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 draft-ietf-roll-rpl-07.txt   draft-ietf-roll-rpl-08.txt 
Networking Working Group T. Winter, Ed. ROLL T. Winter, Ed.
Internet-Draft Internet-Draft
Intended status: Standards Track P. Thubert, Ed. Intended status: Standards Track P. Thubert, Ed.
Expires: September 9, 2010 Cisco Systems Expires: November 29, 2010 Cisco Systems
ROLL Design Team RPL Author Team
IETF ROLL WG IETF ROLL WG
March 8, 2010 May 28, 2010
RPL: IPv6 Routing Protocol for Low power and Lossy Networks RPL: IPv6 Routing Protocol for Low power and Lossy Networks
draft-ietf-roll-rpl-07 draft-ietf-roll-rpl-08
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 (any subset of) processing typically operate with constraints on (any subset of) processing
power, memory and energy (battery), and their interconnects are power, memory and energy (battery), and their interconnects are
characterized by (any subset of) high loss rates, low data rates and characterized by (any subset of) high loss rates, low data rates and
instability. LLNs are comprised of anything from a few dozen and up instability. LLNs are comprised of anything from a few dozen and up
to thousands of LLN routers, and support point-to-point traffic to thousands of routers, and support point-to-point traffic (between
(between devices inside the LLN), point-to-multipoint traffic (from a devices inside the LLN), point-to-multipoint traffic (from a central
central control point to a subset of devices inside the LLN) and control point to a subset of devices inside the LLN) and multipoint-
multipoint-to-point traffic (from devices inside the LLN towards a to-point traffic (from devices inside the LLN towards a central
central control point). This document specifies the IPv6 Routing control point). This document specifies the IPv6 Routing Protocol
Protocol for LLNs (RPL), which provides a mechanism whereby for LLNs (RPL), which provides a mechanism whereby multipoint-to-
multipoint-to-point traffic from devices inside the LLN towards a point traffic from devices inside the LLN towards a central control
central control point, as well as point-to-multipoint traffic from point, as well as point-to-multipoint traffic from the central
the central control point to the devices inside the LLN, is control point to the devices inside the LLN, is supported. Support
supported. Support for point-to-point traffic is also available. for point-to-point traffic is also available.
Status of this Memo Status of this Memo
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Design Principles . . . . . . . . . . . . . . . . . . . . 6 1.1. Design Principles . . . . . . . . . . . . . . . . . . . . 6
1.2. Expectations of Link Layer Type . . . . . . . . . . . . . 7 1.2. Expectations of Link Layer Type . . . . . . . . . . . . . 7
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 9 3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Topology . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.1. Topology . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.1. Topology Identifiers . . . . . . . . . . . . . . . . . 9 3.1.1. Topology Identifiers . . . . . . . . . . . . . . . . . 10
3.1.2. DODAG Information . . . . . . . . . . . . . . . . . . 10 3.2. Instances, DODAGs, and DODAG Versions . . . . . . . . . . 10
3.2. Instances, DODAGs, and DODAG Iterations . . . . . . . . . 11 3.3. Upward Routes and DODAG Construction . . . . . . . . . . . 12
3.3. Traffic Flows . . . . . . . . . . . . . . . . . . . . . . 13 3.3.1. DAG Repair . . . . . . . . . . . . . . . . . . . . . . 12
3.3.1. Multipoint-to-Point Traffic . . . . . . . . . . . . . 13 3.3.2. Grounded and Floating DODAGs . . . . . . . . . . . . . 12
3.3.2. Point-to-Multipoint Traffic . . . . . . . . . . . . . 13 3.3.3. Administrative Preference . . . . . . . . . . . . . . 13
3.3.3. Point-to-Point Traffic . . . . . . . . . . . . . . . . 13 3.3.4. Objective Function (OF) . . . . . . . . . . . . . . . 13
3.4. Upward Routes and DODAG Construction . . . . . . . . . . . 13 3.3.5. Distributed Algorithm Operation . . . . . . . . . . . 13
3.4.1. DODAG Information Object (DIO) . . . . . . . . . . . . 14 3.4. Downward Routes and Destination Advertisement . . . . . . 14
3.4.2. DAG Repair . . . . . . . . . . . . . . . . . . . . . . 14 3.5. Routing Metrics and Constraints Used By RPL . . . . . . . 14
3.4.3. Grounded and Floating DODAGs . . . . . . . . . . . . . 15 3.5.1. Loop Avoidance . . . . . . . . . . . . . . . . . . . . 15
3.4.4. Administrative Preference . . . . . . . . . . . . . . 15 3.5.2. Rank Properties . . . . . . . . . . . . . . . . . . . 16
3.4.5. Objective Function (OF) . . . . . . . . . . . . . . . 15 3.6. Traffic Flows Supported by RPL . . . . . . . . . . . . . . 19
3.4.6. Distributed Algorithm Operation . . . . . . . . . . . 15 3.6.1. Multipoint-to-Point Traffic . . . . . . . . . . . . . 19
3.5. Downward Routes and Destination Advertisement . . . . . . 16 3.6.2. Point-to-Multipoint Traffic . . . . . . . . . . . . . 19
3.5.1. Destination Advertisement Object (DAO) . . . . . . . . 16 3.6.3. Point-to-Point Traffic . . . . . . . . . . . . . . . . 19
3.6. Routing Metrics and Constraints Used By RPL . . . . . . . 17 4. RPL Instance . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.6.1. Loop Avoidance . . . . . . . . . . . . . . . . . . . . 18 4.1. RPL Instance ID . . . . . . . . . . . . . . . . . . . . . 20
3.6.2. Rank Properties . . . . . . . . . . . . . . . . . . . 19 5. ICMPv6 RPL Control Message . . . . . . . . . . . . . . . . . . 21
4. ICMPv6 RPL Control Message . . . . . . . . . . . . . . . . . . 21 5.1. RPL Security Fields . . . . . . . . . . . . . . . . . . . 23
5. Upward Routes . . . . . . . . . . . . . . . . . . . . . . . . 22 5.2. DODAG Information Solicitation (DIS) . . . . . . . . . . . 26
5.1. DODAG Information Object (DIO) . . . . . . . . . . . . . . 22 5.2.1. Format of the DIS Base Object . . . . . . . . . . . . 26
5.1.1. DIO Base Format . . . . . . . . . . . . . . . . . . . 22 5.2.2. Secure DIS . . . . . . . . . . . . . . . . . . . . . . 27
5.1.2. DIO Base Rules . . . . . . . . . . . . . . . . . . . . 24 5.2.3. DIS Options . . . . . . . . . . . . . . . . . . . . . 27
5.1.3. DIO Suboptions . . . . . . . . . . . . . . . . . . . . 25 5.3. DODAG Information Object (DIO) . . . . . . . . . . . . . . 27
5.2. DODAG Information Solicitation (DIS) . . . . . . . . . . . 30 5.3.1. Format of the DIO Base Object . . . . . . . . . . . . 27
5.3. Upward Route Discovery and Maintenance . . . . . . . . . . 30 5.3.2. Secure DIO . . . . . . . . . . . . . . . . . . . . . . 29
5.3.1. RPL Instance . . . . . . . . . . . . . . . . . . . . . 30 5.3.3. DIO Options . . . . . . . . . . . . . . . . . . . . . 29
5.3.2. Neighbors and Parents within a DODAG Iteration . . . . 30 5.4. Destination Advertisement Object (DAO) . . . . . . . . . . 30
5.3.3. Neighbors and Parents across DODAG Iterations . . . . 31 5.4.1. Format of the DAO Base Object . . . . . . . . . . . . 30
5.3.4. DIO Message Communication . . . . . . . . . . . . . . 36 5.4.2. Secure DAO . . . . . . . . . . . . . . . . . . . . . . 31
5.3.5. DIO Transmission . . . . . . . . . . . . . . . . . . . 36 5.4.3. DAO Options . . . . . . . . . . . . . . . . . . . . . 31
5.3.6. DODAG Selection . . . . . . . . . . . . . . . . . . . 39 5.5. Destination Advertisement Object Acknowledgement
5.4. Operation as a Leaf Node . . . . . . . . . . . . . . . . . 39 (DAO-ACK) . . . . . . . . . . . . . . . . . . . . . . . . 31
5.5. Administrative Rank . . . . . . . . . . . . . . . . . . . 40 5.5.1. Format of the DAO-ACK Base Object . . . . . . . . . . 31
5.6. Collision . . . . . . . . . . . . . . . . . . . . . . . . 40 5.5.2. Secure DAO-ACK . . . . . . . . . . . . . . . . . . . . 32
6. Downward Routes . . . . . . . . . . . . . . . . . . . . . . . 40 5.5.3. DAO-ACK Options . . . . . . . . . . . . . . . . . . . 32
6.1. Destination Advertisement Object (DAO) . . . . . . . . . . 41 5.6. RPL Control Message Options . . . . . . . . . . . . . . . 32
6.1.1. DAO Suboptions . . . . . . . . . . . . . . . . . . . . 42 5.6.1. RPL Control Message Option Generic Format . . . . . . 32
6.2. Downward Route Discovery and Maintenance . . . . . . . . . 43 5.6.2. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . . 33
6.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . 43 5.6.3. PadN . . . . . . . . . . . . . . . . . . . . . . . . . 33
6.2.2. Mode of Operation . . . . . . . . . . . . . . . . . . 44 5.6.4. Metric Container . . . . . . . . . . . . . . . . . . . 34
6.2.3. Destination Advertisement Parents . . . . . . . . . . 44 5.6.5. Route Information . . . . . . . . . . . . . . . . . . 35
6.2.4. Operation of DAO Storing Nodes . . . . . . . . . . . . 45 5.6.6. DODAG Configuration . . . . . . . . . . . . . . . . . 36
6.2.5. Operation of DAO Non-storing Nodes . . . . . . . . . . 48 5.6.7. RPL Target . . . . . . . . . . . . . . . . . . . . . . 37
6.2.6. Scheduling to Send DAO (or no-DAO) . . . . . . . . . . 49 5.6.8. Transit Information . . . . . . . . . . . . . . . . . 39
6.2.7. Triggering DAO Message from the Sub-DODAG . . . . . . 49 5.6.9. Solicited Information . . . . . . . . . . . . . . . . 40
6.2.8. Sending DAO Messages to DAO Parents . . . . . . . . . 51 5.6.10. Prefix Information . . . . . . . . . . . . . . . . . . 42
6.2.9. Multicast Destination Advertisement Messages . . . . . 52 6. Upward Routes . . . . . . . . . . . . . . . . . . . . . . . . 44
7. Packet Forwarding and Loop Avoidance/Detection . . . . . . . . 52 6.1. DIO Base Rules . . . . . . . . . . . . . . . . . . . . . . 45
7.1. Suggestions for Packet Forwarding . . . . . . . . . . . . 53 6.2. Upward Route Discovery and Maintenance . . . . . . . . . . 45
7.2. Loop Avoidance and Detection . . . . . . . . . . . . . . . 54 6.2.1. Neighbors and Parents within a DODAG Version . . . . . 45
7.2.1. Source Node Operation . . . . . . . . . . . . . . . . 55 6.2.2. Neighbors and Parents across DODAG Versions . . . . . 46
7.2.2. Router Operation . . . . . . . . . . . . . . . . . . . 55 6.2.3. DIO Message Communication . . . . . . . . . . . . . . 51
8. Multicast Operation . . . . . . . . . . . . . . . . . . . . . 57 6.3. DIO Transmission . . . . . . . . . . . . . . . . . . . . . 52
9. Maintenance of Routing Adjacency . . . . . . . . . . . . . . . 58 6.3.1. Trickle Parameters . . . . . . . . . . . . . . . . . . 52
10. Guidelines for Objective Functions . . . . . . . . . . . . . . 59 6.4. DODAG Selection . . . . . . . . . . . . . . . . . . . . . 53
11. RPL Constants and Variables . . . . . . . . . . . . . . . . . 61 6.5. Operation as a Leaf Node . . . . . . . . . . . . . . . . . 53
12. Manageability Considerations . . . . . . . . . . . . . . . . . 62 6.6. Administrative Rank . . . . . . . . . . . . . . . . . . . 53
12.1. Control of Function and Policy . . . . . . . . . . . . . . 62 7. Downward Routes . . . . . . . . . . . . . . . . . . . . . . . 54
12.1.1. Initialization Mode . . . . . . . . . . . . . . . . . 62 7.1. Downward Route Discovery and Maintenance . . . . . . . . . 54
12.1.2. DIO Base option . . . . . . . . . . . . . . . . . . . 63 7.1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . 54
12.1.3. Trickle Timers . . . . . . . . . . . . . . . . . . . . 63 7.1.2. Mode of Operation . . . . . . . . . . . . . . . . . . 55
12.1.4. DAG Sequence Number Increment . . . . . . . . . . . . 64 7.1.3. Destination Advertisement Parents . . . . . . . . . . 56
12.1.5. Destination Advertisement Timers . . . . . . . . . . . 64 7.1.4. DAO Operation on Storing Nodes . . . . . . . . . . . . 56
12.1.6. Policy Control . . . . . . . . . . . . . . . . . . . . 64 7.1.5. Operation of DAO Non-storing Nodes . . . . . . . . . . 60
12.1.7. Data Structures . . . . . . . . . . . . . . . . . . . 65 7.1.6. Scheduling to Send DAO (or No-Path) . . . . . . . . . 61
12.2. Information and Data Models . . . . . . . . . . . . . . . 65 7.1.7. Triggering DAO Message from the Sub-DODAG . . . . . . 61
12.3. Liveness Detection and Monitoring . . . . . . . . . . . . 65 7.1.8. Sending DAO Messages to DAO Parents . . . . . . . . . 62
12.3.1. Candidate Neighbor Data Structure . . . . . . . . . . 65 7.1.9. Multicast Destination Advertisement Messages . . . . . 63
12.3.2. Directed Acyclic Graph (DAG) Table . . . . . . . . . . 65 8. Packet Forwarding and Loop Avoidance/Detection . . . . . . . . 64
12.3.3. Routing Table . . . . . . . . . . . . . . . . . . . . 66 8.1. Suggestions for Packet Forwarding . . . . . . . . . . . . 64
12.3.4. Other RPL Monitoring Parameters . . . . . . . . . . . 67 8.2. Loop Avoidance and Detection . . . . . . . . . . . . . . . 65
12.3.5. RPL Trickle Timers . . . . . . . . . . . . . . . . . . 67 8.2.1. Source Node Operation . . . . . . . . . . . . . . . . 66
12.4. Verifying Correct Operation . . . . . . . . . . . . . . . 67 8.2.2. Router Operation . . . . . . . . . . . . . . . . . . . 66
12.5. Requirements on Other Protocols and Functional 9. Multicast Operation . . . . . . . . . . . . . . . . . . . . . 68
Components . . . . . . . . . . . . . . . . . . . . . . . . 67 10. Maintenance of Routing Adjacency . . . . . . . . . . . . . . . 69
12.6. Impact on Network Operation . . . . . . . . . . . . . . . 67 11. Guidelines for Objective Functions . . . . . . . . . . . . . . 70
13. Security Considerations . . . . . . . . . . . . . . . . . . . 67 11.1. Objective Function Behavior . . . . . . . . . . . . . . . 70
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 67 12. RPL Constants and Variables . . . . . . . . . . . . . . . . . 72
14.1. RPL Control Message . . . . . . . . . . . . . . . . . . . 68 13. Manageability Considerations . . . . . . . . . . . . . . . . . 73
14.2. New Registry for RPL Control Codes . . . . . . . . . . . . 68 13.1. Control of Function and Policy . . . . . . . . . . . . . . 73
14.3. New Registry for the Control Field of the DIO Base . . . . 68 13.1.1. Initialization Mode . . . . . . . . . . . . . . . . . 73
14.4. DODAG Information Object (DIO) Suboption . . . . . . . . . 69 13.1.2. DIO Base option . . . . . . . . . . . . . . . . . . . 74
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 69 13.1.3. Trickle Timers . . . . . . . . . . . . . . . . . . . . 74
16. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 70 13.1.4. DAG Version Number Increment . . . . . . . . . . . . . 75
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 71 13.1.5. Destination Advertisement Timers . . . . . . . . . . . 75
17.1. Normative References . . . . . . . . . . . . . . . . . . . 71 13.1.6. Policy Control . . . . . . . . . . . . . . . . . . . . 75
17.2. Informative References . . . . . . . . . . . . . . . . . . 72 13.1.7. Data Structures . . . . . . . . . . . . . . . . . . . 75
Appendix A. Requirements . . . . . . . . . . . . . . . . . . . . 74 13.2. Information and Data Models . . . . . . . . . . . . . . . 76
A.1. Protocol Properties Overview . . . . . . . . . . . . . . . 74 13.3. Liveness Detection and Monitoring . . . . . . . . . . . . 76
A.1.1. IPv6 Architecture . . . . . . . . . . . . . . . . . . 74 13.3.1. Candidate Neighbor Data Structure . . . . . . . . . . 76
A.1.2. Typical LLN Traffic Patterns . . . . . . . . . . . . . 74 13.3.2. Directed Acyclic Graph (DAG) Table . . . . . . . . . . 76
A.1.3. Constraint Based Routing . . . . . . . . . . . . . . . 74 13.3.3. Routing Table . . . . . . . . . . . . . . . . . . . . 77
A.2. Deferred Requirements . . . . . . . . . . . . . . . . . . 75 13.3.4. Other RPL Monitoring Parameters . . . . . . . . . . . 77
Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 75 13.3.5. RPL Trickle Timers . . . . . . . . . . . . . . . . . . 78
B.1. DAO Operation When Only the Root Node Stores DAO 13.4. Verifying Correct Operation . . . . . . . . . . . . . . . 78
Information . . . . . . . . . . . . . . . . . . . . . . . 75 13.5. Requirements on Other Protocols and Functional
B.2. DAO Operation When All Nodes Fully Store DAO Components . . . . . . . . . . . . . . . . . . . . . . . . 78
Information . . . . . . . . . . . . . . . . . . . . . . . 77 13.6. Impact on Network Operation . . . . . . . . . . . . . . . 78
B.3. DAO Operation When Nodes Have Mixed Capabilities . . . . . 79 14. Security Considerations . . . . . . . . . . . . . . . . . . . 78
Appendix C. Outstanding Issues . . . . . . . . . . . . . . . . . 81 14.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 78
C.1. Additional Support for P2P Routing . . . . . . . . . . . . 81 14.2. Functional Description of Packet Protection . . . . . . . 80
C.2. Destination Advertisement / DAO Fan-out . . . . . . . . . 81 14.2.1. Transmission of Outgoing Packets . . . . . . . . . . . 80
C.3. Source Routing . . . . . . . . . . . . . . . . . . . . . . 81 14.2.2. Reception of Incoming Packets . . . . . . . . . . . . 81
C.4. Address / Header Compression . . . . . . . . . . . . . . . 81 14.2.3. Cryptographic Mode of Operation . . . . . . . . . . . 81
C.5. Managing Multiple Instances . . . . . . . . . . . . . . . 82 14.3. Protecting RPL ICMPv6 messages . . . . . . . . . . . . . . 82
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 82 14.4. Security State Machine . . . . . . . . . . . . . . . . . . 83
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 83
15.1. RPL Control Message . . . . . . . . . . . . . . . . . . . 83
15.2. New Registry for RPL Control Codes . . . . . . . . . . . . 84
15.3. New Registry for the Mode of Operation (MOP) DIO
Control Field . . . . . . . . . . . . . . . . . . . . . . 84
15.4. RPL Control Message Option . . . . . . . . . . . . . . . . 85
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 85
17. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 86
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 88
18.1. Normative References . . . . . . . . . . . . . . . . . . . 88
18.2. Informative References . . . . . . . . . . . . . . . . . . 88
Appendix A. Requirements . . . . . . . . . . . . . . . . . . . . 90
A.1. Protocol Properties Overview . . . . . . . . . . . . . . . 90
A.1.1. IPv6 Architecture . . . . . . . . . . . . . . . . . . 90
A.1.2. Typical LLN Traffic Patterns . . . . . . . . . . . . . 90
A.1.3. Constraint Based Routing . . . . . . . . . . . . . . . 91
A.2. Deferred Requirements . . . . . . . . . . . . . . . . . . 91
Appendix B. Outstanding Issues . . . . . . . . . . . . . . . . . 91
B.1. Additional Support for P2P Routing . . . . . . . . . . . . 91
B.2. Address / Header Compression . . . . . . . . . . . . . . . 91
B.3. Managing Multiple Instances . . . . . . . . . . . . . . . 92
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 92
1. Introduction 1. Introduction
Low power and Lossy Networks (LLNs) consist of largely of constrained Low power and Lossy Networks (LLNs) consist of 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). These routers are interconnected by when they are battery operated). These routers are interconnected by
lossy links, typically supporting only low data rates, that are lossy links, typically supporting only low data rates, that are
usually unstable with relatively low packet delivery rates. Another usually unstable with relatively low packet delivery rates. Another
characteristic of such networks is that the traffic patterns are not characteristic of such networks is that the traffic patterns are not
simply unicast, but in many cases point-to-multipoint or multipoint- simply point-to-point, but in many cases point-to-multipoint or
to-point. Furthermore such networks may potentially comprise up to multipoint-to-point. Furthermore such networks may potentially
thousands of nodes. These characteristics offer unique challenges to comprise up to thousands of nodes. These characteristics offer
a routing solution: the IETF ROLL Working Group has defined unique challenges to a routing solution: the IETF ROLL Working Group
application-specific routing requirements for a Low power and Lossy has defined application-specific routing requirements for a Low power
Network (LLN) routing protocol, specified in and Lossy Network (LLN) routing protocol, specified in
[I-D.ietf-roll-building-routing-reqs], [I-D.ietf-roll-building-routing-reqs], [RFC5826], [RFC5673], and
[I-D.ietf-roll-home-routing-reqs], [RFC5673], and [RFC5548]. This [RFC5548].
document specifies the IPv6 Routing Protocol for Low power and lossy
networks (RPL). This document specifies the IPv6 Routing Protocol for Low power and
lossy networks (RPL). Note that although RPL was specified according
to the requirements set forth in the aforementioned requirement
documents, its use is in no way limited to these applications.
1.1. Design Principles 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 [I-D.ietf-roll-building-routing-reqs], out in [I-D.ietf-roll-building-routing-reqs], [RFC5826], [RFC5673],
[I-D.ietf-roll-home-routing-reqs], [RFC5673], and [RFC5548]. Because and [RFC5548].
those requirements are heterogeneous and sometimes incompatible in
nature, the approach is first taken to design a protocol capable of
supporting a core set of functionalities corresponding to the
intersection of the requirements. As the RPL design evolves optional
features may be added to address some application specific
requirements. This is a key protocol design decision providing a
granular approach in order to restrict the core of the protocol to a
minimal set of functionalities, and to allow each implementation of
the protocol to be optimized differently. All "MUST" application
requirements that cannot be satisfied by RPL will be specifically
listed in the Appendix A, accompanied by a justification.
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.
RPL is a generic protocol that is to be deployed by instantiating the In order to be useful in a wide range of LLN application domains, RPL
generic operation described in this document with a specific separates packet processing and forwarding from the routing
objective function (OF) (which ties together metrics, constraints, optimization objective. Examples of such objectives include
and an optimization objective) to realize a desired objective in a minimizing energy, minimizing latency, or satisfying constraints.
given environment. This document describes the mode of operation of RPL. Other
companion documents specify routing objective functions. A RPL
implementation, in support of a particular LLN application, will
include the necessary objective function(s) as required by the
application.
A set of companion documents to this specification will provide 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
RPL does not rely on any particular features of a specific link layer In compliance with the layered architecture of IP, RPL does not rely
technology. RPL is designed to be able to operate over a variety of on any particular features of a specific link layer technology. RPL
different link layers, including but not limited to, low power is designed to be able to operate over a variety of different link
wireless or PLC (Power Line Communication) technologies. layers, including but not limited to, low power wireless or PLC
(Power Line Communication) technologies.
Implementers may find RFC 3819 [RFC3819] a useful reference when Implementers may find [RFC3819] a useful reference when designing a
designing a link layer interface between RPL and a particular link link layer interface between RPL and a particular link layer
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
[I-D.ietf-roll-terminology], and introduces the following [I-D.ietf-roll-terminology], and introduces the following
skipping to change at page 8, line 9 skipping to change at page 8, line 8
Rank: The rank of a node in a DAG identifies the nodes position with Rank: The rank of a node in a DAG identifies the nodes position with
respect to a DODAG root. The farther away a node is from a respect to a DODAG root. The farther away a node is from a
DODAG root, the higher is the rank of that node. The rank of a DODAG root, the higher is the rank of that node. The rank of a
node may be a simple topological distance, or may more commonly node may be a simple topological distance, or may more commonly
be calculated as a function of other properties as described be calculated as a function of other properties as described
later. later.
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. The DODAG parent of a node will have a lower rank than root. The DODAG parent of a node will have a lower rank than
the node itself. (See Section 3.6.2.1). the node itself. (See Section 3.5.2.1).
DODAG sibling: A sibling of a node within a DODAG is defined in this DODAG sibling: A sibling of a node within a DODAG is defined in this
specification to be any neighboring node which is located at specification to be any neighboring node which is located at
the same rank within a DODAG. Note that siblings defined in the same rank within a DODAG. Note that siblings defined in
this manner do not necessarily share a common DODAG parent. this manner do not necessarily share a common DODAG parent.
(See Section 3.6.2.1). (See Section 3.5.2.1).
Sub-DODAG The sub-DODAG of a node is the set of other nodes in the Sub-DODAG The sub-DODAG of a node is the set of other nodes in the
DODAG that might use a path towards the DODAG root that DODAG that might use a path towards the DODAG root that
contains that node. Nodes in the sub-DODAG of a node have a contains that node. Nodes in the sub-DODAG of a node have a
greater rank than that node itself (although not all nodes of greater rank than that node itself (although not all nodes of
greater rank are necessarily in the sub-DODAG of that node). greater rank are necessarily in the sub-DODAG of that node).
(See Section 3.6.2.1). (See Section 3.5.2.1).
DODAGID: The identifier of a DODAG root. The DODAGID must be unique DODAGID: The identifier of a DODAG root. The DODAGID must be unique
within the scope of a RPL Instance in the LLN. within the scope of a RPL Instance in the LLN.
DODAG Iteration: A specific sequence number iteration ("version") of DODAG Version: A specific sequence number iteration ("version") of a
a DODAG with a given DODAGID. DODAG with a given DODAGID.
RPL Instance: A set of possibly multiple DODAGs. A network may have RPL Instance: A set of possibly multiple DODAGs. A network may have
more than one RPL Instance, and a RPL node can participate in more than one RPL Instance, and a RPL node can participate in
multiple RPL Instances. Each RPL Instance operates multiple RPL Instances. Each RPL Instance operates
independently of other RPL Instances. This document describes independently of other RPL Instances. This document describes
operation within a single RPL Instance. In RPL, a node can operation within a single RPL Instance. In RPL, a node can
belong to at most one DODAG per RPL Instance. The tuple belong to at most one DODAG per RPL Instance. The tuple
(RPLInstanceID, DODAGID) uniquely identifies a DODAG. (RPLInstanceID, DODAGID) uniquely identifies a DODAG.
RPLInstanceID: Unique identifier of a RPL Instance. RPLInstanceID: Unique identifier of a RPL Instance.
DODAGSequenceNumber: A sequential counter that is incremented by the DODAGVersionNumber: A sequential counter that is incremented by the
root to form a new Iteration of a DODAG. A DODAG Iteration is root to form a new Version of a DODAG. A DODAG Version is
identified uniquely by the (RPLInstanceID, DODAGID, identified uniquely by the (RPLInstanceID, DODAGID,
DODAGSequenceNumber) tuple. DODAGVersionNumber) tuple.
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 the orientation of the edges within the DODAG. following the orientation of the edges within the DODAG. This
follows the common terminology used in graphs and depth-first-
search, where vertices further from the root are "deeper," or
"down," and vertices closer to the root are "shallower," or
"up."
Down: Down refers to the direction from DODAG roots towards leaf Down: Down refers to the direction from DODAG roots towards leaf
nodes, going against the orientation of the edges within the nodes, going against the orientation of the edges within the
DODAG. DODAG. This follows the common terminology used in graphs and
depth-first-search, where vertices further from the root are
"deeper," or "down," and vertices closer to the root are
"shallower," or "up."
Objective Code Point (OCP): An identifier, used to indicate which Objective Code Point (OCP): An identifier, used to indicate which
Objective Function is in use for forming a DODAG. The Objective Function is in use for forming a DODAG. The
Objective Code Point is further described in Objective Code Point is further described in
[I-D.ietf-roll-routing-metrics]. [I-D.ietf-roll-routing-metrics].
Objective Function (OF): Defines which routing metrics, optimization Objective Function (OF): Defines which routing metrics, optimization
objectives, and related functions are in use in a DODAG. The objectives, and related functions are in use in a DODAG.
Objective Function is further described in
[I-D.ietf-roll-routing-metrics].
Goal: The Goal is a host or set of hosts that satisfy a particular Goal: The Goal is a host or set of hosts that satisfy a particular
application objective / OF. Whether or not a DODAG can provide application objective (OF). Whether or not a DODAG can provide
connectivity to a goal is a property of the DODAG. For connectivity to a goal is a property of the DODAG. For
example, a goal might be a host serving as a data collection example, a goal might be a host serving as a data collection
point, or a gateway providing connectivity to an external point, or a gateway providing connectivity to an external
infrastructure. infrastructure.
Grounded: A DODAG is said to be grounded, when the root can reach Grounded: A DODAG is said to be grounded, when the root can reach
the Goal of the objective function. the Goal of the objective function.
Floating: A DODAG is floating if is not Grounded. A floating DODAG Floating: A DODAG is floating if is not Grounded. A floating DODAG
is not expected to reach the Goal defined for the OF. is not expected to reach the Goal defined for the OF.
Typically, a DAG that is only intended to provide inner
connectivity is a Floating DAG.
As they form networks, LLN devices often mix the roles of 'host' and 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
skipping to change at page 9, line 48 skipping to change at page 10, line 7
[RFC4101]. Protocol details can be found in further sections. [RFC4101]. Protocol details can be found in further sections.
3.1. Topology 3.1. Topology
This section describes how the basic RPL topologies, and the rules by This section describes how the basic RPL topologies, and the rules by
which these are constructed, i.e. the rules governing DODAG which these are constructed, i.e. the rules governing DODAG
formation. formation.
3.1.1. Topology Identifiers 3.1.1. Topology Identifiers
RPL uses four identifiers to track and control the topology: RPL uses four identifiers to maintain the 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 DODAGs. All DODAGs in the same RPL Instance use the one or more DODAGs. All DODAGs in the same RPL Instance use the
same OF. A network may have multiple RPLInstanceIDs, each of same OF. A network may have multiple RPLInstanceIDs, each of
which defines an independent set of DODAGs, which may be optimized which defines an independent set of DODAGs, which may be optimized
for different OFs and/or applications. The set of DODAGs for different OFs and/or applications. The set of DODAGs
identified by a RPLInstanceID is called a RPL Instance. identified by a RPLInstanceID is called a RPL Instance.
o The second is a DODAGID. The scope of a DODAGID is a RPL o The second is a DODAGID. The scope of a DODAGID is a RPL
Instance. The combination of RPLInstanceID and DODAGID uniquely Instance. The combination of RPLInstanceID and DODAGID uniquely
identifies a single DODAG in the network. A RPL Instance may have identifies a single DODAG in the network. A RPL Instance may have
multiple DODAGs, each of which has an unique DODAGID. multiple DODAGs, each of which has an unique DODAGID.
o The third is a DODAGSequenceNumber. The scope of a o The third is a DODAGVersionNumber. The scope of a
DODAGSequenceNumber is a DODAG. A DODAG is sometimes DODAGVersionNumber is a DODAG. A DODAG is sometimes reconstructed
reconstructed from the DODAG root, by incrementing the from the DODAG root, by incrementing the DODAGVersionNumber. The
DODAGSequenceNumber. The combination of RPLInstanceID, DODAGID, combination of RPLInstanceID, DODAGID, and DODAGVersionNumber
and DODAGSequenceNumber uniquely identifies a DODAG Iteration. uniquely identifies a DODAG Version.
o The fourth is rank. The scope of rank is a DODAG Iteration. Rank o The fourth is rank. The scope of rank is a DODAG Version. Rank
establishes a partial order over a DODAG Iteration, 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.
3.1.2. DODAG Information 3.2. Instances, DODAGs, and DODAG Versions
For each DODAG that a node is, or may become, a member of, the
implementation should conceptually keep track of the following
information. The data structures described in this section are
intended to illustrate a possible implementation to aid in the
description of the protocol, but are not intended to be normative.
o RPLInstanceID
o DODAGID
o DODAGSequenceNumber
o DAG Metric Container, including DAGObjectiveCodePoint
o A set of Destination Prefixes offered by the DODAG root and
available via paths upwards along the DODAG
o A set of DODAG parents
o A set of DODAG siblings
o A timer to govern the sending of RPL control messages
3.2. Instances, DODAGs, and DODAG Iterations
Each RPL Instance constructs a routing topology optimized for a Each RPL Instance constructs a routing topology optimized for a
certain Objective Function (OF). A RPL Instance may provide routes certain Objective Function (OF) and routing metrics
to certain destination prefixes, reachable via the DODAG roots. A [I-D.ietf-roll-routing-metrics]. A RPL Instance may provide routes
single RPL Instance contains one or more Destination Oriented DAG to certain destination prefixes, reachable via the DODAG roots or
(DODAG) roots. These roots may operate independently, or may alternate paths within the DODAG. A single RPL Instance contains one
coordinate over a non-LLN backchannel. or more Destination Oriented DAG (DODAG) roots. These roots may
operate independently, or may coordinate over a non-LLN backchannel.
Each root has a unique identifier, the DODAGID. Each root has a unique identifier, the DODAGID.
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.
skipping to change at page 11, line 42 skipping to change at page 11, line 23
o a single DODAG with a single virtual root coordinating LLN sinks o a single DODAG with a single virtual root coordinating LLN sinks
(with the same DODAGID) over some non-LLN backbone (with the same DODAGID) over some non-LLN backbone
* For example, multiple border routers operating with a reliable * For example, multiple border routers operating with a reliable
backbone, e.g. in support of a 6LowPAN application, that are backbone, e.g. in support of a 6LowPAN application, that are
capable to act as logically equivalent sinks to the same DODAG. capable to act as logically equivalent sinks to 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.
Traffic is bound to a specific RPL Instance by a marking in the flow Traffic is bound to a specific RPL Instance by meta-data that is
label of the IPv6 header. Traffic originating in support of a carried with the packet and associates the packet to a particular
particular application may be tagged to follow an appropriate RPL RPLInstanceID (Section 8.2). The provisioning or automated discovery
instance which enables certain (path) properties, for example to of a mapping between a RPLInstanceID and a type or service of
follow paths optimized for low latency or low energy. The application traffic is beyond the scope of this specification.
provisioning or automated discovery of a mapping between a
RPLInstanceID and a type or service of application traffic is beyond
the scope of this specification.
An example of a RPL Instance comprising a number of DODAGs is An example of a RPL Instance comprising a number of DODAGs is
depicted in Figure 1. A DODAG Iteration (two "versions" of the same depicted in Figure 1. Revision of a DODAG Version (two iterations of
DODAG) is depicted in Figure 2. the same DODAG) is depicted in Figure 2.
+----------------------------------------------------------------+ +----------------------------------------------------------------+
| | | |
| +--------------+ | | +--------------+ |
| | | | | | | |
| | (R1) | (R2) (Rn) | | | (R1) | (R2) (Rn) |
| | / \ | /| \ / | \ | | | / \ | /| \ / | \ |
| | / \ | / | \ / | \ | | | / \ | / | \ / | \ |
| | (A) (B) | (C) | (D) ... (F) (G) (H) | | | (A) (B) | (C) | (D) ... (F) (G) (H) |
| | /|\ |\ | / | |\ | | | | | | /|\ |\ | / | |\ | | | |
skipping to change at page 12, line 40 skipping to change at page 12, line 20
| (A) (B) | \ | (A) | | (A) (B) | \ | (A) |
| /|\ |\ | ------\ | /|\ | | /|\ |\ | ------\ | /|\ |
| : : (C) : : | \ | : : (C) | | : : (C) : : | \ | : : (C) |
| | / | \ | | | / | \ |
| | ------/ | \ | | | ------/ | \ |
| | / | (B) | | | / | (B) |
| | | |\ | | | | |\ |
| | | : : | | | | : : |
| | | | | | | |
+----------------+ +----------------+ +----------------+ +----------------+
Sequence N Sequence N+1 Version N Version N+1
Figure 2: DODAG Iteration
3.3. Traffic Flows
3.3.1. Multipoint-to-Point Traffic
Multipoint-to-Point (MP2P) is a dominant traffic flow in many LLN
applications ([I-D.ietf-roll-building-routing-reqs],
[I-D.ietf-roll-home-routing-reqs], [RFC5673], [RFC5548]). The
destinations of MP2P flows are designated nodes that have some
application significance, such as providing connectivity to the
larger Internet or core private IP network. RPL supports MP2P
traffic by allowing MP2P destinations to be reached via DODAG roots.
3.3.2. Point-to-Multipoint Traffic
Point-to-multipoint (P2MP) is a traffic pattern required by several
LLN applications ([I-D.ietf-roll-building-routing-reqs],
[I-D.ietf-roll-home-routing-reqs], [RFC5673], [RFC5548]). RPL
supports P2MP traffic by using a destination advertisement mechanism
that provisions routes toward destination prefixes and away from
roots. Destination advertisements can update routing tables as the
underlying DODAG topology changes.
3.3.3. Point-to-Point Traffic
RPL DODAGs provide a basic structure for point-to-point (P2P)
traffic. For a RPL network to support P2P traffic, a root must be
able to route packets to a destination. Nodes within the network may
also have routing tables to destinations. A packet flows towards a
root until it reaches an ancestor that has a known route to the
destination.
RPL also supports the case where a P2P destination is a 'one-hop'
neighbor.
RPL neither specifies nor precludes additional mechanisms for Figure 2: DODAG Version
computing and installing more optimal routes to support arbitrary P2P
traffic.
3.4. Upward Routes and DODAG Construction 3.3. Upward Routes and DODAG Construction
RPL provisions routes up towards DODAG roots, forming a DODAG RPL provisions routes up towards DODAG roots, forming a DODAG
optimized according to the Objective Function (OF) in use. RPL nodes optimized according to the Objective Function (OF) and routing
construct and maintain these DODAGs through exchange of DODAG metrics/constraints in use. RPL nodes construct and maintain these
Information Object (DIO) messages. Undirected links between siblings DODAGs through exchange of DODAG Information Object (DIO) messages.
are also identified during this process, which can be used to provide Undirected links between siblings are also identified during this
additional diversity. process, which can be used to provide additional diversity.
3.4.1. DODAG Information Object (DIO)
A DIO identifies the RPL Instance, the DODAGID, the values used to
compute the RPL Instance's objective function, and the present DODAG
Sequence Number. It can also include additional routing and
configuration information. The DIO includes a measure derived from
the position of the node within the DODAG, the rank, which is used
for nodes to determine their positions relative to each other and to
inform loop avoidance/detection procedures. RPL exchanges DIO
messages to establish and maintain routes.
RPL adapts the rate at which nodes send DIO messages. When a DODAG
is detected to be inconsistent or needs repair, RPL sends DIO
messages more frequently. As the DODAG stabilizes, the DIO message
rate tapers off, reducing the maintenance cost of a steady and well-
working DODAG.
This document defines an ICMPv6 Message Type "RPL Control Message",
which is capable of carrying a DIO.
3.4.2. DAG Repair 3.3.1. DAG Repair
RPL supports global repair over the DODAG. A DODAG Root may RPL supports global repair over the DODAG. A DODAG Root may
increment the DODAG Sequence Number, thereby initiating a new DODAG increment the DODAG Version Number, thereby initiating a new DODAG
iteration. This institutes a global repair operation, revising the version. This institutes a global repair operation, revising the
DODAG and allowing nodes to choose an arbitrary new position within DODAG and allowing nodes to choose an arbitrary new position within
the new DODAG iteration. the new DODAG version. Global repair can be seen as a global
reoptimization mechanism.
RPL supports mechanisms which may be used for local repair within the
DODAG iteration. The DIO message specifies the necessary parameters
as configured from the DODAG root. Local repair options include the
allowing a node, upon detecting a loss of connectivity to a DODAG it
is a member of, to:
o Poison its sub-DODAG by advertising an effective rank of INFINITY
to its sub-DODAG, OR detach and form a floating DODAG in order to
preserve inner connectivity within its sub-DODAG.
o Move down within the DODAG iteration (i.e. increase its rank) in a RPL also supports mechanisms which may be used for local repair
limited manner, no further than a bound configured by the DODAG within the DODAG version. The DIO message specifies the necessary
root via the DIO so as not to count all the way to infinity. Such parameters as configured from the DODAG root, as controlled by policy
a move may be undertaken after waiting an appropriate poisoning at the root.
interval, and should allow the node to restore connectivity to the
DODAG Iteration, if at all possible.
3.4.3. Grounded and Floating DODAGs 3.3.2. Grounded and Floating DODAGs
DODAGs can be grounded or floating. A grounded DODAG offers DODAGs can be grounded or floating. A grounded DODAG offers
connectivity to to a goal. A floating DODAG offers no such connectivity to reach a goal. A floating DODAG offers no such
connectivity, and provides routes only to nodes within the DODAG. connectivity, and provides routes only to nodes within the DODAG.
Floating DODAGs may be used, for example, to preserve inner Floating DODAGs may be used, for example, to preserve inner
connectivity during repair. connectivity during repair.
3.4.4. Administrative Preference 3.3.3. 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.
3.4.5. Objective Function (OF) 3.3.4. Objective Function (OF)
The Objective Function (OF) implements the optimization objectives of The Objective Function (OF) implements the optimization objectives of
route selection within the RPL Instance. The OF is identified by an route selection within the RPL Instance. The OF is identified by an
Objective Code Point (OCP) within the DIO, and its specification also Objective Code Point (OCP) within the DIO. The OF also specifies the
indicates the metrics and constraints in use. The OF also specifies procedure used to select parents and compute rank within a DODAG
the procedure used to compute rank within a DODAG iteration. Further version along with potentially other DODAG characteristics. Further
details may be found in [I-D.ietf-roll-routing-metrics], details may be found in Section 11, [I-D.ietf-roll-routing-metrics],
[I-D.ietf-roll-of0], and related companion specifications. [I-D.ietf-roll-of0], and related companion specifications.
By using defined OFs that are understood by all nodes in a particular 3.3.5. Distributed Algorithm Operation
deployment, and by referencing these in the DIO message, RPL nodes
may work to build optimized LLN routes using a variety of application
and implementation specific metrics and goals.
In the case where a node is unable to encounter a suitable RPL
Instance using a known Objective Function, it may be configured to
join a RPL Instance using an unknown Objective Function - but in that
case only acting as a leaf node.
3.4.6. 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
configuration. configuration.
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. messages.
o Nodes may adjust the rate at which DIO messages are sent in o Nodes may adjust the rate at which DIO messages are sent in
response to stability or detection of routing inconsistencies. response to stability or detection of routing inconsistencies from
both control or data packets (see Section 8.2 for more).
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, or to maintain an existing DODAG, as according to the DODAG, or to maintain an existing DODAG, as according to the
specified Objective Function and rank-based loop avoidance rules. specified Objective Function and rank-based loop avoidance rules.
o Nodes provision routing table entries, for the destinations o Nodes provision routing table entries, for the destinations
specified by the DIO, via their DODAG parents in the DODAG specified by the DIO, via their DODAG parents in the DODAG
iteration. Nodes may provision a DODAG parent as a default version. Nodes MUST provision a DODAG parent as a default route
gateway. for the associated instance. It is up to the end-to-end
application to select the RPL instance to be associated to its
o Nodes may identify DODAG siblings within the DODAG iteration to traffic (should there be more than one instance) and thus the
increase path diversity. default route upwards when no longer-match exists.
o Using DIOs, and possibly information in data packets, RPL nodes o Nodes may identify DODAG siblings within the DODAG version to
detect possible routing loops. When a RPL node detects a possible increase path diversity and decrease convergence time during
routing loop, it may adapt its DIO transmission rate to apply a repair.
local repair to the topology.
3.5. Downward Routes and Destination Advertisement 3.4. Downward Routes and Destination Advertisement
RPL constructs and maintains DODAGs with DIO messages to establish RPL constructs and maintains DODAGs with DIO messages to establish
upward routes: it uses Destination Advertisement Object (DAO) upward routes: it uses Destination Advertisement Object (DAO)
messages to establish downward routes along the DODAG as well as messages to establish downward routes along the DODAG as well as
other routes. DAO messages are an optional feature for applications other P2P routes. DAO messages are an optional feature for
that require P2MP or P2P traffic. DIO messages advertise whether applications that require P2MP or P2P traffic, in either storing
destination advertisements are enabled within a given DODAG. (fully stateful) or non-storing (fully source routed
[I-D.hui-6man-rpl-routing-header]) mode.
3.5.1. Destination Advertisement Object (DAO)
A Destination Advertisement Object (DAO) conveys destination
information upwards along the DODAG so that a DODAG root (and other
intermediate nodes) can provision downward routes. A DAO message
includes prefix information to identify destinations, a capability to
record routes in support of source routing, and information to
determine the freshness of a particular advertisement.
Nodes that are capable of maintaining routing state may aggregate
routes from DAO messages that they receive before transmitting a DAO
message. Nodes that are not capable of maintaining routing state may
attach a next-hop address to the Reverse Route Stack contained within
the DAO message. The Reverse Route Stack is subsequently used to
generate piecewise source routes over regions of the LLN that are
incapable of storing downward routing state.
A special case of the DAO message, termed a no-DAO, is used to clear
downward routing state that has been provisioned through DAO
operation.
This document defines an ICMPv6 Message Type "RPL Control Message",
which is capable of carrying a DAO.
3.5.1.1. 'One-Hop' Neighbors
In addition to sending DAOs toward DODAG roots, RPL nodes may
occasionally emit a link-local multicast DAO message advertising
available destination prefixes. This mechanism allow provisioning a
trivial 'one-hop' route to local neighbors.
3.6. Routing Metrics and Constraints Used By RPL 3.5. 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; in all cases they are static metrics. Some routing characteristics. Some routing protocols support more than one
protocols support more than one metric: in the vast majority of the metric: in the vast majority of the cases, one metric is used per
cases, one metric is used per (sub)topology. Less often, a second (sub)topology. Less often, a second metric may be used as a tie-
metric may be used as a tie-breaker in the presence of Equal Cost breaker in the presence of Equal Cost Multiple Paths (ECMP). The
Multiple Paths (ECMP). The optimization of multiple metrics is known optimization of multiple metrics is known as an NP complete problem
as an NP complete problem and is sometimes supported by some and is sometimes supported by some centralized path computation
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 constrained-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
list, thus leading to a constrained shortest path. list, thus leading to a constrained shortest path.
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 [I-D.ietf-roll-routing-metrics].
The role of the Objective Function is to specify which routing An Objective Function specifies constraints in use, and how these are
metrics and constraints are in use, and how these are used, in used, in addition to the objectives used to compute the (constrained)
addition to the objectives used to compute the (constrained) shortest path. Upstream and Downstream metrics may be merged or advertised
path. separately depending on the OF and the metrics. When they 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
which unicast DAO messages are sent). Yet, all are DODAG parents
with regards to the rules for Rank computation.
Example 1: Shortest path: path offering the shortest end-to-end delay Example 1: Shortest path: path offering the shortest end-to-end delay
Example 2: Constrained shortest path: the path that does not traverse Example 2: Constrained shortest 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
3.6.1. Loop Avoidance 3.5.1. Loop Avoidance
RPL guarantees neither loop free path selection nor strong global RPL guarantees neither loop free path selection nor tight delay
convergence. In order to reduce control overhead, however, such as convergence times. In order to reduce control overhead, however,
the cost of the count-to-infinity problem, RPL avoids creating loops such as the cost of the count-to-infinity problem, RPL avoids
when undergoing topology changes. Furthermore, RPL includes rank- creating loops when undergoing topology changes. Furthermore, RPL
based mechanisms for detecting loops when they do occur. RPL uses includes rank-based datapath validation mechanisms for detecting
this loop detection to ensure that packets make forward progress loops when they do occur. RPL uses this loop detection to ensure
within the DODAG iteration and trigger repairs when necessary. that packets make forward progress within the DODAG version and
trigger repairs when necessary.
3.6.1.1. Greediness and Rank-based Instabilities 3.5.1.1. Greediness and Rank-based Instabilities
Once a node has joined a DODAG iteration, RPL disallows certain A node is greedy if it attempts to move deeper in the DODAG version,
behaviors, including greediness, in order to prevent resulting in order to increase the size of the parent set or improve some other
instabilities in the DODAG iteration. metric. Moving deeper in within a DODAG version in this manner could
result in instability and be detrimental to other nodes.
If a node is allowed to be greedy and attempts to move deeper in the Once a node has joined a DODAG version, RPL disallows certain
DODAG iteration, beyond its most preferred parent, in order to behaviors, including greediness, in order to prevent resulting
increase the size of the parent set, then an instability can result. instabilities in the DODAG version.
Suppose a node is willing to receive and process a DIO messages from Suppose a node is willing to receive and process a DIO messages from
a node in its own sub-DODAG, and in general a node deeper than a 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 itself. In this case, a possibility exists that a feedback loop is
created, wherein two or more nodes continue to try and move in the created, wherein two or more nodes continue to try and move in the
DODAG iteration while attempting to optimize against each other. In DODAG version while attempting to optimize against each other. In
some cases, this will result in instability. It is for this reason some cases, this will result in instability. It is for this reason
that RPL limits the cases where a node may process DIO messages from that 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 forms 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.
3.6.1.2. DODAG Loops 3.5.1.2. 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. This may happen in
particular when DIO messages are missed. Strict use of the DAG particular when DIO messages are missed. Strict use of the DODAG
sequence number can eliminate this type of loop, but this type of Version Number can eliminate this type of loop, but this type of loop
loop may possibly be encountered when using some local repair may possibly be encountered when using some local repair mechanisms.
mechanisms.
3.6.1.3. DAO Loops 3.5.1.3. 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-DAO was missed and persists until all state has been when a No-Path (a DAO message that invalidates a previously announced
cleaned up. RPL includes loop detection mechanisms that may mitigate prefix) was missed and persists until all state has been cleaned up.
the impact of DAO loops and trigger their repair. RPL includes an optional mechanism to acknowledge DAO messages, which
may mitigate the impact of a single DAO message being missed. RPL
includes loop detection mechanisms that may mitigate the impact of
DAO loops and trigger their repair.
In the case where stateless DAO operation is used, i.e. source In the case where stateless DAO operation is used, i.e. source
routing specifies the down routes, then DAO Loops should not occur on routing specifies the down routes, then DAO Loops should not occur on
the stateless portions of the path. the stateless portions of the path.
3.6.1.4. Sibling Loops 3.5.1.4. Sibling Loops
Sibling loops could occur if a group of siblings kept choosing Sibling loops could occur if a group of siblings kept choosing
amongst themselves as successors such that a packet does not make amongst themselves as successors such that a packet does not make
forward progress. This specification limits the number of times that forward progress. This specification limits the number of times that
sibling forwarding may be used at a given rank, in order to prevent sibling forwarding may be used at a given rank, in order to prevent
sibling loops. sibling loops.
3.6.2. Rank Properties 3.5.2. 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 iteration. 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, and may calculation of the rank is left to the Objective Function, and may
depend on parents, link metrics, and the node configuration and depend on parents, link metrics, and the node configuration and
policies. policies.
The rank is not a cost metric, although its value can be derived from The rank is not a cost metric, although its value can be derived from
and influenced by metrics. The rank has properties of its own that and influenced by metrics. The rank has properties of its own that
are not necessarily those of all metrics: are not necessarily those of all metrics:
Type: Rank is an abstract scalar. Some metrics are boolean (e.g. Type: The rank is an abstract decimal value.
grounded), others are statistical and better expressed as a
tuple like an expected value and a variance. Some OCPs use
not one but a set of metrics bound by a piece of logic.
Function: Rank is the expression of a relative position within a Function: The rank is the expression of a relative position within a
DODAG iteration with regard to neighbors and is not DODAG version with regard to neighbors and is not necessarily
necessarily a good indication or a proper expression of a a good indication or a proper expression of a distance or a
distance or a cost to the root. 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 might be routing topology. Some dampening or filtering might be
applied to keep the topology stable, and thus the rank does applied to keep the topology stable, and thus the rank does
not necessarily change as fast as some physical metrics not necessarily change as fast as some physical metrics
would. A new DODAG iteration would be a good opportunity to would. A new DODAG version would be a good opportunity to
reconcile the discrepancies that might form over time between reconcile the discrepancies that might form over time between
metrics and ranks within a DODAG iteration. metrics and ranks within a DODAG version.
Granularity: Rank is coarse grained. A fine granularity would Granularity: The portion of the rank that is used to define a node's
prevent the selection of siblings. position in the DAG, DAGRank(node), is coarse grained. A
fine granularity would make the selection of siblings
difficult, since siblings must have the exact same rank
value.
Properties: Rank is strictly monotonic, and can be used to validate Properties: The rank is strictly monotonic, and can be used to
a progression from or towards the root. A metric, like validate a progression from or towards the root. A metric,
bandwidth or jitter, does not necessarily exhibit this like bandwidth or jitter, does not necessarily exhibit this
property. property.
Abstract: Rank does not have a physical unit, but rather a range of Abstract: The rank does not have a physical unit, but rather a range
increment per hop, where the assignment of each increment is of increment per hop, where the assignment of each increment
to be determined by the implementation. is 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
nodes further options with regard to DODAG parent selection and nodes 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.
3.6.2.1. Rank Comparison (DAGRank()) 3.5.2.1. 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 decimal point between the integer part and the fractional part is the decimal 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. When increase in rank between a node and any of its DODAG parents. When
an objective function computes rank, the objective function operates an objective function computes rank, the objective function operates
on the entire (i.e. 16-bit) rank quantity. When rank is compared, on the entire (i.e. 16-bit) rank quantity. When rank is compared,
e.g. for determination of parent/sibling relationships or loop e.g. for determination of parent/sibling 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: follows:
DAGRank(rank) = floor(rank/MinHopRankIncrease) DAGRank(rank) = floor(rank/MinHopRankIncrease)
MinHopRankIncrease is provisioned at the DODAG Root and propagated in MinHopRankIncrease is provisioned at the DODAG Root and propagated in
the DIO message. For efficient implementation the MinHopRankIncrease the DIO message. For efficient implementation the MinHopRankIncrease
SHOULD be a power of 2. An implementation may configure a value MUST be a power of 2. An implementation may configure a value
MinHopRankIncrease as appropriate to balance between the loop MinHopRankIncrease as appropriate to balance between the loop
avoidance logic of RPL (i.e. selection of eligible parents and avoidance logic of RPL (i.e. selection of eligible parents and
siblings) and the metrics in use. siblings) and the metrics in use.
By convention in this document, using the macro DAGRank(node) may be By convention in this document, using the macro DAGRank(node) may be
interpreted as DAGRank(node.rank), where node.rank is the rank value interpreted as DAGRank(node.rank), where node.rank is the rank value
as maintained by the node. 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).
3.6.2.2. Rank Relationships 3.5.2.2. Rank Relationships
The computation of the rank MUST be done in such a way so as to The computation of the rank MUST be done in such a way so as to
maintain the following properties for any nodes M and N that are maintain the following properties for any nodes M and N that are
neighbors in the LLN: 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): In this case, the position of M
is closer to the DODAG root than the position of N. Node M is closer to the DODAG root than the position of N. Node M
may safely be a DODAG parent for Node N without risk of may safely be a DODAG parent for Node N without risk of
creating a loop. Further, for a node N, all parents in the creating a loop. Further, for a node N, all parents in the
DODAG parent set must be of rank less than DAGRank(N). In DODAG parent set must be of rank less than DAGRank(N). In
skipping to change at page 21, line 43 skipping to change at page 18, line 50
creating a loop (which must be detected and resolved by some creating a loop (which must be detected and resolved by some
other means). other means).
DAGRank(M) is greater than DAGRank(N): In this case, the position of 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. 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 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 node N selects node M as DODAG parent there is a risk to
create a loop. create a loop.
As an example, the rank could be computed in such a way so as to As an example, the rank could be computed in such a way so as to
closely track ETX when the objective function is to minimize ETX, or closely track ETX (Expected Transmission Count, a fairly common
latency when the objective function is to minimize latency, or in a routing metric used in LLN and defined in
more complicated way as appropriate to the objective function being
used within the DODAG.
4. ICMPv6 RPL Control Message [I-D.ietf-roll-routing-metrics]) when the objective function is to
minimize ETX, or latency when the objective function is to minimize
latency, or in a more complicated way as appropriate to the objective
function being used within the DODAG.
3.6. Traffic Flows Supported by RPL
3.6.1. Multipoint-to-Point Traffic
Multipoint-to-Point (MP2P) is a dominant traffic flow in many LLN
applications ([I-D.ietf-roll-building-routing-reqs], [RFC5826],
[RFC5673], [RFC5548]). The destinations of MP2P flows are designated
nodes that have some application significance, such as providing
connectivity to the larger Internet or core private IP network. RPL
supports MP2P traffic by allowing MP2P destinations to be reached via
DODAG roots.
3.6.2. Point-to-Multipoint Traffic
Point-to-multipoint (P2MP) is a traffic pattern required by several
LLN applications ([I-D.ietf-roll-building-routing-reqs], [RFC5826],
[RFC5673], [RFC5548]). RPL supports P2MP traffic by using a
destination advertisement mechanism that provisions routes toward
destination prefixes and away from roots. Destination advertisements
can update routing tables as the underlying DODAG topology changes.
3.6.3. Point-to-Point Traffic
RPL DODAGs provide a basic structure for point-to-point (P2P)
traffic. For a RPL network to support P2P traffic, a root must be
able to route packets to a destination. Nodes within the network may
also have routing tables to destinations. A packet flows towards a
root until it reaches an ancestor that has a known route to the
destination. As pointed out later in this document, in the most
constrained case (when nodes cannot store routes), that common
ancestor may be the DODAG root. In other cases it may be a node
closer to both the source and destination.
RPL also supports the case where a P2P destination is a 'one-hop'
neighbor.
RPL neither specifies nor precludes additional mechanisms for
computing and installing potentially more optimal routes to support
arbitrary P2P traffic.
4. RPL Instance
Within a given LLN, there may be multiple, logically independent RPL
instances. This document describes how a single instance behaves.
A node may belong to multiple RPL Instances.
An instance can be either local to a root or global. When the
instance is local, the DAG is a single DODAG that is rooted at the
node that owns the DODAGID. This is used in particular for the
construction of a temporary DODAG in support of P2P traffic
optimization between the root and some other nodes.
Control and Data Packets that traverse a RPL network MUST be tagged
in such a fashion that the instance is unambiguously identified (TBD
flow label or RPL Hop-by-hop option ([I-D.hui-6man-rpl-option])).
The identifiers include the RPLInstanceID and the DODAGID for local
instances.
4.1. RPL Instance ID
A global RPLInstanceID MUST be unique to the whole LLN. Mechanisms
for allocating and provisioning global RPLInstanceID are out of scope
for this document. There can be up to 128 global instance in the
whole network, and up 64 local instances per DODAGID.
A global RPLinstanceID is encoded in a RPLinstanceID field as
follows:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|0| ID | Global RPLinstanceID in 0..127
+-+-+-+-+-+-+-+-+
Figure 3: RPL Instance ID field format for global instances
A local RPLInstanceID is autoconfigured by the node that owns the
DODAGID and it MUST be unique for that DODAGID. In that case, the
DODAGID MUST be a valid address of the root that is used as an
endpoint of all communications within that instance.
A local RPLinstanceID is encoded in a RPLinstanceID field as follows:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|1|D| ID | Local RPLInstanceID in 0..63
+-+-+-+-+-+-+-+-+
Figure 4: RPL Instance ID field format for local instances
The D flag in a Local RPLInstanceID is always set to 0 in RPL control
messages. It is used in data packets to indicate whether the DODAGID
is the source or the destination of the packet. If the D flag is set
to 1 then the destination address of the IPv6 packet MUST be the
DODAGID. If the D flag is clear then the source address of the IPv6
packet MUST be the DODAGID.
5. ICMPv6 RPL Control Message
This document defines the RPL Control Message, a new ICMPv6 message. This document defines the RPL Control Message, a new ICMPv6 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.
In accordance with [RFC4443], the RPL Control Message has the A RPL Control Message has the scope of a link. The source address is
following format: a link local address. The destination address is either all routers
multicast address (FF02::2) or a link local address.
In accordance with [RFC4443], the RPL Control Message consists of an
ICMPv6 header followed by a message body. The message body is
comprised of a message base and possibly a number of options as
illustrated in Figure 5.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ Message Body + . Base .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Option(s) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: RPL Control Message Figure 5: 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
requested Type of 155. requested Type of 155 (to be confirmed by IANA).
The Code field identifies the type of RPL Control Message. This The Code field identifies the type of RPL Control Message. This
document defines three codes for the following RPL Control Message document defines codes for the following RPL Control Message types
types: (all codes are to be confirmed by the IANA Section 15.2):
o 0x01: DODAG Information Solicitation (Section 5.2) o 0x00: DODAG Information Solicitation (Section 5.2)
o 0x02: DODAG Information Object (Section 5.1) o 0x01: DODAG Information Object (Section 5.3)
o 0x04: Destination Advertisement Object (Section 6.1) o 0x02: Destination Advertisement Object (Section 5.4)
5. Upward Routes o 0x03: Destination Advertisement Object Acknowledgment
(Section 5.5)
This section describes how RPL discovers and maintains upward routes. o 0x80: Secure DODAG Information Solicitation (Section 5.2.2)
It describes DODAG Information Objects (DIOs), the messages used to
discover and maintain these routes. It specifies how RPL generates
and responds to DIOs. It also describes DODAG Information
Solicitation (DIS) messages, which are used to trigger DIO
transmissions.
5.1. DODAG Information Object (DIO) o 0x81: Secure DODAG Information Object (Section 5.3.2)
o 0x82: Secure Destination Advertisement Object (Section 5.4.2)
o 0x83: Secure Destination Advertisement Object Acknowledgment
(Section 5.5.2)
The high order bit (0x80) of the code denotes whether the RPL message
has security enabled. Secure versions of RPL messages have a
modified format to support confidentiality and integrity, illustrated
in Figure Figure 6.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Security .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Base .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Option(s) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Secure RPL Control Message
The remainder of this section describes the currently defined RPL
Control Message Base formats followed by the currently defined RPL
Control Message Options.
5.1. RPL Security Fields
Each RPL message has a secure version. The secure versions provide
integrity and confidentiality. Because security covers the base
message as well as options, in secured messages the security
information lies between the checksum and base, as shown in Figure
Figure 6.
The format of the security section is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|C|KIM| LVL | |
+-+-+-+-+-+-+-+-+ +
| Counter |
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Key Identifier .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Security
All fields are considered as packet payload from a security
processing perspective. The exact placement and format of message
integrity/authentication codes has not yet been determined.
Use of the Security section is further detailed in Section 14.
Security Control Field: The Security Control Field has one flag and
two fields:
Counter Compression (C): If the Counter Compression flag is
set then the Counter field is compressed from 4 bytes
into 1 byte. If the Counter Compression flag is clear
then the Counter field is 4 bytes and uncompressed.
Key Identifier Mode (KIM): The Key Identifier Mode field
indicates whether the key used for packet protection is
determined implicitly or explicitly and indicates the
particular representation of the Key Identifier field.
The Key Identifier Mode is set one of the non-reserved
values from the table below:
+------+-----+-----------------------------+------------+
| Mode | KIM | Meaning | Key |
| | | | Identifier |
| | | | Length |
| | | | (octets) |
+------+-----+-----------------------------+------------+
| 0 | 00 | Peer-to-peer key determined | 0 |
| | | implicitly from originator | |
| | | and recipient of packet. | |
| | | | |
| | | Key Source is not present. | |
| | | Key Index is not present. | |
+------+-----+-----------------------------+------------+
| 1 | 01 | Group key determined | 1 |
| | | implicitly from Key Index | |
| | | and side information. | |
| | | | |
| | | Key Source is not present. | |
| | | Key Index is present. | |
+------+-----+-----------------------------+------------+
| 2 | 10 | Signature key used; group | 0/9 |
| | | key determined explicitly | |
| | | if encryption used. | |
| | | | |
| | | Key Source may be present. | |
| | | Key Index may be present. | |
+------+-----+-----------------------------+------------+
| 3 | 11 | Group key determined | 9 |
| | | explicitly from Key Source | |
| | | Identifier and Key Index. | |
| | | | |
| | | Key Source is present. | |
| | | Key Index is present. | |
+------+-----+-----------------------------+------------+
Key Identifier Mode (KIM) Encoding
Security Level (LVL): The Security Level field indicates the
provided packet protection. This value can be adapted on
a per-packet basis and allows for varying levels of data
authenticity and, optionally, for data confidentiality.
When nontrivial protection is provided, replay protection
is always provided. The Security Level is set to one of
the non-reserved values in the table below:
+--------------------+-------------------+
| Without Signatures | With Signatures |
+----+-----+-------------+------+-------------+-----+
| ID | LVL | Attributes | Auth | Attributes | Sig |
| | | | Len | | Len |
+----+-----+-------------+------+-------------+-----+
| 0 | 000 | None | 0 | None | 37 |
| 1 | 001 | MIC-32 | 4 | Sign-32 | 37 |
| 2 | 010 | MIC-64 | 8 | Sign-64 | 45 |
| 3 | 011 | Rsvd | N/A | Rsvd | N/A |
| 4 | 100 | ENC | 0 | ENC | 37 |
| 5 | 101 | ENC-MIC-32 | 4 | ENC-Sign-32 | 41 |
| 6 | 110 | ENC-MIC-64 | 8 | ENC-Sign-64 | 45 |
| 7 | 111 | Rsvd | N/A | Reserved | N/A |
+----+-----+-------------+------+-------------+-----+
Security Level (LVL) Encoding
Counter: The Counter field indicates the non-repeating value (nonce)
used with the cryptographic mechanism that implements packet
protection and allows for the provision of semantic security.
This value is compressed from 4 octets to 1 octet if the
Counter Compression field of the Security Control Field is set
to one.
Key Identifier: The Key Identifier field indicates which key was
used to protect the packet. This field provides various levels
of granularity of packet protection, including peer-to-peer
keys, group keys, and signature keys. This field is
represented as indicated by the Key Identifier Mode field and
is formatted as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Key Source .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Key Index .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Key Identifier
Key Source: The Key Source field, when present, indicates the
logical identifier of the originator of a group key.
When present this field is 8 bytes in length.
Key Index: The Key Index field, when present, allows unique
identification of different keys with the same
originator. It is the responsibility of each key
originator to make sure that actively used keys that it
issues have distinct key indices and that all key indices
have a value unequal to 0x00. When present this field is
1 byte in length.
Unassigned bits of the Security section are reserved. They MUST be
set to zero on transmission and MUST be ignored on reception.
5.2. DODAG Information Solicitation (DIS)
The DODAG Information Solicitation (DIS) message may be used to
solicit a DODAG Information Object from a RPL node. Its use is
analogous to that of a Router Solicitation as specified in IPv6
Neighbor Discovery; a node may use DIS to probe its neighborhood for
nearby DODAGs. Section 6.3 describes how nodes respond to a DIS.
5.2.1. Format of the DIS Base Object
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: The DIS Base Object
Unassigned bits of the DIS Base are reserved. They MUST be set to
zero on transmission and MUST be ignored on reception.
5.2.2. Secure DIS
A Secure DIS message follows the format in Figure Figure 6, where the
base format is the DIS message shown in Figure Figure 7.
5.2.3. DIS Options
The DIS message MAY carry valid options.
This specification allows for the DIS message to carry the following
options:
0x00 Pad1
0x01 PadN
0x05 RPL Target
0x07 Solicited Information
5.3. DODAG Information Object (DIO)
The DODAG Information Object carries information that allows a node The DODAG Information Object carries information that allows a node
to discover a RPL Instance, learn its configuration parameters, to discover a RPL Instance, learn its configuration parameters,
select a DODAG parent set, and maintain the upward routing topology. select a DODAG parent set, and maintain the upward routing topology.
5.1.1. DIO Base Format 5.3.1. Format of the DIO Base Object
DIO Base is an always-present container option in a DIO message.
Every DIO MUST include a DIO Base.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|G|A|T|S|0| Prf | Sequence | Rank | | RPLInstanceID | Version | Rank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|G|A|T|MOP| Prf | DTSN | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID | DTSN | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| | | |
+ + + +
| DODAGID | | |
+ DODAGID +
| |
+ + + +
| | | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | sub-option(s)... | Option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 4: DIO Base Figure 8: The DIO Base Object
Control Field: The DAG Control Field has three flags and one field: Control Field: The DAG Control Field has three flags and two fields:
Grounded (G): The Grounded (G) flag indicates whether the Grounded (G): The Grounded (G) flag indicates whether the
upward routes this node advertises provide connectivity upward routes this node advertises provide connectivity
to the set of addresses which are application-defined to the set of addresses which are application-defined
goals. If the flag is set, the DODAG is grounded and goals. If the flag is set, the DODAG is grounded and
provides such connectivity. If the flag is cleared, the provides such connectivity. If the flag is cleared, the
DODAG is floating and may not provide such connectivity. DODAG is floating and may not provide such connectivity.
Destination Advertisement Supported (A): The Destination Destination Advertisement Supported (A): The Destination
Advertisement Supported (A) flag indicates whether the Advertisement Supported (A) flag indicates whether the
root of this DODAG can collect and use downward route root of this DODAG can collect and use downward route
state. If the flag is set, nodes in the network are state. If the flag is set, nodes in the network are
enabled to exchange destination advertisements messages enabled to exchange destination advertisements messages
to build downward routes (Section 6). If the flag is to build downward routes (Section 7). If the flag is
cleared, destination advertisement messages are disabled cleared, destination advertisement messages are disabled
and the DODAG maintains only upward routes. and the DODAG maintains only upward routes.
Destination Advertisement Trigger (T): The Destination Destination Advertisement Trigger (T): The Destination
Advertisement Trigger (T) flag indicates a complete Advertisement Trigger (T) flag indicates a complete
refresh of downward routes. If the flag is set, then a refresh of downward routes. If the flag is set, then a
refresh of downward route state is to take place over the refresh of downward route state is to take place over the
entire DODAG. If the flag is cleared, the downward route entire DODAG. If the flag is cleared, the downward route
maintenance is in its normal mode of operation. The maintenance is in its normal mode of operation. The
further details of this process are described in further details of this process are described in
Section 6. Section 7.
Destination Advertisements Stored (S): The Destination Mode of Operation (MOP): The Mode of Operation (MOP) field
Advertisements Stored (S) flag is used to indicate that a identifies the mode of operation of the RPL Instance as
non-root ancestor is storing routing table entries administratively provisioned at and distributed by the
learned from DAO messaging. If the flag is set, then a DODAG Root. All nodes who join the DODAG must be able to
non-root ancestor is known to be storing routing table honor the MOP in order to fully participate as a router,
entries learned from DAO messages. If the flag is or else they must only join as a leaf. MOP is encoded as
cleared, only the root node may be storing routing table in the table below:
entries learned from DAO messaging. This flag is further
described in Section 6. +-----+-------------------------------------------------+
| MOP | Meaning |
+-----+-------------------------------------------------+
| 00 | Non-storing |
| 01 | Storing |
| 10 | Reserved for future specification of mixed-mode |
| 11 | Reserved |
+-----+-------------------------------------------------+
Mode of Operation (MOP) Encoding
DODAGPreference (Prf): A 3-bit unsigned integer that defines DODAGPreference (Prf): A 3-bit unsigned integer that defines
how preferable the root of this DODAG is compared to how preferable the root of this DODAG is compared to
other DODAG roots within the instance. DAGPreference other DODAG roots within the instance. DAGPreference
ranges from 0x00 (least preferred) to 0x07 (most ranges from 0x00 (least preferred) to 0x07 (most
preferred). The default is 0 (least preferred). preferred). The default is 0 (least preferred).
Section 5.3 describes how DAGPreference affects DIO Section 6.2 describes how DAGPreference affects DIO
processing. processing.
Unassigned bits of the Control Field are reserved. They MUST Version Number: 8-bit unsigned integer set by the DODAG root.
be set to zero on transmission and MUST be ignored on Section 6.2 describes the rules for version numbers and how
reception.
Sequence Number: 8-bit unsigned integer set by the DODAG root.
Section 5.3 describes the rules for sequence numbers and how
they affect DIO processing. 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 5.3 describes how Rank is set sending the DIO message. Section 6.2 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
which RPL Instance the DODAG is part of. which RPL Instance the DODAG is part of.
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 6. The details of this process are described in Section 7.
DODAGID: 128-bit unsigned integer set by a DODAG root which uniquely DODAGID: 128-bit unsigned integer set by a DODAG root which uniquely
identifies a DODAG. Possibly derived from the IPv6 address of identifies a DODAG. Possibly derived from the IPv6 address of
the DODAG root. the DODAG root.
5.1.2. DIO Base Rules Unassigned bits of the DIO Base are reserved. They MUST be set to
zero on transmission and MUST be ignored on reception.
1. If the 'A' flag of a DIO Base is cleared, the 'T' flag MUST also 5.3.2. Secure DIO
be cleared.
2. For the following DIO Base fields, a node that is not a DODAG A Secure DIO message follows the format in Figure Figure 6, where the
root MUST advertise the same values as its preferred DODAG parent base format is the DIS message shown in Figure Figure 8.
(defined in Section 5.3.2). Therefore, if a DODAG root does not
change these values, every node in a route to that DODAG root
eventually advertises the same values for these fields. These
fields are:
1. Grounded (G)
2. Destination Advertisement Supported (A)
3. Destination Advertisement Trigger (T)
4. DAGPreference (Prf)
5. Sequence
6. RPLInstanceID
7. DODAGID
3. A node MAY update the following fields at each hop: 5.3.3. DIO Options
1. Destination Advertisements Stored (S)
2. DAGRank
3. DTSN
4. The DODAGID field each root sets MUST be unique within the RPL The DIO message MAY carry valid options.
Instance.
5.1.3. DIO Suboptions This specification allows for the DIO message to carry the following
options:
0x00 Pad1
0x01 PadN
0x02 Metric Container
0x03 Routing Information
0x04 DODAG Configuration
0x09 Prefix Information
This section describes the format of DIO suboptions and the five 5.4. Destination Advertisement Object (DAO)
suboptions this document defines: Pad 1, Pad N, DAG Metric Container,
DAG Destination Prefix, and DAG Configuration.
5.1.3.1. DIO Suboption Format The Destination Advertisement Object (DAO) is used to propagate
destination information upwards along the DODAG. The DAO message is
unicast by the child to the selected parent(s). The DAO message may
optionally, upon explicit request or error, be acknowledged by the
parent with a Destination Advertisement Acknowledgement (DAO-ACK)
message back to the child.
The Pad N, DAG Metric Container, DAG Destination Prefix, and DAG 5.4.1. Format of the DAO Base Object
Configuration suboptions all follow this format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID |K|D| Reserved | DAOSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DODAGID* +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
Figure 9: The DAO Base Object
RPLInstanceID: 8-bit field indicating the topology instance
associated with the DODAG, as learned from the DIO.
K: The 'K' flag indicates that the parent is expected to send a
DAO-ACK back.
D: The 'D' flag indicates that the DODAGID field is present. This
would typically only be set when a local RPLInstanceID is used.
DAOSequence: Incremented at each unique DAO message, echoed in the
DAO-ACK message.
DODAGID*: 128-bit unsigned integer set by a DODAG root which
uniquely identifies a DODAG. This field is only present when
the 'D' flag is set. This field is typically 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 Base are reserved. They MUST be set to
zero on transmission and MUST be ignored on reception.
5.4.2. Secure DAO
A Secure DAO message follows the format in Figure Figure 6, where the
base format is the DAO message shown in Figure Figure 9.
5.4.3. DAO Options
The DAO message MAY carry valid options.
This specification allows for the DAO message to carry the following
options:
0x00 Pad1
0x01 PadN
0x05 RPL Target
0x06 Transit Information
A special case of the DAO message, termed a No-Path, is used to clear
downward routing state that has been provisioned through DAO
operation. The No-Path carries a RPL Transit Information option,
which identifies the destination to which the DAO is associated, with
a lifetime of 0x00000000 to indicate a loss of reachability.
5.5. Destination Advertisement Object Acknowledgement (DAO-ACK)
The DAO-ACK message is sent as a unicast packet by a DAO parent in
response to a unicast DAO message from a child.
5.5.1. Format of the DAO-ACK Base Object
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID | Reserved | DAOSequence | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
Figure 10: The DAO ACK Base Object
RPLInstanceID: 8-bit field indicating the topology instance
associated with the DODAG, as learned from the DIO.
DAOSequence: Incremented at each DAO message from a given child,
echoed in the DAO-ACK by the parent. The DAOSequence serves in
the parent-child communication and is not to be confused with
the Transit Information option Sequence that is associated to a
given target down the DODAG.
Status: Indicates the completion. 0 is unqualified acceptance, above
128 are rejection code indicating that the node should select
an alternate parent.
Unassigned bits of the DAO-ACK Base are reserved. They MUST be set
to zero on transmission and MUST be ignored on reception.
5.5.2. Secure DAO-ACK
A Secure DAO-ACK message follows the format in Figure Figure 6, where
the base format is the DAO-ACK message shown in Figure Figure 10.
5.5.3. DAO-ACK Options
This specification does not define any options to be carried by the
DAO-ACK message.
5.6. RPL Control Message Options
5.6.1. RPL Control Message Option Generic Format
RPL Control Message Options all follow this format:
0 1 2 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Subopt. Type | Suboption Length | Suboption Data | Option Type | Option Length | Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 5: DIO Suboption Generic Format
Suboption Type: 8-bit identifier of the type of suboption. Figure 11: RPL Option Generic Format
Suboption Length: 16-bit unsigned integer, representing the length Option Type: 8-bit identifier of the type of option. The Option
in octets of the suboption, not including the suboption Type Type values are to be confirmed by the IANA Section 15.4.
and Length fields.
Suboption Data: A variable length field that contains data specific Option Length: 8-bit unsigned integer, representing the length in
to the option. octets of the option, not including the Option Type and Length
fields.
The following subsections specify the DIO message suboptions which Option Data: A variable length field that contains data specific to
are currently defined for use in the DODAG Information Object. the option.
When processing a DIO message containing a suboption for which the When processing a RPL message containing an option for which the
Suboption 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 suboption, correctly handling any remaining options in the following option, correctly handling any remaining options in the
the message. message.
DIO message suboptions may have alignment requirements. Following RPL message options may have alignment requirements. Following the
the convention in IPv6, options with alignment requirements are convention in IPv6, options with alignment requirements are aligned
aligned in a packet such that multi-octet values within the Option in a packet such that multi-octet values within the Option Data field
Data field of each option fall on natural boundaries (i.e., fields of of each option fall on natural boundaries (i.e., fields of width n
width n octets are placed at an integer multiple of n octets from the octets are placed at an integer multiple of n octets from the start
start of the header, for n = 1, 2, 4, or 8). of the header, for n = 1, 2, 4, or 8).
5.1.3.2. Pad1 5.6.2. Pad1
The Pad1 suboption format is as follows: The Pad1 option may be present in DIS, DIO, DAO, and DAO-ACK
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 = 0 |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 6: Pad 1 Figure 12: Format of the Pad 1 Option
The Pad1 option is used to insert one or two octets of padding into
the message to enable options alignment. If more than one octet of
padding is required, the PadN option should be used rather than
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.
The Pad1 option is used to insert one or two octets of padding in the 5.6.3. PadN
DIO message to enable suboptions alignment. If more than two octets
of padding is required, the PadN option, described next, should be
used rather than multiple Pad1 options.
5.1.3.3. PadN
The PadN suboption format is as follows: The PadN option may be present in DIS, DIO, DAO, and DAO-ACK
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 | Suboption Length | Suboption Data | Type = 1 | Option Length | 0x00 Padding...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 7: Pad N Figure 13: Format of the Pad N Option
The PadN suboption is used to insert three or more octets of padding The PadN option is used to insert two or more octets of padding into
in the DIO message to enable suboptions alignment. For N (N > 2) the message to enable options alignment. PadN Option data MUST be
octets of padding, the Suboption Length field contains the value N-3, ignored by the receiver.
and the Option Data consists of N-3 zero-valued octets. PadN Option
data MUST be ignored by the receiver.
5.1.3.4. Metric Container Option Type: 0x01 (to be confirmed by IANA)
The Metric Container suboption format is as follows: Option Length: For N (N > 1) octets of padding, the Option Length
field contains the value N-2.
Option Data: For N (N > 1) octets of padding, the Option Data
consists of N-2 zero-valued octets.
5.6.4. Metric Container
The Metric Container option may be present in DIO 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 | Suboption Length | Metric Data | Type = 2 | Option Length | Metric Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 8: Metric Container Figure 14: Format of the Metric Container Option
The Metric Container is used to report metrics along the DODAG. The The Metric Container is used to report metrics along the DODAG. The
Metric Container may contain a number of discrete node, link, and Metric Container may contain a number of discrete node, link, and
aggregate path metrics as chosen by the implementer. The Suboption aggregate path metrics and constraints specified in
Length field contains the length in octets of the Metric Data. The [I-D.ietf-roll-routing-metrics] as chosen by the implementer.
order, content, and coding of the Metric Container data is as
specified in [I-D.ietf-roll-routing-metrics].
The processing and propagation of the Metric Container is governed by The processing and propagation of the Metric Container is governed by
implementation specific policy functions. implementation specific policy functions.
5.1.3.5. Destination Prefix Option Type: 0x02 (to be confirmed by IANA)
The Destination Prefix suboption format is as follows: Option Length: The Option Length field contains the length in octets
of the Metric Data.
Metric Data: The order, content, and coding of the Metric Container
data is as specified in [I-D.ietf-roll-routing-metrics].
5.6.5. Route Information
The Route Information option may be present in DIO messages, and is
equivalent in function to the IPv6 ND Route Information option as
defined in [RFC4191]. The format of the option is modified slightly
(Type, Length) in order to be 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 | Suboption Length |Resvd|Prf|Resvd| | Type = 3 | Option Length | Prefix Length |Resvd|Prf|Resvd|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Lifetime | | Route Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | | | |
+-+-+-+-+-+-+-+-+ | . Prefix (Variable Length) .
| Destination Prefix (Variable Length) | . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: Format of the Route Information Option
The Route Information option is used to indicate that connectivity to
the specified destination prefix is available from the DODAG root.
In the event that a RPL Control Message may need to specify
connectivity to more than one destination, the Route Information
option may be repeated.
[RFC4191] should be consulted as the authoritative reference with
respect to the Route Information option. The field descriptions are
transcribed here for convenience:
Option Type: 0x03 (to be confirmed by IANA)
Option Length: Variable, length of the option in octets excluding
the 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
the Prefix that are valid. The value ranges from 0 to 128.
The Prefix field is 0, 8, or 16 octets depending on Length.
Prf: 2-bit signed integer. The Route Preference indicates whether
to prefer the router associated with this prefix over others,
when multiple identical prefixes (for different routers) have
been received. If the Reserved (10) value is received, the
Route Information Option MUST be ignored.
Resvd: Two 3-bit unused fields. They MUST be initialized to zero by
the sender and MUST be ignored by the receiver.
Route Lifetime 32-bit unsigned integer. The length of time in
seconds (relative to the time the packet is sent) that the
prefix is valid for route determination. A value of all one
bits (0xffffffff) represents infinity.
Prefix Variable-length field containing an IP address or a prefix of
an IP address. The Prefix Length field contains the number of
valid leading bits in the prefix. The bits in the prefix after
the prefix length (if any) are reserved and MUST be initialized
to zero by the sender and ignored by the receiver.
Unassigned bits of the Route Information option are reserved. They
MUST be set to zero on transmission and MUST be ignored on reception.
5.6.6. DODAG Configuration
The DODAG Configuration option may be present in DIO messages, and
its format is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 4 | Option Length | Resvd | PCS | DIOIntDoubl. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DIOIntMin. | DIORedun. | MaxRankIncrease |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MinHopRankIncrease |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: Format of the DODAG Configuration Option
The DODAG Configuration option is used to distribute configuration
information for DODAG Operation through the DODAG.
The information communicated in this option is generally static and
unchanging within the DODAG, therefore it is not necessary to include
in every DIO. This information is configured at the DODAG Root and
distributed throughout the DODAG with the DODAG Configuration Option.
Nodes other than the DODAG Root MUST NOT modify this information when
propagating the DODAG Configuration option. This option MAY be
included occasionally by the DODAG Root (as determined by the DODAG
Root), and MUST be included in response to a unicast request, e.g. a
unicast DODAG Information Solicitation (DIS) message.
Option Type: 0x04 (to be confirmed by IANA)
Option Length: 8 bytes
Path Control Size (PCS): 3-bit unsigned integer used to configure
the number of bits that may be allocated to the Path Control
field (see Section 7.1.4.2).
DIOIntervalDoublings: 8-bit unsigned integer used to configure Imax
of the DIO trickle timer (see Section 6.3.1).
DIOIntervalMin: 8-bit unsigned integer used to configure Imin of the
DIO trickle timer (see Section 6.3.1).
DIORedundancyConstant: 8-bit unsigned integer used to configure k of
the DIO trickle timer (see Section 6.3.1).
MaxRankIncrease: 16-bit unsigned integer used to configure
DAGMaxRankIncrease, the allowable increase in rank in support
of local repair. If DAGMaxRankIncrease is 0 then this
mechanism is disabled.
MinHopRankInc 16-bit unsigned integer used to configure
MinHopRankIncrease as described in Section 3.5.2.1.
5.6.7. RPL Target
The RPL Target option may be present in DAO messages, and its format
is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 5 | Option Length | Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Target Prefix (Variable Length) |
. . . .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: DAG Destination Prefix Figure 17: Format of the RPL Target Option
The Destination Prefix suboption is used to indicate that The RPL Target Option is used to indicate a target IPv6 address,
connectivity to the specified destination prefix is available from prefix, or multicast group that is reachable or queried along the
the DODAG root, or from another node located upwards along the DODAG DODAG. It is used in DIO to identify a resource that the root is
on the path to the DODAG root. This may be useful in cases where trying to reach, and in a DAO to indicate reachability. It is used
more than one LBR is operating within the LLN and offering in a DAO message to indicate reachability. A set of one or more
connectivity to different administrative domains, e.g. a home network Transit Information options MAY directly follow the Target option in
and a utility network. In such cases, upon observing the Destination a DAO message in support of constructing source routes in a non-
Prefixes offered by a particular DODAG, a node MAY decide to join storing mode of operation [I-D.hui-6man-rpl-routing-header]. When
multiple DODAGs in support of a particular application. the same set of Transit Information options apply equally to a set of
DODAG Target options, the group of Target options MUST appear first,
followed by the Transit Information options which apply to those
Targets.
The Suboption Length is coded as the length of the suboption in The RPL Target option may be repeated as necessary to indicate
octets, excluding the Type and Length fields. multiple targets.
Prf is the Route Preference as in [RFC4191]. The reserved fields Option Type: 0x05 (to be confirmed by IANA)
MUST be set to zero on transmission and MUST be ignored on receipt.
The Prefix Lifetime is a 32-bit unsigned integer representing the Option Length: Variable, length of the option in octets excluding
length of time in seconds (relative to the time the packet is sent) the Type and Length fields.
that the Destination Prefix is valid for route determination. The
lifetime is initially set by the node that owns the prefix and
denotes the valid lifetime for that prefix (similar to
AdvValidLifetime [RFC4861]). The value might be reduced by the
originator and/or en-route nodes that will not provide connectivity
for the whole valid lifetime. A value of all one bits (0xFFFFFFFF)
represents infinity. A value of all zero bits (0x00000000) indicates
a loss of reachability.
The Prefix Length is an 8-bit unsigned integer that indicates the Prefix Length: 8-bit unsigned integer. Number of valid leading bits
number of leading bits in the destination prefix. in the IPv6 Prefix.
The Destination Prefix contains Prefix Length significant bits of the Target Prefix: Variable-length field identifying an IPv6 destination
destination prefix. The remaining bits of the Destination Prefix, as address, prefix, or multicast group. The Prefix Length field
required to complete the trailing octet, are set to 0. contains the number of valid leading bits in the prefix. The
bits in the prefix after the prefix length (if any) are
reserved and MUST be set to zero on transmission and MUST be
ignored on receipt.
In the event that a DIO message may need to specify connectivity to 5.6.8. Transit Information
more than one destination, the Destination Prefix suboption may be
repeated.
5.1.3.6. DODAG Configuration The Transit Information option may be present in DAO messages, and
its format is as follows:
The DODAG Configuration suboption format is as follows: 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 6 | Option Length | Path Sequence | Path Control |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Parent Address* +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: Format of the Transit Information option
The Transit Information option is used for a node to indicate
attributes for a path to one or more destinations. The destinations
are indicated as by one or more Target options that immediately
precede the Transit Information option(s).
The Transit Information option can used for a node to indicate its
DODAG parents to an ancestor that is collecting DODAG routing
information, typically for the purpose of constructing source routes.
In the non-storing mode of operation this ancestor will be the DODAG
Root, and this option is carried by the DAO message. The option
length is used to determine whether the Parent Address is present or
not.
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-
storing Destination Advertisement operation. The node may code the
Path Control field in order to signal a preference among parents.
One or more Transit Information options MUST be preceded by one or
more RPL Target options. In this manner the RPL Target option
indicates the child node, and the Transit Information option(s)
enumerate the DODAG parents.
A typical non-storing node will use multiple Transit Information
options, and it will send the DAO thus formed to only one parent that
will forward it to the root. A typical storing node with use one
Transit Information option with no parent field, and will send the
DAO thus formed to multiple parents.
Option Type: 0x06 (to be confirmed by IANA)
Option Length: Variable, depending on whether or not Parent Address
is present.
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
message), that node sets the Path-Sequence and increments the
Path-Sequence each time it issues a RPL Target option.
Path Control: 8-bit bitfield. The Path Control field limits the
number of DAO-Parents to which a DAO message advertising
connectivity to a specific destination may be sent, as well as
providing some indication of relative preference. The limit
provides some bound on overall DAO fan-out in the LLN. The
leftmost bit is associated with a path that contains a most-
preferred link, and the subsequent bits are ordered down to the
rightmost bit which is least preferred.
Path Lifetime: 32-bit unsigned integer. The length of time in
seconds (relative to the time the packet is sent) that the
prefix is valid for route determination. A value of all one
bits (0xFFFFFFFF) represents infinity. A value of all zero
bits (0x00000000) indicates a loss of reachability. This is
referred as a No-Path in this document.
Parent Address (optional): IPv6 Address of the DODAG Parent of the
node originally issuing the Transit Information Option. This
field may not be present, as according to the DODAG Mode of
Operation and indicated by the Transit Information option
length.
Unassigned bits of the Transit Information option are reserved. They
MUST be set to zero on transmission and MUST be ignored on reception.
5.6.9. Solicited Information
The Solicited Information option may be present in DIS messages, and
its format is as follows:
0 1 2 3 0 1 2 3
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 | Length | DIOIntDoubl. | | Type = 7 | Option Length | RPLInstanceID |V|I|D| Rsvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DIOIntMin. | DIORedun. | MaxRankInc | MinHopRankInc | | |
+ +
| |
+ DODAGID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version |
+-+-+-+-+-+-+-+-+
Figure 10: DODAG Configuration Figure 19: Format of the Solicited Information Option
The DODAG Configuration suboption is used to distribute configuration The Solicited Information option is used for a node to request a
information for DODAG Operation through the DODAG. The information subset of neighboring nodes that meet the specified criteria to
communicated in this suboption is generally static and unchanging respond to a DIS message.
within the DODAG, therefore it is not necessary to include in every
DIO. This suboption MAY be included occasionally by the DODAG Root,
and MUST be included in response to a unicast request, e.g. a unicast
DODAG Information Solicitation (DIS) message.
The Length is coded as 5. The Solicited Information option may specify a number of predicate
criteria to be matched by a receiving node. If a node receiving a
multicast DIS message containing a Solicited Information option
matches ALL of the predicates, then it MUST reset its trickle timer
in order to trigger a DIO response to the DIS message. When a node
receives a DIS message containing a Solicited information option, and
the DIS message is unicast OR the node does not match ALL the
predicates, then the node MUST NOT reset the trickle timer.
DIOIntervalDoublings is an 8-bit unsigned integer, configured on the Option Type: 0x07 (to be confirmed by IANA)
DODAG root and used to configure the trickle timer (see
Section 5.3.5.1 for details on trickle timers) governing when DIO
message should be sent within the DODAG. DIOIntervalDoublings is the
number of times that the DIOIntervalMin is allowed to be doubled
during the trickle timer operation.
DIOIntervalMin is an 8-bit unsigned integer, configured on the DODAG Option Length: 19 bytes
root and used to configure the trickle timer governing when DIO
message should be sent within the DODAG. The minimum configured
interval for the DIO trickle timer in units of ms is
2^DIOIntervalMin. For example, a DIOIntervalMin value of 16ms is
expressed as 4.
DIORedundancyConstant is an 8-bit unsigned integer used to configure Control Field: The Solicited Information option Control Field has
suppression of DIO transmissions. DIORedundancyConstant is the three flags:
minimum number of relevant incoming DIOs required to suppress a DIO
transmission. If the value is 0xFF then the suppression mechanism is
disabled.
MaxRankInc, 8-bit unsigned integer, is the DAGMaxRankIncrease. This V: If the V flag is set then the Version field is valid and
is the allowable increase in rank in support of local repair. If a node should only respond if its DODAGVersionNumber
DAGMaxRankIncrease is 0 then this mechanism is disabled. matches the requested version. If the V flag is clear
then the Version field is not valid and the Version field
MUST be set to zero on transmission and ignored upon
receipt.
MinHopRankInc, 8-bit unsigned integer, is the MinHopRankIncrease as I: If the I flag is set then the RPLInstanceID field is
described in Section 3.6.2.1. valid and a node should only respond if it matches the
requested RPLInstanceID. If the I flag is clear then the
RPLInstanceID field is not valid and the RPLInstanceID
field MUST be set to zero on transmission and ignored
upon receipt.
5.2. DODAG Information Solicitation (DIS) D: If the D flag is set then the DODAGID field is valid and
a node should only respond if it matches the requested
DODAGID. If the D flag is clear then the DODAGID field
is not valid and the DODAGID field MUST be set to zero on
transmission and ignored upon receipt.
The DODAG Information Solicitation (DIS) message may be used to Version: 8-bit unsigned integer containing the DODAG Version number
solicit a DODAG Information Object from a RPL node. Its use is that is being solicited when valid.
analogous to that of a Router Solicitation; a node may use DIS to
probe its neighborhood for nearby DODAGs. The DODAG Information
Solicitation carries no additional message body. Section 5.3.5
describes how nodes respond to a DIS.
5.3. Upward Route Discovery and Maintenance RPLInstanceID: 8-bit unsigned integer containing the RPLInstanceID
that is being solicited when valid.
Upward route discovery allows a node to join a DODAG by discovering DODAGID: 128-bit unsigned integer containing the DODAGID that is
neighbors that are members of the DODAG and identifying a set of being solicited when valid.
parents. The exact policies for selecting neighbors and parents is
implementation-dependent. This section specifies the set of rules
those policies must follow for interoperability.
5.3.1. RPL Instance Unassigned bits of the Solicited Information option are reserved.
They MUST be set to zero on transmission and MUST be ignored on
reception.
A RPLInstanceID MUST be unique across an LLN. 5.6.10. Prefix Information
A node MAY belong to multiple RPL Instances. The Prefix Information option may be present in DIO messages, and is
equivalent in function to the IPv6 ND Prefix Information option as
defined in [RFC4861]. The format of the option is modified slightly
(Type, Length) in order to be carried as a RPL option as follows:
Within a given LLN, there may be multiple, logically independent RPL 0 1 2 3
instances. This document describes how a single instance behaves. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 8 | Option Length | Prefix Length |L|A| Reserved1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Prefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.3.2. Neighbors and Parents within a DODAG Iteration Figure 20: Format of the Prefix Information Option
The Prefix Information option may be used to distribute the prefix in
use inside the DODAG, e.g. for address autoconfiguration.
[RFC4861] 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)
Option Length: 30. Note that this length is expressed in units of
single-octets, unlike in IPv6 ND.
Prefix Length 8-bit unsigned integer. The number of leading bits in
the Prefix that are valid. The value ranges from 0 to 128.
The prefix length field provides necessary information for on-
link determination (when combined with the L flag in the prefix
information option). It also assists with address
autoconfiguration as specified in [RFC4862], for which there
may be more restrictions on the prefix length.
L 1-bit on-link flag. When set, indicates that this prefix can
be used for on-link determination. When not set the
advertisement makes no statement about on-link or off-link
properties of the prefix. In other words, if the L flag is not
set a host MUST NOT conclude that an address derived from the
prefix is off-link. That is, it MUST NOT update a previous
indication that the address is on-link.
A 1-bit autonomous address-configuration flag. When set
indicates that this prefix can be used for stateless address
configuration as specified in [RFC4862].
Reserved1 6-bit unused field. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
Valid Lifetime 32-bit unsigned integer. The length of time in
seconds (relative to the time the packet is sent) that the
prefix is valid for the purpose of on-link determination. A
value of all one bits (0xffffffff) represents infinity. The
Valid Lifetime is also used by [RFC4862].
Preferred Lifetime 32-bit unsigned integer. The length of time in
seconds (relative to the time the packet is sent) that
addresses generated from the prefix via stateless address
autoconfiguration remain preferred [RFC4862]. A value of all
one bits (0xffffffff) represents infinity. See [RFC4862].
Note that the value of this field MUST NOT exceed the Valid
Lifetime field to avoid preferring addresses that are no longer
valid.
Reserved2 This field is unused. It MUST be initialized to zero by
the sender and MUST be ignored by the receiver.
Prefix An IP address or a prefix of an IP address. The Prefix
Length field contains the number of valid leading bits in the
prefix. The bits in the prefix after the prefix length are
reserved and MUST be initialized to zero by the sender and
ignored by the receiver. A router SHOULD NOT send a prefix
option for the link-local prefix and a host SHOULD ignore such
a prefix option.
Unassigned bits of the Prefix Information option are reserved. They
MUST be set to zero on transmission and MUST be ignored on reception.
6. Upward Routes
This section describes how RPL discovers and maintains upward routes.
It describes the use of DODAG Information Objects (DIOs), the
messages used to discover and maintain these routes. It specifies
how RPL generates and responds to DIOs. It also describes DODAG
Information Solicitation (DIS) messages, which are used to trigger
DIO transmissions.
6.1. DIO Base Rules
1. If the 'A' flag of a DIO Base is cleared, the 'T' flag MUST also
be cleared.
2. For the following DIO Base fields, a node that is not a DODAG
root MUST advertise the same values as its preferred DODAG parent
(defined in Section 6.2.1). Therefore, if a DODAG root does not
change these values, every node in a route to that DODAG root
eventually advertises the same values for these fields. These
fields are:
1. Grounded (G)
2. Destination Advertisement Supported (A)
3. Destination Advertisement Trigger (T)
4. DAGPreference (Prf)
5. Version
6. RPLInstanceID
7. DODAGID
3. A node MAY update the following fields at each hop:
1. Destination Advertisements Stored (S)
2. DAGRank
3. DTSN
4. The DODAGID field each root sets MUST be unique within the RPL
Instance.
6.2. Upward Route Discovery and Maintenance
Upward route discovery allows a node to join a DODAG by discovering
neighbors that are members of the DODAG of interest and identifying a
set of parents. The exact policies for selecting neighbors and
parents is implementation-dependent and driven by the OF. This
section specifies the set of rules those policies must follow for
interoperability.
6.2.1. 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-
dependent and OF-dependent. Second, the parent set is a restricted dependent and OF-dependent. Second, the parent set is a restricted
subset of the candidate neighbor set. Finally, the preferred parent, subset of the candidate neighbor set. Finally, the preferred parent,
a set of size one, is an element of the parent set that is the a set of size one, is an element of the parent set that is the
preferred next hop in upward routes. preferred next hop in upward routes.
skipping to change at page 31, line 24 skipping to change at page 46, line 24
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), or an equivalent 6. When Neighbor Unreachability Detection (NUD), or an equivalent
mechanism, determines that a neighbor is no longer reachable, a mechanism, determines that a neighbor is no longer reachable, a
RPL node MUST NOT consider this node in the candidate neighbor RPL node MUST NOT consider this node in the candidate neighbor
set when calculating and advertising routes until it determines set when calculating and advertising routes until it determines
that it is again reachable. Routes through an unreachable that it is again reachable. Routes through an unreachable
neighbor MUST be eliminated from the routing table. 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. The OF can guide free, as rank decreases on each hop to the root. The OF can guide
candidate neighbor set and parent set selection, as discussed in candidate neighbor set and parent set selection, as discussed in
[I-D.ietf-roll-routing-metrics]. [I-D.ietf-roll-routing-metrics] and [I-D.ietf-roll-of0].
5.3.3. Neighbors and Parents across DODAG Iterations 6.2.2. Neighbors and Parents across DODAG Versions
The above rules govern a single DODAG iteration. 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
iterations: versions:
5.3.3.1. DODAG Iteration 6.2.2.1. DODAG Version
1. The tuple (RPLInstanceID, DODAGID, DODAGSequenceNumber) uniquely 1. The tuple (RPLInstanceID, DODAGID, DODAGVersionNumber) uniquely
defines a DODAG Iteration. Every element of a node's DODAG defines a DODAG Version. Every element of a node's DODAG parent
parent set, as conveyed by the last heard DIO from each DODAG set, as conveyed by the last heard DIO message from each DODAG
parent, MUST belong to the same DODAG iteration. 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
Iterations. Versions.
2. A node is a member of a DODAG iteration if every element of its 2. A node is a member of a DODAG version if every element of its
DODAG parent set belongs to that DODAG iteration, or if that node DODAG parent set belongs to that DODAG version, or if that node
is the root of the corresponding DODAG. is the root of the corresponding DODAG.
3. A node MUST NOT send DIOs for DODAG iterations of which it is not 3. A node MUST NOT send DIOs for DODAG versions of which it is not a
a member. member.
4. DODAG roots MAY increment the DODAGSequenceNumber that they 4. DODAG roots MAY increment the DODAGVersionNumber that they
advertise and thus move to a new DODAG iteration. When a DODAG advertise and thus move to a new DODAG version. When a DODAG
root increments its DODAGSequenceNumber, it MUST follow the root increments its DODAGVersionNumber, it MUST follow the
conventions of Serial Number Arithmetic as described in conventions of Serial Number Arithmetic as described in
[RFC1982]. [RFC1982].
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 DODAGSequenceNumber higher than the highest advertise a DODAGVersionNumber higher than the highest
DODAGSequenceNumber it has heard. Higher is defined as the DODAGVersionNumber it has heard. Higher is defined as the
greater-than operator in [RFC1982]. greater-than operator in [RFC1982].
6. Once a node has advertised a DODAG iteration by sending a DIO, it 6. Once a node has advertised a DODAG version by sending a DIO, it
MUST NOT be member of a previous DODAG iteration of the same MUST NOT be member of a previous DODAG version of the same DODAG
DODAG (i.e. with the same RPLInstanceID, the same DODAGID, and a (i.e. with the same RPLInstanceID, the same DODAGID, and a lower
lower DODAGSequenceNumber). Lower is defined as the less-than DODAGVersionNumber). Lower is defined as the less-than operator
operator in [RFC1982]. in [RFC1982].
Within a particular implementation, a DODAG root may increment the Within a particular implementation, a DODAG root may increment the
DODAGSequenceNumber periodically, at a rate that depends on the DODAGVersionNumber periodically, at a rate that depends on the
deployment. In other implementations, loop detection may be deployment, in order to trigger a global reoptimization of the DODAG.
considered sufficient to solve routing issues, and the DODAG root may In other implementations, loop detection may be considered sufficient
increment the DODAGSequenceNumber only upon administrative to solve routing issues by triggering local repair mechanisms, and
intervention. Another possibility is that nodes within the LLN have the DODAG root may increment the DODAGVersionNumber only upon
some means by which they can signal detected routing inconsistencies administrative intervention. Another possibility is that nodes
or suboptimalities to the DODAG root, in order to request an on- within the LLN have some means by which they can signal detected
demand DODAGSequenceNumber increment (i.e. request a global repair of routing inconsistencies or suboptimalities to the DODAG root, in
the DODAG). order to request an on-demand DODAGVersionNumber increment (i.e.
request a global repair of the DODAG). Note that such a mechanism is
for further study and out of the scope of this document.
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 to no longer
be associated with that DODAG), then the DODAG information should not be associated with that DODAG), then the DODAG information should not
be suppressed until after the expiration of an implementation- be suppressed until after the expiration of an implementation-
specific local timer in order to observe if the DODAGSequenceNumber specific local timer in order to observe if the DODAGVersionNumber
has been incremented, should any new parents appear for the DODAG. has been incremented, should any new parents appear for the DODAG.
This will help protect against the possibility of loops that may
occur of that node were to inadvertently rejoin the old DODAG version
in its own prior sub-DODAG.
As the DODAGSequenceNumber is incremented, a new DODAG Iteration As the DODAGVersionNumber is incremented, a new DODAG Version spreads
spreads outward from the DODAG root. Thus a parent that advertises outward from the DODAG root. Thus a parent that advertises the new
the new DODAGSequenceNumber can not possibly belong to the sub-DODAG DODAGVersionNumber cannot possibly belong to the sub-DODAG of a node
of a node that still advertises an older DODAGSequenceNumber. A node that still advertises an older DODAGVersionNumber. A node may safely
may safely add such a parent, without risk of forming a loop, without add such a parent, without risk of forming a loop, without regard to
regard to its relative rank in the prior DODAG Iteration. This is its relative rank in the prior DODAG Version. This is equivalent to
equivalent to jumping to a different DODAG. jumping to a different DODAG.
As a node transitions to new DODAG Iterations as a consequence of As a node transitions to new DODAG Versions as a consequence of
following these rules, the node will be unable to advertise the following these rules, the node will be unable to advertise the
previous DODAG Iteration (prior DODAGSequenceNumber) once it has previous DODAG Version (prior DODAGVersionNumber) once it has
committed to advertising the new DODAG Iteration. committed to advertising the new DODAG Version.
During transition to a new DODAG Iteration, a node may decide to During transition to a new DODAG Version, a node may decide to
forward packets via 'future parents' that belong to the same DODAG forward packets via 'future parents' that belong to the same DODAG
(same RPLInstanceID and DODAGID), but are observed to advertise a (same RPLInstanceID and DODAGID), but are observed to advertise a
more recent (incremented) DODAGSequenceNumber. more recent (incremented) DODAGVersionNumber. In that case, the node
MUST act as a leaf with regard to the new version for the purpose of
loop detection as specified in Section 8.2.
5.3.3.2. DODAG Roots 6.2.2.2. DODAG Roots
1. A DODAG root that does not have connectivity to the set of 1. A DODAG root that does not have connectivity to the set of
addresses described as application-level goals, MUST NOT set the addresses described as application-level goals, MUST NOT set the
Grounded bit. 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.
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An LLN node that is a goal for the Objective Function is the root of An LLN node that is a goal for the Objective Function is the root of
its own grounded DODAG, at rank ROOT_RANK. its own grounded DODAG, at rank ROOT_RANK.
In a deployment that uses a backbone link to federate a number of LLN In a deployment that uses a backbone link to federate a number of LLN
roots, it is possible to run RPL over that backbone and use one roots, it is possible to run RPL over that backbone 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 LLN root itself, expose a rank of
ROOT_RANK to the LLN, and are part of the same DODAG, coordinating ROOT_RANK to the LLN, and are part of the same DODAG, coordinating
DODAGSequenceNumber and other DODAG root determined parameters with DODAGVersionNumber and other DODAG root determined parameters with
the virtual root over the backbone. the virtual root over the backbone.
5.3.3.3. DODAG Selection 6.2.2.3. DODAG Selection
The DODAGPreference (Prf) provides an administrative mechanism to The DODAGPreference (Prf) provides an administrative mechanism to
engineer the self-organization of the LLN, for example indicating the engineer the self-organization of the LLN, for example indicating the
most preferred LBR. If a node has the option to join a more most preferred LBR. If a node has the option to join a more
preferred DODAG while still meeting other optimization objectives, preferred DODAG while still meeting other optimization objectives,
then the node will generally seek to join the more preferred DODAG as then the node will generally seek to join the more preferred DODAG as
determined by the OF. All else being equal, it is left to the determined by the OF. All else being equal, it is left to the
implementation to determine which DODAG is most preferred, possibly implementation to determine which DODAG is most preferred, possibly
based on additional criteria beyond Prf and the OF. based on additional criteria beyond Prf and the OF.
5.3.3.4. Rank and Movement within a DODAG Iteration 6.2.2.4. 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 Iteration. 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 Iteration. within the DODAG Version.
3. Let L be the lowest rank within a DODAG iteration that a given 3. Let L be the lowest rank within a DODAG version that a given node
node has advertised. Within the same DODAG Iteration, that node has advertised. Within the same DODAG Version, that node MUST
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 at any time. (This a node MAY advertise an INFINITE_RANK at any time. (This rule
corresponds to a limited rank increase for the purpose of local corresponds to a limited rank increase for the purpose of local
repair within the DODAG Iteration.) repair within the DODAG Version.)
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 Iteration of which that 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 5. A node MAY, at any time after hearing the next DODAGVersionNumber
DODAGSequenceNumber Iteration advertised from suitable DODAG Version advertised from suitable DODAG parents, choose to migrate
parents, choose to migrate to the next DODAG Iteration within the to the next DODAG Version within the DODAG.
DODAG.
Conceptually, an implementation is maintaining a DODAG parent set Conceptually, an implementation is maintaining a DODAG parent set
within the DODAG Iteration. 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 Iteration, the DODAG parent When a node migrates to the next DODAG Version, the DODAG parent and
and sibling sets need to be rebuilt for the new iteration. An sibling sets need to be rebuilt for the new version. An
implementation could defer to migrate for some reasonable amount of implementation could defer to migrate for some reasonable amount of
time, to see if some other neighbors with potentially better metrics time, to see if some other neighbors with potentially better metrics
but higher rank announce themselves. Similarly, when a node jumps but higher rank announce themselves. Similarly, when a node jumps
into a new DODAG it needs to construct new DODAG parent/sibling sets into a new DODAG it needs to construct new DODAG parent/sibling sets
for this new DODAG. for this new DODAG.
When a node moves to improve its position, it must conceptually When a node moves to improve its position, it must conceptually
abandon all DODAG parents and siblings with a rank larger than abandon all DODAG parents and siblings with a rank larger than
itself. As a consequence of the movement it may also add new itself. As a consequence of the movement it may also add new
siblings. Such a movement may occur at any time to decrease the siblings. Such a movement may occur at any time to decrease the
rank, as per the calculation indicated by the OF. Maintenance of the rank, as per the calculation indicated by the OF. Maintenance of the
parent and sibling sets occurs as the rank of candidate neighbors is parent and sibling sets occurs as the rank of candidate neighbors is
observed as reported in their DIOs. observed as reported in their DIOs.
If a node needs to move down a DODAG that it is attached to, causing If a node needs to move down a DODAG that it is attached to, causing
the rank to increase, then it MAY poison its routes and delay before the rank to increase, then it MAY poison its routes and delay before
moving as described in Section 5.3.3.5. moving as described in Section 6.2.2.5.
5.3.3.5. Poisoning a Broken Path 6.2.2.5. Poisoning a Broken Path
1. A node MAY poison, in order to avoid being used as an ancestor by 1. A node MAY poison, in order to avoid being used as an ancestor by
the nodes in its sub-DODAG, by advertising an effective rank of the nodes in its sub-DODAG, by advertising an effective rank of
INFINITE_RANK and resetting the associated DIO trickle timer to INFINITE_RANK and resetting the associated DIO trickle timer to
cause this INFINITE_RANK to be announced promptly. cause this INFINITE_RANK to be announced promptly.
2. The node MAY advertise an effective rank of INFINITE_RANK for an 2. The node MAY advertise an effective rank of INFINITE_RANK for an
arbitrary number of DIO timer events, before announcing a new arbitrary number of DIO timer events, before announcing a new
rank. rank.
3. As per Section 5.3.3.4, the node MUST advertise INFINITE_RANK 3. As per Section 6.2.2.4, the node MUST advertise INFINITE_RANK
within the DODAG iteration in which it participates, if its within the DODAG version in which it participates, if its
revision in rank would exceed the maximum rank increase. revision in rank would exceed the maximum rank increase.
An implementation may choose to employ this poisoning mechanism when An implementation may choose to employ this poisoning mechanism when
a node loses all of its current parents, i.e. the set of DODAG a node loses all of its current parents, i.e. the set of DODAG
parents becomes depleted, and it can not jump to an alternate DODAG. parents becomes depleted, and it can not jump to an alternate DODAG.
An alternate mechanism is to form a floating DODAG. An alternate mechanism is to form a floating DODAG.
The motivation for delaying announcement of the revised route through The motivation for delaying announcement of the revised route through
multiple DIO events is to (i) increase tolerance to DIO loss, (ii) multiple DIO events is to (i) increase tolerance to DIO loss, (ii)
allow time for the poisoning action to propagate, and (iii) to allow time for the poisoning action to propagate, and (iii) to
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effect, since children with alternate parents should be able to effect, since children with alternate parents should be able to
utilize those alternates and retain their rank while the detached utilize those alternates and retain their rank while the detached
parent re-establishes its rank. parent re-establishes its rank.
Although an implementation may advertise INFINITE_RANK for the Although an implementation may advertise INFINITE_RANK for the
purposes of poisoning, it is not expected to be equivalent to setting purposes of poisoning, it is not expected to be equivalent to setting
the rank to INFINITE_RANK, and an implementation would likely retain the rank to INFINITE_RANK, and an implementation would likely retain
its rank value prior to the poisoning in some form, for purpose of its rank value prior to the poisoning in some form, for purpose of
maintaining its effective position within (L + DAGMaxRankIncrease). maintaining its effective position within (L + DAGMaxRankIncrease).
5.3.3.6. Detaching 6.2.2.6. 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
iteration MAY detach from this DODAG iteration. A node that version MAY detach from this DODAG version. A node that detaches
detaches becomes root of its own floating DODAG and SHOULD becomes root of its own floating DODAG and SHOULD immediately
immediately advertise this new situation in a DIO as an alternate advertise this new situation in a DIO as an alternate to
to poisoning. poisoning.
5.3.3.7. Following a Parent 6.2.2.7. 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 Iteration, A DODAG parent may have moved, migrated to the next DODAG Version, or
or jumped to a different DODAG. A node should give some preference jumped to a different DODAG. A node should give some preference to
to remaining in the current DODAG, if possible, but ought to follow remaining in the current DODAG, if possible via an alternate parent,
the parent if there are no other options. but ought to follow the parent if there are no other options.
5.3.4. DIO Message Communication 6.2.3. DIO Message Communication
When an DIO message is received, the receiving node must first When an 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 is silently discarded. A RPL eligible for further processing and MUST be silently discarded.
implementation MAY log the reception of a malformed DIO message. A RPL implementation MAY log the reception of a malformed DIO
message.
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, then the DIO is eligible for further processing. neighbor set, then the DIO is eligible for further processing.
5.3.4.1. DIO Message Processing 6.2.3.1. 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 5.3. When a node places a neighbor discovery as described in Section 6.2. 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 as per an
optimization objective, resulting in a more preferred parent at a optimization objective, resulting in a more preferred parent at a
greater rank). greater rank).
5.3.5. DIO Transmission 6.3. DIO Transmission
Each node maintains a timer, that governs when to multicast DIO
messages. This timer is a trickle timer, as detailed in
Section 5.3.5.1. The DIO Configuration Option includes the
configuration of a RPL Instance's trickle timer.
o When a node detects or causes an inconsistency, it MUST reset the RPL nodes transmit DIOs using a Trickle timer
trickle timer. ([I-D.ietf-roll-trickle]). A DIO from a sender with a lower DAGRank
that causes no changes to the recipient's parent set, preferred
parent, or Rank SHOULD be considered consistent with respect to the
Trickle timer.
o When a node migrates to a new DODAG Iteration it MUST reset the The following packets and events MUST be considered inconsistencies
trickle timer to its minimum value with respect to the Trickle timer, and cause the Trickle timer to
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 7.2, the node MUST reset the trickle timer. detailed in Section 8.2.
o When a node receives a multicast DIS message, it MUST reset the
trickle timer to its minimum value.
o When a node receives a unicast DIS message, it MUST unicast a DIO
message in response, and the response MUST include the DODAG
Configuration Object. This provides a means that an interrogating
node may be guaranteed to receive the DODAG Configuration Object,
which otherwise might not be included at the option of the sender.
In this case the node SHOULD NOT reset the trickle timer.
o If a node is not a member of a DODAG, it MUST suppress
transmission of DIO messages.
o When a node is initialized, it MAY be configured to remain silent
and not multicast any DIO messages until it has encountered and
joined a DODAG (perhaps initially probing for a nearby DODAG with
an DIS message). Alternately, it MAY choose to root its own
floating DODAG and begin multicasting DIO messages using a default
trickle configuration. The second case may be advantageous if it
is desired for independent nodes to begin aggregating into
scattered floating DODAGs, in the absence of a grounded node, for
example in support of LLN installation and commissioning.
5.3.5.1. Trickle Timer for DIO Transmission o When a node receives a multicast DIS message whose constraints
(Solicited Information) it satisfies.
RPL treats the construction of a DODAG as a consistency problem, and o When a node joins a new DODAG Version (e.g. by updating its
uses a trickle timer [Levis08] to control the rate of control DODAGVersionNumber, joining a new RPL Instance, etc.)
broadcasts.
For each DODAG that a node is part of (i.e. one DODAG per RPL Note that this list is not exhaustive, and an implementation MAY
Instance), the node must maintain a single trickle timer. The consider other messages or events to be inconsistencies.
required state contains the following conceptual items:
I: The current length of the communication interval If a node receives a unicast DIS message whose constraints (Solicited
Information) it satisfies, it MUST unicast a DIO in response, and
this DIO MUST include the RPL instance's DODAG Configuration object.
T: A timer with a duration set to a random value in the range 6.3.1. Trickle Parameters
[I/2, I]
C: Redundancy Counter The configuration parameters of the trickle timer are specified as
follows:
I_min: The smallest communication interval in milliseconds. This Imin: learned from the DIO message as (2^DIOIntervalMin)ms. The
value is learned from the DIO message as (2^DIOIntervalMin)ms. default value of DIOIntervalMin is DEFAULT_DIO_INTERVAL_MIN.
The default value is DEFAULT_DIO_INTERVAL_MIN.
I_doublings: The number of times I_min should be doubled before Imax: learned from the DIO message as DIOIntervalDoublings. The
maintaining a constant rate, i.e. I_max = I_min * default value of DIOIntervalDoublings is
2^I_doublings. This value is learned from the DIO message as
DIOIntervalDoublings. The default value is
DEFAULT_DIO_INTERVAL_DOUBLINGS. DEFAULT_DIO_INTERVAL_DOUBLINGS.
5.3.5.1.1. Resetting the Trickle Timer k: learned from the DIO message as DIORedundancyConstant. The
default value of DIORedundancyConstant is
The trickle timer for a DODAG is reset by: DEFAULT_DIO_REDUNDANCY_CONSTANT. In RPL, when k has the value
of 0x00 this is to be treated as a redundancy constant of
1. Setting I_min and I_doublings to the values learned from the infinity in RPL, i.e. Trickle never suppresses messages.
DODAG root via a received DIO message.
2. Setting C to zero.
3. If I is not equal to I_min:
1. Setting I to I_min.
2. Setting T to a random value as described above.
3. Restarting the trickle timer to expire after a duration T
When a node learns about a DODAG through a DIO message, and makes the
decision to join this DODAG, it initializes the state of the trickle
timer by resetting the trickle timer and listening. Each time it
hears a redundant DIO message for this DODAG, it MAY increment C. The
exact determination of what constitutes a redundant DIO message is
left to an implementation; it could for example include DIOs that
advertise the same rank.
When the timer fires at time T, the node compares C to the redundancy
constant, DIORedundancyConstant. If C is less than that value, or if
the DIORedundancyConstant value is 0xFF, the node generates a new DIO
message and multicasts it. When the communication interval I
expires, the node doubles the interval I so long as it has previously
doubled it fewer than I_doubling times, resets C, and chooses a new T
value.
5.3.5.1.2. Determination of Inconsistency
The trickle timer is reset whenever an inconsistency is detected
within the DODAG, for example:
o The node joins a new DODAG
o The node moves within a DODAG
o The node receives a DIO message from a DODAG parent that updates
the information learned from a prior DIO message for that DODAG
Parent
o A DODAG parent forwards a packet intended to move up, indicating
an inconsistency and possible loop.
o A metric communicated in the DIO message is determined to be
inconsistent, as according to a implementation specific path
metric selection engine.
o The rank of a DODAG parent has changed.
5.3.6. DODAG Selection 6.4. DODAG Selection
The DODAG selection is implementation and algorithm dependent. Nodes The DODAG selection is implementation and OF dependent. Nodes SHOULD
SHOULD prefer to join DODAGs for RPLInstanceIDs advertising OCPs and prefer to join DODAGs for RPLInstanceIDs advertising OCPs and
destinations compatible with their implementation specific destinations compatible with their implementation specific
objectives. In order to limit erratic movements, and all metrics objectives. In order to limit erratic movements, and all metrics
being equal, nodes SHOULD keep their previous selection. Also, nodes being equal, nodes SHOULD keep their previous selection. Also, nodes
SHOULD provide a means to filter out a parent whose availability is SHOULD provide a means to filter out a parent whose availability is
detected as fluctuating, at least when more stable choices are detected as fluctuating, at least when more stable choices are
available. available.
When connection to a fixed network 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.
5.4. Operation as a Leaf Node 6.5. 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 the RPL One example of such a case is when a node does not understand the RPL
Instance's OF. A leaf node does not extend DODAG connectivity but Instance's OF or advertised path metric. A leaf node does not extend
still needs to advertise its presence using DIOs. A node operating DODAG connectivity but still needs to advertise its presence using
as a leaf node must obey the following rules: DIOs. 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 transmit unicast DAOs as described in Section 6.2. 3. It MAY transmit unicast DAOs as described in Section 7.1.
4. It MAY transmit multicast DAOs to the '1 hop' neighborhood as 4. It MAY transmit multicast DAOs to the '1 hop' neighborhood as
described in Section 6.2.9. described in Section 7.1.9.
5.5. Administrative Rank 6.6. 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 by
a node beyond that computed by the OF based on some implementation a node beyond that computed by the OF based on some implementation
specific policy and properties of the node. For example, a node that specific policy and properties of the node. For example, a node that
has limited battery should be a leaf unless there is no other choice, has limited battery should be a leaf unless there is no other choice,
and may then augment the rank computation specified by the OF in and may then augment the rank computation specified by the OF in
order to expose an exaggerated rank. order to expose an exaggerated rank.
5.6. Collision 7. Downward Routes
A race condition occurs if 2 nodes send DIO messages at the same time
and then attempt to join each other. This might happen, for example,
between nodes which act as DODAG root of their own DODAGs. In order
to detect the situation, LLN Nodes time stamp the sending of DIO
message. Any DIO message received within a short link-layer-
dependent period introduces a risk. It left to the implementation to
define the duration of the risk window.
There is risk of a collision when a node receives and processes a DIO
within the risk window. For example, it may occur that two nodes are
associated with different DODAGs and near-simultaneously send DIO
messages, which are received and processed by both, and possibly
result in both nodes simultaneously deciding to attach to each other.
As a remedy, in the face of a potential collision, as determined by
receiving a DIO within the risk window, the DIO message is not
processed. It is expected that subsequent DIOs would not cross.
6. Downward Routes
This section describes how RPL discovers and maintains downward This section describes how RPL discovers and maintains downward
routes. Messages containing the Destination Advertisement Object routes. The use of messages containing the Destination Advertisement
(DAO), used to construct downward routes, are described. The Object (DAO), used to construct downward routes, are described. The
downward routes are necessary in support of P2MP flows, from the downward routes are necessary in support of P2MP flows, from the
DODAG roots toward the leaves. It specifies non-storing and storing DODAG roots toward the leaves. It specifies non-storing and storing
behavior of nodes with respect to DAO messaging and DAO routing table behavior of nodes with respect to DAO messaging and DAO routing table
entries. Nodes, as according to their resources and the entries. Nodes, as according to their resources and the
implementation, may selectively store routing table entries learned implementation, may selectively store routing table entries learned
from DAO messages, or may instead propagate the DAO information from DAO messages, or may instead propagate the DAO information
upwards while adding source routing information. A further upwards and independently source local topology information in a new
optimization is described whereby DAO messages may be used to DAO message. information. A further optimization is described
populate routing table entries for the '1-hop' neighbors, which may whereby DAO messages may be used to populate routing table entries
be useful in some cases as a shortcut for P2P flows. for the '1-hop' neighbors, which may be useful in some cases as a
shortcut for P2P flows.
6.1. Destination Advertisement Object (DAO)
The Destination Advertisement Object (DAO) is used to propagate
destination information upwards along the DODAG.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DAO Sequence | DAO Rank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID | Route Tag | Prefix Length | RRCount |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DAO Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Prefix (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Route Stack (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-option(s)...
+-+-+-+-+-+-+-+-+
Figure 11: The Destination Advertisement Object (DAO)
DAO Sequence: 16-bit unsigned integer. Incremented by the node that
owns the prefix for each new DAO message for that prefix.
DAO Rank: 16-bit unsigned integer indicating the DAO Rank associated
with the advertised Destination Prefix. The DAO Rank is
analogous to the Rank in the DIO message in that it may be used
to convey a relative distance to the Destination Prefix as
computed by the Objective Function in use over the DODAG. It
serves as a mechanism by which an ancestor node may order
alternate DAO paths.
RPLInstanceID: 8-bit field indicating the topology instance
associated with the DODAG, as learned from the DIO.
Route Tag: 8-bit unsigned integer. The Route Tag may be used to
give a priority to prefixes that should be stored. This may be
useful in cases where intermediate nodes are capable of storing
a limited amount of routing state. The further specification
of this field and its use is under investigation.
Prefix Length: 8-bit unsigned integer. Number of valid leading bits
in the IPv6 Prefix.
RRCount: 8-bit unsigned integer. This counter is used to count the
number of entries in the Reverse Route Stack. A value of '0'
indicates that no Reverse Route Stack is present.
DAO Lifetime: 32-bit unsigned integer. The length of time in
seconds (relative to the time the packet is sent) that the
prefix is valid for route determination. A value of all one
bits (0xFFFFFFFF) represents infinity. A value of all zero
bits (0x00000000) indicates a loss of reachability.
Destination Prefix: Variable-length field identifying an IPv6
destination address, prefix, or multicast group. The Prefix
Length field contains the number of valid leading bits in the
prefix. The bits in the prefix after the prefix length (if
any) are reserved and MUST be set to zero on transmission and
MUST be ignored on receipt.
Reverse Route Stack: Variable-length field containing a sequence of
RRCount (possibly compressed) IPv6 addresses. A node that adds
on to the Reverse Route Stack will append to the list and
increment the RRCount.
6.1.1. DAO Suboptions
The DAO message may optionally include a number of suboptions.
The DAO suboptions are in the same format as the DIO Suboptions
described in Section 6.1.1.
In particular, a DAO message may include a DAG Metric Container
suboption as described in Section 5.1.3.4. This suboption may be
present in implementations where the DAO Rank is insufficient to
optimize a path to the DAO Destination Prefix.
6.2. Downward Route Discovery and Maintenance 7.1. Downward Route Discovery and Maintenance
6.2.1. Overview 7.1.1. Overview
Destination Advertisement operation produces DAO messages that flow Destination Advertisement operation produces DAO messages that flow
up the DODAG, provisioning downward routing state for destination up the DODAG, provisioning downward routing state for destination
prefixes available in the sub-DODAG of the DODAG root, and possibly prefixes available in the sub-DODAG of the DODAG root, and possibly
other nodes. The routing state provisioned with this mechanism is in other nodes. The routing state provisioned with this mechanism is in
the form of soft-state routing table entries. DAO messages are able the form of soft-state routing table entries. DAO operation is
to record loose source routing information as by propagate up the presently defined in two distinct modes of operation, non-storing and
DODAG. This mechanism is flexible to support the provisioning of storing, and allowance is made for future expansion.
paths which consist of fully specified source routes, piecewise
source routes, or hop-by-hop routes as according to the
implementation and the capabilities of the nodes.
Destination Advertisement may or may not be enabled over a DODAG Destination Advertisement may or may not be enabled over a DODAG
rooted at a DODAG root. This is an a priori configuration determined rooted at a DODAG root. This is an a priori configuration determined
by the implementation/deployment and not generally changed during the by the implementation/deployment and not generally changed during the
operation of the RPL LLN. operation of the RPL LLN.
When Destination Advertisement is enabled: Destination Advertisement may be configured to operate in either a
storing or non-storing mode, as reported in the MOP in the DIO
message. Every node in the network participating in Destination
Advertisement must behave consistently with that configured mode of
operation, or alternately behave only as a leaf node. Hybrid or
mixed-mode operation is not currently specified.
1. Some nodes in the LLN MAY store at least one routing table entry When Destination Advertisement is enabled:
for a particular destination learned from a DAO. Such a node is
termed a 'storing node', with respect to that particular
destination.
2. Some nodes are capable to store at least one routing table entry 1. The RPL Instance will be configured a priori as appropriate to
for every unique destination observed from all DAOs that pass satisfy the application to operate in either non-storing or
through. Such a node is termed a 'fully storing node'. storing mode.
3. DODAG roots nodes SHOULD be fully-storing nodes. 2. All nodes who join the DODAG MUST abide with the MOP setting from
the root. Nodes that would not have the capability to fully
participate as a router (e.g. to operate as a storing node) can
still join as a leaf (i.e. host).
4. Other nodes in the DODAG are not required to store routing table 3. In storing mode operation, all non-root nodes are expected to
entries for any particular destinations observed in DAOs. Nodes either store routing table entries for ALL destinations learned
that do not store routing table entries from DAOs are termed from DAO operation, or to act as a leaf node only.
'non-storing nodes', with respect to a particular destination.
5. Non-storing nodes MUST participate in the construction of 4. In non-storing mode operation, no node other than the DODAG Root
piecewise source routes as they propagate the DAO message, as is expected to store routing table entries learned from DAO
described in Section 6.2.5. messages. Each node is only responsible to report its own set of
parents to the DODAG Root.
6. Storing nodes MUST store any source route information received 5. DODAG roots nodes SHOULD be capable to store routing table
from the DAO (RRStack) in the routing table entry entry. If a entries learned from DAO operation when the RPL Instance is
node is not capable to do this then it must act as a non-storing operated in a non-storing mode.
node with respect to that particular destination.
7. Storing nodes MUST use piecewise source routes in order to 6. The mode of operation in the RPL Instance is signaled from the
forward data across a non-storing region of the LLN. The source DODAG Root in the MOP control field of the DIO message.
routing mechanism is to be described in a companion
specification. (If a node is not capable to do this, then that
node MUST NOT operate as a storing node).
6.2.2. Mode of Operation 7.1.2. Mode of Operation
o DAO Operation may not be required for all use cases. o DAO Operation may not be required for all use cases.
o Some applications may only need support for collection/upward/MP2P o Some applications may only need support for collection/upward/MP2P
flow with no acknowledgement/reciprocal traffic. flow with no acknowledgement/reciprocal traffic.
o Some DODAGs may not support DAO Operation, which could mean that o Some DODAGs may not support DAO Operation, which could mean that
DAO Operation is wasteful overhead. DAO Operation is wasteful overhead.
o As a special case, multicast DAO operation may be used to populate o As a special case, multicast DAO operation may be used to populate
'one-hop' neighborhood routing table entries, and is distinct from 'one-hop' neighborhood routing table entries, and is distinct from
the unicast DAO operation used to establish downward routes along the unicast DAO operation used to establish downward routes along
the DODAG. the DODAG. This special case is an exception to the RPL Instance
mode of operation as well.
1. The 'A' flag in the DIO as conveyed from the DODAG root serves to 1. The 'A' flag in the DIO as conveyed from the DODAG root serves to
enable/disable DAO operation over the entire DODAG. This flag enable/disable DAO operation over the entire DODAG. This flag
should be administratively provisioned a priori at the DODAG root should be administratively provisioned a priori at the DODAG root
as a function of the implementation/deployment and not tend to as a function of the implementation/deployment and not tend to
change. change.
2. When DAO Operation is disabled, a node SHOULD NOT emit DAOs. 2. When DAO Operation is disabled, a node MUST NOT emit DAO
messages.
3. When DAO Operation is disabled, a node MAY ignore received DAOs. 3. When DAO Operation is disabled, a node MAY ignore the MOP field.
6.2.3. Destination Advertisement Parents 4. When DAO Operation is disabled, a node MAY ignore received DAO
messages.
o Nodes will select a subset of their DODAG Parents to whom DAOs 7.1.3. Destination Advertisement Parents
will be sent
o Nodes will select a subset of their DODAG Parents to whom DAO
messages will be sent
* This subset is the set of 'DAO Parents' * This subset is the set of 'DAO Parents'
* Each DAO parent MUST be a DODAG Parent. (Not all DODAG parents * Each DAO parent MUST be a DODAG Parent. (Not all DODAG parents
need to be DAO parents). need to be DAO parents).
* Operation with more than DAO Parent requires consideration of
such issues as DAO fan-out and path diversity, to be elaborated
in a future version of this specification.
o The selection of DAO parents is implementation specific and may be o The selection of DAO parents is implementation specific and may be
based on selecting the DODAG Parents that offer the best upwards based on selecting the DODAG Parents that offer the best upwards
cost (as opposed to downwards or mixed), as determined by the cost (as opposed to downwards or mixed), as determined by the
metrics in use and the Objective Function. metrics in use and the Objective Function.
o When DAO messages are unicast to the DAO Parent, the identity of o When DAO messages are unicast to the DAO Parent, the identity of
the DAO Parent (DODAGID x DAGSequenceNumber) combined with the the DAO Parent (DODAGID and DODAGVersionNumber) combined with the
RPLInstanceID in the DAO message unambiguously associates the DAO RPLInstanceID in the DAO message unambiguously associates the DAO
message, and thus the particular destination prefix, with a DODAG message, and thus the particular destination prefix, with a DODAG
Iteration. Version.
o When DAO messages are unicast to the DAO Parent, the DAO Rank may
be updated as according to the implementation and Objective
Function in use to reflect the relative (aggregated) cost of
reaching the Destination Prefix through that DAO parent. As a
further extension, a DAO Suboption for the Metric Container may be
included.
6.2.4. Operation of DAO Storing Nodes 7.1.4. DAO Operation on Storing Nodes
6.2.4.1. DAO Routing Table Entry 7.1.4.1. DAO Routing Table Entry
A DAO Routing Table Entry conceptually contains the following A DAO Routing Table Entry conceptually contains the following
elements: elements:
o Advertising Neighbor Information o Advertising Neighbor Information
* IPv6 Addr * IPv6 Address
* Interface ID * Interface ID
o To which DAO Parents has this entry been reported o To which DAO Parents has this entry been reported
o Retry Counter o Retry Counter
o Logical equivalent of DAO Content: o Logical equivalent of DAO Content:
* DAO Sequence * DAO Sequence
* DAO Rank
* DAO Lifetime * DAO Lifetime
* Route tag (used to prioritize which destination entries should * DAO Path Control (as learned from each child)
be stored)
* Destination Prefix (or Address or Mcast Group) * Destination Prefix (or Address or Mcast Group)
* RR Stack*
The DAO Routing Table Entry is logically associated with the The DAO Routing Table Entry is logically associated with the
following states: following states:
CONNECTED This entry is 'owned' by the node - it is manually CONNECTED This entry is 'owned' by the node - it is manually
configured and is considered as a 'self' entry for DAO configured and is considered as a 'self' entry for DAO
Operation Operation
REACHABLE This entry has been reported from a neighbor of the node. REACHABLE This entry has been reported from a neighbor of the node.
This state includes the following substates: This state includes the following substates:
skipping to change at page 46, line 22 skipping to change at page 57, line 29
UNREACHABLE This entry is being cleaned up. This entry may be UNREACHABLE This entry is being cleaned up. This entry may be
suppressed when the cleanup process is complete. suppressed when the cleanup process is complete.
When an attempt is to be made to report the DAO entry to DAO Parents, When an attempt is to be made to report the DAO entry to DAO Parents,
the DAO Entry record is logically marked to indicate that an attempt the DAO Entry record is logically marked to indicate that an attempt
has not yet been made for each parent. As the unicast attempts are has not yet been made for each parent. As the unicast attempts are
completed for each parent, this mark may be cleared. This mechanism completed for each parent, this mark may be cleared. This mechanism
may serve to limit DAO entry updates for each parent to a subset that may serve to limit DAO entry updates for each parent to a subset that
needs to be reported. needs to be reported.
6.2.4.1.1. DAO Routing Table Entry Management 7.1.4.1.1. DAO Routing Table Entry Management
+---------------------------------+ +---------------------------------+
| | | |
| REACHABLE | +-------------+ | REACHABLE | +-------------+
| | | | | | | |
| +-----------+ | | CONNECTED | | +-----------+ | | CONNECTED |
(*)----------->| |-------+ | | | (*)----------->| |-------+ | | |
| | Confirmed | | | +-------------+ | | Confirmed | | | +-------------+
| +-->| |---+ | | | +-->| |---+ | |
| | +-----------+ | | | | | +-----------+ | | |
skipping to change at page 46, line 43 skipping to change at page 58, line 4
| | | | | | | | | |
| | | | | | | | | |
| | | | | | | | | |
| | +-----------+ | | | +-------------+ | | +-----------+ | | | +-------------+
| | | |<--+ +-------->| | | | | |<--+ +-------->| |
| +---| Pending | | | UNREACHABLE | | +---| Pending | | | UNREACHABLE |
| | |---------------->| |--->(*) | | |---------------->| |--->(*)
| +-----------+ | +-------------+ | +-----------+ | +-------------+
| | | |
+---------------------------------+ +---------------------------------+
DAO Routing Table Entry FSM DAO Routing Table Entry FSM
6.2.4.1.1.1. Operation in the CONNECTED state 7.1.4.1.1.1. Operation in the CONNECTED state
1. CONNECTED DAO entries are to be provisioned outside of the 1. CONNECTED DAO entries are to be provisioned outside of the
context of RPL, e.g. through a management API. An implementation context of RPL, e.g. through a management API. An implementation
SHOULD provide a means to provision/manage CONNECTED DAO entries, SHOULD provide a means to provision/manage CONNECTED DAO entries,
including whether they are to be redistributed in RPL. including whether they are to be redistributed in RPL.
6.2.4.1.1.2. Operation in the REACHABLE state 7.1.4.1.1.2. Operation in the REACHABLE state
1. When a REACHABLE(*) entry times out, i.e. the DAO Lifetime has 1. When a REACHABLE(*) entry times out, i.e. the DAO Lifetime has
elapsed, the entry MUST be placed into the UNREACHABLE state and elapsed, the entry MUST be placed into the UNREACHABLE state and
no-DAO SHOULD be scheduled to send to the node's DAO Parents. No-Path SHOULD be scheduled to send to the node's DAO Parents.
2. When a no-DAO for a REACHABLE(*) entry is received with a newer 2. When a No-Path for a REACHABLE(*) entry is received with a newer
DAO Sequence Number, the entry MUST be placed into the DAO Sequence Number, the entry MUST be placed into the
UNREACHABLE state and no-DAO SHOULD be scheduled to send to the UNREACHABLE state and No-Path SHOULD be scheduled to send to the
node's DAO Parents. node's DAO Parents.
3. When a REACHABLE(*) entry is to be removed because NUD or 3. When a REACHABLE(*) entry is to be removed because NUD or
equivalent has determined that the next-hop neighbor is no longer equivalent has determined that the next-hop neighbor is no longer
reachable, the entry MUST be placed into the UNREACHABLE state reachable, the entry MUST be placed into the UNREACHABLE state
and no-DAO SHOULD be scheduled to send to the node's DAO Parents. and No-Path SHOULD be scheduled to send to the node's DAO
Parents.
4. When a REACHABLE(*) entry is to be removed because an associated 4. When a REACHABLE(*) entry is to be removed because an associated
Forwarding Error has been returned by the next-hop neighbor, the Forwarding Error has been returned by the next-hop neighbor, the
entry MUST be placed into the UNREACHABLE state and no-DAO SHOULD entry MUST be placed into the UNREACHABLE state and No-Path
be scheduled to send to the node's DAO Parents. SHOULD be scheduled to send to the node's DAO Parents.
5. When a DAO (or no-DAO) for a REACHABLE(*) entry is received with 5. When a DAO (or No-Path) for a REACHABLE(*) entry is received with
an older or unchanged DAO Sequence Number, then the DAO (or no- an older or unchanged DAO Sequence Number, then the DAO (or No-
DAO) SHOULD be ignored and the associated entry MUST NOT be Path) SHOULD be ignored and the associated entry MUST NOT be
updated with the stale information. updated with the stale information.
6.2.4.1.1.2.1. REACHABLE(Confirmed) 7.1.4.1.1.2.1. REACHABLE(Confirmed)
1. When a DAO for a previously unknown (or UNREACHABLE) destination 1. When a DAO for a previously unknown (or UNREACHABLE) destination
is received and is to be stored, it MUST be entered into the is received and is to be stored, it MUST be entered into the
routing table in the REACHABLE(Confirmed) state, and a DAO SHOULD routing table in the REACHABLE(Confirmed) state, and a DAO SHOULD
be scheduled to send to the node's DAO Parents. Alternately the be scheduled to send to the node's DAO Parents.
node may behave as a non-storing node with respect to this
destination.
2. When a DAO for a REACHABLE(Confirmed) entry is received with a 2. When a DAO for a REACHABLE(Confirmed) entry is received with a
newer DAO Sequence Number, the entry MUST be updated with the newer DAO Sequence Number, the entry MUST be updated with the
logical equivalent of the DAO contents and a DAO SHOULD be logical equivalent of the DAO contents and a DAO SHOULD be
scheduled to send to the node's DAO Parents. scheduled to send to the node's DAO Parents.
3. When a DAO for a REACHABLE(Confirmed) entry is expected, e.g. 3. When a DAO for a REACHABLE(Confirmed) entry is expected, e.g.
because a DIO to request a DAO refresh is sent, then the DAO because a DIO to request a DAO refresh is sent, then the DAO
entry MUST be placed in the REACHABLE(Pending) state and the entry MUST be placed in the REACHABLE(Pending) state and the
associated Retry Counter MUST be set to 0. associated Retry Counter MUST be set to 0.
6.2.4.1.1.2.2. REACHABLE(Pending) 7.1.4.1.1.2.2. REACHABLE(Pending)
1. When a DAO for a REACHABLE(Pending) entry is received with a 1. When a DAO for a REACHABLE(Pending) entry is received with a
newer DAO Sequence Number, the entry MUST be updated with the newer DAO Sequence Number, the entry MUST be updated with the
logical equivalent of the DAO contents and the entry MUST be logical equivalent of the DAO contents and the entry MUST be
placed in the REACHABLE(Confirmed) state. placed in the REACHABLE(Confirmed) state.
2. When a DAO for a REACHABLE(Pending) entry is expected, e.g. 2. When a DAO for a REACHABLE(Pending) entry is expected, e.g.
because DAO has (again) been triggered with respect to that because DAO has (again) been triggered with respect to that
neighbor, then the associated Retry Counter MUST be incremented. neighbor, then the associated Retry Counter MUST be incremented.
3. When the associated Retry Counter for a REACHABLE(Pending) entry 3. When the associated Retry Counter for a REACHABLE(Pending) entry
reaches a maximum threshold, the entry MUST be placed into the reaches a maximum threshold, the entry MUST be placed into the
UNREACHABLE state and no-DAO SHOULD be scheduled to send to the UNREACHABLE state and No-Path SHOULD be scheduled to send to the
node's DAO Parents. node's DAO Parents.
6.2.4.1.1.3. Operation in the UNREACHABLE state 7.1.4.1.1.3. Operation in the UNREACHABLE state
1. An implementation SHOULD bound the time that the entry is 1. An implementation SHOULD bound the time that the entry is
allocated in the UNREACHABLE state. Upon the equivalent expiry allocated in the UNREACHABLE state. Upon the equivalent expiry
of the related timer (RemoveTimer), the entry SHOULD be of the related timer (RemoveTimer), the entry SHOULD be
suppressed. suppressed.
2. While the entry is in the UNREACHABLE state a node SHOULD make a 2. While the entry is in the UNREACHABLE state a node SHOULD make a
reasonable attempt to report a no-DAO to each of the DAO parents. reasonable attempt to report a No-Path to each of the DAO
parents.
3. When the node has completed an attempt to report a no-DAO to each 3. When the node has completed an attempt to report a No-Path to
of the DAO parents, the entry SHOULD be suppressed. each of the DAO parents, the entry SHOULD be suppressed.
6.2.5. Operation of DAO Non-storing Nodes 7.1.4.2. Storing Mode DAO Message and Path Control
1. When a DAO is received from a child by a node who will not store In the storing mode of operation, a DAO message from a node will
a routing table entry for the DAO, the node MUST schedule to pass contain one or more Target Options, each Target Option specifying
the DAO contents along to its DAO parents. Prior to passing the either a CONNECTED destination or a destination in the sub-DODAG of
DAO along, the node MUST process the DAO as follows, in order the node.
that information necessary to construct a loose source route may
be accumulated within the DAO payload as it moves up the DODAG:
1. The most recent addition to the RRStack (the 'next waypoint') For each attempt made to report the DAO entry to a set of DAO
is investigated to determine if the node already has a route parents, the Path Control field will be constructed as follows:
provisioned to the waypoint. If the node already has such a
route, then it is not necessary to add additional information
to the RRStack. The node SHOULD NOT modify the RRStack
further.
2. If the node does not have a route provisioned to the next 1. The size of the path control field will be specified by the PCS
waypoint, then the node MUST append the address of the child control field of the DODAG Configuration Option. The default
to the RRStack, and increment RRCount. value is DEFAULT_PATH_CONTROL_SIZE.
6.2.6. Scheduling to Send DAO (or no-DAO) 2. For each unique destination to be reported that is CONNECTED, the
logical equivalent of a path control bitmap that is the size of
the path control field shall be initialized with the leftmost
bits set, where the number of leftmost bits corresponds to the
size of the path control field as specified by PCS.
3. For each unique destination to be reported that is not CONNECTED,
i.e. that destination is contained in the node's sub-DODAG, the
logical equivalent of a path control bitmap that is the size of
the path control field shall be initialized by ORing the content
of all of the Path Control fields received in DAO messages from
the node's children for that destination.
4. For each DAO Parent that the node shall attempt an update to, the
node shall exclusively allocate 1 or more set bits from the path
control bitmap to that DAO Parent. The path control bits SHOULD
be allocated in order of preference, such that the most
significant bits, or groupings of bits, are allocated to the most
preferred DAO parents as determined by the node. Once a bit from
the path control bitmap has been allocated to a DAO Parent for
this attempt, the corresponding bit MUST be set in the Path
Control field in the DAO message sent to that DAO Parent, and
that bit MUST NOT be allocated to any other DAO Parent.
5. A unicast DAO message may be sent for DAO Parents that have a
non-zero Path Control field.
6. If any DAO Parent is left without any bits set in its Path
Control field, then that a unicast DAO message MUST NOT be sent
to that DAO parent for this attempt.
7.1.5. Operation of DAO Non-storing Nodes
1. In the non-storing mode of operation, each node sending a DAO
message to its DODAG Parents will include a RPL Target option to
describe itself, followed by RPL Transit Information option(s) to
describe its parents. This information is sufficient for the
DODAG Root to collect the DODAG topology and construct source
routes in the downward direction.
2. In the non-storing mode of operation, each node receiving a DAO
message will arrange to pass the content of the DAO message along
to the DODAG Root. When possible the content of DAO messages may
be aggregated.
3. When a DAO is received from a child by a node who will not store
a routing table entry for the DAO, the node MUST schedule to pass
the DAO contents along to its DAO parents.
7.1.6. Scheduling to Send DAO (or No-Path)
1. An implementation SHOULD arrange to rate-limit the sending of 1. An implementation SHOULD arrange to rate-limit the sending of
DAOs. DAOs.
2. When scheduling to send a DAO, an implementation SHOULD 2. When scheduling to send a DAO, an implementation SHOULD
equivalently start a timer (DelayDAO) to delay sending the DAO. equivalently start a timer (DelayDAO) to delay sending the DAO.
If the DelayDAO timer is already running then the DAO may be If the DelayDAO timer is already running then the DAO may be
considered as already scheduled, and implementation SHOULD leave considered as already scheduled, and implementation SHOULD leave
the timer running at its present duration. the timer running at its present duration.
o When computing the delay before sending a DAO, in order to o When computing the delay before sending a DAO, in order to
increase the effectiveness of aggregation, an implementation MAY increase the effectiveness of aggregation, an implementation MAY
allow time to receive DAOs from its sub-DODAG prior to emitting allow time to receive DAOs from its sub-DODAG prior to emitting
DAOs to its DAO Parents. DAOs to its DAO Parents.
* The scheduled delay in such cases may be, for example, such * Suppose there is an implementation parameter DAO_LATENCY which
that DAO_LATENCY/DAGRank(self_rank) <= DelayDAO < DAO_LATENCY/ represents the maximum expected time for a DAO operation to
traverse the LLN from the farthest node to the root. The
scheduled delay in such cases may be, for example, such that
DAO_LATENCY/DAGRank(self_rank) <= DelayDAO < DAO_LATENCY/
DAGRank(parent_rank), where DAGRank() is defined as in DAGRank(parent_rank), where DAGRank() is defined as in
Section 3.6.2, such that nodes deeper in the DODAG may tend to Section 3.5.2, such that nodes deeper in the DODAG may tend to
report DAO messages first before their parent nodes will report report DAO messages first before their parent nodes will report
DAO messages. Note that this suggestion is intended as an DAO messages. Note that this suggestion is intended as an
optimization to allow efficient aggregation -- it is not optimization to allow efficient aggregation -- it is not
required for correct operation in the general case. required for correct operation in the general case.
6.2.7. Triggering DAO Message from the Sub-DODAG 7.1.7. Triggering DAO Message from the Sub-DODAG
Triggering DAO messages from the Sub-DODAG occurs by using the Triggering DAO messages from the Sub-DODAG occurs by using the
following control fields with the rules described below: following control fields with the rules described below:
The DTSN field from the DIO is a sequence number that is part of the The DTSN field from the DIO is a sequence number that is part of the
mechanism to trigger DAO messages. The motivation to use a sequence mechanism to trigger DAO messages. The motivation to use a sequence
number is to provide some means of reliable signaling to the sub- number is to provide some means of reliable signaling to the sub-
DODAG-- whereas a control flag that is activated for a short time may DODAG. Whereas a control flag that is activated for a short time may
be unobserved by the sub-DODAG if the triggering DIO messages are be unobserved by the sub-DODAG if the triggering DIO messages are
lost, the DTSN increment may be observed later even if some DIO lost, the DTSN increment may be observed later even if some
messages have been lost since the sequence number increment. intervening DIO messages have been lost.
The 'T' flag provides a way to signal the refresh of DAO information The 'T' flag provides a way to signal the refresh of DAO information
over the entire DODAG iteration. Whereas a DTSN increment may only over the entire DODAG version. Whereas a DTSN increment may only
trigger a DAO refresh as far as the nearest storing node (because a trigger a DAO refresh as far as the next storing node (because a
storing node will not increment its own DTSN in response, as storing node will not increment its own DTSN in response, as
described in the rules below), the assertion of the 'T' flag in described in the rules below), the assertion of the 'T' flag in
conjunction with an incremented DTSN will 'punch through' storing conjunction with an incremented DTSN will result in a DAO refresh
nodes to elicit a DAO refresh from the entire DODAG Iteration. from the entire DODAG.
The 'S' flag provides a way to signal to a sub-DODAG that there is at
least one non-root node somewhere in the set of DODAG ancestors,
where that non-root node is a storing node. This allows for an
optimization-- when it is clear to a non-storing node that the root
node can be the only storing ancestor, then that node does not
necessarily need to trigger updates from its sub-DODAG when it
modifies its DAO parent set. The motivation here is that the root
node should be able to update its stored source routing information
for the affected sub-DODAG based only on receiving DAO information
concerning the link that changed. In the other case, when the 'S'
flag is set, the non-storing node does not have a means to determine
which DAO information may (or may not) need to be updated in the
intermediate storing node so it must trigger DAO messages in order to
update the intermediate storing node. Please note that some aspects
of the proper use of the 'S' flag remain under investigation.
Further examples of triggering DAO messages are contained in
Appendix B.
The control fields are used to trigger DAO messages as follows: The control fields are used to trigger DAO messages as follows:
1. The DODAG root MUST clear the 'S' flag when it emits DIO 1. A DAO Trigger Sequence Number (DTSN) MUST be maintained by each
messages. node per RPL Instance. The DTSN, in conjunction with the 'T'
flag from the DIO message, provides a means by which DAO messages
2. Non-root nodes that store routing table entries learned from may be reliably triggered in the event of topology change.
DAOs MUST set the 'S' flag when they emit DIO messages.
3. A node that has any DAO Parent with the 'S' flag set MUST also
set the 'S' flag when it emits DIO messages.
4. A node that has all DAO Parents with cleared 'S' flags, and does
not store routing table entries learned from DAOs, MUST clear
the 'S' flag when it emits DIO messages.
5. A DAO Trigger Sequence Number (DTSN) MUST be maintained by each
node per RPL Instance. The DTSN, in conjunction with the 'T'
flag from the DIO message, provides a means by which DAO
messages may be reliably triggered in the event of topology
change.
6. The DTSN MUST be advertised by the node in the DIO message.
7. A node keeps track of the DTSN that it has heard from the last
DIO from each of its DAO Parents. Note that there is one DTSN
maintained per DAO Parent- each DAO Parent may independently
increment it at will.
8. A node that is not a fully-storing node SHOULD increment its own
DTSN when it adds a new parent, that parent having the 'S' flag
set, to its DAO Parent set. It MAY defer advertising the
increment as long as it has a DAO parent that already provides
adequate connectivity.
9. A node that is not a fully-storing node MUST increment its own
DTSN when it receives a DIO from a DAO Parent that contains a
newly incremented DTSN. (The newly incremented DTSN is detected
by comparing the value received in the DIO with the value last
recorded for that DAO parent).
10. A fully-storing node MUST increment its own DTSN when it 2. The DTSN MUST be advertised by the node in the DIO message.
receives a DIO from a DAO Parent that contains a newly
incremented DTSN and a set 'T' flag.
11. When a storing or non-storing node joins a new DODAG iteration, 3. A node keeps track of the DTSN that it has heard from the last
it SHOULD increment its DTSN as if the 'T' flag has been set. DIO from each of its DAO Parents. Note that there is one DTSN
maintained per DAO Parent- each DAO Parent may independently
increment it at will.
12. DAO Transmission SHOULD be scheduled when a new parent is added 4. DAO Transmission SHOULD be scheduled when a new parent is added
to the DAO Parent set. to the DAO Parent set.
13. A node that receives a newly incremented DTSN from a DAO Parent 5. A node that receives a newly incremented DTSN from a DAO Parent
MUST schedule a DAO transmission. MUST schedule a DAO transmission.
o When a node that is not fully-storing sees a DTSN increment, it o In storing mode operation, when a node sees a DTSN increment, it
will increment its own DTSN. This will cause the DTSN increment is caused to reissue its entire set of routing table entries
to extend down the DODAG to the first fully-storing node, which learned from DAO messages (or an aggregated subset thereof), but
will send its DAOs back up, rebuilding source routes information will not need to increment its own DTSN.
along the way to the first node that incremented the DTSN, who
then may report the new DAO information to its new parent.
o When a fully-storing node sees a DTSN increment, it is caused to o In either storing or non-storing modes of operation, when a node
reissue its entire set of routing table entries learned from DAOs sees a DTSN increment AND the 'T' flag is set, it does increment
(or an aggregated subset thereof), but will not need to increment its own DTSN as well. The 'T' flag 'punches through' all nodes,
its own DTSN. The 'DTSN increment wave' stops when it encounters causing all routing state from the entire sub-DODAG to be
fully-storing nodes. refreshed.
o When a fully-storing node sees a DTSN increment AND the 'T' flag 7.1.8. Sending DAO Messages to DAO Parents
is set, it does increment its own DTSN as well. The 'T' flag
'punches through' all nodes, causing all routing tables in the
entire sub-DODAG to be refreshed.
6.2.8. Sending DAO Messages to DAO Parents 1. DAO Messages sent to DAO Parents MUST be unicast.
1. When storing nodes send DAO messages for stored entries the * The IPv6 Source Address is a link local address of the node
RRStack SHOULD be cleared in the DAO message. sending the DAO message.
2. DAO Messages sent to DAO Parents MUST be unicast. * The IPv6 Destination Address is a link local address of the
DAO parent.
* The IPv6 Source Address is the node sending the DAO message. 2. A node MUST send the DAO with the same sequence to all its DAO
parents that are to be used on the way back to the DAO target.
* The IPv6 Destination Address is DAO parent. 3. When using source routing, a Destination that builds the DAO also
indicates its parent in the DAO as a Transit Information option.
If the node has multiple DAO parents, it MAY include one Transit
Information Option per parent and pass the DAO to one or more
parent. The Transit Information option indicates the preference
for that parent encoded in the Path Control bitfield.
3. When the appointed time arrives (DelayDAO) for the transmission 4. When the appointed time arrives (DelayDAO) for the transmission
of DAO messages (with jitter as appropriate) for the requested of DAO messages (with jitter as appropriate) for the requested
entries, the implementation MAY aggregate the the entries into a entries, the implementation MAY aggregate the the entries into a
reduced numbers of DAOs to be reported to each parent, and reduced numbers of DAOs to be reported to each parent, and
perform compression if possible. perform compression if possible.
4. Note: it is NOT RECOMMENDED that a DAO Transmission (No-DAO) be 5. Note: it is NOT RECOMMENDED that a DAO Transmission (No-Path) be
scheduled when a DAO Parent is removed from the DAO Parent set. scheduled when a DAO Parent is removed from the DAO Parent set.
6.2.9. Multicast Destination Advertisement Messages 6. A node MAY set the K flag in a unicast DAO message to solicit a
unicast DAO-ACK in response in order to confirm the attempt. A
node receiving a unicast DAO message with the K flag set SHOULD
respond with a DAO-ACK. A node receiving a DAO message without
the K flag set MAY respond with a DAO-ACK, especially to report
an error condition.
7.1.9. Multicast Destination Advertisement Messages
A special case of DAO operation, distinct from unicast DAO operation, A special case of DAO operation, distinct from unicast DAO operation,
is multicast DAO operation which may be used to populate '1-hop' is multicast DAO operation which may be used to populate '1-hop'
routing table entries. routing table entries.
1. A node MAY multicast a DAO message to the link-local scope all- 1. A node MAY multicast a DAO message to the link-local scope all-
nodes multicast address FF02::1. nodes multicast address FF02::1.
2. A multicast DAO message MUST be used only to advertise 2. A multicast DAO message MUST be used only to advertise
information about self, i.e. prefixes directly connected to or information about self, i.e. prefixes directly connected to or
skipping to change at page 52, line 48 skipping to change at page 64, line 5
5. A node MUST NOT perform any other DAO related processing on a 5. A node MUST NOT perform any other DAO related processing on a
received multicast DAO, in particular a node MUST NOT perform the received multicast DAO, in particular a node MUST NOT perform the
actions of a DAO parent upon receipt of a multicast DAO. actions of a DAO parent upon receipt of a multicast DAO.
o The multicast DAO may be used to enable direct P2P communication, o The multicast DAO may be used to enable direct P2P communication,
without needing the RPL routing structure to relay the packets. without needing the RPL routing structure to relay the packets.
o The multicast DAO does not presume any DODAG relationship between o The multicast DAO does not presume any DODAG relationship between
the emitter and the receiver. the emitter and the receiver.
7. Packet Forwarding and Loop Avoidance/Detection 8. Packet Forwarding and Loop Avoidance/Detection
7.1. Suggestions for Packet Forwarding
8.1. Suggestions for Packet Forwarding
When forwarding a packet to a destination, precedence is given to When forwarding a packet to a destination, precedence is given to
selection of a next-hop successor as follows: selection of a next-hop successor as follows:
1. In the scope of this specification, it is preferred to select a 1. This specification only covers how a successor is selected from
successor from a DODAG iteration that matches the RPLInstanceID the DODAG version that matches the RPLInstanceID marked in the
marked in the IPv6 header of the packet being forwarded. IPv6 header of the packet being forwarded. Routing outside the
instance can be done as long as additional rules are put in place
such as strict ordering of instances and routing protocols to
protect against loops.
2. If a local administrative preference favors a route that has been 2. If a local administrative preference favors a route that has been
learned from a different routing protocol than RPL, then use that learned from a different routing protocol than RPL, then use that
successor. successor.
3. If there is an entry in the routing table matching the 3. If there is an entry in the routing table matching the
destination that has been learned from a multicast destination destination that has been learned from a multicast destination
advertisement (e.g. the destination is a one-hop neighbor), then advertisement (e.g. the destination is a one-hop neighbor), then
use that successor. use that successor.
4. If there is an entry in the routing table matching the 4. If there is an entry in the routing table matching the
destination that has been learned from a unicast destination destination that has been learned from a unicast destination
advertisement (e.g. the destination is located down the sub- advertisement (e.g. the destination is located down the sub-
DODAG), then use that successor. DODAG), then use that successor. If there are DAO Path Control
bits associated with multiple successors, then consult the Path
Control bits to order the successors by preference when choosing.
5. If there is a DODAG iteration offering a route to a prefix 5. If there is a DODAG version offering a route to a prefix matching
matching the destination, then select one of those DODAG parents the destination, then select one of those DODAG parents as a
as a successor. successor according to the OF and routing metrics.
6. If there is a DODAG parent offering a default route then select 6. Any other as-yet-unattempted DODAG parent may be chosen for the
that DODAG parent as a successor. next attempt to forward a unicast packet when no better match
exists.
7. If there is a DODAG iteration offering a route to a prefix 7. If there is a DODAG version offering a route to a prefix matching
matching the destination, but all DODAG parents have been tried the destination, but all DODAG parents have been tried and are
and are temporarily unavailable (as determined by the forwarding temporarily unavailable (as determined by the forwarding
procedure), then select a DODAG sibling as a successor. procedure), then select a DODAG sibling as a successor (after
appropriate packet marking for loop detection as described in
Section 8.2.
8. Finally, if no DODAG siblings are available, the packet is 8. Finally, if no DODAG siblings are available, the packet is
dropped. ICMP Destination Unreachable may be invoked. An dropped. ICMP Destination Unreachable may be invoked (an
inconsistency is detected. inconsistency is detected).
TTL MUST be decremented when forwarding. If the packet is being TTL must be decremented when forwarding. If the packet is being
forwarded via a sibling, then the TTL MAY be decremented more forwarded via a sibling, then the TTL may be decremented more
aggressively (by more than one) to limit the impact of possible aggressively (by more than one) to limit the impact of possible
loops. loops.
Note that the chosen successor MUST NOT be the neighbor that was the Note that the chosen successor MUST NOT be the neighbor that was the
predecessor of the packet (split horizon), except in the case where predecessor of the packet (split horizon), except in the case where
it is intended for the packet to change from an up to an down flow, it is intended for the packet to change from an up to an down flow,
such as switching from DIO routes to DAO routes as the destination is such as switching from DIO routes to DAO routes as the destination is
neared. neared.
7.2. Loop Avoidance and Detection 8.2. Loop Avoidance and Detection
RPL loop avoidance mechanisms are kept simple and designed to RPL loop avoidance mechanisms are kept simple and designed to
minimize churn and states. Loops may form for a number of reasons, minimize churn and states. Loops may form for a number of reasons,
from control packet loss to sibling forwarding. RPL includes a from control packet loss to sibling forwarding. RPL includes a
reactive loop detection technique that protects from meltdown and reactive loop detection technique that protects from meltdown and
triggers repair of broken paths. triggers repair of broken paths.
RPL loop detection uses information that is placed into the packet in RPL loop detection uses information that is placed into the packet.
the IPv6 flow label. The IPv6 flow label is defined in [RFC2460] and A future version of this specification will detail how this
its operation is further specified in [RFC3697]. For the purpose of information is carried with the packet (e.g. a hop-by-hop option
RPL operations, the flow label is constructed as follows: ([I-D.hui-6man-rpl-option]) or summarized somehow into the flow
label). For the purpose of RPL operations, the information carried
with a packet is constructed follows:
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|O|S|R|F| SenderRank | RPLInstanceID | |O|S|R|F|0|0|0|0| RPLInstanceID | SenderRank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: RPL Flow Label RPL Packet Information
Down 'O' bit: 1-bit flag indicating whether the packet is expected Down 'O' bit: 1-bit flag indicating whether the packet is expected
to progress up or down. A router sets the 'O' bit when the to progress up or down. A router sets the 'O' bit when the
packet is expect to progress down (using DAO routes), and packet is expect to progress down (using DAO routes), and
resets it when forwarding towards the root of the DODAG resets it when forwarding towards the root of the DODAG
iteration. A host MUST set the bit to 0. version. A host or RPL leaf node MUST set the bit to 0.
Sibling 'S' bit: 1-bit flag indicating whether the packet has been Sibling 'S' bit: 1-bit flag indicating whether the packet has been
forwarded via a sibling at the present rank, and denotes a risk forwarded via a sibling at the present rank, and denotes a risk
of a sibling loop. A host sets the bit to 0. of a sibling loop. A host or RPL leaf node MUST set the bit to
0.
Rank-Error 'R' bit: 1-bit flag indicating whether a rank error was Rank-Error 'R' bit: 1-bit flag indicating whether a rank error was
detected. A rank error is detected when there is a mismatch in detected. A rank error is detected when there is a mismatch in
the relative ranks and the direction as indicated in the 'O' the relative ranks and the direction as indicated in the 'O'
bit. A host MUST set the bit to 0. bit. A host or RPL leaf node MUST set the bit to 0.
Forwarding-Error 'F' bit: 1-bit flag indicating that this node can Forwarding-Error 'F' bit: 1-bit flag indicating that this node can
not forward the packet further towards the destination. The not forward the packet further towards the destination. The
'F' bit might be set by sibling that can not forward to a 'F' bit might be set by sibling that can not forward to a
parent a packet with the Sibling 'S' bit set, or by a child parent a packet with the Sibling 'S' bit set, or by a child
node that does not have a route to destination for a packet node that does not have a route to destination for a packet
with the down 'O' bit set. A host MUST set the bit to 0. with the down 'O' bit set. A host or RPL leaf node MUST set
the bit to 0.
SenderRank: 8-bit field set to zero by the source and to
DAGRank(rank) by a router that forwards inside the RPL network.
(Note that the case where DAGRank(rank) does not fit into 8
bits is under investigation.)
RPLInstanceID: 8-bit field indicating the DODAG instance along which RPLInstanceID: 8-bit field indicating the DODAG instance along which
the packet is sent. the packet is sent.
7.2.1. Source Node Operation SenderRank: 16-bit field set to zero by the source and to
DAGRank(rank) by a router that forwards inside the RPL network.
A packet that is sourced at a node connected to a RPL network or 8.2.1. Source Node Operation
destined to a node connected to a RPL network MUST be issued with the
flow label zeroed out, but for the RPLInstanceID field.
If the source is aware of the RPLInstanceID that is preferred for the If the source is aware of the RPLInstanceID that is preferred for the
flow, then it MUST set the RPLInstanceID field in the flow label packet, then it MUST set the RPLInstanceID field associated with the
accordingly, otherwise it MUST set it to the RPL_DEFAULT_INSTANCE. packet accordingly, otherwise it MUST set it to the
RPL_DEFAULT_INSTANCE.
If a compression mechanism such as 6LoWPAN is applied to the packet,
the flow label MUST NOT be compressed even if it is set to all
zeroes.
7.2.2. Router Operation
7.2.2.1. Conformance to RFC 3697
[RFC3697] mandates that the Flow Label value set by the source MUST
be delivered unchanged to the destination node(s).
In order to restore the flow label to its original value, an RPL 8.2.2. Router Operation
router that delivers a packet to a destination connected to a RPL
network or that routes a packet outside the RPL network MUST zero out
all the fields but the RPLInstanceID field that must be delivered
without a change.
7.2.2.2. Instance Forwarding 8.2.2.1. Instance Forwarding
Instance IDs are used to avoid loops between DODAGs from different Instance IDs are used to avoid loops between DODAGs from different
origins. DODAGs that constructed for antagonistic constraints might origins. DODAGs that constructed for antagonistic constraints might
contain paths that, if mixed together, would yield loops. Those contain paths that, if mixed together, would yield loops. Those
loops are avoided by forwarding a packet along the DODAG that is loops are avoided by forwarding a packet along the DODAG that is
associated to a given instance. associated to a given instance.
The RPLInstanceID is placed by the source in the flow label. This The RPLInstanceID is associated by the source with the packet. This
RPLInstanceID MUST match the RPL Instance onto which the packet is RPLInstanceID MUST match the RPL Instance onto which the packet is
placed by any node, be it a host or router. placed by any node, be it a host or router. For traffic originating
outside of the RPL domain there may be a mapping occurring at the
gateway into the RPL domain, possibly based on an encoding within the
flow label. This aspect of RPL operation is to be clarified in a
future version of this specification.
When a router receives a packet that specifies a given RPLInstanceID When a router receives a packet that specifies a given RPLInstanceID
and the node can forward the packet along the DODAG associated to and the node can forward the packet along the DODAG associated to
that instance, then the router MUST do so and leave the RPLInstanceID that instance, then the router MUST do so and leave the RPLInstanceID
flag unchanged. value unchanged.
If any node can not forward a packet along the DODAG associated to If any node can not forward a packet along the DODAG associated to
the RPLInstanceID in the flow label, then the node SHOULD discard the the RPLInstanceID, then the node SHOULD discard the packet and send
packet. an ICMP error message.
7.2.2.3. DAG Inconsistency Loop Detection 8.2.2.2. DAG Inconsistency Loop Detection
The DODAG is inconsistent if the direction of a packet does not match The DODAG is inconsistent if the direction of a packet does not match
the rank relationship. A receiver detects an inconsistency if it the rank relationship. A receiver detects an inconsistency if it
receives a packet with either: receives a packet with either:
the 'O' bit set (to down) from a node of a higher rank. the 'O' bit set (to down) from a node of a higher rank.
the 'O' bit reset (for up) from a node of a lesser rank. the 'O' bit reset (for up) from a node of a lesser rank.
the 'S' bit set (to sibling) from a node of a different rank. the 'S' bit set (to sibling) from a node of a different rank.
When the DODAG root increments the DODAGSequenceNumber a temporary When the DODAG root increments the DODAGVersionNumber a temporary
rank discontinuity may form between the next iteration and the prior rank discontinuity may form between the next version and the prior
iteration, in particular if nodes are adjusting their rank in the version, in particular if nodes are adjusting their rank in the next
next iteration and deferring their migration into the next iteration. version and deferring their migration into the next version. A
A router that is still a member of the prior iteration may choose to router that is still a member of the prior version may choose to
forward a packet to a (future) parent that is in the next iteration. forward a packet to a (future) parent that is in the next version.
In some cases this could cause the parent to detect an inconsistency In some cases this could cause the parent to detect an inconsistency
because the rank-ordering in the prior iteration is not necessarily because the rank-ordering in the prior version is not necessarily the
the same as in the next iteration and the packet may be judged to not same as in the next version and the packet may be judged to not be
be making forward progress. If the sending router is aware that the making forward progress. If the sending router is aware that the
chosen successor has already joined the next iteration, then the chosen successor has already joined the next version, then the
sending router MUST update the SenderRank to INFINITE_RANK as it sending router MUST update the SenderRank to INFINITE_RANK as it
forwards the packets across the discontinuity into the next DODAG forwards the packets across the discontinuity into the next DODAG
iteration in order to avoid a false detection of rank inconsistency. version in order to avoid a false detection of rank inconsistency.
One inconsistency along the path is not considered as a critical One inconsistency along the path is not considered as a critical
error and the packet may continue. But a second detection along the error and the packet may continue. But a second detection along the
path of a same packet should not occur and the packet is dropped. path of a same packet should not occur and the packet is dropped.
This process is controlled by the Rank-Error bit in the Flow Label. This process is controlled by the Rank-Error bit associated with the
When an inconsistency, is detected on a packet, if the Rank-Error bit packet. When an inconsistency is detected on a packet, if the Rank-
was not set then the Rank-Error bit is set. If it was set the packet Error bit was not set then the Rank-Error bit is set. If it was set
is discarded and the trickle timer is reset. the packet is discarded and the trickle timer is reset.
7.2.2.4. Sibling Loop Avoidance 8.2.2.3. Sibling Loop Avoidance
When a packet is forwarded along siblings, it cannot be checked for When a packet is forwarded along siblings, it cannot be checked for
forward progress and may loop between siblings. Experimental forward progress and may loop between siblings. Experimental
evidence has shown that one sibling hop can be very useful but is evidence has shown that one sibling hop can be very useful and is
generally sufficient to avoid loops. Based on that evidence, this generally sufficient to avoid loops. Based on that evidence, this
specification enforces the simple rule that a packet may not make 2 specification enforces the simple rule that a packet may not make 2
sibling hops in a row. sibling hops in a row.
When a host issues a packet or when a router forwards a packet to a When a host issues a packet or when a router forwards a packet to a
non-sibling, the Sibling bit in the packet must be reset. When a non-sibling, the Sibling bit in the packet must be reset. When a
router forwards to a sibling: if the Sibling bit was not set then the router forwards to a sibling: if the Sibling bit was not set then the
Sibling bit is set. If the Sibling bit was set then then the router Sibling bit is set. If the Sibling bit was set then then the router
SHOULD return the packet to the sibling that that passed it with the SHOULD return the packet to the sibling that that passed it with the
Forwarding-Error 'F' bit set. Forwarding-Error 'F' bit set and the 'S' bit left untouched.
7.2.2.5. DAO Inconsistency Loop Detection and Recovery 8.2.2.4. DAO Inconsistency Loop Detection and Recovery
A DAO inconsistency happens when router that has an down DAO route A DAO inconsistency happens when router that has an down DAO route
via a child that is a remnant from an obsolete state that is not via a child that is a remnant from an obsolete state that is not
matched in the child. With DAO inconsistency loop recovery, a packet matched in the child. With DAO inconsistency loop recovery, a packet
can be used to recursively explore and cleanup the obsolete DAO can be used to recursively explore and cleanup the obsolete DAO
states along a sub-DODAG. states along a sub-DODAG.
In a general manner, a packet that goes down should never go up In a general manner, a packet that goes down should never go up
again. If DAO inconsistency loop recovery is applied, then the again. If DAO inconsistency loop recovery is applied, then the
router SHOULD send the packet to the parent that passed it with the router SHOULD send the packet back to the parent that passed it with
Forwarding-Error 'F' bit set. Otherwise the router MUST silently the Forwarding-Error 'F' bit set and the 'O' bit left untouched.
discard the packet. Otherwise the router MUST silently discard the packet.
7.2.2.6. Forward Path Recovery 8.2.2.5. Forward Path Recovery
Upon receiving a packet with a Forwarding-Error bit set, the node Upon receiving a packet with a Forwarding-Error bit set, the node
MUST remove the routing states that caused forwarding to that MUST remove the routing states that caused forwarding to that
neighbor, clear the Forwarding-Error bit and attempt to send the neighbor, clear the Forwarding-Error bit and attempt to send the
packet again. The packet may its way to an alternate neighbor. If packet again. The packet may be sent to an alternate neighbor. If
that alternate neighbor still has an inconsistent DAO state via this that alternate neighbor still has an inconsistent DAO state via this
node, the process will recurse, this node will set the Forwarding- node, the process will recurse, this node will set the Forwarding-
Error 'F' bit and the routing state in the alternate neighbor will be Error 'F' bit and the routing state in the alternate neighbor will be
cleaned up as well. cleaned up as well.
8. Multicast Operation 9. Multicast Operation
This section describes further the multicast routing operations over This section describes further the multicast routing operations over
an IPv6 RPL network, and specifically how unicast DAOs can be used to an IPv6 RPL network, and specifically how unicast DAOs can be used to
relay group registrations up. Wherever the following text mentions relay group registrations up. Wherever the following text mentions
Multicast Listener Discovery (MLD), one can read MLDv2 ([RFC3810]) or Multicast Listener Discovery (MLD), one can read MLDv1 ([RFC2710]) or
v3. MLDv2 ([RFC3810]).
As is traditional, a listener uses a protocol such as MLD with a As is traditional, a listener uses a protocol such as MLD with a
router to register to a multicast group. router to register to a multicast group.
Along the path between the router and the DODAG root, MLD requests Along the path between the router and the DODAG root, MLD requests
are mapped and transported as DAO messages within the RPL protocol; are mapped and transported as DAO messages within the RPL protocol;
each hop coalesces the multiple requests for a same group as a single each hop coalesces the multiple requests for a same group as a single
DAO message to the parent(s), in a fashion similar to proxy IGMP, but DAO message to the parent(s), in a fashion similar to proxy IGMP, but
recursively between child router and parent up to the root. recursively between child router and parent up to the root.
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the router will need to prune. the router will need to prune.
As a result, multicast routing states are installed in each router on As a result, multicast routing states are installed in each router on
the way from the listeners to the root, enabling the root to copy a the way from the listeners to the root, enabling the root to copy a
multicast packet to all its children routers that had issued a DAO multicast packet to all its children routers that had issued a DAO
message including a DAO for that multicast group, as well as all the message including a DAO for that multicast group, as well as all the
attached nodes that registered over MLD. attached nodes that registered over MLD.
For unicast traffic, it is expected that the grounded root of an For unicast traffic, it is expected that the grounded root of an
DODAG terminates RPL and MAY redistribute the RPL routes over the DODAG terminates RPL and MAY redistribute the RPL routes over the
external infrastructure using whatever routing protocol is used external infrastructure using whatever routing protocol is used in
there. For multicast traffic, the root MAY proxy MLD for all the the other routing domain. For multicast traffic, the root MAY proxy
nodes attached to the RPL routers (this would be needed if the MLD for all the nodes attached to the RPL domain (this would be
multicast source is located in the external infrastructure). For needed if the multicast source is located in the external
such a source, the packet will be replicated as it flows down the infrastructure). For such a source, the packet will be replicated as
DODAG based on the multicast routing table entries installed from the it flows down the DODAG based on the multicast routing table entries
DAO message. installed from the DAO message.
For a source inside the DODAG, the packet is passed to the preferred For a source inside the DODAG, the packet is passed to the preferred
parents, and if that fails then to the alternates in the DODAG. The parents, and if that fails then to the alternates in the DODAG. The
packet is also copied to all the registered children, except for the packet is also copied to all the registered children, except for the
one that passed the packet. Finally, if there is a listener in the one that passed the packet. Finally, if there is a listener in the
external infrastructure then the DODAG root has to further propagate external infrastructure then the DODAG root has to further propagate
the packet into the external infrastructure. the packet into the external infrastructure.
As a result, the DODAG Root acts as an automatic proxy Rendezvous As a result, the DODAG Root acts as an automatic proxy Rendezvous
Point for the RPL network, and as source towards the Internet for all Point for the RPL network, and as source towards the Internet for all
multicast flows started in the RPL LLN. So regardless of whether the multicast flows started in the RPL LLN. So regardless of whether the
root is actually attached to the Internet, and regardless of whether root is actually attached to the Internet, and regardless of whether
the DODAG is grounded or floating, the root can serve inner multicast the DODAG is grounded or floating, the root can serve inner multicast
streams at all times. streams at all times.
9. Maintenance of Routing Adjacency 10. Maintenance of Routing Adjacency
The selection of successors, along the default paths up along the The selection of successors, along the default paths up along the
DODAG, or along the paths learned from destination advertisements DODAG, or along the paths learned from destination advertisements
down along the DODAG, leads to the formation of routing adjacencies down along the DODAG, leads to the formation of routing adjacencies
that require maintenance. that require maintenance.
In IGPs such as OSPF [RFC4915] or IS-IS [RFC5120], the maintenance of In IGPs such as OSPF [RFC4915] or IS-IS [RFC5120], the maintenance of
a routing adjacency involves the use of Keepalive mechanisms (Hellos) a routing adjacency involves the use of Keepalive mechanisms (Hellos)
or other protocols such as BFD ([I-D.ietf-bfd-base]) and MANET or other protocols such as BFD ([I-D.ietf-bfd-base]) and MANET
Neighborhood Discovery Protocol (NHDP [I-D.ietf-manet-nhdp]). Neighborhood Discovery Protocol (NHDP [I-D.ietf-manet-nhdp]).
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Thus RPL makes use of a different approach consisting of probing the Thus RPL makes use of a different approach consisting of probing the
neighbor using a Neighbor Solicitation message (see [RFC4861]). The neighbor using a Neighbor Solicitation message (see [RFC4861]). The
reception of a Neighbor Advertisement (NA) message with the reception of a Neighbor Advertisement (NA) message with the
"Solicited Flag" set is used to verify the validity of the routing "Solicited Flag" set is used to verify the validity of the routing
adjacency. Such mechanism MAY be used prior to sending a data adjacency. Such mechanism MAY be used prior to sending a data
packet. This allows for detecting whether or not the routing packet. This allows for detecting whether or not the routing
adjacency is still valid, and should it not be the case, select adjacency is still valid, and should it not be the case, select
another feasible successor to forward the packet. another feasible successor to forward the packet.
10. Guidelines for Objective Functions 11. Guidelines for Objective Functions
An Objective Function (OF) allows for the selection of a DODAG to An Objective Function (OF) allows for the selection of a DODAG to
join, and a number of peers in that DODAG as parents. The OF is used join, and a number of peers in that DODAG as parents. The OF is used
to compute an ordered list of parents. The OF is also responsible to to compute an ordered list of parents. The OF is also responsible to
compute the rank of the device within the DODAG iteration. compute the rank of the device within the DODAG version.
The Objective Function is indicated in the DIO message using an The Objective Function is indicated in the DIO message using an
Objective Code Point (OCP), as specified in Objective Code Point (OCP), as specified in
[I-D.ietf-roll-routing-metrics], and indicates the method that must [I-D.ietf-roll-routing-metrics], and indicates the method that must
be used to construct the DODAG (e.g. "minimize the path cost using be used to construct the DODAG. The Objective Code Points are
the ETX metric and avoid 'Blue' links"). The Objective Code Points specified in [I-D.ietf-roll-routing-metrics], [I-D.ietf-roll-of0],
are specified in [I-D.ietf-roll-routing-metrics], and related companion specifications.
[I-D.ietf-roll-of0], and related companion specifications.
11.1. Objective Function Behavior
Most Objective Functions are expected to follow the same abstract Most Objective Functions are expected to follow the same abstract
behavior: behavior:
o The parent selection is triggered each time an event indicates o The parent selection is triggered each time an event indicates
that a potential next hop information is updated. This might that a potential next hop information is updated. This might
happen upon the reception of a DIO message, a timer elapse, or a happen upon the reception of a DIO message, a timer elapse, all
trigger indicating that the state of a candidate neighbor has DODAG parents are unavailable, or a trigger indicating that the
changed. state of a candidate neighbor has changed.
o An OF scans all the interfaces on the device. Although there may o An OF scans all the interfaces on the device. Although there may
typically be only one interface in most application scenarios, typically be only one interface in most application scenarios,
there might be multiple of them and an interface might be there might be multiple of them and an interface might be
configured to be usable or not for RPL operation. An interface configured to be usable or not for RPL operation. An interface
can also be configured with a preference or dynamically learned to can also be configured with a preference or dynamically learned to
be better than another by some heuristics that might be link-layer be better than another by some heuristics that might be link-layer
dependent and are out of scope. Finally an interface might or not dependent and are out of scope. Finally an interface might or not
match a required criterion for an Objective Function, for instance match a required criterion for an Objective Function, for instance
a degree of security. As a result some interfaces might be a degree of security. As a result some interfaces might be
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o An OF scans all the candidate neighbors on the possible interfaces o An OF scans all the candidate neighbors on the possible interfaces
to check whether they can act as a router for a DODAG. There to check whether they can act as a router for a DODAG. There
might be multiple of them and a candidate neighbor might need to might be multiple of them and a candidate neighbor might need to
pass some validation tests before it can be used. In particular, pass some validation tests before it can be used. In particular,
some link layers require experience on the activity with a router some link layers require experience on the activity with a router
to enable the router as a next hop. to enable the router as a next hop.
o An OF computes self's rank by adding to the rank of the candidate o An OF computes self's rank by adding to the rank of the candidate
a value representing the relative locations of self and the a value representing the relative locations of self and the
candidate in the DODAG iteration. candidate in the DODAG version.
* The increase in rank must be at least MinHopRankIncrease. * The increase in rank must be at least MinHopRankIncrease.
(This prevents the creation of a path of sibling links
connecting a child with its parent.)
* To keep loop avoidance and metric optimization in alignment, * To keep loop avoidance and metric optimization in alignment,
the increase in rank should reflect any increase in the metric the increase in rank should reflect any increase in the metric
value. For example, with a purely additive metric such as ETX, value. For example, with a purely additive metric such as ETX,
the increase in rank can be made proportional to the increase the increase in rank can be made proportional to the increase
in the metric. in the metric.
* Candidate neighbors that would cause self's rank to increase * Candidate neighbors that would cause self's rank to increase
are not considered for parent selection are not considered for parent selection
o Candidate neighbors that advertise an OF incompatible with the set o Candidate neighbors that advertise an OF incompatible with the set
of OF specified by the policy functions are ignored. of OF specified by the policy functions are ignored.
o As it scans all the candidate neighbors, the OF keeps the current o As it scans all the candidate neighbors, the OF keeps the current
best parent and compares its capabilities with the current best parent and compares its capabilities with the current
candidate neighbor. The OF defines a number of tests that are candidate neighbor. The OF defines a number of tests that are
critical to reach the objective. A test between the routers critical to reach the objective. A test between the routers
determines an order relation. determines an order relation.
* If the routers are roughly equal for that relation then the * If the routers are equal for that relation then the next test
next test is attempted between the routers, is attempted between the routers,
* Else the best of the 2 becomes the current best parent and the * Else the best of the two routers becomes the current best
scan continues with the next candidate neighbor parent and the scan continues with the next candidate neighbor
* Some OFs may include a test to compare the ranks that would * Some OFs may include a test to compare the ranks that would
result if the node joined either router result if the node joined either router
o When the scan is complete, the preferred parent is elected and o When the scan is complete, the preferred parent is elected and
self's rank is computed as the preferred parent rank plus the step self's rank is computed as the preferred parent rank plus the step
in rank with that parent. in rank with that parent.
o Other rounds of scans might be necessary to elect alternate o Other rounds of scans might be necessary to elect alternate
parents and siblings. In the next rounds: parents and siblings. In the next rounds:
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* Candidate neighbors that are of greater rank than self are * Candidate neighbors that are of greater rank than self are
ignored ignored
* Candidate neighbors of an equal rank to self (siblings) are * Candidate neighbors of an equal rank to self (siblings) are
ignored for parent selection ignored for parent selection
* Candidate neighbors of a lesser rank than self (non-siblings) * Candidate neighbors of a lesser rank than self (non-siblings)
are preferred are preferred
11. RPL Constants and Variables 12. RPL Constants and Variables
Following is a summary of RPL constants and variables. Following is a summary of RPL constants and variables.
BASE_RANK This is the rank for a virtual root that might be used to BASE_RANK This is the rank for a virtual root that might be used to
coordinate multiple roots. BASE_RANK has a value of 0. coordinate multiple roots. BASE_RANK has a value of 0.
ROOT_RANK This is the rank for a DODAG root. ROOT_RANK has a value ROOT_RANK This is the rank for a DODAG root. ROOT_RANK has a value
of 1. of MinHopRankIncrease (as advertised by the DODAG root), such
that DAGRank(ROOT_RANK) is 1.
INFINITE_RANK This is the constant maximum for the rank. INFINITE_RANK This is the constant maximum for the rank.
INFINITE_RANK has a value of 0xFFFF. INFINITE_RANK has a value of 0xFFFF.
RPL_DEFAULT_INSTANCE This is the RPLInstanceID that is used by this RPL_DEFAULT_INSTANCE This is the RPLInstanceID that is used by this
protocol by a node without any overriding policy. protocol by a node without any overriding policy.
RPL_DEFAULT_INSTANCE has a value of 0. RPL_DEFAULT_INSTANCE has a value of 0.
DEFAULT_PATH_CONTROL_SIZE TBD (To be determined)
DEFAULT_DIO_INTERVAL_MIN TBD (To be determined) DEFAULT_DIO_INTERVAL_MIN TBD (To be determined)
DEFAULT_DIO_INTERVAL_DOUBLINGS TBD (To be determined) DEFAULT_DIO_INTERVAL_DOUBLINGS TBD (To be determined)
DEFAULT_DIO_REDUNDANCY_CONSTANT TBD (To be determined) DEFAULT_DIO_REDUNDANCY_CONSTANT TBD (To be determined)
DEFAULT_MIN_HOP_RANK_INCREASE TBD a power of two (To be determined)
DIO Timer One instance per DODAG that a node is a member of. Expiry DIO Timer One instance per DODAG that a node is a member of. Expiry
triggers DIO message transmission. Trickle timer with variable triggers DIO message transmission. Trickle timer with variable
interval in [0, DIOIntervalMin..2^DIOIntervalDoublings]. See interval in [0, DIOIntervalMin..2^DIOIntervalDoublings]. See
Section 5.3.5.1 Section 6.3.1
DAG Sequence Number Increment Timer Up to one instance per DODAG DAG Version Increment Timer Up to one instance per DODAG that the
that the node is acting as DODAG root of. May not be supported node is acting as DODAG root of. May not be supported in all
in all implementations. Expiry triggers revision of implementations. Expiry triggers increment of
DODAGSequenceNumber, causing a new series of updated DIO DODAGVersionNumber, causing a new series of updated DIO message
message to be sent. Interval should be chosen appropriate to to be sent. Interval should be chosen appropriate to
propagation time of DODAG and as appropriate to application propagation time of DODAG and as appropriate to application
requirements (e.g. response time vs. overhead). requirements (e.g. response time vs. overhead).
DelayDAO Timer Up to one instance per DAO parent (the subset of DelayDAO Timer Up to one instance per DAO parent (the subset of
DODAG parents chosen to receive destination advertisements) per DODAG parents chosen to receive destination advertisements) per
DODAG. Expiry triggers sending of DAO message to the DAO DODAG. Expiry triggers sending of DAO message to the DAO
parent. See Section 6.2.6 parent. See Section 7.1.6
RemoveTimer Up to one instance per DAO entry per neighbor (i.e. RemoveTimer Up to one instance per DAO entry per neighbor (i.e.
those neighbors that have given DAO messages to this node as a those neighbors that have given DAO messages to this node as a
DODAG parent) Expiry triggers a change in state for the DAO DODAG parent) Expiry triggers a change in state for the DAO
entry, setting up to do unreachable (No-DAO) advertisements or entry, setting up to do unreachable (No-Path) advertisements or
immediately deallocating the DAO entry if there are no DAO immediately deallocating the DAO entry if there are no DAO
parents. See Section 6.2.4.1.1.3 parents. See Section 7.1.4.1.1.3
12. Manageability Considerations 13. Manageability Considerations
The aim of this section is to give consideration to the manageability The aim of this section is to give consideration to the manageability
of RPL, and how RPL will be operated in LLN beyond the use of a MIB of RPL, and how RPL will be operated in LLN beyond the use of a MIB
module. The scope of this section is to consider the following module. The scope of this section is to consider the following
aspects of manageability: fault management, configuration, accounting aspects of manageability: fault management, configuration, accounting
and performance. and performance.
12.1. Control of Function and Policy 13.1. Control of Function and Policy
12.1.1. Initialization Mode 13.1.1. Initialization Mode
When a node is first powered up, it may either choose to stay silent When a node is first powered up, it may either choose to stay silent
and not send any multicast DIO message until it has joined a DODAG, and not send any multicast DIO message until it has joined a DODAG,
or to immediately root a transient DODAG and start sending multicast or to immediately root a transient DODAG and start sending multicast
DIO messages. A RPL implementation SHOULD allow configuring whether DIO messages. A RPL implementation SHOULD allow configuring whether
the node should stay silent or should start advertising DIO messages. the node should stay silent or should start advertising DIO messages.
Furthermore, the implementation SHOULD to allow configuring whether Furthermore, the implementation SHOULD to allow configuring whether
or not the node should start sending an DIS message as an initial or not the node should start sending an DIS message as an initial
probe for nearby DODAGs, or should simply wait until it received DIO probe for nearby DODAGs, or should simply wait until it received DIO
messages from other nodes that are part of existing DODAGs. messages from other nodes that are part of existing DODAGs.
12.1.2. DIO Base option 13.1.2. DIO Base option
RPL specifies a number of protocol parameters. RPL specifies a number of protocol parameters.
A RPL implementation SHOULD allow configuring the following routing A RPL implementation SHOULD allow configuring the following routing
protocol parameters, which are further described in Section 5.1.1: protocol parameters, which are further described in Section 5.3:
DAGPreference DAGPreference
RPLInstanceID RPLInstanceID
DAGObjectiveCodePoint DAGObjectiveCodePoint
DODAGID DODAGID
Destination Prefixes Routing Information
Prefix Information
DIOIntervalDoublings DIOIntervalDoublings
DIOIntervalMin DIOIntervalMin
DIORedundancyConstant DIORedundancyConstant
DAG Root behavior: In some cases, a node may not want to permanently DAG Root behavior: In some cases, a node may not want to permanently
act as a DODAG root if it cannot join a grounded DODAG. For act as a DODAG root if it cannot join a grounded DODAG. For
example a battery-operated node may not want to act as a DODAG example a battery-operated node may not want to act as a DODAG
root for a long period of time. Thus a RPL implementation MAY root for a long period of time. Thus a RPL implementation MAY
support the ability to configure whether or not a node could support the ability to configure whether or not a node could
act as a DODAG root for a configured period of time. act as a DODAG root for a configured period of time.
DODAG Table Entry Suppression A RPL implementation SHOULD provide DODAG Table Entry Suppression A RPL implementation SHOULD provide
the ability to configure a timer after the expiration of which the ability to configure a timer after the expiration of which
logical equivalent of the DODAG table that contains all the logical equivalent of the DODAG table that contains all the
records about a DODAG is suppressed, to be invoked if the DODAG records about a DODAG is suppressed, to be invoked if the DODAG
parent set becomes empty. parent set becomes empty.
12.1.3. Trickle Timers 13.1.3. Trickle Timers
A RPL implementation makes use of trickle timer to govern the sending A RPL implementation makes use of trickle timer to govern the sending
of DIO message. Such an algorithm is determined a by a set of of DIO message. Such an algorithm is determined a by a set of
configurable parameters that are then advertised by the DODAG root configurable parameters that are then advertised by the DODAG root
along the DODAG in DIO messages. along the DODAG in DIO messages.
For each DODAG, a RPL implementation MUST allow for the monitoring of For each DODAG, a RPL implementation MUST allow for the monitoring of
the following parameters, further described in Section 5.3.5.1: the following parameters, further described in Section 6.3.1:
I I
T T
C C
I_min I_min
I_doublings I_doublings
A RPL implementation SHOULD provide a command (for example via API, A RPL implementation SHOULD provide a command (for example via API,
CLI, or SNMP MIB) whereby any procedure that detects an inconsistency CLI, or SNMP MIB) whereby any procedure that detects an inconsistency
may cause the trickle timer to reset. may cause the trickle timer to reset.
12.1.4. DAG Sequence Number Increment 13.1.4. DAG Version Number Increment
A RPL implementation may allow by configuration at the DODAG root to A RPL implementation may allow by configuration at the DODAG root to
refresh the DODAG states by updating the DODAGSequenceNumber. A RPL refresh the DODAG states by updating the DODAGVersionNumber. A RPL
implementation SHOULD allow configuring whether or not periodic or implementation SHOULD allow configuring whether or not periodic or
event triggered mechanism are used by the DODAG root to control event triggered mechanism are used by the DODAG root to control
DODAGSequenceNumber change. DODAGVersionNumber change.
12.1.5. Destination Advertisement Timers 13.1.5. Destination Advertisement Timers
The following set of parameters of the DAO messages SHOULD be The following set of parameters of the DAO messages SHOULD be
configurable: configurable:
o The DelayDAO timer o The DelayDAO timer
o The Remove timer o The Remove timer
12.1.6. Policy Control 13.1.6. Policy Control
DAG discovery enables nodes to implement different policies for DAG discovery enables nodes to implement different policies for
selecting their DODAG parents. selecting their DODAG parents.
A RPL implementation SHOULD allow configuring the set of acceptable A RPL implementation SHOULD allow configuring the set of acceptable
or preferred Objective Functions (OF) referenced by their Objective or preferred Objective Functions (OF) referenced by their Objective
Codepoints (OCPs) for a node to join a DODAG, and what action should Codepoints (OCPs) for a node to join a DODAG, and what action should
be taken if none of a node's candidate neighbors advertise one of the be taken if none of a node's candidate neighbors advertise one of the
configured allowable Objective Functions. configured allowable Objective Functions.
A node in an LLN may learn routing information from different routing A node in an LLN may learn routing information from different routing
protocols including RPL. It is in this case desirable to control via protocols including RPL. It is in this case desirable to control via
administrative preference which route should be favored. An administrative preference which route should be favored. An
implementation SHOULD allow for specifying an administrative implementation SHOULD allow for specifying an administrative
preference for the routing protocol from which the route was learned. preference for the routing protocol from which the route was learned.
A RPL implementation SHOULD allow for the configuration of the "Route 13.1.7. Data Structures
Tag" field of the DAO messages according to a set of rules defined by
policy.
12.1.7. Data Structures
Some RPL implementation may limit the size of the candidate neighbor Some RPL implementation may limit the size of the candidate neighbor
list in order to bound the memory usage, in which case some otherwise list in order to bound the memory usage, in which case some otherwise
viable candidate neighbors may not be considered and simply dropped viable candidate neighbors may not be considered and simply dropped
from the candidate neighbor list. from the candidate neighbor list.
A RPL implementation MAY provide an indicator on the size of the A RPL implementation MAY provide an indicator on the size of the
candidate neighbor list. candidate neighbor list.
12.2. Information and Data Models 13.2. Information and Data Models
The information and data models necessary for the operation of RPL The information and data models necessary for the operation of RPL
will be defined in a separate document specifying the RPL SNMP MIB. will be defined in a separate document specifying the RPL SNMP MIB.
12.3. Liveness Detection and Monitoring 13.3. Liveness Detection and Monitoring
The aim of this section is to describe the various RPL mechanisms The aim of this section is to describe the various RPL mechanisms
specified to monitor the protocol. specified to monitor the protocol.
As specified in Section 3.1, an implementation is expected to As specified in Section 3.1, an implementation is expected to
maintain a set of data structures in support of DODAG discovery: maintain a set of data structures in support of DODAG discovery:
o The candidate neighbors data structure o The candidate neighbors data structure
o For each DODAG: o For each DODAG:
* A set of DODAG parents * A set of DODAG parents
12.3.1. Candidate Neighbor Data Structure 13.3.1. Candidate Neighbor Data Structure
A node in the candidate neighbor list is a node discovered by the A node in the candidate neighbor list is a node discovered by the
some means and qualified to potentially become of neighbor or a some means and qualified to potentially become of neighbor or a
sibling (with high enough local confidence). A RPL implementation sibling (with high enough local confidence). A RPL implementation
SHOULD provide a way monitor the candidate neighbors list with some SHOULD provide a way monitor the candidate neighbors list with some
metric reflecting local confidence (the degree of stability of the metric reflecting local confidence (the degree of stability of the
neighbors) measured by some metrics. neighbors) measured by some metrics.
A RPL implementation MAY provide a counter reporting the number of A RPL implementation MAY provide a counter reporting the number of
times a candidate neighbor has been ignored, should the number of times a candidate neighbor has been ignored, should the number of
candidate neighbors exceeds the maximum authorized value. candidate neighbors exceeds the maximum authorized value.
12.3.2. Directed Acyclic Graph (DAG) Table 13.3.2. Directed Acyclic Graph (DAG) Table
For each DAG, a RPL implementation is expected to keep track of the For each DAG, a RPL implementation is expected to keep track of the
following DODAG table values: following DODAG table values:
o DODAGID o DODAGID
o DAGObjectiveCodePoint o DAGObjectiveCodePoint
o A set of prefixes offered upwards along the DODAG
o A set of Destination Prefixes offered upwards along the DODAG
o A set of DODAG Parents o A set of DODAG Parents
o timer to govern the sending of DIO messages for the DODAG o timer to govern the sending of DIO messages for the DODAG
o DODAGSequenceNumber o DODAGVersionNumber
The set of DODAG parents structure is itself a table with the The set of DODAG parents structure is itself a table with the
following entries: following entries:
o A reference to the neighboring device which is the DAG parent o A reference to the neighboring device which is the DAG parent
o A record of most recent information taken from the DAG Information o A record of most recent information taken from the DAG Information
Object last processed from the DODAG Parent Object last processed from the DODAG Parent
o A flag reporting if the Parent is a DAO Parent as described in o A flag reporting if the Parent is a DAO Parent as described in
Section 6 Section 7
12.3.3. Routing Table 13.3.3. Routing Table
For each route provisioned by RPL operation, a RPL implementation For each route provisioned by RPL operation, a RPL implementation
MUST keep track of the following: MUST keep track of the following:
o Destination Prefix o Routing Information (prefix, prefix length, ...)
o Destination Prefix Length
o Lifetime Timer o Lifetime Timer
o Next Hop o Next Hop
o Next Hop Interface o Next Hop Interface
o Flag indicating that the route was provisioned from one of: o Flag indicating that the route was provisioned from one of:
* Unicast DAO message * Unicast DAO message
* DIO message * DIO message
* Multicast DAO message * Multicast DAO message
12.3.4. Other RPL Monitoring Parameters 13.3.4. Other RPL Monitoring Parameters
A RPL implementation SHOULD provide a counter reporting the number of A RPL implementation SHOULD provide a counter reporting the number of
a times the node has detected an inconsistency with respect to a a times the node has detected an inconsistency with respect to a
DODAG parent, e.g. if the DODAGID has changed. DODAG parent, e.g. if the DODAGID has changed.
A RPL implementation MAY log the reception of a malformed DIO message A RPL implementation MAY log the reception of a malformed DIO message
along with the neighbor identification if avialable. along with the neighbor identification if avialable.
12.3.5. RPL Trickle Timers 13.3.5. RPL Trickle Timers
A RPL implementation operating on a DODAG root MUST allow for the A RPL implementation operating on a DODAG root MUST allow for the
configuration of the following trickle parameters: configuration of the following trickle parameters:
o The DIOIntervalMin expressed in ms o The DIOIntervalMin expressed in ms
o The DIOIntervalDoublings o The DIOIntervalDoublings
o The DIORedundancyConstant o The DIORedundancyConstant
A RPL implementation MAY provide a counter reporting the number of A RPL implementation MAY provide a counter reporting the number of
times an inconsistency (and thus the trickle timer has been reset). times an inconsistency (and thus the trickle timer has been reset).
12.4. Verifying Correct Operation 13.4. Verifying Correct Operation
This section has to be completed in further revision of this document This section has to be completed in further revision of this document
to list potential Operations and Management (OAM) tools that could be to list potential Operations and Management (OAM) tools that could be
used for verifying the correct operation of RPL. used for verifying the correct operation of RPL.
12.5. Requirements on Other Protocols and Functional Components 13.5. Requirements on Other Protocols and Functional Components
RPL does not have any impact on the operation of existing protocols. RPL does not have any impact on the operation of existing protocols.
12.6. Impact on Network Operation 13.6. Impact on Network Operation
To be completed. To be completed.
13. Security Considerations 14. Security Considerations
Security Considerations for RPL are to be developed in accordance +----------------------------------------------------------------+
with recommendations laid out in, for example, | |
[I-D.tsao-roll-security-framework]. | TBD |
| Under Construction |
| Deference given to Security Design Team |
| |
+----------------------------------------------------------------+
14. IANA Considerations 14.1. Overview
14.1. RPL Control Message
From a security perspective, RPL networks are no different from any
other network. They are vulnerable to passive eavesdropping attacks
and potentially even active tampering when physical access to a wire
is not required to participate in communications. The very nature of
ad hoc networks and their cost objectives impose additional security
constraints, which perhaps make these networks the most difficult
environments to secure. Devices are low-cost and have limited
capabilities in terms of computing power, available storage, and
power drain; and it cannot always be assumed they have neither a
trusted computing base nor a high-quality random number generator
aboard. Communications cannot rely on the online availability of a
fixed infrastructure and might involve short-term relationships
between devices that may never have communicated before. These
constraints might severely limit the choice of cryptographic
algorithms and protocols and influence the design of the security
architecture because the establishment and maintenance of trust
relationships between devices need to be addressed with care. In
addition, battery lifetime and cost constraints put severe limits on
the security overhead these networks can tolerate, something that is
of far less concern with higher bandwidth networks. Most of these
security architectural elements can be implemented at higher layers
and may, therefore, be considered to be outside the scope of this
standard. Special care, however, needs to be exercised with respect
to interfaces to these higher layers.
The security mechanisms in this standard are based on symmetric-key
and public-key cryptography and use keys that are to be provided by
higher layer processes. The establishment and maintenance of these
keys are outside the scope of this standard. The mechanisms assume a
secure implementation of cryptographic operations and secure and
authentic storage of keying material.
The security mechanisms specified provide particular combinations of
the following security services:
Data confidentiality: Assurance that transmitted information is only
disclosed to parties for which it is intended.
Data authenticity: Assurance of the source of transmitted
information (and, hereby, that information was not
modified in transit).
Replay protection: Assurance that a duplicate of transmitted
information is detected.
Timeliness (delay protection): Assurance that transmitted
information was received in a timely manner.
The actual protection provided can be adapted on a per-packet basis
and allows for varying levels of data authenticity (to minimize
security overhead in transmitted packets where required) and for
optional data confidentiality. When nontrivial protection is
required, replay protection is always provided.
Replay protection is provided via the use of a non-repeating value
(nonce) in the packet protection process and storage of some status
information for each originating device on the receiving device,
which allows detection of whether this particular nonce value was
used previously by the originating device. In addition, so-called
delay protection is provided amongst those devices that have a
loosely synchronized clock on board. The acceptable time delay can
be adapted on a per-packet basis and allows for varying latencies (to
facilitate longer latencies in packets transmitted over a multi-hop
communication path).
Cryptographic protection may use a key shared between two peer
devices (link key) or a key shared among a group of devices (group
key), thus allowing some flexibility and application-specific
tradeoffs between key storage and key maintenance costs versus the
cryptographic protection provided. If a group key is used for peer-
to-peer communication, protection is provided only against outsider
devices and not against potential malicious devices in the key-
sharing group.
Data authenticity may be provided using symmetric-key based or
public-key based techniques. With public-key based techniques (via
signatures), one corroborates evidence as to the unique originator of
transmitted information, whereas with symmetric-key based techniques
data authenticity is only provided relative to devices in a key-
sharing group. Thus, public-key based authentication may be useful
in scenarios that require a more fine-grained authentication than can
be provided with symmetric-key based authentication techniques alone,
such as with group communications (broadcast, multicast), or in
scenarios that require non-repudiation.
14.2. Functional Description of Packet Protection
14.2.1. Transmission of Outgoing Packets
This section describes the transmission of secured RPL control
packets. Give an outgoing RPL control packet and required security
protection, this section describes how RPL generates the secured
packet to transmit. It describes the order of cryptographic
operations to provide the required protection.
A RPL node MUST set the security section in the RPL packet to
describes the required protection level.
The Counter field of the security header MUST be an increment of the
last Counter field transmitted.
If the RPL packet is not a response to a Consistency Check message,
the node MAY set the Counter Compression field of the security
option. If the packet is a response to a Consistency Check message,
the node MUST clear the Counter Compression field.
A node sets the Key Identifier Mode (KIM) of the packet based on its
understanding of what keys destinations have.
A node MUST replaced the original packet payload with that payload
encrypted using the security protection, key, and nonce specified in
the security section.
14.2.2. Reception of Incoming Packets
This section describes the reception of a secured RPL packet. Given
an incoming RPL packet, this section describes now RPL generates an
unencrypted version of the packet and validates its integrity.
The receiver uses the security control field of the security section
to determine what processing to do. If the described level of
security does not meet locally maintained security policies, a node
MAY discard the packet without further processing. These policies
can include security levels, keys used, or source identifiers.