The field MUST be initialized to zero by the sender for flags. The field MUST be initialized to zero by the sender
and MUST be ignored by the receiver. and MUST be ignored by the receiver.
Reserved: 8-bit unused field. The field MUST be initialized to zero Reserved: 8-bit unused field. The field MUST be initialized to zero
by the sender and MUST be ignored by the receiver. by the sender and MUST be ignored by the receiver.
DAOSequence: Incremented at each unique DAO message from a node and DAOSequence: Incremented at each unique DAO message from a node and
echoed in the DAO-ACK message. echoed in the DAO-ACK message.
DODAGID (optional): 128-bit unsigned integer set by a DODAG root DODAGID (optional): 128-bit unsigned integer set by a DODAG root that
which uniquely identifies a DODAG. This field is only present uniquely identifies a DODAG. This field is only present when
when the 'D' flag is set. This field is typically only present the 'D' flag is set. This field is typically only present when
when a local RPLInstanceID is in use, in order to identify the a local RPLInstanceID is in use, in order to identify the
DODAGID that is associated with the RPLInstanceID. When a DODAGID that is associated with the RPLInstanceID. When a
global RPLInstanceID is in use this field need not be present. global RPLInstanceID is in use, this field need not be present.
Unassigned bits of the DAO Base are reserved. They MUST be set to Unassigned bits of the DAO Base are reserved. They MUST be set to
zero on transmission and MUST be ignored on reception. zero on transmission and MUST be ignored on reception.
6.4.2. Secure DAO 6.4.2. Secure DAO
A Secure DAO message follows the format in Figure 7, where the base A Secure DAO message follows the format in Figure 7, where the base
format is the DAO message shown in Figure 16. format is the DAO message shown in Figure 16.
6.4.3. DAO Options 6.4.3. DAO Options
skipping to change at page 43, line 17 skipping to change at page 43, line 19
A Secure DAO message follows the format in Figure 7, where the base A Secure DAO message follows the format in Figure 7, where the base
format is the DAO message shown in Figure 16. format is the DAO message shown in Figure 16.
6.4.3. DAO Options 6.4.3. DAO Options
The DAO message MAY carry valid options. The DAO message MAY carry valid options.
This specification allows for the DAO message to carry the following This specification allows for the DAO message to carry the following
options: options:
0x00 Pad1 0x00 Pad1
0x01 PadN 0x01 PadN
0x05 RPL Target 0x05 RPL Target
0x06 Transit Information 0x06 Transit Information
0x09 RPL Target Descriptor 0x09 RPL Target Descriptor
A special case of the DAO message, termed a No-Path, is used in A special case of the DAO message, termed a No-Path, is used in
storing mode to clear downward routing state that has been Storing mode to clear Downward routing state that has been
provisioned through DAO operation. The No-Path carries a Target provisioned through DAO operation. The No-Path carries a Target
option and an associated Transit Information option with a lifetime option and an associated Transit Information option with a lifetime
of 0x00000000 to indicate a loss of reachability to that Target. of 0x00000000 to indicate a loss of reachability to that Target.
6.5. Destination Advertisement Object Acknowledgement (DAO-ACK) 6.5. Destination Advertisement Object Acknowledgement (DAO-ACK)
The DAO-ACK message is sent as a unicast packet by a DAO recipient (a The DAO-ACK message is sent as a unicast packet by a DAO recipient (a
DAO parent or DODAG root) in response to a unicast DAO message. DAO parent or DODAG root) in response to a unicast DAO message.
6.5.1. Format of the DAO-ACK Base Object 6.5.1. Format of the DAO-ACK Base Object
skipping to change at page 44, line 25 skipping to change at page 44, line 28
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)... | Option(s)...
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
The '*' denotes that the DODAGID is not always present, as described The '*' denotes that the DODAGID is not always present, as described
below. below.
Figure 17: The DAO ACK Base Object Figure 17: The DAO ACK Base Object
RPLInstanceID: 8-bit field indicating the topology instance RPLInstanceID: 8-bit field indicating the topology instance
associated with the DODAG, as learned from the DIO. associated with the DODAG, as learned from the DIO.
D: The 'D' flag indicates that the DODAGID field is present. This D: The 'D' flag indicates that the DODAGID field is present. This
would typically only be set when a local RPLInstanceID is used. would typically only be set when a local RPLInstanceID is used.
Flags: The 7-bits remaining unused in the Flags field are reserved Reserved: The 7-bit field, reserved for flags.
for flags. The field MUST be initialized to zero by the sender
and MUST be ignored by the receiver.
DAOSequence: Incremented at each DAO message from a node, and echoed DAOSequence: Incremented at each DAO message from a node, and echoed
in the DAO-ACK by the recipient. The DAOSequence is used to in the DAO-ACK by the recipient. The DAOSequence is used to
correlate a DAO message and a DAO ACK message and is not to be correlate a DAO message and a DAO ACK message and is not to be
confused with the Transit Information option Path Sequence that confused with the Transit Information option Path Sequence that
is associated to a given target Down the DODAG. is associated to a given Target Down the DODAG.
Status: Indicates the completion. Status 0 is defined as Status: Indicates the completion. Status 0 is defined as unqualified
unqualified acceptance in this specification. The remaining acceptance in this specification. The remaining status values
status values are reserved as rejection codes. No rejection are reserved as rejection codes. No rejection status codes are
status codes are defined in this specification, although status defined in this specification, although status codes SHOULD be
codes SHOULD be allocated according to the following guidelines allocated according to the following guidelines in future
in future specifications: specifications:
0: Unqualified acceptance (i.e. the node receiving the
DAO-ACK is not rejected).
1-127: Not an outright rejection; the node sending the DAO- 0: Unqualified acceptance (i.e., the node receiving the
ACK is willing to act as a Parent, but the receiving DAO-ACK is not rejected).
node is suggested to find and use an alternate parent
instead.
127-255: Rejection; the node sending the DAO-ACK is unwilling
to act as a Parent.
DODAGID (optional): 128-bit unsigned integer set by a DODAG root 1-127: Not an outright rejection; the node sending the DAO-ACK
which uniquely identifies a DODAG. This field is only present is willing to act as a parent, but the receiving node is
when the 'D' flag is set. This field is typically only present suggested to find and use an alternate parent instead.
when a local RPLInstanceID is in use, in order to identify the 127-255: Rejection; the node sending the DAO-ACK is unwilling to
DODAGID that is associated with the RPLInstanceID. When a act as a parent.
global RPLInstanceID is in use this field need not be present.
DODAGID (optional): 128-bit unsigned integer set by a DODAG root that
uniquely identifies a DODAG. This field is only present
when the 'D' flag is set. Typically, this field is only
present when a local RPLInstanceID is in use in order to
identify the DODAGID that is associated with the
RPLInstanceID. When a global RPLInstanceID is in use,
this field need not be present.
Unassigned bits of the DAO-ACK Base are reserved. They MUST be set Unassigned bits of the DAO-ACK Base are reserved. They MUST be set
to zero on transmission and MUST be ignored on reception. to zero on transmission and MUST be ignored on reception.
6.5.2. Secure DAO-ACK 6.5.2. Secure DAO-ACK
A Secure DAO-ACK message follows the format in Figure 7, where the A Secure DAO-ACK message follows the format in Figure 7, where the
base format is the DAO-ACK message shown in Figure 17. base format is the DAO-ACK message shown in Figure 17.
6.5.3. DAO-ACK Options 6.5.3. DAO-ACK Options
This specification does not define any options to be carried by the This specification does not define any options to be carried by the
DAO-ACK message. DAO-ACK message.
6.6. Consistency Check (CC) 6.6. Consistency Check (CC)
The CC message is used to check secure message counters and issue The CC message is used to check secure message counters and issue
challenge/responses. A CC message MUST be sent as a secured RPL challenge-responses. A CC message MUST be sent as a secured RPL
message. message.
6.6.1. Format of the CC Base Object 6.6.1. Format of the CC Base Object
0 1 2 3 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 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID |R| Flags | CC Nonce | | RPLInstanceID |R| Flags | CC Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ DODAGID + + DODAGID +
| | | |
skipping to change at page 46, line 24 skipping to change at page 46, line 27
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Counter | | Destination Counter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)... | Option(s)...
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 18: The CC Base Object Figure 18: The CC Base Object
RPLInstanceID: 8-bit field indicating the topology instance RPLInstanceID: 8-bit field indicating the topology instance
associated with the DODAG, as learned from the DIO. associated with the DODAG, as learned from the DIO.
R: The 'R' flag indicates whether the CC message is a response. A R: The 'R' flag indicates whether the CC message is a response. A
message with the 'R' flag cleared is a request; a message with message with the 'R' flag cleared is a request; a message with
the 'R' flag set is a response. the 'R' flag set is a response.
Flags: The 7-bits remaining unused in the Flags field are reserved Flags: The 7 bits remaining unused in the Flags field are reserved
for flags. The field MUST be initialized to zero by the sender for flags. The field MUST be initialized to zero by the sender
and MUST be ignored by the receiver. and MUST be ignored by the receiver.
CC Nonce: 16-bit unsigned integer set by a CC request. The CC Nonce: 16-bit unsigned integer set by a CC request. The
corresponding CC response includes the same CC nonce value as corresponding CC response includes the same CC nonce value as
the request. the request.
Destination Counter: 32-bit unsigned integer value indicating the DODAGID: 128-bit field, contains the identifier of the DODAG root.
sender's estimate of the destination's current security Counter
Destination Counter: 32-bit unsigned integer value indicating the
sender's estimate of the destination's current security counter
value. If the sender does not have an estimate, it SHOULD set value. If the sender does not have an estimate, it SHOULD set
the Destination Counter field to zero. the Destination Counter field to zero.
Unassigned bits of the CC Base are reserved. They MUST be set to Unassigned bits of the CC Base are reserved. They MUST be set to
zero on transmission and MUST be ignored on reception. zero on transmission and MUST be ignored on reception.
The Destination Counter value allows new or recovered nodes to The Destination Counter value allows new or recovered nodes to
resynchronize through CC message exchanges. This is important to resynchronize through CC message exchanges. This is important to
ensure that a Counter value is not repeated for a given security key ensure that a Counter value is not repeated for a given security key
even in the event of devices recovering from a failure that created a even in the event of devices recovering from a failure that created a
loss of Counter state. For example, where a CC request or other RPL loss of Counter state. For example, where a CC request or other RPL
message is received with an initialized Counter within the message message is received with an initialized counter within the message
security section, the provision of the Incoming Counter within the CC Security section, the provision of the Incoming Counter within the CC
response message allows the requesting node to reset its Outgoing response message allows the requesting node to reset its Outgoing
Counter to a value greater than the last value received by the Counter to a value greater than the last value received by the
responding node; the Incoming Counter will also be updated from the responding node; the Incoming Counter will also be updated from the
received CC response. received CC response.
6.6.2. CC Options 6.6.2. CC Options
This specification allows for the CC message to carry the following This specification allows for the CC message to carry the following
options: options:
0x00 Pad1 0x00 Pad1
0x01 PadN 0x01 PadN
6.7. RPL Control Message Options 6.7. RPL Control Message Options
6.7.1. RPL Control Message Option Generic Format 6.7.1. RPL Control Message Option Generic Format
RPL Control Message Options all follow this format: RPL Control Message options all follow this format:
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Option Type | Option Length | Option Data | Option Type | Option Length | Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 19: RPL Option Generic Format Figure 19: RPL Option Generic Format
Option Type: 8-bit identifier of the type of option. The Option Option Type: 8-bit identifier of the type of option. The Option Type
Type values are to be confirmed by IANA Section 20.4. values are assigned by IANA (see Section 20.4.)
Option Length: 8-bit unsigned integer, representing the length in Option Length: 8-bit unsigned integer, representing the length in
octets of the option, not including the Option Type and Length octets of the option, not including the Option Type and Length
fields. fields.
Option Data: A variable length field that contains data specific to Option Data: A variable length field that contains data specific to
the option. the option.
When processing a RPL message containing an option for which the When processing a RPL message containing an option for which the
Option Type value is not recognized by the receiver, the receiver Option Type value is not recognized by the receiver, the receiver
MUST silently ignore the unrecognized option and continue to process MUST silently ignore the unrecognized option and continue to process
the following option, correctly handling any remaining options in the the following option, correctly handling any remaining options in the
message. message.
RPL message options may have alignment requirements. Following the RPL message options may have alignment requirements. Following the
convention in IPv6, options with alignment requirements are aligned convention in IPv6, options with alignment requirements are aligned
skipping to change at page 48, line 15 skipping to change at page 48, line 26
of the header, for n = 1, 2, 4, or 8). of the header, for n = 1, 2, 4, or 8).
6.7.2. Pad1 6.7.2. Pad1
The Pad1 option MAY be present in DIS, DIO, DAO, DAO-ACK, and CC The Pad1 option MAY be present in DIS, DIO, DAO, DAO-ACK, and CC
messages, and its format is as follows: messages, and its format is as follows:
0 0
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Type = 0 | | Type = 0x00 |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 20: Format of the Pad 1 Option Figure 20: Format of the Pad1 Option
The Pad1 option is used to insert a single octet of padding into the The Pad1 option is used to insert a single octet of padding into the
message to enable options alignment. If more than one octet of message to enable options alignment. If more than one octet of
padding is required, the PadN option should be used rather than padding is required, the PadN option should be used rather than
multiple Pad1 options. multiple Pad1 options.
NOTE! the format of the Pad1 option is a special case - it has NOTE! The format of the Pad1 option is a special case -- it has
neither Option Length nor Option Data fields. neither Option Length nor Option Data fields.
6.7.3. PadN 6.7.3. PadN
The PadN option MAY be present in DIS, DIO, DAO, DAO-ACK, and CC The PadN option MAY be present in DIS, DIO, DAO, DAO-ACK, and CC
messages, and its format is as follows: messages, and its format is as follows:
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Type = 1 | Option Length | 0x00 Padding... | Type = 0x01 | Option Length | 0x00 Padding...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 21: Format of the Pad N Option Figure 21: Format of the Pad N Option
The PadN option is used to insert two or more octets of padding into The PadN option is used to insert two or more octets of padding into
the message to enable options alignment. PadN Option data MUST be the message to enable options alignment. PadN option data MUST be
ignored by the receiver. ignored by the receiver.
Option Type: 0x01 (to be confirmed by IANA) Option Type: 0x01
Option Length: For N octets of padding, where 2 <= N <= 7, the
Option Length field contains the value N-2. An Option Length
of 0 indicates a total padding of 2 octets. An Option Length
of 5 indicates a total padding of 7 octets, which is the
maximum padding size allowed with the PadN option.
Option Data: For N (N > 1) octets of padding, the Option Data Option Length: For N octets of padding, where 2 <= N <= 7, the Option
Length field contains the value N-2. An Option Length of 0
indicates a total padding of 2 octets. An Option Length of 5
indicates a total padding of 7 octets, which is the maximum
padding size allowed with the PadN option.
Option Data: For N (N > 1) octets of padding, the Option Data
consists of N-2 zero-valued octets. consists of N-2 zero-valued octets.
6.7.4. Metric Container 6.7.4. DAG Metric Container
The Metric Container option MAY be present in DIO or DAO messages, The DAG Metric Container option MAY be present in DIO or DAO
and its format is as follows: messages, and its format is as follows:
0 1 2 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 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 | Type = 0x02 | Option Length | Metric Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 22: Format of the Metric Container Option Figure 22: Format of the DAG Metric Container Option
The Metric Container is used to report metrics along the DODAG. The The DAG Metric Container is used to report metrics along the DODAG.
Metric Container may contain a number of discrete node, link, and The DAG Metric Container may contain a number of discrete node, link,
aggregate path metrics and constraints specified in and aggregate path metrics and constraints specified in [RFC6551] as
[I-D.ietf-roll-routing-metrics] as chosen by the implementer. chosen by the implementer.
The Metric Container MAY appear more than once in the same RPL The DAG Metric Container MAY appear more than once in the same RPL
control message, for example to accommodate a use case where the control message, for example, to accommodate a use case where the
Metric Data is longer than 256 bytes. More information is in Metric Data is longer than 256 bytes. More information is in
[I-D.ietf-roll-routing-metrics]. [RFC6551].
The processing and propagation of the Metric Container is governed by The processing and propagation of the DAG Metric Container is
implementation specific policy functions. governed by implementation specific policy functions.
Option Type: 0x02 (to be confirmed by IANA) Option Type: 0x02
Option Length: The Option Length field contains the length in octets Option Length: The Option Length field contains the length in octets
of the Metric Data. of the Metric Data.
Metric Data: The order, content, and coding of the Metric Container Metric Data: The order, content, and coding of the DAG Metric
data is as specified in [I-D.ietf-roll-routing-metrics]. Container data is as specified in [RFC6551].
6.7.5. Route Information 6.7.5. Route Information
The Route Information option MAY be present in DIO messages, and The Route Information Option (RIO) MAY be present in DIO messages,
carries the same information as the IPv6 Neighbor Discovery (ND) and it carries the same information as the IPv6 Neighbor Discovery
Route Information option as defined in [RFC4191]. The root of a (ND) RIO as defined in [RFC4191]. The root of a DODAG is
DODAG is authoritative for setting that information and the authoritative for setting that information and the information is
information is unchanged as propagated down the DODAG. A RPL router unchanged as propagated down the DODAG. A RPL router may trivially
may trivially transform it back into a ND option to advertise in its transform it back into an ND option to advertise in its own RAs so a
own RAs so a node attached to the RPL router will end up using the node attached to the RPL router will end up using the DODAG for which
DODAG for which the root has the best preference for the destination the root has the best preference for the destination of a packet. In
of a packet. In addition to the existing ND semantics, it is addition to the existing ND semantics, it is possible for an
possible for an Objective function to use this information to favor a Objective Function to use this information to favor a DODAG whose
DODAG which root is most preferred for a specific destination. The root is most preferred for a specific destination. The format of the
format of the option is modified slightly (Type, Length, Prefix) in option is modified slightly (Type, Length, Prefix) in order to be
order to be carried as a RPL option as follows: carried as a RPL option as follows:
0 1 2 3 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 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| | Type = 0x03 | Option Length | Prefix Length |Resvd|Prf|Resvd|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Lifetime | | Route Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Prefix (Variable Length) . . Prefix (Variable Length) .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: Format of the Route Information Option Figure 23: Format of the Route Information Option
The Route Information option is used to indicate that connectivity to The RIO is used to indicate that connectivity to the specified
the specified destination prefix is available from the DODAG root. destination prefix is available from the DODAG root.
In the event that a RPL Control Message may need to specify In the event that a RPL control message may need to specify
connectivity to more than one destination, the Route Information connectivity to more than one destination, the RIO may be repeated.
option may be repeated.
[RFC4191] should be consulted as the authoritative reference with [RFC4191] should be consulted as the authoritative reference with
respect to the Route Information option. The field descriptions are respect to the RIO. The field descriptions are transcribed here for
transcribed here for convenience: convenience:
Option Type: 0x03 (to be confirmed by IANA)
Option Length: Variable, length of the option in octets excluding Option Type: 0x03
the Type and Length fields. Note that this length is expressed Option Length: Variable, length of the option in octets excluding the
in units of single-octets, unlike in IPv6 ND. Type and Length fields. 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 Prefix Length: 8-bit unsigned integer. The number of leading bits in
the Prefix that are valid. The value ranges from 0 to 128. the prefix that are valid. The value ranges from 0 to 128.
The Prefix field has the number of bytes inferred from the The Prefix field has the number of bytes inferred from the
Option Length field, that must be at least the Prefix Length. Option Length field, that must be at least the Prefix Length.
Note that in RPL this means that the Prefix field may have Note that in RPL, this means that the Prefix field may have
lengths other than 0, 8, or 16. lengths other than 0, 8, or 16.
Prf: 2-bit signed integer. The Route Preference indicates whether Prf: 2-bit signed integer. The Route Preference indicates whether to
to prefer the router associated with this prefix over others, prefer the router associated with this prefix over others, when
when multiple identical prefixes (for different routers) have multiple identical prefixes (for different routers) have been
been received. If the Reserved (10) value is received, the received. If the Reserved (10) value is received, the RIO MUST
Route Information Option MUST be ignored. As per [RFC4191], be ignored. Per [RFC4191], the Reserved (10) value MUST NOT be
the Reserved (10) value MUST NOT be sent. ([RFC4191] restricts sent. ([RFC4191] restricts the Preference to just three values
the Preference to just three values to reinforce that it is not to reinforce that it is not a metric.)
a metric).
Resvd: Two 3-bit unused fields. They MUST be initialized to zero by Resvd: Two 3-bit unused fields. They MUST be initialized to zero by
the sender and MUST be ignored by the receiver. the sender and MUST be ignored by the receiver.
Route Lifetime 32-bit unsigned integer. The length of time in Route Lifetime: 32-bit unsigned integer. The length of time in
seconds (relative to the time the packet is sent) that the seconds (relative to the time the packet is sent) that the
prefix is valid for route determination. A value of all one prefix is valid for route determination. A value of all one
bits (0xffffffff) represents infinity. bits (0xFFFFFFFF) represents infinity.
Prefix Variable-length field containing an IP address or a prefix of Prefix: Variable-length field containing an IP address or a prefix of
an IPv6 address. The Prefix Length field contains the number an IPv6 address. The Prefix Length field contains the number
of valid leading bits in the prefix. The bits in the prefix of valid leading bits in the prefix. The bits in the prefix
after the prefix length (if any) are reserved and MUST be after the prefix length (if any) are reserved and MUST be
initialized to zero by the sender and ignored by the receiver. initialized to zero by the sender and ignored by the receiver.
Note that in RPL this field may have lengths other than 0, 8, Note that in RPL, this field may have lengths other than 0, 8,
or 16. or 16.
Unassigned bits of the Route Information option are reserved. They Unassigned bits of the RIO are reserved. They MUST be set to zero on
MUST be set to zero on transmission and MUST be ignored on reception. transmission and MUST be ignored on reception.
6.7.6. DODAG Configuration 6.7.6. DODAG Configuration
The DODAG Configuration option MAY be present in DIO messages, and The DODAG Configuration option MAY be present in DIO messages, and
its format is as follows: its format is as follows:
0 1 2 3 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 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 |Opt Length = 14| Flags |A| PCS | DIOIntDoubl. | | Type = 0x04 |Opt Length = 14| Flags |A| PCS | DIOIntDoubl. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DIOIntMin. | DIORedun. | MaxRankIncrease | | DIOIntMin. | DIORedun. | MaxRankIncrease |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MinHopRankIncrease | OCP | | MinHopRankIncrease | OCP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Def. Lifetime | Lifetime Unit | | Reserved | Def. Lifetime | Lifetime Unit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24: Format of the DODAG Configuration Option Figure 24: Format of the DODAG Configuration Option
The DODAG Configuration option is used to distribute configuration The DODAG Configuration option is used to distribute configuration
information for DODAG Operation through the DODAG. information for DODAG Operation through the DODAG.
The information communicated in this option is generally static and The information communicated in this option is generally static and
unchanging within the DODAG, therefore it is not necessary to include unchanging within the DODAG, therefore it is not necessary to include
in every DIO. This information is configured at the DODAG Root and in every DIO. This information is configured at the DODAG root and
distributed throughout the DODAG with the DODAG Configuration Option. distributed throughout the DODAG with the DODAG Configuration option.
Nodes other than the DODAG Root MUST NOT modify this information when Nodes other than the DODAG root MUST NOT modify this information when
propagating the DODAG Configuration option. This option MAY be propagating the DODAG Configuration option. This option MAY be
included occasionally by the DODAG Root (as determined by the DODAG included occasionally by the DODAG root (as determined by the DODAG
Root), and MUST be included in response to a unicast request, e.g. a root), and MUST be included in response to a unicast request, e.g. a
unicast DODAG Information Solicitation (DIS) message. unicast DODAG Information Solicitation (DIS) message.
Option Type: 0x04 (to be confirmed by IANA) Option Type: 0x04
Option Length: 14 Option Length: 14
Flags: The 4-bits remaining unused in the Flags field are reserved Flags: The 4-bits remaining unused in the Flags field are reserved
for flags. The field MUST be initialized to zero by the sender for flags. The field MUST be initialized to zero by the sender
and MUST be ignored by the receiver. and MUST be ignored by the receiver.
Authentication Enabled (A): One bit flag describing the security Authentication Enabled (A): 1-bit flag describing the security mode
mode of the network. The bit describe whether a node must of the network. The bit describes whether a node must
authenticate with a key authority before joining the network as authenticate with a key authority before joining the network as
a router. If the DIO is not a secure DIO, the 'A' bit MUST be a router. If the DIO is not a secure DIO, the 'A' bit MUST be
zero. zero.
Path Control Size (PCS): 3-bit unsigned integer used to configure Path Control Size (PCS): 3-bit unsigned integer used to configure the
the number of bits that may be allocated to the Path Control number of bits that may be allocated to the Path Control field
field (see Section 9.9). Note that when PCS is consulted to (see Section 9.9). Note that when PCS is consulted to
determine the width of the Path Control field a value of 1 is determine the width of the Path Control field, a value of 1 is
added, i.e. a PCS value of 0 results in 1 active bit in the added, i.e., a PCS value of 0 results in 1 active bit in the
Path Control field. The default value of PCS is Path Control field. The default value of PCS is
DEFAULT_PATH_CONTROL_SIZE. DEFAULT_PATH_CONTROL_SIZE.
DIOIntervalDoublings: 8-bit unsigned integer used to configure Imax DIOIntervalDoublings: 8-bit unsigned integer used to configure Imax
of the DIO trickle timer (see Section 8.3.1). The default of the DIO Trickle timer (see Section 8.3.1). The default
value of DIOIntervalDoublings is value of DIOIntervalDoublings is
DEFAULT_DIO_INTERVAL_DOUBLINGS. DEFAULT_DIO_INTERVAL_DOUBLINGS.
DIOIntervalMin: 8-bit unsigned integer used to configure Imin of the DIOIntervalMin: 8-bit unsigned integer used to configure Imin of the
DIO trickle timer (see Section 8.3.1). The default value of DIO Trickle timer (see Section 8.3.1). The default value of
DIOIntervalMin is DEFAULT_DIO_INTERVAL_MIN. DIOIntervalMin is DEFAULT_DIO_INTERVAL_MIN.
DIORedundancyConstant: 8-bit unsigned integer used to configure k of DIORedundancyConstant: 8-bit unsigned integer used to configure k of
the DIO trickle timer (see Section 8.3.1). The default value the DIO Trickle timer (see Section 8.3.1). The default value
of DIORedundancyConstant is DEFAULT_DIO_REDUNDANCY_CONSTANT. of DIORedundancyConstant is DEFAULT_DIO_REDUNDANCY_CONSTANT.
MaxRankIncrease: 16-bit unsigned integer used to configure MaxRankIncrease: 16-bit unsigned integer used to configure
DAGMaxRankIncrease, the allowable increase in rank in support DAGMaxRankIncrease, the allowable increase in Rank in support
of local repair. If DAGMaxRankIncrease is 0 then this of local repair. If DAGMaxRankIncrease is 0, then this
mechanism is disabled. mechanism is disabled.
MinHopRankInc 16-bit unsigned integer used to configure MinHopRankIncrease: 16-bit unsigned integer used to configure
MinHopRankIncrease as described in Section 3.5.1. The default MinHopRankIncrease as described in Section 3.5.1. The default
value of MinHopRankInc is DEFAULT_MIN_HOP_RANK_INCREASE. value of MinHopRankInc is DEFAULT_MIN_HOP_RANK_INCREASE.
Default Lifetime: 8-bit unsigned integer. This is the lifetime that Objective Code Point (OCP): 16-bit unsigned integer. The OCP field
identifies the OF and is managed by the IANA.
Reserved: 7-bit unused field. The field MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
Default Lifetime: 8-bit unsigned integer. This is the lifetime that
is used as default for all RPL routes. It is expressed in is used as default for all RPL routes. It is expressed in
units of Lifetime Units, e.g. the default lifetime in seconds units of Lifetime Units, e.g., the default lifetime in seconds
is (Default Lifetime) * (Lifetime Unit). is (Default Lifetime) * (Lifetime Unit).
Lifetime Unit: 16-bit unsigned integer. Provides the unit in Lifetime Unit: 16-bit unsigned integer. Provides the unit in seconds
seconds that is used to express route lifetimes in RPL. For that is used to express route lifetimes in RPL. For very
very stable networks, it can be hours to days. stable networks, it can be hours to days.
Objective Code Point (OCP) 16-bit unsigned integer. The OCP field
identifies the OF and is managed by the IANA.
6.7.7. RPL Target 6.7.7. RPL Target
The RPL Target option MAY be present in DAO messages, and its format The RPL Target option MAY be present in DAO messages, and its format
is as follows: is as follows:
0 1 2 3 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 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 | Flags | Prefix Length | | Type = 0x05 | Option Length | Flags | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| Target Prefix (Variable Length) | | Target Prefix (Variable Length) |
. . . .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25: Format of the RPL Target Option Figure 25: Format of the RPL Target Option
The RPL Target Option is used to indicate a target IPv6 address, The RPL Target option is used to indicate a Target IPv6 address,
prefix, or multicast group that is reachable or queried along the prefix, or multicast group that is reachable or queried along the
DODAG. In a DAO, the RPL Target option indicates reachability. DODAG. In a DAO, the RPL Target option indicates reachability.
A RPL Target Option May optionally be paired with a RPL Target A RPL Target option MAY optionally be paired with a RPL Target
Descriptor Option (Figure 30) that qualifies the target. Descriptor option (Figure 30) that qualifies the target.
A set of one or more Transit Information options (Section 6.7.8) MAY A set of one or more Transit Information options (Section 6.7.8) MAY
directly follow a set of one or more Target option in a DAO message directly follow a set of one or more Target options in a DAO message
(where each Target Option MAY be paired with a RPL Target Descriptor (where each Target option MAY be paired with a RPL Target Descriptor
Option as above). The structure of the DAO message, detailing how option as above). The structure of the DAO message, detailing how
Target options are used in conjunction with Transit Information Target options are used in conjunction with Transit Information
options, is further described in Section 9.4. options is further described in Section 9.4.
The RPL Target option may be repeated as necessary to indicate The RPL Target option may be repeated as necessary to indicate
multiple targets. multiple targets.
Option Type: 0x05 (to be confirmed by IANA) Option Type: 0x05
Option Length: Variable, length of the option in octets excluding Option Length: Variable, length of the option in octets excluding the
the Type and Length fields. Type and Length fields.
Flags: 8-bit unused field reserved for flags. The field MUST be Flags: 8-bit unused field reserved for flags. The field MUST be
initialized to zero by the sender and MUST be ignored by the initialized to zero by the sender and MUST be ignored by the
receiver. receiver.
Prefix Length: 8-bit unsigned integer. Number of valid leading bits Prefix Length: 8-bit unsigned integer. Number of valid leading bits
in the IPv6 Prefix. in the IPv6 Prefix.
Target Prefix: Variable-length field identifying an IPv6 destination Target Prefix: Variable-length field identifying an IPv6 destination
address, prefix, or multicast group. The Prefix Length field address, prefix, or multicast group. The Prefix Length field
contains the number of valid leading bits in the prefix. The contains the number of valid leading bits in the prefix. The
bits in the prefix after the prefix length (if any) are bits in the prefix after the prefix length (if any) are
reserved and MUST be set to zero on transmission and MUST be reserved and MUST be set to zero on transmission and MUST be
ignored on receipt. ignored on receipt.
6.7.8. Transit Information 6.7.8. Transit Information
The Transit Information option MAY be present in DAO messages, and The Transit Information option MAY be present in DAO messages, and
its format is as follows: its format is as follows:
0 1 2 3 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 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 6 | Option Length |E| Flags | Path Control | | Type = 0x06 | Option Length |E| Flags | Path Control |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Sequence | Path Lifetime | | | Path Sequence | Path Lifetime | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| | | |
+ + + +
| | | |
+ Parent Address* + + Parent Address* +
| | | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The '*' denotes that the Parent Address is not always present, as The '*' denotes that the DODAG Parent Address subfield is not always
described below. present, as described below.
Figure 26: Format of the Transit Information option Figure 26: Format of the Transit Information Option
The Transit Information option is used for a node to indicate The Transit Information option is used for a node to indicate
attributes for a path to one or more destinations. The destinations attributes for a path to one or more destinations. The destinations
are indicated by one or more Target options that immediately precede are indicated by one or more Target options that immediately precede
the Transit Information option(s). the Transit Information option(s).
The Transit Information option can be used for a node to indicate its The Transit Information option can be used for a node to indicate its
DODAG parents to an ancestor that is collecting DODAG routing DODAG parents to an ancestor that is collecting DODAG routing
information, typically for the purpose of constructing source routes. information, typically, for the purpose of constructing source
In the non-storing mode of operation this ancestor will be the DODAG routes. In the Non-Storing mode of operation, this ancestor will be
Root, and this option is carried by the DAO message. In the storing the DODAG root, and this option is carried by the DAO message. In
mode of operation the Parent Address is not needed, since the DAO the Storing mode of operation, the DODAG Parent Address subfield is
message is sent directly to the parent. The option length is used to not needed, since the DAO message is sent directly to the parent.
determine whether the Parent Address is present or not. The option length is used to determine whether or not the DODAG
Parent Address subfield is present.
A non-storing node that has more than one DAO parent MAY include a A non-storing node that has more than one DAO parent MAY include a
Transit Information option for each DAO parent as part of the non- Transit Information option for each DAO parent as part of the non-
storing destination advertisement operation. The node may distribute storing destination advertisement operation. The node may distribute
the bits in the Path Control field among different groups of DAO the bits in the Path Control field among different groups of DAO
parents in order to signal a preference among parents. That parents in order to signal a preference among parents. That
preference may influence the decision of the DODAG root when preference may influence the decision of the DODAG root when
selecting among the alternate parents/paths for constructing downward selecting among the alternate parents/paths for constructing Downward
routes. routes.
One or more Transit Information options MUST be preceded by one or One or more Transit Information options MUST be preceded by one or
more RPL Target options. In this manner the RPL Target option more RPL Target options. In this manner, the RPL Target option
indicates the child node, and the Transit Information option(s) indicates the child node, and the Transit Information option(s)
enumerate the DODAG parents. The structure of the DAO message, enumerates the DODAG parents. The structure of the DAO message,
further detailing how Target options are used in conjunction with further detailing how Target options are used in conjunction with
Transit Information options, is further described in Section 9.4. Transit Information options, is further described in Section 9.4.
A typical non-storing node will use multiple Transit Information A typical non-storing node will use multiple Transit Information
options, and it will send the DAO message thus formed directly to the options, and it will send the DAO message thus formed directly to the
root. A typical storing node will use one Transit Information option root. A typical storing node will use one Transit Information option
with no parent field, and will send the DAO message thus formed, with with no parent field and will send the DAO message thus formed, with
additional adjustments to Path Control as detailed later, to one or additional adjustments, to Path Control as detailed later, to one or
multiple parents. multiple parents.
For example, in a non-storing mode of operation let Tgt(T) denote a For example, in a Non-Storing mode of operation let Tgt(T) denote a
Target option for a target T. Let Trnst(P) denote a Transit Target option for a Target T. Let Trnst(P) denote a Transit
Information option that contains a parent address P. Consider the Information option that contains a parent address P. Consider the
case of a non-storing node N that advertises the self-owned targets case of a non-storing Node N that advertises the self-owned targets
N1 and N2 and has parents P1, P2, and P3. In that case the DAO N1 and N2 and has parents P1, P2, and P3. In that case, the DAO
message would be expected to contain the sequence ( (Tgt(N1), message would be expected to contain the sequence ((Tgt(N1),
Tgt(N2)), (Trnst(P1), Trnst(P2), Trnst(P3)) ), such that the group of Tgt(N2)), (Trnst(P1), Trnst(P2), Trnst(P3))), such that the group of
Target options {N1, N2} are described by the Transit Information Target options {N1, N2} is described by the Transit Information
options as having the parents {P1, P2, P3}. The non-storing node options as having the parents {P1, P2, P3}. The non-storing node
would then address that DAO message directly to the DODAG root, and would then address that DAO message directly to the DODAG root and
forward that DAO message through one of the DODAG parents P1, P2, or forward that DAO message through one of the DODAG parents: P1, P2, or
P3. P3.
Option Type: 0x06 (to be confirmed by IANA) Option Type: 0x06
Option Length: Variable, depending on whether or not Parent Address Option Length: Variable, depending on whether or not the DODAG Parent
is present. Address subfield is present.
External (E): 1-bit flag. The 'E' flag is set to indicate that the External (E): 1-bit flag. The 'E' flag is set to indicate that the
parent router redistributes external targets into the RPL parent router redistributes external targets into the RPL
network. An external target is a target that has been learned network. An external Target is a Target that has been learned
through an alternate protocol. The external targets are listed through an alternate protocol. The external targets are listed
in the target options that immediately precede the Transit in the Target options that immediately precede the Transit
Information option. An external target is not expected to Information option. An external Target is not expected to
support RPL messages and options. support RPL messages and options.
Flags: The 7-bits remaining unused in the Flags field are reserved Flags: The 7 bits remaining unused in the Flags field are reserved
for flags. The field MUST be initialized to zero by the sender for flags. The field MUST be initialized to zero by the sender
and MUST be ignored by the receiver. and MUST be ignored by the receiver.
Path Control: 8-bit bitfield. The Path Control field limits the Path Control: 8-bit bit field. The Path Control field limits the
number of DAO-Parents to which a DAO message advertising number of DAO parents to which a DAO message advertising
connectivity to a specific destination may be sent, as well as connectivity to a specific destination may be sent, as well as
providing some indication of relative preference. The limit providing some indication of relative preference. The limit
provides some bound on overall DAO message fan-out in the LLN. provides some bound on overall DAO message fan-out in the LLN.
The assignment and ordering of the bits in the path control The assignment and ordering of the bits in the Path Control
also serves to communicate preference. Not all of these bits also serves to communicate preference. Not all of these bits
may be enabled as according to the PCS in the DODAG may be enabled as according to the PCS in the DODAG
Configuration. The Path Control field is divided into four Configuration. The Path Control field is divided into four
subfields which contain two bits each: PC1, PC2, PC3, and PC4, subfields that contain two bits each: PC1, PC2, PC3, and PC4,
as illustrated in Figure 27. The subfields are ordered by as illustrated in Figure 27. The subfields are ordered by
preference, with PC1 being the most preferred and PC4 being the preference, with PC1 being the most preferred and PC4 being the
least preferred. Within a subfield there is no order of least preferred. Within a subfield, there is no order of
preference. By grouping the parents (as in ECMP) and ordering preference. By grouping the parents (as in ECMP) and ordering
them, the parents may be associated with specific bits in the them, the parents may be associated with specific bits in the
Path Control field in a way that communicates preference. Path Control field in a way that communicates preference.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|PC1|PC2|PC3|PC4| |PC1|PC2|PC3|PC4|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 27: Path Control Preference Sub-field Encoding Figure 27: Path Control Preference Subfield Encoding
Path Sequence: 8-bit unsigned integer. When a RPL Target option is Path Sequence: 8-bit unsigned integer. When a RPL Target option is
issued by the node that owns the Target Prefix (i.e. in a DAO issued by the node that owns the Target prefix (i.e., in a DAO
message), that node sets the Path Sequence and increments the message), that node sets the Path Sequence and increments the
Path Sequence each time it issues a RPL Target option with Path Sequence each time it issues a RPL Target option with
updated information. updated information.
Path Lifetime: 8-bit unsigned integer. The length of time in Path Lifetime: 8-bit unsigned integer. The length of time in
Lifetime Units (obtained from the Configuration option) that Lifetime Units (obtained from the Configuration option) that
the prefix is valid for route determination. The period starts the prefix is valid for route determination. The period starts
when a new Path Sequence is seen. A value of all one bits when a new Path Sequence is seen. A value of all one bits
(0xFF) represents infinity. A value of all zero bits (0x00) (0xFF) represents infinity. A value of all zero bits (0x00)
indicates a loss of reachability. A DAO message that contains indicates a loss of reachability. A DAO message that contains
a Transit Information option with a Path Lifetime of 0x00 for a a Transit Information option with a Path Lifetime of 0x00 for a
Target is referred as a No-Path (for that Target) in this Target is referred as a No-Path (for that Target) in this
document. document.
Parent Address (optional): IPv6 Address of the DODAG Parent of the Parent Address (optional): IPv6 address of the DODAG parent of the
node originally issuing the Transit Information Option. This node originally issuing the Transit Information option. This
field may not be present, as according to the DODAG Mode of field may not be present, as according to the DODAG Mode of
Operation (storing or non-storing) and indicated by the Transit Operation (Storing or Non-Storing) and indicated by the Transit
Information option length. Information option length.
Unassigned bits of the Transit Information option are reserved. They Unassigned bits of the Transit Information option are reserved. They
MUST be set to zero on transmission and MUST be ignored on reception. MUST be set to zero on transmission and MUST be ignored on reception.
6.7.9. Solicited Information 6.7.9. Solicited Information
The Solicited Information option MAY be present in DIS messages, and The Solicited Information option MAY be present in DIS messages, and
its format is as follows: its format is as follows:
0 1 2 3 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 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 7 |Opt Length = 19| RPLInstanceID |V|I|D| Flags | | Type = 0x07 |Opt Length = 19| RPLInstanceID |V|I|D| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ DODAGID + + DODAGID +
| | | |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version Number | |Version Number |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 28: Format of the Solicited Information Option Figure 28: Format of the Solicited Information Option
The Solicited Information option is used for a node to request DIO The Solicited Information option is used for a node to request DIO
messages from a subset of neighboring nodes. The Solicited messages from a subset of neighboring nodes. The Solicited
Information option may specify a number of predicate criteria to be Information option may specify a number of predicate criteria to be
matched by a receiving node. This is used by the requester to limit matched by a receiving node. This is used by the requester to limit
the number of replies from "non-interesting" nodes. These predicates the number of replies from "non-interesting" nodes. These predicates
affect whether a node resets its DIO trickle timer, as described in affect whether a node resets its DIO Trickle timer, as described in
Section 8.3. Section 8.3.
The Solicited Information option contains flags that indicate which The Solicited Information option contains flags that indicate which
predicates a node should check when deciding whether to reset its predicates a node should check when deciding whether to reset its
Trickle timer. A node resets its Trickle timer when all predicates Trickle timer. A node resets its Trickle timer when all predicates
are true. If a flag is set, then the RPL node MUST check the are true. If a flag is set, then the RPL node MUST check the
associated predicate. If a flag is cleared, then the RPL node MUST associated predicate. If a flag is cleared, then the RPL node MUST
NOT check the associated predicate. (If a flag is cleared, the RPL NOT check the associated predicate. (If a flag is cleared, the RPL
node assumes that the associated predicate is true). node assumes that the associated predicate is true.)
Option Type: 0x07
Option Type: 0x07 (to be confirmed by IANA)
Option Length: 19 Option Length: 19
V: The V flag is the Version predicate. The Version predicate is V: The 'V' flag is the Version predicate. The Version predicate is
true if the receiver's DODAGVersionNumber matches the requested true if the receiver's DODAGVersionNumber matches the requested
Version Number. If the V flag is cleared then the Version Version Number. If the 'V' flag is cleared, then the Version
field is not valid and the Version field MUST be set to zero on field is not valid and the Version field MUST be set to zero on
transmission and ignored upon receipt. transmission and ignored upon receipt.
I: The I flag is the InstanceID predicate. The InstanceID I: The 'I' flag is the InstanceID predicate. The InstanceID
predicate is true when the RPL node's current RPLInstanceID predicate is true when the RPL node's current RPLInstanceID
matches the requested RPLInstanceID. If the I flag is cleared matches the requested RPLInstanceID. If the 'I' flag is
then the RPLInstanceID field is not valid and the RPLInstanceID cleared, then the RPLInstanceID field is not valid and the
field MUST be set to zero on transmission and ignored upon RPLInstanceID field MUST be set to zero on transmission and
receipt. ignored upon receipt.
D: The D flag is the DODAGID predicate. The DODAGID predicate is D: The 'D' flag is the DODAGID predicate. The DODAGID predicate is
true if the RPL node's parent set has the same DODAGID as the true if the RPL node's parent set has the same DODAGID as the
DODAGID field. If the D flag is cleared then the DODAGID field DODAGID field. If the 'D' flag is cleared, then the DODAGID
is not valid and the DODAGID field MUST be set to zero on field is not valid and the DODAGID field MUST be set to zero on
transmission and ignored upon receipt. transmission and ignored upon receipt.
Flags: The 5-bits remaining unused in the Flags field are reserved Flags: The 5 bits remaining unused in the Flags field are reserved
for flags. The field MUST be initialized to zero by the sender for flags. The field MUST be initialized to zero by the sender
and MUST be ignored by the receiver. and MUST be ignored by the receiver.
Version Number: 8-bit unsigned integer containing the value of Version Number: 8-bit unsigned integer containing the value of
DODAGVersionNumber that is being solicited when valid. DODAGVersionNumber that is being solicited when valid.
RPLInstanceID: 8-bit unsigned integer containing the RPLInstanceID RPLInstanceID: 8-bit unsigned integer containing the RPLInstanceID
that is being solicited when valid. that is being solicited when valid.
DODAGID: 128-bit unsigned integer containing the DODAGID that is DODAGID: 128-bit unsigned integer containing the DODAGID that is
being solicited when valid. being solicited when valid.
Unassigned bits of the Solicited Information option are reserved. Unassigned bits of the Solicited Information option are reserved.
They MUST be set to zero on transmission and MUST be ignored on They MUST be set to zero on transmission and MUST be ignored on
reception. reception.
6.7.10. Prefix Information 6.7.10. Prefix Information
The Prefix Information option MAY be present in DIO messages, and The Prefix Information Option (PIO) MAY be present in DIO messages,
carries the information that is specified for the IPv6 ND Prefix and carries the information that is specified for the IPv6 ND Prefix
Information Option in [RFC4861], [RFC4862] and [RFC3775] for use by Information option in [RFC4861], [RFC4862], and [RFC6275] for use by
RPL nodes and IPv6 hosts. In particular, a RPL node may use this RPL nodes and IPv6 hosts. In particular, a RPL node may use this
option for the purpose of State-Less Address Auto-Configuration option for the purpose of Stateless Address Autoconfiguration (SLAAC)
(SLAAC) from a prefix advertised by a parent as specified in from a prefix advertised by a parent as specified in [RFC4862], and
[RFC4862], and advertise its own address as specified in [RFC3775]. advertise its own address as specified in [RFC6275]. The root of a
The root of a DODAG is authoritative for setting that information. DODAG is authoritative for setting that information. The information
The information is propagated down the DODAG unchanged, with the is propagated down the DODAG unchanged, with the exception that a RPL
exception that a RPL router may overwrite the Interface ID if the 'R' router may overwrite the Interface ID if the 'R' flag is set to
flag is set to indicate its full address in the PIO The format of the indicate its full address in the PIO. The format of the option is
option is modified (Type, Length, Prefix) in order to be carried as a modified (Type, Length, Prefix) in order to be carried as a RPL
RPL option as follows: option as follows:
If the only desired effect of a received PIO in a DIO is to provide
the global address of the parent node to the receiving node, then the
sender resets the 'A' and 'L' bits and sets the 'R' bit. Upon
receipt, the RPL will not autoconfigure an address or a connected
route from the prefix [RFC4862]. As in all cases, when the 'L' bit
is not set, the RPL node MAY include the prefix in PIOs it sends to
its children.
0 1 2 3 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 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 8 |Opt Length = 30| Prefix Length |L|A|R|Reserved1| | Type = 0x08 |Opt Length = 30| Prefix Length |L|A|R|Reserved1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime | | Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred Lifetime | | Preferred Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved2 | | Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ Prefix + + Prefix +
| | | |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29: Format of the Prefix Information Option Figure 29: Format of the Prefix Information Option
The Prefix Information option may be used to distribute the prefix in The PIO may be used to distribute the prefix in use inside the DODAG,
use inside the DODAG, e.g. for address autoconfiguration. e.g., for address autoconfiguration.
[RFC4861] and [RFC3775] should be consulted as the authoritative
reference with respect to the Prefix Information option. The field
descriptions are transcribed here for convenience:
Option Type: 0x08 (to be confirmed by IANA) [RFC4861] and [RFC6275] should be consulted as the authoritative
reference with respect to the PIO. The field descriptions are
transcribed here for convenience:
Option Length: 30. Note that this length is expressed in units of Option Type: 0x08
single-octets, unlike in IPv6 ND. 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 Prefix Length: 8-bit unsigned integer. The number of leading bits in
the Prefix that are valid. The value ranges from 0 to 128. the Prefix field that are valid. The value ranges from 0 to
The prefix length field provides necessary information for on- 128. The Prefix Length field provides necessary information
link determination (when combined with the L flag in the prefix for on-link determination (when combined with the 'L' flag in
information option). It also assists with address the PIO). It also assists with address autoconfiguration as
autoconfiguration as specified in [RFC4862], for which there specified in [RFC4862], for which there may be more
may be more restrictions on the prefix length. restrictions on the prefix length.
L 1-bit on-link flag. When set, indicates that this prefix can L: 1-bit on-link flag. When set, it indicates that this prefix
be used for on-link determination. When not set the can be used for on-link determination. When not set, the
advertisement makes no statement about on-link or off-link advertisement makes no statement about on-link or off-link
properties of the prefix. In other words, if the L flag is not properties of the prefix. In other words, if the 'L' flag is
set a RPL node MUST NOT conclude that an address derived from not set, a RPL node MUST NOT conclude that an address derived
the prefix is off-link. That is, it MUST NOT update a previous from the prefix is off-link. That is, it MUST NOT update a
indication that the address is on-link. A RPL node acting as a previous indication that the address is on-link. A RPL node
router MUST NOT propagate a PIO with the L flag set. A RPL acting as a router MUST NOT propagate a PIO with the 'L' flag
node acting as a router MAY propagate a PIO with the L flag not set. A RPL node acting as a router MAY propagate a PIO with
set. the 'L' flag not set.
A 1-bit autonomous address-configuration flag. When set A: 1-bit autonomous address-configuration flag. When set, it
indicates that this prefix can be used for stateless address indicates that this prefix can be used for stateless address
configuration as specified in [RFC4862]. When both protocols configuration as specified in [RFC4862]. When both protocols
(ND RAs and RPL DIOs) are used to carry PIOs on the same link, (ND RAs and RPL DIOs) are used to carry PIOs on the same link,
it is possible to use either one for SLAAC by a RPL node. It it is possible to use either one for SLAAC by a RPL node. It
is also possible to make either protocol ineligible for SLAAC is also possible to make either protocol ineligible for SLAAC
operation by forcing the A flag to 0 for PIOs carried in that operation by forcing the 'A' flag to 0 for PIOs carried in that
protocol. protocol.
R 1-bit Router address flag. When set, indicates that the Prefix R: 1-bit router address flag. When set, it indicates that the
field contains a complete IPv6 address assigned to the sending Prefix field contains a complete IPv6 address assigned to the
router that can be used as parent in a target option. The sending router that can be used as parent in a target option.
indicated prefix is the first Prefix Length bits of the Prefix The indicated prefix is the first prefix length bits of the
field. The router IPv6 address has the same scope and conforms Prefix field. The router IPv6 address has the same scope and
to the same lifetime values as the advertised prefix. This use conforms to the same lifetime values as the advertised prefix.
of the Prefix field is compatible with its use in advertising This use of the Prefix field is compatible with its use in
the prefix itself, since Prefix Advertisement uses only the advertising the prefix itself, since Prefix Advertisement uses
leading bits. Interpretation of this flag bit is thus only the leading bits. Interpretation of this flag bit is thus
independent of the processing required for the On-Link (L) and independent of the processing required for the on-link (L) and
Autonomous Address-Configuration (A) flag bits. autonomous address-configuration (A) flag bits.
Reserved1 5-bit unused field. It MUST be initialized to zero by the Reserved1: 5-bit unused field. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver. sender and MUST be ignored by the receiver.
Valid Lifetime 32-bit unsigned integer. The length of time in Valid Lifetime: 32-bit unsigned integer. The length of time in
seconds (relative to the time the packet is sent) that the seconds (relative to the time the packet is sent) that the
prefix is valid for the purpose of on-link determination. A prefix is valid for the purpose of on-link determination. A
value of all one bits (0xffffffff) represents infinity. The value of all one bits (0xFFFFFFFF) represents infinity. The
Valid Lifetime is also used by [RFC4862]. Valid Lifetime is also used by [RFC4862].
Preferred Lifetime 32-bit unsigned integer. The length of time in Preferred Lifetime: 32-bit unsigned integer. The length of time in
seconds (relative to the time the packet is sent) that seconds (relative to the time the packet is sent) that
addresses generated from the prefix via stateless address addresses generated from the prefix via stateless address
autoconfiguration remain preferred [RFC4862]. A value of all autoconfiguration remain preferred [RFC4862]. A value of all
one bits (0xffffffff) represents infinity. See [RFC4862]. one bits (0xFFFFFFFF) represents infinity. See [RFC4862].
Note that the value of this field MUST NOT exceed the Valid Note that the value of this field MUST NOT exceed the Valid
Lifetime field to avoid preferring addresses that are no longer Lifetime field to avoid preferring addresses that are no longer
valid. valid.
Reserved2 This field is unused. It MUST be initialized to zero by Reserved2: This field is unused. It MUST be initialized to zero by
the sender and MUST be ignored by the receiver. the sender and MUST be ignored by the receiver.
Prefix An IPv6 address or a prefix of an IPv6 address. The Prefix Prefix: An IPv6 address or a prefix of an IPv6 address. The Prefix
Length field contains the number of valid leading bits in the Length field contains the number of valid leading bits in the
prefix. The bits in the prefix after the prefix length are prefix. The bits in the prefix after the prefix length are
reserved and MUST be initialized to zero by the sender and reserved and MUST be initialized to zero by the sender and
ignored by the receiver. A router SHOULD NOT send a prefix ignored by the receiver. A router SHOULD NOT send a prefix
option for the link-local prefix and a host SHOULD ignore such option for the link-local prefix, and a host SHOULD ignore such
a prefix option. A non-storing node SHOULD refrain from a prefix option. A non-storing node SHOULD refrain from
advertising a prefix till it owns an address of that prefix, advertising a prefix till it owns an address of that prefix,
and then it SHOULD advertise its full address in this field, and then it SHOULD advertise its full address in this field,
with the 'R' flag set. The children of a node that so with the 'R' flag set. The children of a node that so
advertises a full address with the 'R' flag set may then use advertises a full address with the 'R' flag set may then use
that address to determine the content of the Parent Address that address to determine the content of the DODAG Parent
field of the Transit Information Option. Address subfield of the Transit Information option.
Unassigned bits of the Prefix Information option are reserved. They Unassigned bits of the PIO are reserved. They MUST be set to zero on
MUST be set to zero on transmission and MUST be ignored on reception. transmission and MUST be ignored on reception.
6.7.11. RPL Target Descriptor 6.7.11. RPL Target Descriptor
The RPL Target option MAY be immediately followed by one opaque The RPL Target option MAY be immediately followed by one opaque
descriptor that qualifies that specific target. descriptor that qualifies that specific target.
0 1 2 3 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 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 9 |Opt Length = 4 | Descriptor | Type = 0x09 |Opt Length = 4 | Descriptor
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Descriptor (cont.) | Descriptor (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 30: Format of the RPL Target Descriptor Option Figure 30: Format of the RPL Target Descriptor Option
The RPL Target Descriptor Option is used to qualify a target, The RPL Target Descriptor option is used to qualify a target,
something that is sometimes called tagging. something that is sometimes called "tagging".
There can be at most one descriptor per target. The descriptor is At most, there can be one descriptor per target. The descriptor is
set by the node that injects the target in the RPL network. It MUST set by the node that injects the Target in the RPL network. It MUST
be copied but not modified by routers that propagate the target Up be copied but not modified by routers that propagate the Target Up
the DODAG in DAO messages. the DODAG in DAO messages.
Option Type: 0x09 (to be confirmed by IANA) Option Type: 0x09
Option Length: 4 Option Length: 4
Descriptor: 32-bit unsigned integer. Opaque. Descriptor: 32-bit unsigned integer. Opaque.
7. Sequence Counters 7. Sequence Counters
This section describes the general scheme for bootstrap and operation This section describes the general scheme for bootstrap and operation
of sequence counters in RPL, such as the DODAGVersionNumber in the of sequence counters in RPL, such as the DODAGVersionNumber in the
DIO message, the DAOSequence in the DAO message, and the Path DIO message, the DAOSequence in the DAO message, and the Path
Sequence in the Transit Information option. Sequence in the Transit Information option.
7.1. Sequence Counter Overview 7.1. Sequence Counter Overview
This specification utilizes three different sequence numbers to This specification utilizes three different sequence numbers to
validate the freshness and the synchronization of protocol validate the freshness and the synchronization of protocol
information: information:
DODAGVersionNumber: This sequence counter is present in the DIO DODAGVersionNumber: This sequence counter is present in the DIO Base
base to indicate the Version of the DODAG being formed. The to indicate the Version of the DODAG being formed. The
DODAGVersionNumber is monotonically incremented by the root DODAGVersionNumber is monotonically incremented by the root
each time the root decides to form a new Version of the DODAG each time the root decides to form a new Version of the DODAG
in order to revalidate the integrity and allow a global repairs in order to revalidate the integrity and allow a global repair
to occur. The DODAGVersionNumber is propagated unchanged Down to occur. The DODAGVersionNumber is propagated unchanged Down
the DODAG as routers join the new DODAG Version. The the DODAG as routers join the new DODAG Version. The
DODAGVersionNumber is globally significant in a DODAG and DODAGVersionNumber is globally significant in a DODAG and
indicates the Version of the DODAG that a router is operating indicates the Version of the DODAG in which a router is
in. An older (lesser) value indicates that the originating operating. An older (lesser) value indicates that the
router has not migrated to the new DODAG Version and can not be originating router has not migrated to the new DODAG Version
used as a parent once the receiving node has migrated to the and cannot be used as a parent once the receiving node has
newer DODAG Version. migrated to the newer DODAG Version.
DAOSequence: This sequence counter is present in the DAO base to DAOSequence: This sequence counter is present in the DAO Base to
correlate a DAO message and a DAO ACK message. The DAOSequence correlate a DAO message and a DAO ACK message. The DAOSequence
number is locally significant to the node that issues a DAO number is locally significant to the node that issues a DAO
message for its own consumption to detect the loss of a DAO message for its own consumption to detect the loss of a DAO
message and enable retries. message and enable retries.
Path Sequence: This sequence counter is present in the Transit Path Sequence: This sequence counter is present in the Transit
Information option in a DAO message. The purpose of this Information option in a DAO message. The purpose of this
counter is to differentiate a movement where a newer route counter is to differentiate a movement where a newer route
supersedes a stale one from a route redundancy scenario where supersedes a stale one from a route redundancy scenario where
multiple routes exist in parallel for a same target. The Path multiple routes exist in parallel for the same target. The
Sequence is globally significant in a DODAG and indicates the Path Sequence is globally significant in a DODAG and indicates
freshness of the route to the associated target. An older the freshness of the route to the associated target. An older
(lesser) value received from an originating router indicates (lesser) value received from an originating router indicates
that the originating router holds stale routing states and the that the originating router holds stale routing states and the
originating router should not be considered anymore as a originating router should not be considered anymore as a
potential next-hop for the target. The Path Sequence is potential next hop for the target. The Path Sequence is
computed by the node that advertises the target, that is the computed by the node that advertises the target, that is the
target itself or a router that advertises a target on behalf of Target itself or a router that advertises a Target on behalf of
a host, and is unchanged as the DAO content is propagated a host, and is unchanged as the DAO content is propagated
towards the root by parent routers. If a host does not pass a towards the root by parent routers. If a host does not pass a
counter to its router, then the router is in charge of counter to its router, then the router is in charge of
computing the Path Sequence on behalf of the host and the host computing the Path Sequence on behalf of the host and the host
can only register to one router for that purpose. If a DAO can only register to one router for that purpose. If a DAO
message containing a same target is issued to multiple parents message containing the same Target is issued to multiple
at a given point of time for the purpose of route redundancy, parents at a given point in time for the purpose of route
then the Path Sequence is the same in all the DAO messages for redundancy, then the Path Sequence is the same in all the DAO
that same target. messages for that same target.
7.2. Sequence Counter Operation 7.2. Sequence Counter Operation
RPL sequence counters are subdivided in a 'lollipop' fashion RPL sequence counters are subdivided in a 'lollipop' fashion
([Perlman83]), where the values from 128 and greater are used as a [Perlman83], where the values from 128 and greater are used as a
linear sequence to indicate a restart and bootstrap the counter, and linear sequence to indicate a restart and bootstrap the counter, and
the values less than or equal to 127 used as a circular sequence the values less than or equal to 127 used as a circular sequence
number space of size 128 as in [RFC1982]. Consideration is given to number space of size 128 as in [RFC1982]. Consideration is given to
the mode of operation when transitioning from the linear region to the mode of operation when transitioning from the linear region to
the circular region. Finally, when operating in the circular region, the circular region. Finally, when operating in the circular region,
if sequence numbers are detected to be too far apart then they are if sequence numbers are detected to be too far apart, then they are
not comparable, as detailed below. not comparable, as detailed below.
A window of comparison, SEQUENCE_WINDOW = 16, is configured based on A window of comparison, SEQUENCE_WINDOW = 16, is configured based on
a value of 2^N, where N is defined to be 4 in this specification. a value of 2^N, where N is defined to be 4 in this specification.
For a given sequence counter, For a given sequence counter:
1. The sequence counter SHOULD be initialized to an implementation 1. The sequence counter SHOULD be initialized to an implementation
defined value which is 128 or greater prior to use. A defined value, which is 128 or greater prior to use. A
recommended value is 240 (256 - SEQUENCE_WINDOW). recommended value is 240 (256 - SEQUENCE_WINDOW).
2. When a sequence counter increment would cause the sequence 2. When a sequence counter increment would cause the sequence
counter to increment beyond its maximum value, the sequence counter to increment beyond its maximum value, the sequence
counter MUST wrap back to zero. When incrementing a sequence counter MUST wrap back to zero. When incrementing a sequence
counter greater than or equal to 128, the maximum value is 255. counter greater than or equal to 128, the maximum value is 255.
When incrementing a sequence counter less than 128, the maximum When incrementing a sequence counter less than 128, the maximum
value is 127. value is 127.
3. When comparing two sequence counters, the following rules MUST be 3. When comparing two sequence counters, the following rules MUST be
skipping to change at page 66, line 7 skipping to change at page 65, line 36
1. If (256 + B - A) is less than or equal to 1. If (256 + B - A) is less than or equal to
SEQUENCE_WINDOW, then B is greater than A, A is less than SEQUENCE_WINDOW, then B is greater than A, A is less than
B, and the two are not equal. B, and the two are not equal.
2. If (256 + B - A) is greater than SEQUENCE_WINDOW, then A 2. If (256 + B - A) is greater than SEQUENCE_WINDOW, then A
is greater than B, B is less than A, and the two are not is greater than B, B is less than A, and the two are not
equal. equal.
For example, if A is 240, and B is 5, then (256 + 5 - 240) is For example, if A is 240, and B is 5, then (256 + 5 - 240) is
21. 21 is greater than SEQUENCE_WINDOW (16), thus 240 is 21. 21 is greater than SEQUENCE_WINDOW (16); thus, 240 is
greater than 5. As another example, if A is 250 and B is 5, greater than 5. As another example, if A is 250 and B is 5,
then (256 + 5 - 250) is 11. 11 is less than SEQUENCE_WINDOW then (256 + 5 - 250) is 11. 11 is less than SEQUENCE_WINDOW
(16), thus 250 is less than 5. (16); thus, 250 is less than 5.
2. In the case where both sequence counters to be compared are 2. In the case where both sequence counters to be compared are
less than or equal to 127, and in the case where both less than or equal to 127, and in the case where both
sequence counters to be compared are greater than or equal to sequence counters to be compared are greater than or equal to
128: 128:
1. If the absolute magnitude of difference between the two 1. If the absolute magnitude of difference between the two
sequence counters is less than or equal to sequence counters is less than or equal to
SEQUENCE_WINDOW, then a comparison as described in SEQUENCE_WINDOW, then a comparison as described in
[RFC1982] is used to determine the relationships greater [RFC1982] is used to determine the relationships greater
than, less than, and equal. than, less than, and equal.
2. If the absolute magnitude of difference of the two 2. If the absolute magnitude of difference of the two
sequence counters is greater than SEQUENCE_WINDOW, then a sequence counters is greater than SEQUENCE_WINDOW, then a
desynchronization has occurred and the two sequence desynchronization has occurred and the two sequence
numbers are not comparable. numbers are not comparable.
4. If two sequence numbers are determined to be not comparable, i.e. 4. If two sequence numbers are determined not to be comparable,
the results of the comparison are not defined, then a node should i.e., the results of the comparison are not defined, then a node
consider the comparison as if it has evaluated in such a way so should consider the comparison as if it has evaluated in such a
as to give precedence to the sequence number that has most way so as to give precedence to the sequence number that has most
recently been observed to increment. Failing this, the node recently been observed to increment. Failing this, the node
should consider the comparison as if it has evaluated in such a should consider the comparison as if it has evaluated in such a
way so as to minimize the resulting changes to its own state. way so as to minimize the resulting changes to its own state.
8. Upward Routes 8. Upward Routes
This section describes how RPL discovers and maintains upward routes. This section describes how RPL discovers and maintains Upward routes.
It describes the use of DODAG Information Objects (DIOs), the It describes the use of DODAG Information Objects (DIOs), the
messages used to discover and maintain these routes. It specifies messages used to discover and maintain these routes. It specifies
how RPL generates and responds to DIOs. It also describes DODAG how RPL generates and responds to DIOs. It also describes DODAG
Information Solicitation (DIS) messages, which are used to trigger Information Solicitation (DIS) messages, which are used to trigger
DIO transmissions. DIO transmissions.
As mentioned in Section 3.2.8, nodes that decide to join a DODAG MUST As mentioned in Section 3.2.8, nodes that decide to join a DODAG MUST
provision at least one DODAG parent as a default route for the provision at least one DODAG parent as a default route for the
associated instance. This default route enables a packet to be associated instance. This default route enables a packet to be
forwarded upwards until it eventually hits a common ancestor from forwarded Upward until it eventually hits a common ancestor from
which it will be routed downwards to the destination. If the which it will be routed Downward to the destination. If the
destination is not in the DODAG, then the DODAG root may be able to destination is not in the DODAG, then the DODAG root may be able to
forward the packet using connectivity to the outside of the DODAG; if forward the packet using connectivity to the outside of the DODAG; if
it can not forward the packet outside then the DODAG root has to drop it cannot forward the packet outside, then the DODAG root has to drop
it. it.
A DIO message can also transport explicit routing information: A DIO message can also transport explicit routing information:
DODAGID The DODAGID is a Global or Unique Local IPv6 Address of the DODAGID: The DODAGID is a Global or Unique Local IPv6 address of the
root. A node that joins a DODAG SHOULD provision a host route root. A node that joins a DODAG SHOULD provision a host route
via a DODAG parent to the address used by the root as DODAGID. via a DODAG parent to the address used by the root as the
DODAGID.
RIO Prefix The root MAY place one or more Route Information options RIO Prefix: The root MAY place one or more Route Information options
in a DIO message. The RIO is used to advertise an external in a DIO message. The RIO is used to advertise an external
route that is reachable via the root, associated with a route that is reachable via the root, associated with a
preference, as presented in Section 6.7.5, which incorporates preference, as presented in Section 6.7.5, which incorporates
the RIO from [RFC4191]. It is interpreted as a capability of the RIO from [RFC4191]. It is interpreted as a capability of
the root as opposed to a routing advertisement and it MUST NOT the root as opposed to a routing advertisement, and it MUST NOT
be redistributed in another routing protocol though it SHOULD be redistributed in another routing protocol though it SHOULD
be used by an ingress RPL router to select a DODAG when a be used by an ingress RPL router to select a DODAG when a
packet is injected in a RPL domain from a node attached to that packet is injected in a RPL domain from a node attached to that
RPL router. An Objective Function MAY use the routes RPL router. An Objective Function MAY use the routes
advertised in RIO or the preference for those routes in order advertised in RIO or the preference for those routes in order
to favor a DODAG versus another one for a same instance. to favor a DODAG versus another one for the same instance.
8.1. DIO Base Rules 8.1. DIO Base Rules
1. For the following DIO Base fields, a node that is not a DODAG 1. For the following DIO Base fields, a node that is not a DODAG
root MUST advertise the same values as its preferred DODAG parent root MUST advertise the same values as its preferred DODAG parent
(defined in Section 8.2.1). In this way these values will (defined in Section 8.2.1). In this way, these values will
propagate Down the DODAG unchanged and advertised by every node propagate Down the DODAG unchanged and advertised by every node
that has a route to that DODAG root. These fields are: that has a route to that DODAG root. These fields are as
follows:
1. Grounded (G) 1. Grounded (G)
2. Mode of Operation (MOP) 2. Mode of Operation (MOP)
3. DAGPreference (Prf) 3. DAGPreference (Prf)
4. Version 4. Version
5. RPLInstanceID 5. RPLInstanceID
6. DODAGID 6. DODAGID
2. A node MAY update the following fields at each hop: 2. A node MAY update the following fields at each hop:
1. Rank 1. Rank
2. DTSN 2. DTSN
3. The DODAGID field each root sets MUST be unique within the RPL 3. The DODAGID field each root sets MUST be unique within the RPL
Instance and MUST be a routable IPv6 address belonging to the Instance and MUST be a routable IPv6 address belonging to the
root. root.
8.2. Upward Route Discovery and Maintenance 8.2. Upward Route Discovery and Maintenance
Upward route discovery allows a node to join a DODAG by discovering Upward route discovery allows a node to join a DODAG by discovering
neighbors that are members of the DODAG of interest and identifying a neighbors that are members of the DODAG of interest and identifying a
set of parents. The exact policies for selecting neighbors and set of parents. The exact policies for selecting neighbors and
parents is implementation-dependent and driven by the OF. This parents is implementation dependent and driven by the OF. This
section specifies the set of rules those policies must follow for section specifies the set of rules those policies must follow for
interoperability. interoperability.
8.2.1. Neighbors and Parents within a DODAG Version 8.2.1. Neighbors and Parents within a DODAG Version
RPL's upward route discovery algorithms and processing are in terms RPL's Upward route discovery algorithms and processing are in terms
of three logical sets of link-local nodes. First, the candidate of three logical sets of link-local nodes. First, the candidate
neighbor set is a subset of the nodes that can be reached via link- neighbor set is a subset of the nodes that can be reached via link-
local multicast. The selection of this set is implementation- local multicast. The selection of this set is implementation and OF
dependent and OF-dependent. Second, the parent set is a restricted dependent. Second, the parent set is a restricted subset of the
subset of the candidate neighbor set. Finally, the preferred parent candidate neighbor set. Finally, the preferred parent is a member of
is a member of the parent set that is the preferred next hop in the parent set that is the preferred next hop in Upward routes.
upward routes. The preferred parent is conceptually a single parent Conceptually, the preferred parent is a single parent; although, it
although it may be a set of multiple parents if those parents are may be a set of multiple parents if those parents are equally
equally preferred and have identical rank. preferred and have identical Rank.
More precisely: More precisely:
1. The DODAG parent set MUST be a subset of the candidate neighbor 1. The DODAG parent set MUST be a subset of the candidate neighbor
set. set.
2. A DODAG root MUST have a DODAG parent set of size zero. 2. A DODAG root MUST have a DODAG parent set of size zero.
3. A node that is not a DODAG root MAY maintain a DODAG parent set 3. A node that is not a DODAG root MAY maintain a DODAG parent set
of size greater than or equal to one. of size greater than or equal to one.
4. A node's preferred DODAG parent MUST be a member of its DODAG 4. A node's preferred DODAG parent MUST be a member of its DODAG
parent set. parent set.
5. A node's rank MUST be greater than all elements of its DODAG 5. A node's Rank MUST be greater than all elements of its DODAG
parent set. parent set.
6. When Neighbor Unreachability Detection (NUD) [RFC4861], or an 6. When Neighbor Unreachability Detection (NUD) [RFC4861], or an
equivalent mechanism, determines that a neighbor is no longer equivalent mechanism, determines that a neighbor is no longer
reachable, a RPL node MUST NOT consider this node in the reachable, a RPL node MUST NOT consider this node in the
candidate neighbor set when calculating and advertising routes candidate neighbor set when calculating and advertising routes
until it determines that it is again reachable. Routes through until it determines that it is again reachable. Routes through
an unreachable neighbor MUST be removed from the routing table. an unreachable neighbor MUST be removed from the routing table.
These rules ensure that there is a consistent partial order on nodes These rules ensure that there is a consistent partial order on nodes
within the DODAG. As long as node ranks do not change, following the within the DODAG. As long as node Ranks do not change, following the
above rules ensures that every node's route to a DODAG root is loop- above rules ensures that every node's route to a DODAG root is loop-
free, as rank decreases on each hop to the root. free, as Rank decreases on each hop to the root.
The OF can guide candidate neighbor set and parent set selection, as The OF can guide candidate neighbor set and parent set selection, as
discussed in [I-D.ietf-roll-of0]. discussed in [RFC6552].
8.2.2. Neighbors and Parents across DODAG Versions 8.2.2. Neighbors and Parents across DODAG Versions
The above rules govern a single DODAG Version. The rules in this The above rules govern a single DODAG Version. The rules in this
section define how RPL operates when there are multiple DODAG section define how RPL operates when there are multiple DODAG
Versions: Versions.
8.2.2.1. DODAG Version 8.2.2.1. DODAG Version
1. The tuple (RPLInstanceID, DODAGID, DODAGVersionNumber) uniquely 1. The tuple (RPLInstanceID, DODAGID, DODAGVersionNumber) uniquely
defines a DODAG Version. Every element of a node's DODAG parent defines a DODAG Version. Every element of a node's DODAG parent
set, as conveyed by the last heard DIO message from each DODAG set, as conveyed by the last heard DIO message from each DODAG
parent, MUST belong to the same DODAG Version. Elements of a parent, MUST belong to the same DODAG Version. Elements of a
node's candidate neighbor set MAY belong to different DODAG node's candidate neighbor set MAY belong to different DODAG
Versions. Versions.
skipping to change at page 70, line 12 skipping to change at page 69, line 27
DODAGVersionNumber are described later in this section and in DODAGVersionNumber are described later in this section and in
Section 18. Section 18.
5. Within a given DODAG, a node that is a not a root MUST NOT 5. Within a given DODAG, a node that is a not a root MUST NOT
advertise a DODAGVersionNumber higher than the highest advertise a DODAGVersionNumber higher than the highest
DODAGVersionNumber it has heard. Higher is defined as the DODAGVersionNumber it has heard. Higher is defined as the
greater-than operator in Section 7. greater-than operator in Section 7.
6. Once a node has advertised a DODAG Version by sending a DIO, it 6. Once a node has advertised a DODAG Version by sending a DIO, it
MUST NOT be a member of a previous DODAG Version of the same MUST NOT be a member of a previous DODAG Version of the same
DODAG (i.e. with the same RPLInstanceID, the same DODAGID, and a DODAG (i.e., with the same RPLInstanceID, the same DODAGID, and a
lower DODAGVersionNumber). Lower is defined as the less-than lower DODAGVersionNumber). Lower is defined as the less-than
operator in Section 7. operator in Section 7.
When the DODAG parent set becomes empty on a node that is not a root, When the DODAG parent set becomes empty on a node that is not a root,
(i.e. the last parent has been removed, causing the node to no longer (i.e., the last parent has been removed, causing the node no longer
be associated with that DODAG), then the DODAG information should not to be associated with that DODAG), then the DODAG information should
be suppressed until after the expiration of an implementation- not be suppressed until after the expiration of an implementation-
specific local timer. During the interval prior to suppression of specific local timer. During the interval prior to suppression of
the 'old' DODAG state, the node will be able to observe if the the "old" DODAG state, the node will be able to observe if the
DODAGVersionNumber has been incremented should any new parents DODAGVersionNumber has been incremented should any new parents
appear. This will help protect against the possibility of loops that appear. This will help protect against the possibility of loops that
may occur if that node were to inadvertently rejoin the old DODAG may occur if that node were to inadvertently rejoin the old DODAG
Version in its own prior sub-DODAG. Version in its own prior sub-DODAG.
As the DODAGVersionNumber is incremented, a new DODAG Version spreads As the DODAGVersionNumber is incremented, a new DODAG Version spreads
outward from the DODAG root. A parent that advertises the new outward from the DODAG root. A parent that advertises the new
DODAGVersionNumber cannot belong to the sub-DODAG of a node DODAGVersionNumber cannot belong to the sub-DODAG of a node
advertising an older DODAGVersionNumber. Therefore a node can safely advertising an older DODAGVersionNumber. Therefore, a node can
add a parent of any Rank with a newer DODAGVersionNumber without safely add a parent of any Rank with a newer DODAGVersionNumber
forming a loop. without forming a loop.
For example, suppose that a node has left a DODAG with For example, suppose that a node has left a DODAG with
DODAGVersionNumber N. Suppose that node had a sub-DODAG, and did DODAGVersionNumber N. Suppose that a node had a sub-DODAG and did
attempt to poison that sub-DODAG by advertising a rank of attempt to poison that sub-DODAG by advertising a Rank of
INFINITE_RANK, but those advertisements may have become lost in the INFINITE_RANK, but those advertisements may have become lost in the
LLN. Then, if the node did observe a candidate neighbor advertising LLN. Then, if the node did observe a candidate neighbor advertising
a position in that original DODAG at DODAGVersionNumber N, that a position in that original DODAG at DODAGVersionNumber N, that
candidate neighbor could possibly have been in the node's former sub- candidate neighbor could possibly have been in the node's former sub-
DODAG and there is a possible case where to add that candidate DODAG, and there is a possible case where adding that candidate
neighbor as a parent could cause a loop. If that candidate neighbor neighbor as a parent could cause a loop. In this case, if that
in this case is observed to advertise a DODAGVersionNumber N+1, then candidate neighbor is observed to advertise a DODAGVersionNumber N+1,
that candidate neighbor is certain to be safe, since it is certain then that candidate neighbor is certain to be safe, since it is
not to be in that original node's sub-DODAG as it has been able to certain not to be in that original node's sub-DODAG, as it has been
increment the DODAGVersionNumber by hearing from the DODAG root while able to increment the DODAGVersionNumber by hearing from the DODAG
that original node was detached. It is for this reason that it is root while that original node was detached. For this reason, it is
useful for the detached node to remember the original DODAG useful for the detached node to remember the original DODAG
information, including the DODAGVersionNumber N. information, including the DODAGVersionNumber N.
Exactly when a DODAG Root increments the DODAGVersionNumber is Exactly when a DODAG root increments the DODAGVersionNumber is
implementation dependent and out of scope for this specification. implementation dependent and out of scope for this specification.
Examples include incrementing the DODAGVersionNumber periodically, Examples include incrementing the DODAGVersionNumber periodically,
upon administrative intervention, or on application-level detection upon administrative intervention, or on application-level detection
of lost connectivity or DODAG inefficiency. of lost connectivity or DODAG inefficiency.
After a node transitions to and advertises a new DODAG Version, the After a node transitions to and advertises a new DODAG Version, the
rules above make it unable to advertise the previous DODAG Version rules above make it unable to advertise the previous DODAG Version
(prior DODAGVersionNumber) once it has committed to advertising the (prior DODAGVersionNumber) once it has committed to advertising the
new DODAG Version. new DODAG Version.
8.2.2.2. DODAG Roots 8.2.2.2. DODAG Roots
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After a node transitions to and advertises a new DODAG Version, the After a node transitions to and advertises a new DODAG Version, the
rules above make it unable to advertise the previous DODAG Version rules above make it unable to advertise the previous DODAG Version
(prior DODAGVersionNumber) once it has committed to advertising the (prior DODAGVersionNumber) once it has committed to advertising the
new DODAG Version. new DODAG Version.
8.2.2.2. DODAG Roots 8.2.2.2. DODAG Roots
1. A DODAG root without possibility to satisfy the application- 1. A DODAG root without possibility to satisfy the application-
defined goal MUST NOT set the Grounded bit. defined goal MUST NOT set the Grounded bit.
2. A DODAG root MUST advertise a rank of ROOT_RANK. 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 3. A node whose DODAG parent set is empty MAY become the DODAG root
of a floating DODAG. It MAY also set its DAGPreference such that of a floating DODAG. It MAY also set its DAGPreference such that
it is less preferred. it is less preferred.
In a deployment that uses non-RPL links to federate a number of LLN In a deployment that uses non-LLN links to federate a number of LLN
roots, it is possible to run RPL over those non-RPL links and use one roots, it is possible to run RPL over those non-RPL links and use one
router as a "backbone root". The backbone root is the virtual root router as a "backbone root". The backbone root is the virtual root
of the DODAG, and exposes a rank of BASE_RANK over the backbone. All of the DODAG and exposes a Rank of BASE_RANK over the backbone. All
the LLN roots that are parented to that backbone root, including the 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 backbone root if it also serves as the LLN root itself, expose a Rank
ROOT_RANK to the LLN. These virtual roots are part of the same DODAG of ROOT_RANK to the LLN. These virtual roots are part of the same
and advertise the same DODAGID. They coordinate DODAGVersionNumbers DODAG and advertise the same DODAGID. They coordinate
and other DODAG parameters with the virtual root over the backbone. DODAGVersionNumbers and other DODAG parameters with the virtual root
The method of coordination is out of scope for this specification (to over the backbone. The method of coordination is out of scope for
be defined in future companion specifications). this specification (to be defined in future companion
specifications).
8.2.2.3. DODAG Selection 8.2.2.3. DODAG Selection
The objective function and the set of advertised routing metrics and The Objective Function and the set of advertised routing metrics and
constraints of a DAG determines how a node selects its neighbor set, constraints of a DAG determine how a node selects its neighbor set,
parent set, and preferred parents. This selection implicitly also parent set, and preferred parents. This selection implicitly also
determines the DODAG within a DAG. Such selection can include determines the DODAG within a DAG. Such selection can include
administrative preference (Prf) as well as metrics or other administrative preference (Prf) as well as metrics or other
considerations. considerations.
If a node has the option to join a more preferred DODAG while still If a node has the option to join a more preferred DODAG while still
meeting other optimization objectives, then the node will generally meeting other optimization objectives, then the node will generally
seek to join the more preferred DODAG as determined by the OF. All seek to join the more preferred DODAG as determined by the OF. All
else being equal, it is left to the implementation to determine which else being equal, it is left to the implementation to determine which
DODAG is most preferred (since, as a reminder, a node must only join DODAG is most preferred (since, as a reminder, a node must only join
one DODAG per RPL Instance). one DODAG per RPL Instance).
8.2.2.4. Rank and Movement within a DODAG Version 8.2.2.4. Rank and Movement within a DODAG Version
1. A node MUST NOT advertise a Rank less than or equal to any member 1. A node MUST NOT advertise a Rank less than or equal to any member
of its parent set within the DODAG Version. of its parent set within the DODAG Version.
2. A node MAY advertise a Rank lower than its prior advertisement 2. A node MAY advertise a Rank lower than its prior advertisement
within the DODAG Version. within the DODAG Version.
3. Let L be the lowest rank within a DODAG Version that a given node 3. Let L be the lowest Rank within a DODAG Version that a given node
has advertised. Within the same DODAG Version, that node MUST has advertised. Within the same DODAG Version, that node MUST
NOT advertise an effective rank higher than L + NOT advertise an effective Rank higher than L +
DAGMaxRankIncrease. INFINITE_RANK is an exception to this rule: DAGMaxRankIncrease. INFINITE_RANK is an exception to this rule:
a node MAY advertise an INFINITE_RANK within a DODAG version a node MAY advertise an INFINITE_RANK within a DODAG Version
without restriction. If a node's Rank were to be higher than without restriction. If a node's Rank were to be higher than
allowed by L + DAGMaxRankIncrease, when it advertises Rank it allowed by L + DAGMaxRankIncrease, when it advertises Rank, it
MUST advertise its Rank as INFINITE_RANK. MUST advertise its Rank as INFINITE_RANK.
4. A node MAY, at any time, choose to join a different DODAG within 4. A node MAY, at any time, choose to join a different DODAG within
a RPL Instance. Such a join has no rank restrictions, unless a RPL Instance. Such a join has no Rank restrictions, unless
that different DODAG is a DODAG Version of which this node has that different DODAG is a DODAG Version of which this node has
previously been a member, in which case the rule of the previous previously been a member; in which case, the rule of the previous
bullet (3) must be observed. Until a node transmits a DIO bullet (3) must be observed. Until a node transmits a DIO
indicating its new DODAG membership, it MUST forward packets indicating its new DODAG membership, it MUST forward packets
along the previous DODAG. along the previous DODAG.
5. A node MAY, at any time after hearing the next DODAGVersionNumber 5. A node MAY, at any time after hearing the next DODAGVersionNumber
advertised from suitable DODAG parents, choose to migrate to the advertised from suitable DODAG parents, choose to migrate to the
next DODAG Version within the DODAG. next DODAG Version within the DODAG.
Conceptually, an implementation is maintaining a DODAG parent set Conceptually, an implementation is maintaining a DODAG parent set
within the DODAG Version. Movement entails changes to the DODAG within the DODAG Version. Movement entails changes to the DODAG
parent set. Moving Up does not present the risk to create a loop but parent set. Moving Up does not present the risk to create a loop but
moving Down might, so that operation is subject to additional moving Down might, so that operation is subject to additional
constraints. constraints.
When a node migrates to the next DODAG Version, the DODAG parent set When a node migrates to the next DODAG Version, the DODAG parent set
needs to be rebuilt for the new Version. An implementation could needs to be rebuilt for the new Version. An implementation could
defer to migrate for some reasonable amount of time, to see if some defer to migrate for some reasonable amount of time, to see if some
other neighbors with potentially better metrics but higher rank other neighbors with potentially better metrics but higher Rank
announce themselves. Similarly, when a node jumps into a new DODAG announce themselves. Similarly, when a node jumps into a new DODAG,
it needs to construct a new DODAG parent set for this new DODAG. it needs to construct a new DODAG parent set for this new DODAG.
If a node needs to move Down a DODAG that it is attached to, If a node needs to move Down a DODAG that it is attached to,
increasing its Rank, then it MAY poison its routes and delay before increasing its Rank, then it MAY poison its routes and delay before
moving as described in Section 8.2.2.5. moving as described in Section 8.2.2.5.
A node is allowed to join any DODAG Version that it has never been a A node is allowed to join any DODAG Version that it has never been a
prior member of without any restrictions, but if the node has been a prior member of without any restrictions, but if the node has been a
prior member of the DODAG Version then it must continue to observe prior member of the DODAG Version, then it must continue to observe
the rule that it may not advertise a rank higher than the rule that it may not advertise a Rank higher than
L+DAGMaxRankIncrease at any point in the life of the DODAG Version. L+DAGMaxRankIncrease at any point in the life of the DODAG Version.
This rule must be observed so as not to create a loophole that would This rule must be observed so as not to create a loophole that would
allow the node to effectively increment its rank all the way to allow the node to effectively increment its Rank all the way to
INFINITE_RANK, which may have impact on other nodes and create a INFINITE_RANK, which may have impact on other nodes and create a
resource-wasting count-to-infinity scenario. resource-wasting count-to-infinity scenario.
8.2.2.5. Poisoning 8.2.2.5. Poisoning
1. A node poisons routes by advertising a Rank of INFINITE_RANK. 1. A node poisons routes by advertising a Rank of INFINITE_RANK.
2. A node MUST NOT have any nodes with a Rank of INFINITE_RANK in 2. A node MUST NOT have any nodes with a Rank of INFINITE_RANK in
its parent set. its parent set.
Although an implementation may advertise INFINITE_RANK for the Although an implementation may advertise INFINITE_RANK for the
purposes of poisoning, doing so is not the same as setting Rank to purposes of poisoning, doing so is not the same as setting Rank to
INFINITE_RANK. For example, a node may continue to send data packets INFINITE_RANK. For example, a node may continue to send data packets
whose RPL Packet Information includes a Rank that is not whose RPL Packet Information includes a Rank that is not
INFINITE_RANK, yet still advertise INFINITE_RANK in its DIOs. INFINITE_RANK, yet still advertise INFINITE_RANK in its DIOs.
When a (former) parent is observed to advertise a Rank of When a (former) parent is observed to advertise a Rank of
INFINITE_RANK, that (former) parent has detached from the DODAG and INFINITE_RANK, that (former) parent has detached from the DODAG and
is no longer able to act as a parent, nor is there any way that is no longer able to act as a parent, nor is there any way that
another node may be considered to have a Rank greater-than another node may be considered to have a Rank greater-than
INFINITE_RANK. Therefore that (former) parent cannot act as a parent INFINITE_RANK. Therefore, that (former) parent cannot act as a
any longer and is removed from the parent set. parent any longer and is removed from the parent set.
8.2.2.6. Detaching 8.2.2.6. Detaching
1. A node unable to stay connected to a DODAG within a given DODAG 1. A node unable to stay connected to a DODAG within a given DODAG
Version, i.e. that cannot retain non-empty parent set without Version, i.e., that cannot retain non-empty parent set without
violating the rules of this specification, MAY detach from this violating the rules of this specification, MAY detach from this
DODAG Version. A node that detaches becomes root of its own DODAG Version. A node that detaches becomes the root of its own
floating DODAG and SHOULD immediately advertise this new floating DODAG and SHOULD immediately advertise this new
situation in a DIO as an alternate to poisoning. situation in a DIO as an alternate to poisoning.
8.2.2.7. Following a Parent 8.2.2.7. Following a Parent
1. If a node receives a DIO from one of its DODAG parents, 1. If a node receives a DIO from one of its DODAG parents,
indicating that the parent has left the DODAG, that node SHOULD indicating that the parent has left the DODAG, that node SHOULD
stay in its current DODAG through an alternative DODAG parent, if stay in its current DODAG through an alternative DODAG parent, if
possible. It MAY follow the leaving parent. possible. It MAY follow the leaving parent.
A DODAG parent may have moved, migrated to the next DODAG Version, or A DODAG parent may have moved, migrated to the next DODAG Version, or
jumped to a different DODAG. A node ought to give some preference to jumped to a different DODAG. A node ought to give some preference to
remaining in the current DODAG, if possible via an alternate parent, remaining in the current DODAG, if possible via an alternate parent,
but ought to follow the parent if there are no other options. but ought to follow the parent if there are no other options.
8.2.3. DIO Message Communication 8.2.3. DIO Message Communication
When an DIO message is received, the receiving node must first When a DIO message is received, the receiving node must first
determine whether or not the DIO message should be accepted for determine whether or not the DIO message should be accepted for
further processing, and subsequently present the DIO message for further processing, and subsequently present the DIO message for
further processing if eligible. further processing if eligible.
1. If the DIO message is malformed, then the DIO message is not 1. If the DIO message is malformed, then the DIO message is not
eligible for further processing and a node MUST silently discard eligible for further processing and a node MUST silently discard
it. (See Section 18 for error logging). it. (See Section 18 for error logging).
2. If the sender of the DIO message is a member of the candidate 2. If the sender of the DIO message is a member of the candidate
neighbor set and the DIO message is not malformed, the node MUST neighbor set and the DIO message is not malformed, the node MUST
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8.2.3.1. DIO Message Processing 8.2.3.1. DIO Message Processing
As DIO messages are received from candidate neighbors, the neighbors As DIO messages are received from candidate neighbors, the neighbors
may be promoted to DODAG parents by following the rules of DODAG may be promoted to DODAG parents by following the rules of DODAG
discovery as described in Section 8.2. When a node places a neighbor discovery as described in Section 8.2. When a node places a neighbor
into the DODAG parent set, the node becomes attached to the DODAG into the DODAG parent set, the node becomes attached to the DODAG
through the new DODAG parent node. through the new DODAG parent node.
The most preferred parent should be used to restrict which other The most preferred parent should be used to restrict which other
nodes may become DODAG parents. Some nodes in the DODAG parent set nodes may become DODAG parents. Some nodes in the DODAG parent set
may be of a rank less than or equal to the most preferred DODAG may be of a Rank less than or equal to the most preferred DODAG
parent. (This case may occur, for example, if an energy constrained parent. (This case may occur, for example, if an energy-constrained
device is at a lesser rank but should be avoided as per an device is at a lesser Rank but should be avoided per an optimization
optimization objective, resulting in a more preferred parent at a objective, resulting in a more preferred parent at a greater Rank.)
greater rank).
8.3. DIO Transmission 8.3. DIO Transmission
RPL nodes transmit DIOs using a Trickle timer RPL nodes transmit DIOs using a Trickle timer [RFC6206]. A DIO from
([I-D.ietf-roll-trickle]). A DIO from a sender with a lesser DAGRank a sender with a lesser DAGRank that causes no changes to the
that causes no changes to the recipient's parent set, preferred recipient's parent set, preferred parent, or Rank SHOULD be
parent, or Rank SHOULD be considered consistent with respect to the considered consistent with respect to the Trickle timer.
Trickle timer.
The following packets and events MUST be considered inconsistencies The following packets and events MUST be considered inconsistencies
with respect to the Trickle timer, and cause the Trickle timer to with respect to the Trickle timer, and cause the Trickle timer to
reset: reset:
o When a node detects an inconsistency when forwarding a packet, as o When a node detects an inconsistency when forwarding a packet, as
detailed in Section 11.2. detailed in Section 11.2.
o When a node receives a multicast DIS message without a Solicited o When a node receives a multicast DIS message without a Solicited
Information option, unless a DIS flag restricts this behavior. Information option, unless a DIS flag restricts this behavior.
o When a node receives a multicast DIS with a Solicited Information o When a node receives a multicast DIS with a Solicited Information
option and the node matches all of the predicates in the Solicited option and the node matches all of the predicates in the Solicited
Information option, unless a DIS flag restricts this behavior. Information option, unless a DIS flag restricts this behavior.
o When a node joins a new DODAG Version (e.g. by updating its o When a node joins a new DODAG Version (e.g., by updating its
DODAGVersionNumber, joining a new RPL Instance, etc.). DODAGVersionNumber, joining a new RPL Instance, etc.).
Note that this list is not exhaustive, and an implementation MAY Note that this list is not exhaustive, and an implementation MAY
consider other messages or events to be inconsistencies. consider other messages or events to be inconsistencies.
A node SHOULD NOT reset its DIO trickle timer in response to unicast A node SHOULD NOT reset its DIO Trickle timer in response to unicast
DIS messages. When a node receives a unicast DIS without a Solicited DIS messages. When a node receives a unicast DIS without a Solicited
Information option, it MUST unicast a DIO to the sender in response. Information option, it MUST unicast a DIO to the sender in response.
This DIO MUST include a DODAG Configuration option. When a node This DIO MUST include a DODAG Configuration option. When a node
receives a unicast DIS message with a Solicited Information option receives a unicast DIS message with a Solicited Information option
and matches the predicates of that Solicited Information option, it and matches the predicates of that Solicited Information option, it
MUST unicast a DIO to the sender in response. This unicast DIO MUST MUST unicast a DIO to the sender in response. This unicast DIO MUST
include a DODAG Configuration Option. Thus a node MAY transmit a include a DODAG Configuration option. Thus, a node MAY transmit a
unicast DIS message to a potential DODAG parent in order to probe for unicast DIS message to a potential DODAG parent in order to probe for
DODAG Configuration and other parameters. DODAG Configuration and other parameters.
8.3.1. Trickle Parameters 8.3.1. Trickle Parameters
The configuration parameters of the trickle timer are specified as The configuration parameters of the Trickle timer are specified as
follows: follows:
Imin: learned from the DIO message as (2^DIOIntervalMin)ms. The Imin: learned from the DIO message as (2^DIOIntervalMin) ms. The
default value of DIOIntervalMin is DEFAULT_DIO_INTERVAL_MIN. default value of DIOIntervalMin is DEFAULT_DIO_INTERVAL_MIN.
Imax: learned from the DIO message as DIOIntervalDoublings. The Imax: learned from the DIO message as DIOIntervalDoublings. The
default value of DIOIntervalDoublings is default value of DIOIntervalDoublings is
DEFAULT_DIO_INTERVAL_DOUBLINGS. DEFAULT_DIO_INTERVAL_DOUBLINGS.
k: learned from the DIO message as DIORedundancyConstant. The k: learned from the DIO message as DIORedundancyConstant. The
default value of DIORedundancyConstant is default value of DIORedundancyConstant is
DEFAULT_DIO_REDUNDANCY_CONSTANT. In RPL, when k has the value DEFAULT_DIO_REDUNDANCY_CONSTANT. In RPL, when k has the value
of 0x00 this is to be treated as a redundancy constant of of 0x00, this is to be treated as a redundancy constant of
infinity in RPL, i.e. Trickle never suppresses messages. infinity in RPL, i.e., Trickle never suppresses messages.
8.4. DODAG Selection 8.4. DODAG Selection
The DODAG selection is implementation and OF dependent. In order to The DODAG selection is implementation and OF dependent. In order to
limit erratic movements, and all metrics being equal, nodes SHOULD limit erratic movements, and all metrics being equal, nodes SHOULD
keep their previous selection. Also, nodes SHOULD provide a means to keep their previous selection. Also, nodes SHOULD provide a means to
filter out a parent whose availability is detected as fluctuating, at filter out a parent whose availability is detected as fluctuating, at
least when more stable choices are available. least when more stable choices are available.
When connection to a grounded DODAG is not possible or preferable for When connection to a grounded DODAG is not possible or preferable for
security or other reasons, scattered DODAGs MAY aggregate as much as security or other reasons, scattered DODAGs MAY aggregate as much as
possible into larger DODAGs in order to allow connectivity within the possible into larger DODAGs in order to allow connectivity within the
LLN. LLN.
A node SHOULD verify that bidirectional connectivity and adequate A node SHOULD verify that bidirectional connectivity and adequate
link quality is available with a candidate neighbor before it link quality is available with a candidate neighbor before it
considers that candidate as a DODAG parent. considers that candidate as a DODAG parent.
8.5. Operation as a Leaf Node 8.5. Operation as a Leaf Node
In some cases a RPL node may attach to a DODAG as a leaf node only. In some cases, a RPL node may attach to a DODAG as a leaf node only.
One example of such a case is when a node does not understand or does One example of such a case is when a node does not understand or does
not support (policy) the RPL Instance's OF or advertised metric/ not support (policy) the RPL Instance's OF or advertised metric/
constraint. As specified in Section 18.6 related to policy function, constraint. As specified in Section 18.6, related to policy
the node may either join the DODAG as a leaf node or may not join the function, the node may either join the DODAG as a leaf node or may
DODAG. As mentioned in Section 18.5, it is then recommended to log a not join the DODAG. As mentioned in Section 18.5, it is then
fault. recommended to log a fault.
A leaf node does not extend DODAG connectivity but in some cases the A leaf node does not extend DODAG connectivity; however, in some
leaf node may still need to transmit DIOs on occasion, in particular cases, the leaf node may still need to transmit DIOs on occasion, in
when the leaf node may not have always been acting as a leaf node and particular, when the leaf node may not have always been acting as a
an inconsistency is detected. leaf node and an inconsistency is detected.
A node operating as a leaf node must obey the following rules: A node operating as a leaf node must obey the following rules:
1. It MUST NOT transmit DIOs containing the DAG Metric Container. 1. It MUST NOT transmit DIOs containing the DAG Metric Container.
2. Its DIOs MUST advertise a DAGRank of INFINITE_RANK. 2. Its DIOs MUST advertise a DAGRank of INFINITE_RANK.
3. It MAY suppress DIO transmission, unless the DIO transmission has 3. It MAY suppress DIO transmission, unless the DIO transmission has
been triggered due to detection of inconsistency when a packet is been triggered due to detection of inconsistency when a packet is
being forwarded or in response to a unicast DIS message, in which being forwarded or in response to a unicast DIS message, in which
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5. It MAY transmit multicast DAOs to the '1 hop' neighborhood as 5. It MAY transmit multicast DAOs to the '1 hop' neighborhood as
described in Section 9.10. described in Section 9.10.
A particular case that requires a leaf node to send a DIO is if that A particular case that requires a leaf node to send a DIO is if that
leaf node was a prior member of another DODAG and another node leaf node was a prior member of another DODAG and another node
forwards a message assuming the old topology, triggering an forwards a message assuming the old topology, triggering an
inconsistency. The leaf node needs to transmit a DIO in order to inconsistency. The leaf node needs to transmit a DIO in order to
repair the inconsistency. Note that due to the lossy nature of LLNs, repair the inconsistency. Note that due to the lossy nature of LLNs,
even though the leaf node may have optimistically poisoned its routes even though the leaf node may have optimistically poisoned its routes
by advertising a rank of INFINITE_RANK in the old DODAG prior to by advertising a Rank of INFINITE_RANK in the old DODAG prior to
becoming a leaf node, that advertisement may have become lost and a becoming a leaf node, that advertisement may have become lost and a
leaf node must be capable to send a DIO later in order to repair the leaf node must be capable to send a DIO later in order to repair the
inconsistency. inconsistency.
In the general case, the leaf node MUST NOT advertise itself as a In the general case, the leaf node MUST NOT advertise itself as a
router (i.e. send DIOs). router (i.e., send DIOs).
8.6. Administrative Rank 8.6. Administrative Rank
In some cases it might be beneficial to adjust the rank advertised by In some cases, it might be beneficial to adjust the Rank advertised
a node beyond that computed by the OF based on some implementation by a node beyond that computed by the OF based on some
specific policy and properties of the node. For example, a node that implementation-specific policy and properties of the node. For
has limited battery should be a leaf unless there is no other choice, example, a node that has a limited battery should be a leaf unless
and may then augment the rank computation specified by the OF in there is no other choice, and may then augment the Rank computation
order to expose an exaggerated rank. specified by the OF in order to expose an exaggerated Rank.
9. Downward Routes 9. Downward Routes
This section describes how RPL discovers and maintains downward This section describes how RPL discovers and maintains Downward
routes. RPL constructs and maintains downward routes with routes. RPL constructs and maintains Downward routes with
Destination Advertisement Object (DAO) messages. Downward routes Destination Advertisement Object (DAO) messages. Downward routes
support P2MP flows, from the DODAG roots toward the leaves. Downward support P2MP flows, from the DODAG roots toward the leaves. Downward
routes also support P2P flows: P2P messages can flow toward a DODAG routes also support P2P flows: P2P messages can flow toward a DODAG
Root (or a common ancestor) through an upward route, then away from root (or a common ancestor) through an Upward route, then away from
the DODAG Root to a destination through a downward route. the DODAG root to a destination through a Downward route.
This specification describes the two modes a RPL Instance may choose This specification describes the two modes a RPL Instance may choose
from for maintaining downward routes. In the first mode, called from for maintaining Downward routes. In the first mode, called
"storing", nodes store downward routing tables for their sub-DODAG. "Storing", nodes store Downward routing tables for their sub-DODAG.
Each hop on a downward route in a storing network examines its Each hop on a Downward route in a storing network examines its
routing table to decide on the next hop. In the second mode, called routing table to decide on the next hop. In the second mode, called
"non-storing", nodes do not store downward routing tables. Downward "Non-Storing", nodes do not store Downward routing tables. Downward
packets are routed with source routes populated by a DODAG Root packets are routed with source routes populated by a DODAG root
[I-D.ietf-6man-rpl-routing-header]. [RFC6554].
RPL allows a simple one-hop P2P optimization for both storing and RPL allows a simple one-hop P2P optimization for both storing and
non-storing networks. A node may send a P2P packet destined to a non-storing networks. A node may send a P2P packet destined to a
one-hop neighbor directly to that node. one-hop neighbor directly to that node.
9.1. Destination Advertisement Parents 9.1. Destination Advertisement Parents
To establish downward routes, RPL nodes send DAO messages upwards. To establish Downward routes, RPL nodes send DAO messages Upward.
The next hop destinations of these DAO messages are called DAO The next-hop destinations of these DAO messages are called "DAO
parents. The collection of a node's DAO parents is called the DAO parents". The collection of a node's DAO parents is called the "DAO
parent set. parent set".
1. A node MAY send DAO messages using the all-RPL-nodes multicast 1. A node MAY send DAO messages using the all-RPL-nodes multicast
address, which is an optimization to provision one-hop routing. address, which is an optimization to provision one-hop routing.
The 'K' bit MUST be cleared on transmission of the multicast DAO. The 'K' bit MUST be cleared on transmission of the multicast DAO.
2. A node's DAO parent set MUST be a subset of its DODAG parent set. 2. A node's DAO parent set MUST be a subset of its DODAG parent set.
3. In storing mode operation, a node MUST NOT address unicast DAO 3. In Storing mode operation, a node MUST NOT address unicast DAO
messages to nodes that are not DAO parents. messages to nodes that are not DAO parents.
4. In storing mode operation, the IPv6 source and destination 4. In Storing mode operation, the IPv6 source and destination
addresses of a DAO message MUST be link-local addresses. addresses of a DAO message MUST be link-local addresses.
5. In non-storing mode operation, a node MUST NOT address unicast 5. In Non-Storing mode operation, a node MUST NOT address unicast
DAO messages to nodes that are not DODAG roots. DAO messages to nodes that are not DODAG roots.
6. In non-storing mode operation, the IPv6 source and destination 6. In Non-Storing mode operation, the IPv6 source and destination
addresses of a DAO message MUST be a unique-local or a global addresses of a DAO message MUST be a unique-local or a global
addresses. address.
The selection of DAO parents is implementation and objective function The selection of DAO parents is implementation and Objective Function
specific. specific.
9.2. Downward Route Discovery and Maintenance 9.2. Downward Route Discovery and Maintenance
Destination Advertisement may be configured to be entirely disabled, Destination Advertisement may be configured to be entirely disabled,
or operate in either a storing or non-storing mode, as reported in or operate in either a Storing or Non-Storing mode, as reported in
the MOP in the DIO message. the MOP in the DIO message.
1. All nodes who join a DODAG MUST abide by the MOP setting from the 1. All nodes who join a DODAG MUST abide by the MOP setting from the
root. Nodes that do not have the capability to fully participate root. Nodes that do not have the capability to fully participate
as a router, e.g. that does not match the advertised MOP, MAY as a router, e.g., that do not match the advertised MOP, MAY join
join the DODAG as a leaf. the DODAG as a leaf.
2. If the MOP is 0, indicating no downward routing, nodes MUST NOT 2. If the MOP is 0, indicating no Downward routing, nodes MUST NOT
transmit DAO messages, and MAY ignore DAO messages. transmit DAO messages and MAY ignore DAO messages.
3. In non-storing mode, the DODAG Root SHOULD store source routing 3. In Non-Storing mode, the DODAG root SHOULD store source routing
table entries for destinations learned from DAOs. The DODAG Root table entries for destinations learned from DAOs. The DODAG root
MUST be able to generate source routes for those destinations MUST be able to generate source routes for those destinations
learned from DAOs which were stored. learned from DAOs that were stored.
4. In storing mode, all non-root, non-leaf nodes MUST store routing 4. In Storing mode, all non-root, non-leaf nodes MUST store routing
table entries for destinations learned from DAOs. table entries for destinations learned from DAOs.
A DODAG can have one of several possible modes of operation, as A DODAG can have one of several possible modes of operation, as
defined by the MOP field. Either it does not support downward defined by the MOP field. Either it does not support Downward
routes, it supports downward routes through source routing from DODAG routes, it supports Downward routes through source routing from DODAG
Roots, or it supports downward routes through in-network routing roots, or it supports Downward routes through in-network routing
tables. tables.
When downward routes are supported through source routing from DODAG When Downward routes are supported through source routing from DODAG
Roots, it is generally expected that the DODAG Root has stored the roots, it is generally expected that the DODAG root has stored the
source routing information learned from DAOs in order to construct source routing information learned from DAOs in order to construct
the source routes. If the DODAG Root fails to store some the source routes. If the DODAG root fails to store some
information, then some destinations may be unreachable. information, then some destinations may be unreachable.
When downward routes are supported through in-network routing tables, When Downward routes are supported through in-network routing tables,
the multicast operation defined in this specification may or may not the multicast operation defined in this specification may or may not
be supported, also as indicated by the MOP field. be supported, also as indicated by the MOP field.
When downward routes are supported through in-network routing tables When Downward routes are supported through in-network routing tables,
as described in this specification, it is expected that nodes acting as described in this specification, it is expected that nodes acting
as routers have been provisioned sufficiently to hold the required as routers have been provisioned sufficiently to hold the required
routing table state. If a node acting as a router is unable to hold routing table state. If a node acting as a router is unable to hold
the full routing table state then the routing state is not complete, the full routing table state then the routing state is not complete,
messages may be dropped as a consequence, and a fault may be logged messages may be dropped as a consequence, and a fault may be logged
(Section 18.5). Future extensions to RPL may elaborate on refined (Section 18.5). Future extensions to RPL may elaborate on refined
actions/behaviors to manage this case. actions/behaviors to manage this case.
As of this specification RPL does not support mixed-mode operation, As of the writing of this specification, RPL does not support mixed-
where some nodes source route and other store routing tables: future mode operation, where some nodes source route and other store routing
extensions to RPL may support this mode of operation. tables: future extensions to RPL may support this mode of operation.
9.2.1. Maintenance of Path Sequence 9.2.1. Maintenance of Path Sequence
For each Target that is associated with (owned by) a node, that node For each Target that is associated with (owned by) a node, that node
is responsible to emit DAO messages in order to provision the is responsible to emit DAO messages in order to provision the
downward routes. The Target+Transit information contained in those Downward routes. The Target+Transit information contained in those
DAO messages subsequently propagates Up the DODAG. The Path Sequence DAO messages subsequently propagates Up the DODAG. The Path Sequence
counter in the Transit information option is used to indicate counter in the Transit information option is used to indicate
freshness and update stale downward routing information as described freshness and update stale Downward routing information as described
in Section 7. in Section 7.
For a Target that is associated with (owned by) a node, that node For a Target that is associated with (owned by) a node, that node
MUST increment the Path Sequence counter, and generate a new DAO MUST increment the Path Sequence counter, and generate a new DAO
message, when: message, when:
1. The Path Lifetime is to be updated (e.g. a refresh or a no-Path) 1. the Path Lifetime is to be updated (e.g., a refresh or a no-
Path).
2. The Parent Address list is to be changed 2. the DODAG Parent Address subfield list is to be changed.
For a Target that is associated with (owned by) a node, that node MAY For a Target that is associated with (owned by) a node, that node MAY
increment the Path Sequence counter, and generate a new DAO message, increment the Path Sequence counter, and generate a new DAO message,
on occasion in order to refresh the downward routing information. In on occasion in order to refresh the Downward routing information. In
storing mode, the node generates such DAO to each of its DAO parents Storing mode, the node generates such a DAO to each of its DAO
in order to enable multipath. All DAOs generated at the same time parents in order to enable multipath. All DAOs generated at the same
for a same target MUST be sent with the same path sequence in the time for the same Target MUST be sent with the same Path Sequence in
transit information. the Transit Information.
9.2.2. Generation of DAO Messages 9.2.2. Generation of DAO Messages
A node might send DAO messages when it receives DAO messages, as a A node might send DAO messages when it receives DAO messages, as a
result of changes in its DAO parent set, or in response to another result of changes in its DAO parent set, or in response to another
event such as the expiry of a related prefix lifetime. In the case event such as the expiry of a related prefix lifetime. In the case
of receiving DAOs, it matters whether the DAO message is "new," or of receiving DAOs, it matters whether the DAO message is "new" or
contains new information. In non-storing mode, every DAO message a contains new information. In Non-Storing mode, every DAO message a
node receives is "new." In storing mode, a DAO message is "new" if node receives is "new". In Storing mode, a DAO message is "new" if
it satisfies any of these criteria for a contained Target: it satisfies any of these criteria for a contained Target:
1. it has a newer Path Sequence number, 1. it has a newer Path Sequence number,
2. it has additional Path Control bits, or 2. it has additional Path Control bits, or
3. it is a No-Path DAO message that removes the last Downward route
3. is a No-Path DAO message that removes the last downward route to to a prefix.
a prefix.
A node that receives a DAO message from its sub-DODAG MAY suppress A node that receives a DAO message from its sub-DODAG MAY suppress
scheduling a DAO message transmission if that DAO message is not new. scheduling a DAO message transmission if that DAO message is not new.
9.3. DAO Base Rules 9.3. DAO Base Rules
1. If a node sends a DAO message with newer or different information 1. If a node sends a DAO message with newer or different information
than the prior DAO message transmission, it MUST increment the than the prior DAO message transmission, it MUST increment the
DAOSequence field by at least one. A DAO message transmission DAOSequence field by at least one. A DAO message transmission
that is identical to the prior DAO message transmission MAY that is identical to the prior DAO message transmission MAY
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5. A node that sets the 'K' flag in a unicast DAO message but does 5. A node that sets the 'K' flag in a unicast DAO message but does
not receive a DAO-ACK in response MAY reschedule the DAO message not receive a DAO-ACK in response MAY reschedule the DAO message
transmission for another attempt, up until an implementation- transmission for another attempt, up until an implementation-
specific number of retries. specific number of retries.
6. Nodes SHOULD ignore DAOs without newer sequence numbers and MUST 6. Nodes SHOULD ignore DAOs without newer sequence numbers and MUST
NOT process them further. NOT process them further.
Unlike the Version field of a DIO, which is incremented only by a Unlike the Version field of a DIO, which is incremented only by a
DODAG Root and repeated unchanged by other nodes, DAOSequence values DODAG root and repeated unchanged by other nodes, DAOSequence values
are unique to each node. The sequence number space for unicast and are unique to each node. The sequence number space for unicast and
multicast DAO messages can be either the same or distinct. It is multicast DAO messages can be either the same or distinct. It is
RECOMMENDED to use the same sequence number space. RECOMMENDED to use the same sequence number space.
9.4. Structure of DAO Messages 9.4. Structure of DAO Messages
DAOs follow a common structure in both storing and non-storing DAOs follow a common structure in both storing and non-storing
networks. In the most general form, a DAO message may include networks. In the most general form, a DAO message may include
several groups of options, where each group consists of one or more several groups of options, where each group consists of one or more
Target options followed by one or more Transit Information options. Target options followed by one or more Transit Information options.
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are unique to each node. The sequence number space for unicast and are unique to each node. The sequence number space for unicast and
multicast DAO messages can be either the same or distinct. It is multicast DAO messages can be either the same or distinct. It is
RECOMMENDED to use the same sequence number space. RECOMMENDED to use the same sequence number space.
9.4. Structure of DAO Messages 9.4. Structure of DAO Messages
DAOs follow a common structure in both storing and non-storing DAOs follow a common structure in both storing and non-storing
networks. In the most general form, a DAO message may include networks. In the most general form, a DAO message may include
several groups of options, where each group consists of one or more several groups of options, where each group consists of one or more
Target options followed by one or more Transit Information options. Target options followed by one or more Transit Information options.
The entire group of Transit Information options applies to the entire The entire group of Transit Information options applies to the entire
group of Target options. Later sections describe further details for group of Target options. Later sections describe further details for
each mode of operation. each mode of operation.
1. RPL nodes MUST include one or more RPL Target Options in each DAO 1. RPL nodes MUST include one or more RPL Target options in each DAO
message they transmit. One RPL Target Option MUST have a prefix message they transmit. One RPL Target option MUST have a prefix
that includes the node's IPv6 address if that node needs the that includes the node's IPv6 address if that node needs the
DODAG to provision downward routes to that node. The RPL Target DODAG to provision Downward routes to that node. The RPL Target
Option MAY be immediately followed by an opaque RPL Target option MAY be immediately followed by an opaque RPL Target
Descriptor Option that qualifies it. Descriptor option that qualifies it.
2. When a node updates the information in a Transit Information 2. When a node updates the information in a Transit Information
option for a Target option that covers one of its addresses, it option for a Target option that covers one of its addresses, it
MUST increment the Path Sequence number in that Transit MUST increment the Path Sequence number in that Transit
Information option. The Path Sequence number MAY be incremented Information option. The Path Sequence number MAY be incremented
occasionally to cause a refresh to the downward routes. occasionally to cause a refresh to the Downward routes.
3. One or more RPL Target Option in a unicast DAO message MUST be 3. One or more RPL Target options in a unicast DAO message MUST be
followed by one or more Transit Information Option. All the followed by one or more Transit Information options. All the
transit options apply to all the target options that immediately transit options apply to all the Target options that immediately
precede them. precede them.
4. Multicast DAOs MUST NOT include the Parent Address in Transit 4. Multicast DAOs MUST NOT include the DODAG Parent Address subfield
Information options. in Transit Information options.
5. A node that receives and processes a DAO message containing 5. A node that receives and processes a DAO message containing
information for a specific Target, and that has prior information information for a specific Target, and that has prior information
for that Target, MUST use the Path Sequence number in the Transit for that Target, MUST use the Path Sequence number in the Transit
Information option associated with that Target in order to Information option associated with that Target in order to
determine whether or not the DAO message contains updated determine whether or not the DAO message contains updated
information as per Section 7. information per Section 7.
6. If a node receives a DAO message that does not follow the above 6. If a node receives a DAO message that does not follow the above
rules, it MUST discard the DAO message without further rules, it MUST discard the DAO message without further
processing. processing.
In non-storing mode, the root builds a strict source routing header, In Non-Storing mode, the root builds a strict source routing header,
hop-by-hop, by recursively looking up one-hop information that ties a hop-by-hop, by recursively looking up one-hop information that ties a
target (address or prefix) and a transit address together. In some Target (address or prefix) and a transit address together. In some
cases, when a child address is derived from a prefix that is owned cases, when a child address is derived from a prefix that is owned
and advertised by a parent, that parent-child relationship may be and advertised by a parent, that parent-child relationship may be
inferred by the root for the purpose of constructing the source inferred by the root for the purpose of constructing the source
routing header. In all other cases it is necessary to inform the routing header. In all other cases, it is necessary to inform the
root of the transit-target relationship from a reachable target, so root of the transit-Target relationship from a reachable target, so
as to later enable the recursive construction of the routing header. as to later enable the recursive construction of the routing header.
An address that is advertised as target in a DAO message MUST be An address that is advertised as a Target in a DAO message MUST be
collocated in the same router, or reachable onlink by the router that collocated in the same router, or reachable on-link by the router
owns the address that is indicated in the associated transit that owns the address that is indicated in the associated Transit
information. The following additional rules apply to ensure the Information. The following additional rules apply to ensure the
continuity of the end-to-end source route path: continuity of the end-to-end source route path:
1. The address of a parent used in the transit option MUST be taken 1. The address of a parent used in the transit option MUST be taken
from a PIO from that parent with the 'R' flag set. The 'R' flag from a PIO from that parent with the 'R' flag set. The 'R' flag
in a PIO indicates that the prefix field actually contains the in a PIO indicates that the prefix field actually contains the
full parent address but the child SHOULD NOT assume that the full parent address but the child SHOULD NOT assume that the
parent address is onlink. parent address is on-link.
2. A PIO with a 'A' flag set indicates that the RPL child node may 2. A PIO with an 'A' flag set indicates that the RPL child node may
use the prefix to autoconfigure an address. A parent that use the prefix to autoconfigure an address. A parent that
advertises a prefix in a PIO with the 'A' flag set MUST ensure advertises a prefix in a PIO with the 'A' flag set MUST ensure
that the address or the whole prefix in the PIO is reachable from that the address or the whole prefix in the PIO is reachable from
the root by advertising it as a DAO target. If the parent also the root by advertising it as a DAO target. If the parent also
sets the 'L' flag indicating that the prefix is onlink, then it sets the 'L' flag indicating that the prefix is on-link, then it
MUST advertise the whole prefix as target in a DAO message. If MUST advertise the whole prefix as Target in a DAO message. If
the 'L' flag is cleared, indicating a subnet operation, and the the 'L' flag is cleared and the 'R' flag is set, indicating that
'R' flag is set, indicating that the parent provides its own the parent provides its own address in the PIO, then the parent
address in the PIO, then the parent MUST advertise that address MUST advertise that address as a DAO target.
as a DAO target.
3. An address that is advertised as target in a DAO message MUST be 3. An address that is advertised as Target in a DAO message MUST be
collocated in the same router or reachable onlink by the router collocated in the same router or reachable on-link by the router
that owns the address that is indicated in the associated transit that owns the address that is indicated in the associated Transit
information. Information.
4. In order to enable an optimum compression of the routing header, 4. In order to enable an optimum compression of the routing header,
the parent SHOULD set the 'R' flag in all PIOs with the 'A' flag the parent SHOULD set the 'R' flag in all PIOs with the 'A' flag
set and the 'L' flag cleared, and the child SHOULD prefer to use set and the 'L' flag cleared, and the child SHOULD prefer to use
as transit the address of the parent that is found in the PIO as transit the address of the parent that is found in the PIO
that is used to autoconfigure the address that is advertised as that is used to autoconfigure the address that is advertised as
target in the DAO message. Target in the DAO message.
5. A router might have targets that are not known to be on-link for 5. A router might have targets that are not known to be on-link for
a parent, either because they are addresses located on an a parent, either because they are addresses located on an
alternate interface or because they belong to nodes that are alternate interface or because they belong to nodes that are
external to RPL, for instance connected hosts. In order to external to RPL, for instance connected hosts. In order to
inject such a target in the RPL network, the router MUST inject such a Target in the RPL network, the router MUST
advertise itself as the Parent Address in the Transit Information advertise itself as the DODAG Parent Address subfield in the
option for that target, using an address that is on-link for that Transit Information option for that target, using an address that
nodes DAO parent. If the target belongs to an external node then is on-link for that nodes DAO parent. If the Target belongs to
the router MUST set the External 'E' flag in the transit an external node, then the router MUST set the External 'E' flag
information. in the Transit Information.
A child node that has autoconfigured an address from a parent PIO A child node that has autoconfigured an address from a parent PIO
with the 'L' flag set does not need to advertise that address as a with the 'L' flag set does not need to advertise that address as a
DAO target since the parent insures that the whole prefix is already DAO Target since the parent ensures that the whole prefix is already
reachable from the root. But if the 'L' flag is not set then it is reachable from the root. However, if the 'L' flag is not set, then
necessary in non-storing mode for the child node to inform the root it is necessary, in Non-Storing mode, for the child node to inform
of the parent-child relationship, using a reachable address of the the root of the parent-child relationship, using a reachable address
parent, so as to enable the recursive construction of the routing of the parent, so as to enable the recursive construction of the
header. This is done by associating an address of the parent as routing header. This is done by associating an address of the parent
transit with the address of the child as target in a DAO message. as transit with the address of the child as Target in a DAO message.
9.5. DAO Transmission Scheduling 9.5. DAO Transmission Scheduling
Because DAOs flow upwards, receiving a unicast DAO can trigger Because DAOs flow Upward, receiving a unicast DAO can trigger sending
sending a unicast DAO to a DAO parent. a unicast DAO to a DAO parent.
1. On receiving a unicast DAO message with updated information, such 1. On receiving a unicast DAO message with updated information, such
as containing a Transit Information option with a new Path as containing a Transit Information option with a new Path
Sequence, a node SHOULD send a DAO. It SHOULD NOT send this DAO Sequence, a node SHOULD send a DAO. It SHOULD NOT send this DAO
message immediately. It SHOULD delay sending the DAO message in message immediately. It SHOULD delay sending the DAO message in
order to aggregate DAO information from other nodes for which it order to aggregate DAO information from other nodes for which it
is a DAO parent. is a DAO parent.
2. A node SHOULD delay sending a DAO message with a timer 2. A node SHOULD delay sending a DAO message with a timer
(DelayDAO). Receiving a DAO message starts the DelayDAO timer. (DelayDAO). Receiving a DAO message starts the DelayDAO timer.
DAO messages received while the DelayDAO timer is active do not DAO messages received while the DelayDAO timer is active do not
reset the timer. When the DelayDAO timer expires, the node sends reset the timer. When the DelayDAO timer expires, the node sends
a DAO. a DAO.
3. When a node adds a node to its DAO parent set, it SHOULD schedule 3. When a node adds a node to its DAO parent set, it SHOULD schedule
a DAO message transmission. a DAO message transmission.
DelayDAO's value and calculation is implementation-dependent. A DelayDAO's value and calculation is implementation dependent. A
default value of DEFAULT_DAO_DELAY is defined in this specification. default value of DEFAULT_DAO_DELAY is defined in this specification.
9.6. Triggering DAO Messages 9.6. Triggering DAO Messages
Nodes can trigger their sub-DODAG to send DAO messages. Each node Nodes can trigger their sub-DODAG to send DAO messages. Each node
maintains a DAO Trigger Sequence Number (DTSN), which it communicates maintains a DAO Trigger Sequence Number (DTSN), which it communicates
through DIO messages. through DIO messages.
1. If a node hears one of its DAO parents increment its DTSN, the 1. If a node hears one of its DAO parents increment its DTSN, the
node MUST schedule a DAO message transmission using rules in node MUST schedule a DAO message transmission using rules in
Section 9.3 and Section 9.5. Sections 9.3 and 9.5.
2. In non-storing mode, if a node hears one of its DAO parents 2. In Non-Storing mode, if a node hears one of its DAO parents
increment its DTSN, the node MUST increment its own DTSN. increment its DTSN, the node MUST increment its own DTSN.
In a storing mode of operation, as part of routine routing table In a Storing mode of operation, as part of routine routing table
updates and maintenance, a storing node MAY increment DTSN in order updates and maintenance, a storing node MAY increment DTSN in order
to reliably trigger a set of DAO updates from its immediate children. to reliably trigger a set of DAO updates from its immediate children.
In a storing mode of operation it is not necessary to trigger DAO
In a Storing mode of operation, it is not necessary to trigger DAO
updates from the entire sub-DODAG, since that state information will updates from the entire sub-DODAG, since that state information will
propagate hop-by-hop Up the DODAG. propagate hop-by-hop Up the DODAG.
In a non-storing mode of operation, a DTSN increment will also cause In a Non-Storing mode of operation, a DTSN increment will also cause
the immediate children of a node to increment their DTSN in turn, the immediate children of a node to increment their DTSN in turn,
triggering a set of DAO updates from the entire sub-DODAG. In a non- triggering a set of DAO updates from the entire sub-DODAG.
storing mode of operation typically only the root would independently Typically, in a Non-Storing mode of operation, only the root would
increment the DTSN when a DAO refresh is needed but a global repair independently increment the DTSN when a DAO refresh is needed but a
(such as by incrementing DODAGVersionNumber) is not desired. In a global repair (such as by incrementing DODAGVersionNumber) is not
non-storing mode of operation typically all non-root nodes would desired. Typically, in a Non-Storing mode of operation, all non-root
increment their DTSN only when their parent(s) are observed to do so. nodes would increment their DTSN only when their parent(s) are
observed to do so.
In the general, a node may trigger DAO updates according to In general, a node may trigger DAO updates according to
implementation specific logic, such as based on the detection of a implementation-specific logic, such as based on the detection of a
downward route inconsistency or occasionally based upon an internal Downward route inconsistency or occasionally based upon an internal
timer. timer.
In the case of triggered DAOs, selecting a proper DAODelay can In a storing network, selecting a proper DelayDAO for triggered DAOs
greatly reduce the number of DAOs transmitted. The trigger flows can greatly reduce the number of DAOs transmitted. The trigger flows
Down the DODAG; in the best case the DAOs flow Up the DODAG such that Down the DODAG; in the best case, the DAOs flow Up the DODAG such
leaves send DAOs first, with each node sending a DAO message only that leaves send DAOs first, with each node sending a DAO message
once. Such a scheduling could be approximated by setting DAODelay only once. Such a scheduling could be approximated by setting
inversely proportional to Rank. Note that this suggestion is DelayDAO inversely proportional to Rank. Note that this suggestion
intended as an optimization to allow efficient aggregation (it is not is intended as an optimization to allow efficient aggregation (it is
required for correct operation in the general case). not required for correct operation in the general case).
9.7. Non-storing Mode 9.7. Non-Storing Mode
In non-storing mode, RPL routes messages downward using IP source In Non-Storing mode, RPL routes messages Downward using IP source
routing. The following rule applies to nodes that are in non-storing routing. The following rule applies to nodes that are in Non-Storing
mode. Storing mode has a separate set of rules, described in mode. Storing mode has a separate set of rules, described in
Section 9.8. Section 9.8.
1. The Parent Address field of a Transit Information Option MUST 1. The DODAG Parent Address subfield of a Transit Information option
contain one or more addresses. All of these addresses MUST be MUST contain one or more addresses. All of these addresses MUST
addresses of DAO parents of the sender. be addresses of DAO parents of the sender.
2. DAOs are sent directly to the root along a default route 2. DAOs are sent directly to the root along a default route
installed as part of the parent selection. installed as part of the parent selection.
3. When a node removes a node from its DAO parent set, it MAY 3. When a node removes a node from its DAO parent set, it MAY
generate a new DAO message with an updated Transit Information generate a new DAO message with an updated Transit Information
option. option.
In non-storing mode, a node uses DAOs to report its DAO parents to In Non-Storing mode, a node uses DAOs to report its DAO parents to
the DODAG Root. The DODAG Root can piece together a downward route the DODAG root. The DODAG root can piece together a Downward route
to a node by using DAO parent sets from each node in the route. The to a node by using DAO parent sets from each node in the route. The
Path Sequence information may be used to detect stale DAO Path Sequence information may be used to detect stale DAO
information. The purpose of this per-hop route calculation is to information. The purpose of this per-hop route calculation is to
minimize traffic when DAO parents change. If nodes reported complete minimize traffic when DAO parents change. If nodes reported complete
source routes, then on a DAO parent change the entire sub-DODAG would source routes, then on a DAO parent change, the entire sub-DODAG
have to send new DAOs to the DODAG Root. Therefore, in non-storing would have to send new DAOs to the DODAG root. Therefore, in Non-
mode, a node can send a single DAO, although it might choose to send Storing mode, a node can send a single DAO, although it might choose
more than one DAO message to each of multiple DAO parents. to send more than one DAO message to each of multiple DAO parents.
Nodes pack DAOs by sending a single DAO message with multiple RPL Nodes pack DAOs by sending a single DAO message with multiple RPL
Target Options. Each RPL Target Option has its own, immediately Target options. Each RPL Target option has its own, immediately
following, Transit Information options. following, Transit Information options.
9.8. Storing Mode 9.8. Storing Mode
In storing mode, RPL routes messages downward by the IPv6 destination In Storing mode, RPL routes messages Downward by the IPv6 destination
address. The following rule apply to nodes that are in storing mode: address. The following rules apply to nodes that are in Storing
mode:
1. The Parent Address field of a Transmit Information option MUST be 1. The DODAG Parent Address subfield of a Transmit Information
empty. option MUST be empty.
2. On receiving a unicast DAO, a node MUST compute if the DAO would 2. On receiving a unicast DAO, a node MUST compute if the DAO would
change the set of prefixes that the node itself advertises. This change the set of prefixes that the node itself advertises. This
computation SHOULD include consultation of the Path Sequence computation SHOULD include consultation of the Path Sequence
information in the Transit Information options associated with information in the Transit Information options associated with
the DAO, to determine if the DAO message contains newer the DAO, to determine if the DAO message contains newer
information that supersedes the information already stored at the information that supersedes the information already stored at the
node. If so, the node MUST generate a new DAO message and node. If so, the node MUST generate a new DAO message and
transmit it, following the rules in Section 9.5. Such a change transmit it, following the rules in Section 9.5. Such a change
includes receiving a No-Path DAO. includes receiving a No-Path DAO.
3. When a node generates a new DAO, it SHOULD unicast it to each of 3. When a node generates a new DAO, it SHOULD unicast it to each of
its DAO parents. It MUST NOT unicast the DAO message to nodes its DAO parents. It MUST NOT unicast the DAO message to nodes
that are not DAO parents. that are not DAO parents.
4. When a node removes a node from its DAO parent set, it SHOULD 4. When a node removes a node from its DAO parent set, it SHOULD
send a No-Path DAO message (Section 6.4.3) to that removed DAO send a No-Path DAO message (Section 6.4.3) to that removed DAO
parent to invalidate the existing route. parent to invalidate the existing route.
5. If messages to an advertised downwards address suffer from a 5. If messages to an advertised Downward address suffer from a
forwarding error, neighbor unreachable detected (NUD), or similar forwarding error, Neighbor Unreachable Detection (NUD), or
failure, a node MAY mark the address as unreachable and generate similar failure, a node MAY mark the address as unreachable and
an appropriate No-Path DAO. generate an appropriate No-Path DAO.
DAOs advertise what destination addresses and prefixes a node has DAOs advertise to which destination addresses and prefixes a node has
routes to. Unlike in non-storing mode, these DAOs do not communicate routes. Unlike in Non-Storing mode, these DAOs do not communicate
information about the routes themselves: that information is stored information about the routes themselves: that information is stored
within the network and is implicit from the IPv6 source address. within the network and is implicit from the IPv6 source address.
When a storing node generates a DAO, it uses the stored state of DAOs When a storing node generates a DAO, it uses the stored state of DAOs
it has received to produce a set of RPL Target options and their it has received to produce a set of RPL Target options and their
associated Transmit Information options. associated Transmit Information options.
Because this information is stored within each node's routing tables, Because this information is stored within each node's routing tables,
in storing mode DAOs are communicated directly to DAO parents, who in Storing mode, DAOs are communicated directly to DAO parents, who
store this information. store this information.
9.9. Path Control 9.9. Path Control
A DAO message from a node contains one or more Target Options. Each A DAO message from a node contains one or more Target options. Each
Target Option specifies either a prefix advertised by the node, a Target option specifies either a prefix advertised by the node, a
prefix of addresses reachable outside the LLN, the address of prefix of addresses reachable outside the LLN, the address of a
destination in the node's sub-DODAG, or a multicast group that a node destination in the node's sub-DODAG, or a multicast group to which a
in the sub-DODAG is listening to. The Path Control field of the node in the sub-DODAG is listening. The Path Control field of the
Transit Information option allows nodes to request or allow for Transit Information option allows nodes to request or allow for
multiple downward routes. A node constructs the Path Control field multiple Downward routes. A node constructs the Path Control field
of a Transit Information option as follows: of a Transit Information option as follows:
1. The bit width of the path control field MUST be equal to the 1. The bit width of the Path Control field MUST be equal to the
value (PCS + 1), where PCS is specified in the control field of value (PCS + 1), where PCS is specified in the control field of
the DODAG Configuration Option. Bits greater than or equal to the DODAG Configuration option. Bits greater than or equal to
the value (PCS + 1) MUST be cleared on transmission and MUST be the value (PCS + 1) MUST be cleared on transmission and MUST be
ignored on reception. Bits below that value are considered ignored on reception. Bits below that value are considered
"active" bits. "active" bits.
2. The node MUST logically construct groupings of its DAO parents 2. The node MUST logically construct groupings of its DAO parents
while populating the Path Control field, where each group while populating the Path Control field, where each group
consists of DAO parents of equal preference. Those groups MUST consists of DAO parents of equal preference. Those groups MUST
then be ordered according to preference, which allows for a then be ordered according to preference, which allows for a
logical mapping of DAO parents onto Path Control subfields (See logical mapping of DAO parents onto Path Control subfields (see
Figure 27). Groups MAY be repeated in order to extend over the Figure 27). Groups MAY be repeated in order to extend over the
entire bit width of the patch control field, but the order, entire bit width of the patch control field, but the order,
including repeated groups, MUST be retained so that preference is including repeated groups, MUST be retained so that preference is
properly communicated. properly communicated.
3. For a RPL Target option describing a node's own address or a 3. For a RPL Target option describing a node's own address or a
prefix outside the LLN, at least one active bit of the Path prefix outside the LLN, at least one active bit of the Path
Control field MUST be set. More active bits of the Path Control Control field MUST be set. More active bits of the Path Control
field MAY be set. field MAY be set.
4. If a node receives multiple DAOs with the same RPL Target option, 4. If a node receives multiple DAOs with the same RPL Target option,
it MUST bitwise-OR the Path Control fields it receives. This it MUST bitwise-OR the Path Control fields it receives. This
aggregated bitwise-OR represents the number of downward routes aggregated bitwise-OR represents the number of Downward routes
the prefix requests. the prefix requests.
5. When a node sends a DAO message to one of its DAO parents, it 5. When a node sends a DAO message to one of its DAO parents, it
MUST select one or more of the bits that are set active in the MUST select one or more of the bits that are set active in the
subfield that is mapped to the group containing that DAO parent subfield that is mapped to the group containing that DAO parent
from the aggregated Path Control field. A given bit can only be from the aggregated Path Control field. A given bit can only be
presented as active to one parent. The DAO message it transmits presented as active to one parent. The DAO message it transmits
to its parent MUST have these active bits set and all other to its parent MUST have these active bits set and all other
active bits cleared. active bits cleared.
6. For the RPL Target option and DAOSequence number, the DAOs a node 6. For the RPL Target option and DAOSequence number, the DAOs a node
sends to different DAO parents MUST have disjoint sets of active sends to different DAO parents MUST have disjoint sets of active
Path Control bits. A node MUST NOT set the same active bit on Path Control bits. A node MUST NOT set the same active bit on
DAOs to two different DAO parents. DAOs to two different DAO parents.
7. Path control bits SHOULD be allocated according to the preference 7. Path Control bits SHOULD be allocated according to the preference
mapping of DAO parents onto Path Control subfields, such that the mapping of DAO parents onto Path Control subfields, such that the
active Path Control bits, or groupings of bits, that belong to a active Path Control bits, or groupings of bits, that belong to a
particular Path Control subfield are allocated to DAO parents particular Path Control subfield are allocated to DAO parents
within the group that was mapped to that subfield. within the group that was mapped to that subfield.
8. In a non-storing mode of operation, a node MAY pass DAOs through 8. In a Non-Storing mode of operation, a node MAY pass DAOs through
without performing any further processing on the Path Control without performing any further processing on the Path Control
field. field.
9. A node MUST NOT unicast a DAO message that has no active bits in 9. A node MUST NOT unicast a DAO message that has no active bits in
the Path Control field set. It is possible that, for a given the Path Control field set. It is possible that, for a given
Target option, that a node does not have enough aggregate Path Target option, a node does not have enough aggregate Path Control
Control bits to send a DAO message containing that Target to each bits to send a DAO message containing that Target to each of its
of its DAO Parents, in which case those least preferred DAO DAO parents, in which case those least preferred DAO Parents may
Parents may not get a DAO message for that Target. not get a DAO message for that Target.
The Path Control field allows a node to bound how many downward The Path Control field allows a node to bound how many Downward
routes will be generated to it. It sets a number of bits in the Path routes will be generated to it. It sets a number of bits in the Path
Control field equal to the maximum number of downward routes it Control field equal to the maximum number of Downward routes it
prefers. Each bit is sent to at most one DAO parent; clusters of prefers. At most, each bit is sent to one DAO parent; clusters of
bits can be sent to a single DAO parent for it to divide among its bits can be sent to a single DAO parent for it to divide among its
own DAO parents. own DAO parents.
A node that provisions a DAO route for a Target that has an A node that provisions a DAO route for a Target that has an
associated Path Control field SHOULD use the content of that Path associated Path Control field SHOULD use the content of that Path
Control field in order to determine an order of preference among Control field in order to determine an order of preference among
multiple alternative DAO routes for that Target. The Path Control multiple alternative DAO routes for that Target. The Path Control
field assignment is derived from preference (of the DAO parents), as field assignment is derived from preference (of the DAO parents), as
determined on the basis of this node's best knowledge of the "end-to- determined on the basis of this node's best knowledge of the "end-to-
end" aggregated metrics in the "downward" direction as per the end" aggregated metrics in the Downward direction as per the
objective function. In non storing mode the root can determine the Objective Function. In Non-Storing mode the root can determine the
downward route by aggregating the information from each received DAO, Downward route by aggregating the information from each received DAO,
which includes the Path Control indications of preferred DAO parents. which includes the Path Control indications of preferred DAO parents.
9.9.1. Path Control Example 9.9.1. Path Control Example
Suppose that there is an LLN operating in storing mode that contains Suppose that there is an LLN operating in Storing mode that contains
a Node N with four parents, P1, P2, P3, and P4. Let N have three a Node N with four parents, P1, P2, P3, and P4. Let N have three
children, C1, C2, and C3 in its sub-DODAG. Let PCS be 7, such that children, C1, C2, and C3 in its sub-DODAG. Let PCS be 7, such that
there will be 8 active bits in the Path Control field: 11111111b. there will be 8 active bits in the Path Control field: 11111111b.
Consider the following example: Consider the following example:
The Path Control field is split into 4 subfields, PC1 (11000000b), The Path Control field is split into four subfields, PC1 (11000000b),
PC2 (00110000b), PC3 (00001100b), and PC4 (00000011b), such that PC2 (00110000b), PC3 (00001100b), and PC4 (00000011b), such that
those 4 subfields represent 4 different levels of preference as per those four subfields represent four different levels of preference
Figure 27. The implementation at Node N, in this example, groups per Figure 27. The implementation at Node N, in this example, groups
{P1, P2} to be of equal preference to each other, and the most {P1, P2} to be of equal preference to each other and the most
preferred group overall. {P3} is less preferred to {P1, P2}, and more preferred group overall. {P3} is less preferred to {P1, P2}, and more
preferred to {P4}. Let Node N then perform its path control mapping preferred to {P4}. Let Node N then perform its Path Control mapping
such that: such that:
{P1, P2} -> PC1 (11000000b) in the Path Control field {P1, P2} -> PC1 (11000000b) in the Path Control field
{P3} -> PC2 (00110000b) in the Path Control field {P3} -> PC2 (00110000b) in the Path Control field
{P4} -> PC3 (00001100b) in the Path Control field {P4} -> PC3 (00001100b) in the Path Control field
{P4} -> PC4 (00000011b) in the Path Control field {P4} -> PC4 (00000011b) in the Path Control field
Note that the implementation repeated {P4} in order to get complete Note that the implementation repeated {P4} in order to get complete
coverage of the Path Control field. coverage of the Path Control field.
skipping to change at page 89, line 34 skipping to change at page 88, line 46
the Path Control field for C1 and Target T. the Path Control field for C1 and Target T.
2. Let C2 send a DAO containing a Target T with a Path Control 2. Let C2 send a DAO containing a Target T with a Path Control
00010000b. Node N stores an entry associating 00010000b with 00010000b. Node N stores an entry associating 00010000b with
the Path Control field for C1 and Target T. the Path Control field for C1 and Target T.
3. Let C3 send a DAO containing a Target T with a Path Control 3. Let C3 send a DAO containing a Target T with a Path Control
00001100b. Node N stores an entry associating 00001100b with 00001100b. Node N stores an entry associating 00001100b with
the Path Control field for C1 and Target T. the Path Control field for C1 and Target T.
4. At some later time, Node N generates a DAO for Target T. Node N 4. At some later time, Node N generates a DAO for Target T. Node N
will construct an aggregate Path Control field by ORing together will construct an aggregate Path Control field by ORing together
the contribution from each of its children that have given a DAO the contribution from each of its children that have given a DAO
for Target T. The aggregate Path Control field thus has the for Target T. Thus, the aggregate Path Control field has the
active bits set as: 10011100b. active bits set as: 10011100b.
5. Node N then distributes the aggregate Path Control bits among 5. Node N then distributes the aggregate Path Control bits among
its parents P1, P2, P3, and P4 in order to prepare the DAO its parents P1, P2, P3, and P4 in order to prepare the DAO
messages. messages.
6. P1 and P2 are eligible to receive active bits from the most 6. P1 and P2 are eligible to receive active bits from the most
preferred subfield (11000000b). Those bits are 10000000b in the preferred subfield (11000000b). Those bits are 10000000b in the
aggregate Path Control field. Node N must the bit to one of the aggregate Path Control field. Node N must set the bit to one of
two parents only. In this case, Node P1 is allocated the bit, the two parents only. In this case, Node P1 is allocated the
and gets the Path Control field 10000000b for its DAO. There bit and gets the Path Control field 10000000b for its DAO.
are no bits left to allocate to Node P2, thus Node P2 would have There are no bits left to allocate to Node P2; thus, Node P2
a Path Control field of 00000000b and a DAO cannot be generated would have a Path Control field of 00000000b and a DAO cannot be
to Node P2 since there are no active bits. generated to Node P2 since there are no active bits.
7. The second-most preferred subfield (00110000b) has the active 7. The second-most preferred subfield (00110000b) has the active
bits 00010000b. Node N has mapped P3 to this subfield. Node N bits 00010000b. Node N has mapped P3 to this subfield. Node N
may allocates the active bit to P3, constructing a DAO for P3 may allocates the active bit to P3, constructing a DAO for P3
containing Target T with a Path Control of 00010000b. containing Target T with a Path Control of 00010000b.
8. The third-most preferred subfield (00001100b) has the active 8. The third-most preferred subfield (00001100b) has the active
bits 00001100b. Node N has mapped P4 to this subfield. Node N bits 00001100b. Node N has mapped P4 to this subfield. Node N
may allocate both bits to P4, constructing a DAO for P4 may allocate both bits to P4, constructing a DAO for P4
containing Target T with a Path Control of 00001100b. containing Target T with a Path Control of 00001100b.
9. The least preferred subfield (00000011b) has no active bits. 9. The least preferred subfield (00000011b) has no active bits.
Had there been active bits, those bits would have been added to Had there been active bits, those bits would have been added to
the Path Control field of the DAO constructed for P4. the Path Control field of the DAO constructed for P4.
10. The process of populating the DAO messages destined for P1, P2, 10. The process of populating the DAO messages destined