draft-ietf-roll-rpl-05.txt   draft-ietf-roll-rpl-06.txt 
Networking Working Group T. Winter, Ed. Networking Working Group T. Winter, Ed.
Internet-Draft Internet-Draft
Intended status: Standards Track P. Thubert, Ed. Intended status: Standards Track P. Thubert, Ed.
Expires: June 10, 2010 Cisco Systems Expires: August 7, 2010 Cisco Systems
ROLL Design Team ROLL Design Team
IETF ROLL WG IETF ROLL WG
December 7, 2009 February 03, 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-05 draft-ietf-roll-rpl-06
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 LLN routers, and support point-to-point traffic
skipping to change at page 2, line 8 skipping to change at page 2, line 8
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Design Principles . . . . . . . . . . . . . . . . . . . . 5 1.1. Design Principles . . . . . . . . . . . . . . . . . . . . 6
1.2. Expectations of Link Layer Type . . . . . . . . . . . . . 6 1.2. Expectations of Link Layer Type . . . . . . . . . . . . . 7
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Protocol Model . . . . . . . . . . . . . . . . . . . . . . . . 8 3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Instances, DODAGs, and DODAG Iterations . . . . . . . . . 8 3.1. Topology . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Traffic Flows . . . . . . . . . . . . . . . . . . . . . . 10 3.1.1. Topology Identifiers . . . . . . . . . . . . . . . . . 9
3.2.1. Multipoint-to-Point Traffic . . . . . . . . . . . . . 10 3.1.2. DODAG Information . . . . . . . . . . . . . . . . . . 10
3.2.2. Point-to-Multipoint Traffic . . . . . . . . . . . . . 10 3.2. Instances, DODAGs, and DODAG Iterations . . . . . . . . . 11
3.2.3. Point-to-Point Traffic . . . . . . . . . . . . . . . . 10 3.3. Traffic Flows . . . . . . . . . . . . . . . . . . . . . . 13
3.3. DODAG Construction . . . . . . . . . . . . . . . . . . . . 11 3.3.1. Multipoint-to-Point Traffic . . . . . . . . . . . . . 13
3.3.1. DAG Information Object (DIO) . . . . . . . . . . . . . 11 3.3.2. Point-to-Multipoint Traffic . . . . . . . . . . . . . 13
3.3.2. DAG Repair . . . . . . . . . . . . . . . . . . . . . . 11 3.3.3. Point-to-Point Traffic . . . . . . . . . . . . . . . . 13
3.3.3. Grounded and Floating DODAGs . . . . . . . . . . . . . 12 3.4. Upward Routes and DODAG Construction . . . . . . . . . . . 13
3.3.4. Administrative Preference . . . . . . . . . . . . . . 12 3.4.1. DAG Information Object (DIO) . . . . . . . . . . . . . 14
3.3.5. Objective Function (OF) . . . . . . . . . . . . . . . 12 3.4.2. DAG Repair . . . . . . . . . . . . . . . . . . . . . . 14
3.3.6. Distributed Algorithm Operation . . . . . . . . . . . 13 3.4.3. Grounded and Floating DODAGs . . . . . . . . . . . . . 15
3.4. Destination Advertisement . . . . . . . . . . . . . . . . 13 3.4.4. Administrative Preference . . . . . . . . . . . . . . 15
3.4.1. Destination Advertisement Object (DAO) . . . . . . . . 13 3.4.5. Objective Function (OF) . . . . . . . . . . . . . . . 15
4. Routing Metrics and Constraints Used By RPL . . . . . . . . . 14 3.4.6. Distributed Algorithm Operation . . . . . . . . . . . 15
5. Rank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.5. Downward Routes and Destination Advertisement . . . . . . 16
5.1. Loop Avoidance . . . . . . . . . . . . . . . . . . . . . . 15 3.5.1. Destination Advertisement Object (DAO) . . . . . . . . 16
5.1.1. Greediness and Rank-based Instabilities . . . . . . . 15 3.6. Routing Metrics and Constraints Used By RPL . . . . . . . 17
5.1.2. DODAG Loops . . . . . . . . . . . . . . . . . . . . . 16 3.6.1. Loop Avoidance . . . . . . . . . . . . . . . . . . . . 18
5.1.3. DAO Loops . . . . . . . . . . . . . . . . . . . . . . 16 3.6.2. Rank Properties . . . . . . . . . . . . . . . . . . . 19
5.1.4. Sibling Loops . . . . . . . . . . . . . . . . . . . . 16 4. ICMPv6 RPL Control Message . . . . . . . . . . . . . . . . . . 21
5.2. Rank Properties . . . . . . . . . . . . . . . . . . . . . 16 5. Upward Routes . . . . . . . . . . . . . . . . . . . . . . . . 22
6. RPL Protocol Specification . . . . . . . . . . . . . . . . . . 18 5.1. DODAG Information Object (DIO) . . . . . . . . . . . . . . 22
6.1. RPL Messages . . . . . . . . . . . . . . . . . . . . . . . 18 5.1.1. DIO Base Format . . . . . . . . . . . . . . . . . . . 22
6.1.1. ICMPv6 RPL Control Message . . . . . . . . . . . . . . 18 5.1.2. DIO Base Rules . . . . . . . . . . . . . . . . . . . . 24
6.1.2. DAG Information Solicitation (DIS) . . . . . . . . . . 19 5.1.3. DIO Suboptions . . . . . . . . . . . . . . . . . . . . 25
6.1.3. DAG Information Object (DIO) . . . . . . . . . . . . . 19 5.2. DODAG Information Solicitation (DIS) . . . . . . . . . . . 30
6.1.4. Destination Advertisement Object (DAO) . . . . . . . . 26 5.3. Upward Route Discovery and Maintenance . . . . . . . . . . 30
6.2. Protocol Elements . . . . . . . . . . . . . . . . . . . . 28 5.3.1. RPL Instance . . . . . . . . . . . . . . . . . . . . . 30
6.2.1. Topological Elements . . . . . . . . . . . . . . . . . 28 5.3.2. Neighbors and Parents within a DODAG Iteration . . . . 30
6.2.2. Neighbors, Parents, and Siblings . . . . . . . . . . . 28 5.3.3. Neighbors and Parents across DODAG Iterations . . . . 31
6.2.3. DODAG Information . . . . . . . . . . . . . . . . . . 29 5.3.4. DIO Message Communication . . . . . . . . . . . . . . 36
6.3. DAG Discovery and Maintenance . . . . . . . . . . . . . . 30 5.3.5. DIO Transmission . . . . . . . . . . . . . . . . . . . 36
6.3.1. DAG Discovery Rules . . . . . . . . . . . . . . . . . 31 5.3.6. DODAG Selection . . . . . . . . . . . . . . . . . . . 39
6.3.2. DIO Message Communication . . . . . . . . . . . . . . 35 5.4. Operation as a Leaf Node . . . . . . . . . . . . . . . . . 39
6.3.3. DIO Transmission . . . . . . . . . . . . . . . . . . . 36 5.5. Administrative Rank . . . . . . . . . . . . . . . . . . . 39
6.3.4. Trickle Timer for DIO Transmission . . . . . . . . . . 37 5.6. Collision . . . . . . . . . . . . . . . . . . . . . . . . 40
6.4. DAG Selection . . . . . . . . . . . . . . . . . . . . . . 38 6. Downward Routes . . . . . . . . . . . . . . . . . . . . . . . 40
6.5. Operation as a Leaf Node . . . . . . . . . . . . . . . . . 39 6.1. Destination Advertisement Object (DAO) . . . . . . . . . . 40
6.6. Administrative rank . . . . . . . . . . . . . . . . . . . 39 6.1.1. DAO Suboptions . . . . . . . . . . . . . . . . . . . . 42
6.7. Collision . . . . . . . . . . . . . . . . . . . . . . . . 39 6.2. Downward Route Discovery and Maintenance . . . . . . . . . 42
6.8. Establishing Routing State Down the DODAG . . . . . . . . 40 6.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . 42
6.8.1. Destination Advertisement Operation . . . . . . . . . 41 6.2.2. Mode of Operation . . . . . . . . . . . . . . . . . . 43
6.9. Loop Detection . . . . . . . . . . . . . . . . . . . . . . 48 6.2.3. Destination Advertisement Parents . . . . . . . . . . 44
6.9.1. Source Node Operation . . . . . . . . . . . . . . . . 49 6.2.4. Operation of DAO Storing Nodes . . . . . . . . . . . . 45
6.9.2. Router Operation . . . . . . . . . . . . . . . . . . . 49 6.2.5. Operation of DAO Non-storing Nodes . . . . . . . . . . 48
6.10. Multicast Operation . . . . . . . . . . . . . . . . . . . 51 6.2.6. Scheduling to Send DAO (or no-DAO) . . . . . . . . . . 48
6.11. Maintenance of Routing Adjacency . . . . . . . . . . . . . 52 6.2.7. Triggering DAO Message from the Sub-DODAG . . . . . . 49
7. Suggestions for Packet Forwarding . . . . . . . . . . . . . . 53 6.2.8. Sending DAO Messages to DAO Parents . . . . . . . . . 50
8. Guidelines for Objective Functions . . . . . . . . . . . . . . 54 6.2.9. Multicast Destination Advertisement Messages . . . . . 51
9. RPL Constants and Variables . . . . . . . . . . . . . . . . . 56 7. Packet Forwarding and Loop Avoidance/Detection . . . . . . . . 51
10. Manageability Considerations . . . . . . . . . . . . . . . . . 58 7.1. Suggestions for Packet Forwarding . . . . . . . . . . . . 51
10.1. Control of Function and Policy . . . . . . . . . . . . . . 58 7.2. Loop Avoidance and Detection . . . . . . . . . . . . . . . 52
10.1.1. Initialization Mode . . . . . . . . . . . . . . . . . 58 7.2.1. Source Node Operation . . . . . . . . . . . . . . . . 53
10.1.2. DIO Base option . . . . . . . . . . . . . . . . . . . 58 7.2.2. Router Operation . . . . . . . . . . . . . . . . . . . 54
10.1.3. Trickle Timers . . . . . . . . . . . . . . . . . . . . 59 8. Multicast Operation . . . . . . . . . . . . . . . . . . . . . 56
10.1.4. DAG Sequence Number Increment . . . . . . . . . . . . 59 9. Maintenance of Routing Adjacency . . . . . . . . . . . . . . . 57
10.1.5. Destination Advertisement Timers . . . . . . . . . . . 59 10. Guidelines for Objective Functions . . . . . . . . . . . . . . 58
10.1.6. Policy Control . . . . . . . . . . . . . . . . . . . . 59 11. RPL Constants and Variables . . . . . . . . . . . . . . . . . 60
10.1.7. Data Structures . . . . . . . . . . . . . . . . . . . 60 12. Manageability Considerations . . . . . . . . . . . . . . . . . 61
10.2. Information and Data Models . . . . . . . . . . . . . . . 60 12.1. Control of Function and Policy . . . . . . . . . . . . . . 61
10.3. Liveness Detection and Monitoring . . . . . . . . . . . . 60 12.1.1. Initialization Mode . . . . . . . . . . . . . . . . . 61
10.3.1. Candidate Neighbor Data Structure . . . . . . . . . . 61 12.1.2. DIO Base option . . . . . . . . . . . . . . . . . . . 62
10.3.2. Directed Acyclic Graph (DAG) Table . . . . . . . . . . 61 12.1.3. Trickle Timers . . . . . . . . . . . . . . . . . . . . 62
10.3.3. Routing Table . . . . . . . . . . . . . . . . . . . . 61 12.1.4. DAG Sequence Number Increment . . . . . . . . . . . . 63
10.3.4. Other RPL Monitoring Parameters . . . . . . . . . . . 62 12.1.5. Destination Advertisement Timers . . . . . . . . . . . 63
10.3.5. RPL Trickle Timers . . . . . . . . . . . . . . . . . . 62 12.1.6. Policy Control . . . . . . . . . . . . . . . . . . . . 63
10.4. Verifying Correct Operation . . . . . . . . . . . . . . . 62 12.1.7. Data Structures . . . . . . . . . . . . . . . . . . . 63
10.5. Requirements on Other Protocols and Functional 12.2. Information and Data Models . . . . . . . . . . . . . . . 64
Components . . . . . . . . . . . . . . . . . . . . . . . . 63 12.3. Liveness Detection and Monitoring . . . . . . . . . . . . 64
10.6. Impact on Network Operation . . . . . . . . . . . . . . . 63 12.3.1. Candidate Neighbor Data Structure . . . . . . . . . . 64
11. Security Considerations . . . . . . . . . . . . . . . . . . . 63 12.3.2. Directed Acyclic Graph (DAG) Table . . . . . . . . . . 64
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 63 12.3.3. Routing Table . . . . . . . . . . . . . . . . . . . . 65
12.1. RPL Control Message . . . . . . . . . . . . . . . . . . . 63 12.3.4. Other RPL Monitoring Parameters . . . . . . . . . . . 65
12.2. New Registry for RPL Control Codes . . . . . . . . . . . . 63 12.3.5. RPL Trickle Timers . . . . . . . . . . . . . . . . . . 66
12.3. New Registry for the Control Field of the DIO Base . . . . 64 12.4. Verifying Correct Operation . . . . . . . . . . . . . . . 66
12.4. DAG Information Object (DIO) Suboption . . . . . . . . . . 64 12.5. Requirements on Other Protocols and Functional
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 65 Components . . . . . . . . . . . . . . . . . . . . . . . . 66
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 65 12.6. Impact on Network Operation . . . . . . . . . . . . . . . 66
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 67 13. Security Considerations . . . . . . . . . . . . . . . . . . . 66
15.1. Normative References . . . . . . . . . . . . . . . . . . . 67 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 66
15.2. Informative References . . . . . . . . . . . . . . . . . . 67 14.1. RPL Control Message . . . . . . . . . . . . . . . . . . . 66
Appendix A. Requirements . . . . . . . . . . . . . . . . . . . . 69 14.2. New Registry for RPL Control Codes . . . . . . . . . . . . 67
A.1. Protocol Properties Overview . . . . . . . . . . . . . . . 69 14.3. New Registry for the Control Field of the DIO Base . . . . 67
A.1.1. IPv6 Architecture . . . . . . . . . . . . . . . . . . 69 14.4. DAG Information Object (DIO) Suboption . . . . . . . . . . 68
A.1.2. Typical LLN Traffic Patterns . . . . . . . . . . . . . 69 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 68
A.1.3. Constraint Based Routing . . . . . . . . . . . . . . . 70 16. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 69
A.2. Deferred Requirements . . . . . . . . . . . . . . . . . . 70 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 70 17.1. Normative References . . . . . . . . . . . . . . . . . . . 70
B.1. Destination Advertisement . . . . . . . . . . . . . . . . 72 17.2. Informative References . . . . . . . . . . . . . . . . . . 70
B.2. Example: DAG Parent Selection . . . . . . . . . . . . . . 73 Appendix A. Requirements . . . . . . . . . . . . . . . . . . . . 72
B.3. Example: DAG Maintenance . . . . . . . . . . . . . . . . . 75 A.1. Protocol Properties Overview . . . . . . . . . . . . . . . 72
B.4. Example: Greedy Parent Selection and Instability . . . . . 76 A.1.1. IPv6 Architecture . . . . . . . . . . . . . . . . . . 72
Appendix C. Outstanding Issues . . . . . . . . . . . . . . . . . 78 A.1.2. Typical LLN Traffic Patterns . . . . . . . . . . . . . 73
C.1. Additional Support for P2P Routing . . . . . . . . . . . . 78 A.1.3. Constraint Based Routing . . . . . . . . . . . . . . . 73
C.2. Loop Detection . . . . . . . . . . . . . . . . . . . . . . 78 A.2. Deferred Requirements . . . . . . . . . . . . . . . . . . 73
C.3. Destination Advertisement / DAO Fan-out . . . . . . . . . 78 Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 74
C.4. Source Routing . . . . . . . . . . . . . . . . . . . . . . 79 B.1. Destination Advertisement . . . . . . . . . . . . . . . . 75
C.5. Address / Header Compression . . . . . . . . . . . . . . . 79 B.2. Example: DODAG Parent Selection . . . . . . . . . . . . . 76
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 79 B.3. Example: DODAG Maintenance . . . . . . . . . . . . . . . . 78
B.4. Example: Greedy Parent Selection and Instability . . . . . 79
Appendix C. Outstanding Issues . . . . . . . . . . . . . . . . . 81
C.1. Additional Support for P2P Routing . . . . . . . . . . . . 81
C.2. Destination Advertisement / DAO Fan-out . . . . . . . . . 81
C.3. Source Routing . . . . . . . . . . . . . . . . . . . . . . 81
C.4. Address / Header Compression . . . . . . . . . . . . . . . 82
C.5. Managing Multiple Instances . . . . . . . . . . . . . . . 82
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 82
1. Introduction 1. Introduction
Low power and Lossy Networks (LLNs) are made 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 unicast, but in many cases point-to-multipoint or multipoint-
to-point. Furthermore such networks may potentially comprise up to to-point. Furthermore such networks may potentially comprise up to
thousands of nodes. These characteristics offer unique challenges to thousands of nodes. These characteristics offer unique challenges to
a routing solution: the IETF ROLL Working Group has defined a routing solution: the IETF ROLL Working Group has defined
application-specific routing requirements for a Low power and Lossy application-specific routing requirements for a Low power and Lossy
Network (LLN) routing protocol, specified in Network (LLN) routing protocol, specified in
[I-D.ietf-roll-building-routing-reqs], [I-D.ietf-roll-building-routing-reqs],
[I-D.ietf-roll-home-routing-reqs], [RFC5673], and [RFC5548]. This [I-D.ietf-roll-home-routing-reqs], [RFC5673], and [RFC5548]. This
document specifies the IPv6 Routing Protocol for Low power and Lossy document specifies the IPv6 Routing Protocol for Low power and lossy
Networks (RPL). networks (RPL).
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],
[I-D.ietf-roll-home-routing-reqs], [RFC5673], and [RFC5548]. Because [I-D.ietf-roll-home-routing-reqs], [RFC5673], and [RFC5548]. Because
those requirements are heterogeneous and sometimes incompatible in those requirements are heterogeneous and sometimes incompatible in
nature, the approach is first taken to design a protocol capable of nature, the approach is first taken to design a protocol capable of
supporting a core set of functionalities corresponding to the supporting a core set of functionalities corresponding to the
intersection of the requirements. As the RPL design evolves optional intersection of the requirements. As the RPL design evolves optional
skipping to change at page 7, line 10 skipping to change at page 7, line 10
and an optimization objective) to realize a desired objective in a and an optimization objective) to realize a desired objective in a
given environment. given environment.
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
As RPL is a routing protocol, it of course does not rely on any RPL does not rely on any particular features of a specific link layer
particular features of a specific link layer technology. RPL should technology. RPL is designed to be able to operate over a variety of
be able to operate over a variety of different link layers, including different link layers, including but not limited to, low power
but not limited to low power wireless or PLC (Power Line wireless or PLC (Power Line Communication) technologies.
Communication) technologies.
Implementers may find RFC 3819 [RFC3819] a useful reference when Implementers may find RFC 3819 [RFC3819] a useful reference when
designing a link layer interface between RPL and a particular link designing a link layer interface between RPL and a particular link
layer technology. layer 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].
This document requires readers to be familiar with the terminology Additionally, this document uses terminology from
described in `Terminology in Low power And Lossy Networks' [I-D.ietf-roll-terminology], and introduces the following
[I-D.ietf-roll-terminology]. terminology:
DAG: Directed Acyclic Graph. A directed graph having the property DAG: Directed Acyclic Graph. A directed graph having the property
that all edges are oriented in such a way that no cycles exist. that all edges are oriented in such a way that no cycles exist.
All edges are contained in paths oriented toward and All edges are contained in paths oriented toward and
terminating at one or more root nodes. terminating at one or more root nodes.
DAG Instance: A DAG Instance is a set of possibly multiple DAG root: A DAG root is a node within the DAG that has no outgoing
Destination Oriented DAGs. A network may have more than one edges. Because the graph is acyclic, by definition all DAGs
DAG Instance, and a RPL router can participate to multiple DAG must have at least one DAG root and all paths terminate at a
instances. Each DAG Instance operates independently of other DAG root.
DAG Instances. This document describes operation within a
single DAG instance.
InstanceID: Unique identifier of a DAG Instance.
Destination Oriented DAG (DODAG): A DAG rooted at a single Destination Oriented DAG (DODAG): A DAG rooted at a single
destination, which is a node with no outgoing edges. The tuple destination, i.e. at a single DAG root (the DODAG root) with no
(InstanceID, DAGID) uniquely identifies a Destination Oriented outgoing edges.
DAG (DODAG). In the RPL context, a router can can belong to at
most one DODAG per DAG Instance.
DAGID: The identifier of a DODAG root. The DAGID must be unique
within the scope of a DAG Instance in the LLN.
DODAG Iteration: A specific sequence number iteration of a DODAG. DODAG root: A DODAG root is the DAG root of a DODAG.
DAGSequenceNumber: A sequential counter that is incremented by the Rank: The rank of a node in a DAG identifies the nodes position with
root to form a new Iteration of a DODAG. A DODAG Iteration is respect to a DODAG root. The farther away a node is from a
identified uniquely by the (InstanceID, DAGID, DODAG root, the higher is the rank of that node. The rank of a
DAGSequenceNumber) tuple. node may be a simple topological distance, or may more commonly
be calculated as a function of other properties as described
later.
DAG parent: A parent of a node within a DAG is one of the immediate DODAG parent: A parent of a node within a DODAG is one of the
successors of the node on a path towards the DAG root. immediate successors of the node on a path towards the DODAG
root. The DODAG parent of a node will have a lower rank than
the node itself. (See Section 3.6.2.1).
DAG sibling: A sibling of a node within a DAG 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 DAG. Note that siblings defined in this the same rank within a DODAG. Note that siblings defined in
manner do not necessarily share a common parent. this manner do not necessarily share a common DODAG parent.
(See Section 3.6.2.1).
DAG root: A DAG root is a node within the DAG that has no outgoing Sub-DODAG The sub-DODAG of a node is the set of other nodes in the
edges. Because the graph is acyclic, by definition all DAGs DODAG that might use a path towards the DODAG root that
must have at least one DAG root and all paths terminate at a contains that node. Nodes in the sub-DODAG of a node have a
DAG root. greater rank than that node itself (although not all nodes of
greater rank are necessarily in the sub-DODAG of that node).
(See Section 3.6.2.1).
Sub-DAG The sub-DAG of a node is the set of other nodes in the DAG DODAGID: The identifier of a DODAG root. The DODAGID must be unique
that might use a path towards the DAG root that contains the within the scope of a RPL Instance in the LLN.
node. Nodes in the sub-DAG of a node have a greater rank
(although not all nodes of greater rank are in the sub-DAG). DODAG Iteration: A specific sequence number iteration ("version") of
a DODAG with a given DODAGID.
RPL Instance: A set of possibly multiple DODAGs. A network may have
more than one RPL Instance, and a RPL node can participate in
multiple RPL Instances. Each RPL Instance operates
independently of other RPL Instances. This document describes
operation within a single RPL Instance. In RPL, a node can
belong to at most one DODAG per RPL Instance. The tuple
(RPLInstanceID, DODAGID) uniquely identifies a DODAG.
RPLInstanceID: Unique identifier of a RPL Instance.
DODAGSequenceNumber: A sequential counter that is incremented by the
root to form a new Iteration of a DODAG. A DODAG Iteration is
identified uniquely by the (RPLInstanceID, DODAGID,
DODAGSequenceNumber) 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.
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.
OCP: Objective Code Point. The Objective Code Point is used to Objective Code Point (OCP): An identifier, used to indicate which
indicate which Objective Function is in use in 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].
OF: Objective Function. The Objective Function (OF) defines which Objective Function (OF): Defines which routing metrics, optimization
routing metrics, optimization objectives, and related functions objectives, and related functions are in use in a DODAG. The
are in use in a DODAG. The Objective Function is further Objective Function is further described in
described in [I-D.ietf-roll-routing-metrics]. [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 DAG is grounded when the root can reach the Goal of the Grounded: A DODAG is said to be grounded, when the root can reach
objective function. the Goal of the objective function.
Floating: A DAG is floating if is not Grounded. A floating DAG is Floating: A DODAG is floating if is not Grounded. A floating DODAG
not expected to reach the Goal defined for the OF. is not expected to reach the Goal defined for the OF.
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 Model 3. Protocol Overview
The aim of this section is to describe RPL in the spirit of The aim of this section is to describe RPL in the spirit of
[RFC4101]. Protocol details can be found in further sections. [RFC4101]. Protocol details can be found in further sections.
3.1. Instances, DODAGs, and DODAG Iterations 3.1. Topology
Each DAG instance constructs a routing topology optimized for a This section describes how the basic RPL topologies, and the rules by
certain Objective Function (OF). A DAG instance may provide routes which these are constructed, i.e. the rules governing DODAG
to certain destination prefixes. A single DAG instance contains one formation.
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 DAGID, such that nodes can 3.1.1. Topology Identifiers
identify the DODAG root.
A DAG instance may comprise: RPL uses four identifiers to track and control the topology:
o The first is a RPLInstanceID. A RPLInstanceID identifies a set of
one or more DODAGs. All DODAGs in the same RPL Instance use the
same OF. A network may have multiple RPLInstanceIDs, each of
which defines an independent set of DODAGs, which may be optimized
for different OFs and/or applications. The set of DODAGs
identified by a RPLInstanceID is called a RPL Instance.
o The second is a DODAGID. The scope of a DODAGID is a RPL
Instance. The combination of RPLInstanceID and DODAGID uniquely
identifies a single DODAG in the network. A RPL Instance may have
multiple DODAGs, each of which has an unique DODAGID.
o The third is a DODAGSequenceNumber. The scope of a
DODAGSequenceNumber is a DODAG. A DODAG is sometimes
reconstructed from the DODAG root, by incrementing the
DODAGSequenceNumber. The combination of RPLInstanceID, DODAGID,
and DODAGSequenceNumber uniquely identifies a DODAG Iteration.
o The fourth is rank. The scope of rank is a DODAG Iteration. Rank
establishes a partial order over a DODAG Iteration, defining
individual node positions with respect to the DODAG root.
3.1.2. DODAG Information
For each DODAG that a node is, or may become, a member of, the
implementation should conceptually keep track of the following
information for each DODAG. 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 DIO messages
3.2. Instances, DODAGs, and DODAG Iterations
Each RPL Instance constructs a routing topology optimized for a
certain Objective Function (OF). A RPL Instance may provide routes
to certain destination prefixes, reachable via the DODAG roots. A
single RPL Instance contains one or more Destination Oriented DAG
(DODAG) roots. These roots may operate independently, or may
coordinate over a non-LLN backchannel.
Each root has a unique identifier, the DODAGID.
A RPL Instance may comprise:
o a single DODAG with a single root o a single DODAG with a single root
* For example, a DODAG optimized to minimize latency rooted at a * For example, a DODAG optimized to minimize latency rooted at a
single centralized lighting controller in a home automation single centralized lighting controller in a home automation
application. application.
o multiple uncoordinated DODAGs with independent roots (differing o multiple uncoordinated DODAGs with independent roots (differing
DAGIDs) DODAGIDs)
* For example, multiple data collection points in an urban data * For example, multiple data collection points in an urban data
collection application that do not have an always-on backbone collection application that do not have an always-on backbone
suitable to coordinate to form a single DODAG, and further use suitable to coordinate to form a single DODAG, and further use
the formation of multiple DODAGs as a means to dynamically and the formation of multiple DODAGs as a means to dynamically and
autonomously partition the network. autonomously partition the network.
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 DAGID) 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 one of the above as suited to some application o a combination of one of the above as suited to some application
scenario. scenario.
Traffic is bound to a specific DODAG Instance by a marking in the Traffic is bound to a specific RPL Instance by a marking in the flow
flow label of the IPv6 header. Traffic originating in support of a label of the IPv6 header. Traffic originating in support of a
particular application may be tagged to follow an appropriate DAG particular application may be tagged to follow an appropriate RPL
instance, for example to follow paths optimized for low latency or instance which enables certain (path) properties, for example to
low energy. The provisioning or automated discovery of a mapping follow paths optimized for low latency or low energy. The
between an InstanceID and a type or service of application traffic is provisioning or automated discovery of a mapping between a
beyond the scope of this specification. RPLInstanceID and a type or service of application traffic is beyond
the scope of this specification.
An example of a DAG 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 is depicted in Figure 2. depicted in Figure 1. A DODAG Iteration (two "versions" of 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) |
| | /|\ |\ | / | |\ | | | | | | /|\ |\ | / | |\ | | | |
| | : : : : : | : (E) : : : : : | | | : : : : : | : (E) : : : : : |
| | | / \ | | | | / \ |
| +--------------+ : : | | +--------------+ : : |
| DODAG | | DODAG |
| | | |
+----------------------------------------------------------------+ +----------------------------------------------------------------+
DAG Instance RPL Instance
Figure 1: DAG Instance Figure 1: RPL Instance
+----------------+ +----------------+ +----------------+ +----------------+
| | | | | | | |
| (R1) | | (R1) | | (R1) | | (R1) |
| / \ | | / | | / \ | | / |
| / \ | | / | | / \ | | / |
| (A) (B) | \ | (A) | | (A) (B) | \ | (A) |
| /|\ |\ | ------\ | /|\ | | /|\ |\ | ------\ | /|\ |
| : : (C) : : | \ | : : (C) | | : : (C) : : | \ | : : (C) |
| | / | \ | | | / | \ |
| | ------/ | \ | | | ------/ | \ |
| | / | (B) | | | / | (B) |
| | | |\ | | | | |\ |
| | | : : | | | | : : |
| | | | | | | |
+----------------+ +----------------+ +----------------+ +----------------+
Sequence N Sequence N+1 Sequence N Sequence N+1
Figure 2: DODAG Iteration Figure 2: DODAG Iteration
3.2. Traffic Flows 3.3. Traffic Flows
3.2.1. Multipoint-to-Point Traffic 3.3.1. Multipoint-to-Point Traffic
Multipoint-to-Point (MP2P) is a dominant traffic flow in many LLN Multipoint-to-Point (MP2P) is a dominant traffic flow in many LLN
applications ([I-D.ietf-roll-building-routing-reqs], applications ([I-D.ietf-roll-building-routing-reqs],
[I-D.ietf-roll-home-routing-reqs], [RFC5673], [RFC5548]). The [I-D.ietf-roll-home-routing-reqs], [RFC5673], [RFC5548]). The
destinations of MP2P flows are designated nodes that have some destinations of MP2P flows are designated nodes that have some
application significance, such as providing connectivity to the application significance, such as providing connectivity to the
larger Internet or core private IP network. RPL supports MP2P larger Internet or core private IP network. RPL supports MP2P
traffic by allowing MP2P destinations to be reached via DODAG roots. traffic by allowing MP2P destinations to be reached via DODAG roots.
3.2.2. Point-to-Multipoint Traffic 3.3.2. Point-to-Multipoint Traffic
Point-to-multipoint (P2MP) is a traffic pattern required by several Point-to-multipoint (P2MP) is a traffic pattern required by several
LLN applications ([I-D.ietf-roll-building-routing-reqs], LLN applications ([I-D.ietf-roll-building-routing-reqs],
[I-D.ietf-roll-home-routing-reqs], [RFC5673], [RFC5548]). RPL [I-D.ietf-roll-home-routing-reqs], [RFC5673], [RFC5548]). RPL
supports P2MP traffic by using a destination advertisement mechanism supports P2MP traffic by using a destination advertisement mechanism
that provisions routes toward destination prefixes and away from that provisions routes toward destination prefixes and away from
roots. Destination advertisements can update routing tables as the roots. Destination advertisements can update routing tables as the
underlying DODAG topology changes. underlying DODAG topology changes.
3.2.3. Point-to-Point Traffic 3.3.3. Point-to-Point Traffic
RPL DODAGs provide a basic structure for point-to-point (P2P) RPL DODAGs provide a basic structure for point-to-point (P2P)
traffic. For a RPL network to support P2P traffic, a root must be traffic. For a RPL network to support P2P traffic, a root must be
able to route packets to a destination. Nodes within the network may able to route packets to a destination. Nodes within the network may
also have routing tables to destinations. A packet flows towards a also have routing tables to destinations. A packet flows towards a
root until it reaches an ancestor that has a known route to the root until it reaches an ancestor that has a known route to the
destination. destination.
RPL also supports the case where a P2P destination is a `one-hop' RPL also supports the case where a P2P destination is a 'one-hop'
neighbor. neighbor.
RPL neither specifies nor precludes additional mechanisms for RPL neither specifies nor precludes additional mechanisms for
computing and installing more optimal routes to support arbitrary P2P computing and installing more optimal routes to support arbitrary P2P
traffic. traffic.
3.3. DODAG Construction 3.4. 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) in use. RPL nodes
construct and maintain these DODAGs through exchange of DAG construct and maintain these DODAGs through exchange of DODAG
Information Object (DIO) messages. Undirected links between siblings Information Object (DIO) messages. Undirected links between siblings
are also identified during this process, which are used to provide are also identified during this process, which can be used to provide
additional diversity. additional diversity.
3.3.1. DAG Information Object (DIO) 3.4.1. DAG Information Object (DIO)
A DIO identifies the DAG Instance, the DAGID, the values used to A DIO identifies the RPL Instance, the DODAGID, the values used to
compute the DAG Instance's objective function, and the present DODAG compute the RPL Instance's objective function, and the present DODAG
Sequence Number. It can also include additional routing and Sequence Number. It can also include additional routing and
configuration information. The DIO includes a measure derived from configuration information. The DIO includes a measure derived from
the position of the node within the DODAG, the rank, which is used 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 for nodes to determine their positions relative to each other and to
inform loop avoidance/detection procedures. RPL exchanges DIO inform loop avoidance/detection procedures. RPL exchanges DIO
messages to establish and maintain routes. messages to establish and maintain routes.
RPL adapts the rate at which nodes send DIO messages. When a DODAG RPL adapts the rate at which nodes send DIO messages. When a DODAG
is detected to be inconsistent or needs repair, RPL sends DIO is detected to be inconsistent or needs repair, RPL sends DIO
messages more frequently. As the DODAG stabilizes, the DIO message messages more frequently. As the DODAG stabilizes, the DIO message
rate tapers off, reducing the maintenance cost of a steady and well- rate tapers off, reducing the maintenance cost of a steady and well-
working DODAG. working DODAG.
This document defines an ICMPv6 Message Type RPL Control Message, This document defines an ICMPv6 Message Type "RPL Control Message",
which is capable of carrying a DIO. which is capable of carrying a DIO.
3.3.2. DAG Repair 3.4.2. 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 to institute a global repair, increment the DODAG Sequence Number, thereby initiating a new DODAG
revising the DODAG and allowing nodes to choose an arbitrary new iteration. This institutes a global repair operation, revising the
position within the new DODAG iteration. DODAG and allowing nodes to choose an arbitrary new position within
the new DODAG iteration.
RPL may support mechanisms for local repair within the DODAG RPL supports mechanisms which may be used for local repair within the
iteration. The DIO message will specify the necessary parameters as DODAG iteration. The DIO message specifies the necessary parameters
configured from the DODAG root. Local repair options include the as configured from the DODAG root. Local repair options include the
allowing a node, upon detecting a loss of connectivity to a DODAG it allowing a node, upon detecting a loss of connectivity to a DODAG it
is a member of, to: is a member of, to:
o Poison its sub-DAG by advertising an effective rank of INFINITY, o Poison its sub-DODAG by advertising an effective rank of INFINITY
OR detach and form a floating DODAG in order to preserve inner to its sub-DODAG, OR detach and form a floating DODAG in order to
connectivity within its sub-DAG. preserve inner connectivity within its sub-DODAG.
o Move down the DODAG iteration in a limited manner, no further than o Move down within the DODAG iteration (i.e. increase its rank) in a
a bound configured via the DIO so as not to count all the way to limited manner, no further than a bound configured by the DODAG
infinity. Such a move may be undertaken after waiting an root via the DIO so as not to count all the way to infinity. Such
appropriate poisoning interval, and should allow the node to a move may be undertaken after waiting an appropriate poisoning
restore connectivity to the DODAG Iteration if possible. interval, and should allow the node to restore connectivity to the
DODAG Iteration, if at all possible.
3.3.3. Grounded and Floating DODAGs 3.4.3. 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 to 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.
3.3.4. Administrative Preference 3.4.4. 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.
3.3.5. Objective Function (OF) 3.4.5. 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 DAG 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, and its specification also
indicates the metrics and constraints in use. The OF also specifies indicates the metrics and constraints in use. The OF also specifies
the procedure used to compute rank within a DODAG iteration. Further the procedure used to compute rank within a DODAG iteration. Further
details may be found in [I-D.ietf-roll-routing-metrics] and related details may be found in [I-D.ietf-roll-routing-metrics],
companion specifications. [I-D.ietf-roll-of0], and related companion specifications.
By using defined OFs that are understood by all nodes in a particular By using defined OFs that are understood by all nodes in a particular
implementation, and by referencing them in the DIO message, RPL nodes deployment, and by referencing these in the DIO message, RPL nodes
may work to build optimized LLN routes using a variety of application may work to build optimized LLN routes using a variety of application
and implementation specific metrics and goals. and implementation specific metrics and goals.
In the case where a node is unable to encounter a suitable DAG In the case where a node is unable to encounter a suitable RPL
Instance using a known Objective Function, it may be configured to Instance using a known Objective Function, it may be configured to
join DAG Instance using and unknown Objective Function but only join a RPL Instance using an unknown Objective Function - but in that
acting as a leaf node. case only acting as a leaf node.
3.3.6. Distributed Algorithm Operation 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.
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 The nodes provision routing table entries for the destinations o Nodes provision routing table entries, for the destinations
specified by the DIO towards their parents in the DODAG iteration. specified by the DIO, via their DODAG parents in the DODAG
Nodes may provision a parent as a default gateway. iteration. Nodes may provision a DODAG parent as a default
gateway.
o Nodes may identify siblings within the DODAG iteration to increase o Nodes may identify DODAG siblings within the DODAG iteration to
path diversity. increase path diversity.
o Using both DIOs and possibly information in data packets, RPL o Using DIOs, and possibly information in data packets, RPL nodes
nodes detect possible routing loops. When a RPL node detects a detect possible routing loops. When a RPL node detects a possible
possible routing loop, it may adapt its DIO transmission rate to routing loop, it may adapt its DIO transmission rate to apply a
apply a local repair to the topology. This process and its local repair to the topology.
limitations is discussed in greater detail in 3.4.
3.4. Destination Advertisement 3.5. Downward Routes and Destination Advertisement
As RPL constructs and maintains DODAGs with DIO messages to establish RPL constructs and maintains DODAGs with DIO messages to establish
upward routes, it may use Destination Advertisement Object (DAO) upward routes: it uses Destination Advertisement Object (DAO)
messages to establish downward routes along the DODAG. DAO messages messages to establish downward routes along the DODAG as well as
and support for downward routes are an optional feature for other routes. DAO messages are an optional feature for applications
applications that require P2MP or P2P traffic. DIO messages that require P2MP or P2P traffic. DIO messages advertise whether
advertise whether the destination advertisement mechanism is enabled. destination advertisements are enabled within a given DODAG.
3.4.1. Destination Advertisement Object (DAO) 3.5.1. Destination Advertisement Object (DAO)
A Destination Advertisement Object (DAO) conveys destination A Destination Advertisement Object (DAO) conveys destination
information upwards along the DODAG so that a DODAG root (an other information upwards along the DODAG so that a DODAG root (an other
intermediate nodes) can provision downward routes. A DAO message intermediate nodes) can provision downward routes. A DAO message
includes prefix information to identify destinations, a capability to includes prefix information to identify destinations, a capability to
record routes in support of source routing, and information to record routes in support of source routing, and information to
determine the freshness of a particular advertisement. determine the freshness of a particular advertisement.
Nodes that are capable of maintaining routing state may aggregate Nodes that are capable of maintaining routing state may aggregate
routes from DAO messages that they receive before transmitting a DAO routes from DAO messages that they receive before transmitting a DAO
message. Nodes that are not capable to maintain routing state may message. Nodes that are not capable of maintaining routing state may
attach a next-hop address to the Reverse Route Stack contained within attach a next-hop address to the Reverse Route Stack contained within
the DAO message. The Reverse Route Stack is subsequently used to the DAO message. The Reverse Route Stack is subsequently used to
generate piecewise source routes over regions of the LLN that are generate piecewise source routes over regions of the LLN that are
incapable of storing downward routing state. incapable of storing downward routing state.
A special case of the DAO message, termed a no-DAO, is used to clear A special case of the DAO message, termed a no-DAO, is used to clear
downward routing state that has been provisioned through DAO downward routing state that has been provisioned through DAO
operation. operation.
This document defines an ICMPv6 Message Type RPL Control Message, This document defines an ICMPv6 Message Type "RPL Control Message",
which is capable to carry the DAO. which is capable of carrying a DAO.
3.4.1.1. `One-Hop' Neighbors 3.5.1.1. 'One-Hop' Neighbors
In addition to sending DAOs toward DODAG roots, RPL nodes may In addition to sending DAOs toward DODAG roots, RPL nodes may
occasionally emit a link-local multicast DAO message advertising occasionally emit a link-local multicast DAO message advertising
available destination prefixes. This mechanism allow provisioning a available destination prefixes. This mechanism allow provisioning a
trivial `one-hop' route to local neighbors. trivial 'one-hop' route to local neighbors.
4. Routing Metrics and Constraints Used By RPL 3.6. Routing Metrics and Constraints Used By RPL
Routing metrics are used by routing protocols to compute the 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; in all cases they are static metrics. Some routing
protocols support more than one metric: in the vast majority of the protocols support more than one metric: in the vast majority of the
cases, one metric is used per (sub)topology. Less often, a second cases, one metric is used per (sub)topology. Less often, a second
metric may be used as a tie-breaker in the presence of Equal Cost metric may be used as a tie-breaker in the presence of Equal Cost
Multiple Paths (ECMP). The optimization of multiple metrics is known Multiple Paths (ECMP). The optimization of multiple metrics is known
as an NP complete problem and is sometimes supported by some as an NP complete problem and is sometimes supported by some
centralized path computation engine. centralized path computation 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, 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 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 list satisfy a required constraint, it is 'pruned' from the candidate
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 advertise routing metrics The role of the Objective Function is to specify which routing
and constraints in addition to the objectives used to compute the metrics and constraints are in use, and how these are used, in
(constrained) shortest path. addition to the objectives used to compute the (constrained) shortest
path.
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
5. Rank 3.6.1. Loop Avoidance
5.1. Loop Avoidance
RPL guarantees neither loop free path selection nor strong global RPL guarantees neither loop free path selection nor strong global
convergence. In order to reduce control overhead, however, such as convergence. In order to reduce control overhead, however, such as
the cost of the count-to-infinity problem, RPL avoids creating loops the cost of the count-to-infinity problem, RPL avoids creating loops
when undergoing topology changes. Furthermore, RPL includes rank- when undergoing topology changes. Furthermore, RPL includes rank-
based mechanisms for detecting loops when they do occur. RPL uses based mechanisms for detecting loops when they do occur. RPL uses
this loop detection to ensure that packets make forward progress this loop detection to ensure that packets make forward progress
within the DODAG iteration and trigger repairs when necessary. within the DODAG iteration and trigger repairs when necessary.
5.1.1. Greediness and Rank-based Instabilities 3.6.1.1. Greediness and Rank-based Instabilities
Once a node has joined a DODAG, RPL disallows certain behaviors, Once a node has joined a DODAG iteration, RPL disallows certain
including greediness, in order to prevent resulting instabilities in behaviors, including greediness, in order to prevent resulting
the DODAG. instabilities in the DODAG iteration.
If a node is allowed to be greedy and attempts to move deeper in the If a node is allowed to be greedy and attempts to move deeper in the
DODAG, beyond its most preferred parent, in order to increase the DODAG iteration, beyond its most preferred parent, in order to
size of the parent set, then an instability can result. This is increase the size of the parent set, then an instability can result.
illustrated in Figure 16. This is illustrated in Figure 16.
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-DAG, and in general a node deeper than it. In a node in its own sub-DODAG, and in general a node deeper than
such cases a chance exists to create a feedback loop, wherein two or itself. In this case, a possibility exists that a feedback loop is
more nodes continue to try and move in the DODAG in order to optimize created, wherein two or more nodes continue to try and move in the
against each other. In some cases this will result in an DODAG iteration while attempting to optimize against each other. In
instability. It is for this reason that RPL limits the cases where a some cases, this will result in instability. It is for this reason
node may process DIO messages from deeper nodes to some forms of that RPL limits the cases where a node may process DIO messages from
local repair. This approach creates an `event horizon', whereby a deeper nodes to some forms of local repair. This approach creates an
node cannot be influenced beyond some limit into an instability by 'event horizon', whereby a node cannot be influenced beyond some
the action of nodes that may be in its own sub-DAG. limit into an instability by the action of nodes that may be in its
own sub-DODAG.
A further example of the consequences of greedy operation, and A further example of the consequences of greedy operation, and
instability related to processing DIO messages from nodes of greater instability related to processing DIO messages from nodes of greater
rank, may be found in Appendix B.4 rank, may be found in Appendix B.4
5.1.2. DODAG Loops 3.6.1.2. 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-DAG. 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 DAG
sequence number can eliminate this type of loop, but this type of sequence number can eliminate this type of loop, but this type of
loop may possibly be encountered when using some local repair loop may possibly be encountered when using some local repair
mechanisms. mechanisms.
5.1.3. DAO Loops 3.6.1.3. 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 state. This loop happens when a no- has subsequently cleaned up the state. This loop happens when a no-
DAO was missed until a heartbeat cleans up all states. RPL includes DAO was missed and persists until all state has been cleaned up. RPL
loop detection mechanisms that may mitigate the impact of DAO loops includes loop detection mechanisms that may mitigate the impact of
and trigger their repair. 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.
5.1.4. Sibling Loops 3.6.1.4. 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 to prevent sibling sibling forwarding may be used at a given rank, in order to prevent
loops. sibling loops.
5.2. Rank Properties 3.6.2. 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 iteration. 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 that of all metrics: are not necessarily those of all metrics:
Type: Rank is an abstract scalar. Some metrics are boolean (e.g. Type: Rank is an abstract scalar. Some metrics are boolean (e.g.
grounded), others are statistical and better expressed as a grounded), others are statistical and better expressed as a
tuple like an expected value and a variance. Some OCPs use tuple like an expected value and a variance. Some OCPs use
not one but a set of metrics bound by a piece of logic. 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: Rank is the expression of a relative position within a
DODAG iteration with regard to neighbors and, not necessarily DODAG iteration with regard to neighbors and is not
a good indication or a proper expression of a distance or a necessarily a good indication or a proper expression of a
cost to the root. distance or a cost to the root.
Stability: The stability of the rank determines that of the routing Stability: The stability of the rank determines the stability of the
topology. Some dampening or filtering might be applied to routing topology. Some dampening or filtering might be
keep the topology stable and the rank does not necessarily applied to keep the topology stable, and thus the rank does
change as fast as some physical metrics would. A new not necessarily change as fast as some physical metrics
iteration is a good opportunity to reconcile the would. A new DODAG iteration would be a good opportunity to
discrepancies that might form over time between the metrics reconcile the discrepancies that might form over time between
and the ranks. metrics and ranks within a DODAG iteration.
Granularity: Rank is coarse grained. A fine granularity would Granularity: Rank is coarse grained. A fine granularity would
prevent the selection of siblings. prevent the selection of siblings.
Properties: Rank is strictly monotonic and can be used to validate a Properties: Rank is strictly monotonic, and can be used to validate
progression from or towards the root. A metric like a progression from or towards the root. A metric, like
bandwidth or jitter does not necessarily exhibit such bandwidth or jitter, does not necessarily exhibit this
property. property.
Abstract: Rank does not have a physical unit, but rather a range of Abstract: Rank does not have a physical unit, but rather a range of
increment per hop that varies from 1 (best) to 16 (worst), increment per hop that varies from 1 (best) to 16 (worst),
where the assignment of each value is to be determined by the where the assignment of each value is to be determined by the
implementation. implementation.
The rank value feeds back into the DAG parent selection according to The rank value feeds into DODAG parent selection, according to the
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 DAG 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.
The computation of the DAG rank MUST be done in such a way so as to 3.6.2.1. Rank Comparison
Rank may be thought of as a fixed point number, where the position of
the decimal point is determined by MinHopRankIncrease. The integer
portion of the Rank is determined by floor(Rank/MinHopRankIncrease).
MinHopRankIncrease is provisioned at the DODAG Root and propagated in
the DIO message. For efficient implementation the MinHopRankIncrease
SHOULD be a power of 2. An implementation may configure a value
MinHopRankIncrease as appropriate to balance between the loop
avoidance logic of RPL (i.e. selection of eligible parents and
siblings) and the metrics in use.
A node A has a rank less than the rank of a node B if floor(Rank(A) /
MinHopRankIncrease) is less than floor (Rank(B) /
MinHopRankIncrease).
A node A has a rank equal to the rank of a node B if floor(Rank(A) /
MinHopRankIncrease) is equal to floor (Rank(B) / MinHopRankIncrease).
A node A has a rank greater than the rank of a node B if
floor(Rank(A) / MinHopRankIncrease) is greater than floor (Rank(B) /
MinHopRankIncrease).
3.6.2.2. Rank Relationships
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, M is probably DAGRank(M) is less than DAGRank(N): In this case, the position of M
located in a more preferred position than N in the DODAG with is closer to the DODAG root than the position of N. Node M
respect to the metrics and optimizations defined by the may safely be a DODAG parent for Node N without risk of
objective code point. In any fashion, Node M may safely be a creating a loop. Further, for a node N, all parents in the
DAG parent for Node N without risk of creating a loop. DODAG parent set must be of rank less than DAGRank(N). In
Further, for a node N, all parents in the DAG parent set must other words, the rank presented by a node N MUST be greater
be of rank less than self's DAGRank(N). In other words, the than that presented by any of its parents.
rank presented by a node N MUST be greater (deeper) than that
presented by any of its parents.
DAGRank(M) equals DAGRank(N): In this case M and N are located DAGRank(M) equals DAGRank(N): In this case the positions of M and N
positions of relatively the same optimality within the DODAG. within the DODAG and with respect to the DODAG root are
In some cases, Node M may be used as a successor by Node N, similar (identical). In some cases, Node M may be used as a
but with related chance of creating a loop that must be successor by Node N, which however entails the probability of
detected and broken by some other means. creating a loop (which must be detected and resolved by some
other means).
DAGRank(M) is greater than DAGRank(N): In this case, then node M is DAGRank(M) is greater than DAGRank(N): In this case, the position of
located in a less preferred position than N in the DODAG with M is farther from the DODAG root than the position of N.
respect to the metrics and optimizations defined by the Further, Node M may in fact be in the sub-DODAG of Node N. If
objective code point. Further, Node (M) may in fact be in node N selects node M as DODAG parent there is a risk to
Node (N)'s sub-DAG. There is a higher risk to Node (N)
selecting Node (M) as a DAG parent, as such a selection may
create a loop. create a loop.
As an example, the DAG 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 when the objective function is to minimize ETX, or
latency when the objective function is to minimize latency, or in a latency when the objective function is to minimize latency, or in a
more complicated way as appropriate to the objective code point being more complicated way as appropriate to the objective code point being
used within the DODAG. used within the DODAG.
6. RPL Protocol Specification 4. ICMPv6 RPL Control Message
6.1. RPL Messages
6.1.1. 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.
The RPL Control Message has the following general format, in In accordance with [RFC4443], the RPL Control Message has the
accordance with [RFC4443]: following format:
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 + + Message Body +
| | | |
Figure 3: RPL Control Message Figure 3: 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.
The Code will be used to identify RPL Control Messages as follows: The Code field identifies the type of RPL Control Message. This
document defines three types:
o 0x01: DAG Information Solicitation (Section 6.1.2) o 0x01: DAG Information Solicitation (Section 5.2)
o 0x02: DAG Information Object (Section 6.1.3) o 0x02: DAG Information Object (Section 5.1)
o 0x04: Destination Advertisement Object (Section 6.1.4) o 0x04: Destination Advertisement Object (Section 6.1)
6.1.2. DAG Information Solicitation (DIS) 5. Upward Routes
The DAG Information Solicitation (DIS) message may be used to solicit This section describes how RPL discovers and maintains upward routes.
a DAG Information Object from a RPL node. Its use is analogous to It describes DODAG Information Objects (DIOs), the messages used to
that of a Router Solicitation; a node may use DIS to probe its discover and maintain these routes. It specifies how RPL generates
neighborhood for nearby DAGs. The DAG Information Solicitation and responds to DIOs. It also describes DAG Information Solicitation
carries no additional message body. (DIS) messages, which are used to trigger DIO transmissions.
6.1.3. DAG Information Object (DIO) 5.1. DODAG Information Object (DIO)
The DAG Information Object carries a number of metrics and other The DODAG Information Object carries information that allows a node
information that allows a node to discover a DAG Instance, select its to discover a RPL Instance, learn its configuration parameters,
DAG parents, and identify its siblings while employing loop avoidance select a DODAG parent set, and maintain the upward routing topology.
strategies.
6.1.3.1. DIO Base 5.1.1. DIO Base Format
The DIO Base is a container option, which is always present, and DIO Base is an always-present container option in a DIO message.
might contain a number of suboptions. The base option regroups the Every DIO MUST include a DIO Base.
minimum information set that is mandatory in all cases.
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|D|A|0|0| Prf | Sequence | InstanceID | DAGRank | |G|A|T|S|0| Prf | Sequence | Rank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID | DTSN | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| | | |
+ + + +
| DAGID | | DODAGID |
+ +
| |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-option(s)... | | sub-option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: DIO Base Figure 4: DIO Base
Control Field: The DAG Control Field is currently allocated as Control Field: The DAG Control Field has three flags and one field:
follows:
Grounded (G): The Grounded (G) flag is set when the DODAG root
is a Goal for the OF.
Destination Advertisement Trigger (D): The Destination Grounded (G): The Grounded (G) flag indicates whether the
Advertisement Trigger (D) flag is set when the DODAG root upward routes this node advertises provide connectivity
or another node in the successor chain decides to trigger to the set of addresses which are application-defined
the sending of destination advertisements in order to goals. If the flag is set, the DODAG is grounded and
update routing state for the down direction along the provides such connectivity. If the flag is cleared, the
DODAG, as further detailed in Section 6.8. Note that the DODAG is floating and may not provide such connectivity.
use and semantics of this flag are still under
investigation.
Destination Advertisement Supported (A): The Destination Destination Advertisement Supported (A): The Destination
Supported (A) bit is set when the DODAG root is capable Advertisement Supported (A) bit indicates whether the
to support the collection of destination advertisement root of this DODAG can collect and use downward route
related routing state and enables the operation of the state. The flag is set when nodes in the network are to
destination advertisement mechanism within the DODAG. exchange destination advertisements messages to build
downward routes (Section 6). The flag is cleared when
the DODAG maintains only upward routes.
DAGPreference (Prf): 3-bit unsigned integer set by the DODAG Destination Advertisement Trigger (T): The Destination
root to its preference and unchanged at propagation. Advertisement Trigger (T) flag is used to trigger a
DAGPreference ranges from 0x00 (least preferred) to 0x07 complete refresh of downward routes. The details of this
(most preferred). The default is 0 (least preferred). process are described in Section 6.
The DAG preference provides an administrative mechanism
to engineer the self-organization of the LLN, for example
indicating the most preferred LBR. If a node has the
option to join a more preferred DODAG while still meeting
other optimization objectives, then the node will
generally seek to join the more preferred DODAG as
determined by the OF.
Unassigned bits of the Control Field are considered as Destination Advertisements Stored (S): The Destination
reserved. They MUST be set to zero on transmission and MUST be Advertisements Stored (S) flag is used to indicate that a
ignored on receipt. non-root ancestor is storing routing table entries
learned from DAO messaging. The meaning and further use
of this flag is described in Section 6.
Sequence Number: 8-bit unsigned integer set by the DODAG root, DODAGPreference (Prf): A 3-bit unsigned integer that defines
incremented according to a policy provisioned at the DODAG how preferable the root of this DODAG is compared to
root, and propagated with no change down the DODAG. Each other DODAG roots within the DODAG. DAGPreference ranges
increment SHOULD have a value of 1 and may cause a wrap back to from 0x00 (least preferred) to 0x07 (most preferred).
zero. The default is 0 (least preferred). Section 5.3
describes how DAGPreference affects DIO processing.
InstanceID: 8-bit field indicating the topology instance associated Unassigned bits of the Control Field are reserved. They MUST
with the DODAG, as provisioned at the DODAG root. be set to zero on transmission and MUST be ignored on
reception.
DAGRank: 8-bit unsigned integer indicating the DAG rank of the node Sequence Number: 8-bit unsigned integer set by the DODAG root.
sending the DIO message. The DAGRank of the DODAG root is Section 5.3 describes the rules for sequence numbers and how
ROOT_RANK. DAGRank is further described in Section 6.3. they affect DIO processing.
DAGID: 128-bit unsigned integer which uniquely identify a DODAG. Rank: 8-bit unsigned integer indicating the DODAG rank of the node
This value is set by the DODAG root. The global IPv6 address sending the DIO message. Section 5.3 describes how Rank is set
of the DODAG root can be used. the DAGID MUST be unique per DAG and how it affects DIO processing.
Instance within the scope of the LLN.
The following values MUST NOT change during the propagation of DIO RPLInstanceID: 8-bit field set by the DODAG root that indicates
messages down the DAG: which RPL Instance the DODAG is part of.
Grounded (G)
Destination Advertisement Supported (A)
DAGPreference (Prf)
Sequence
InstanceID
DAGID
All other fields of the DIO message may be updated at each hop of the
propagation.
6.1.3.1.1. DIO Suboptions Destination Advertisement Trigger Sequence Number (DTSN): 8-bit
unsigned integer set by the node issuing the DIO message. The
Destination Advertisement Trigger Sequence Number (DTSN) flag
is used as part of the procedure to maintain downward routes.
The details of this process are described in Section 6.
In addition to the minimum options presented in the base option, DODAGID: 128-bit unsigned integer set by a DODAG root which uniquely
several suboptions are defined for the DIO message: identifies a DODAG. Possibly derived from the IPv6 address of
the DODAG root.
5.1.2. DIO Base Rules
1. If the 'A' flag of a DIO Base is cleared, the 'T' flag MUST also
be cleared.
2. For the following DIO Base fields, a node that is not a DODAG
root MUST advertise the same values as its preferred DODAG parent
(defined in Section 5.3.2). Therefore, if a DODAG root does not
change these values, every node in a route to that DODAG root
eventually advertises the same values for these fields. These
fields are:
1. Grounded (G)
2. Destination Advertisement Supported (A)
3. Destination Advertisement Trigger (T)
4. DAGPreference (Prf)
5. Sequence
6. RPLInstanceID
7. DODAGID
3. A node MAY update the following fields at each hop:
1. DAGRank
2. DTSN
4. The DODAGID field each root sets MUST be unique within the RPL
Instance.
5.1.3. DIO Suboptions
This section describes the format of DIO suboptions and the five
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 Pad N, DAG Metric Container, DAG Destination Prefix, and DAG
Configuration suboptions all follow this format:
6.1.3.1.1.1. 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 | Subopt Length | Subopt Data | Subopt. Type | Subopt Length | Subopt Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 5: DIO Suboption Generic Format Figure 5: DIO Suboption Generic Format
Suboption Type: 8-bit identifier of the type of suboption. When Suboption Type: 8-bit identifier of the type of suboption.
processing a DIO message containing a suboption for which the
Suboption Type value is not recognized by the receiver, the
receiver MUST silently ignore the unrecognized option, continue
to process the following suboption, correctly handling any
remaining options in the message.
Suboption Length: 16-bit unsigned integer, representing the length Suboption Length: 16-bit unsigned integer, representing the length
in octets of the suboption, not including the suboption Type in octets of the suboption, not including the suboption Type
and Length fields. and Length fields.
Suboption Data: A variable length field that contains data specific Suboption Data: A variable length field that contains data specific
to the option. to the option.
The following subsections specify the DIO message suboptions which The following subsections specify the DIO message suboptions which
are currently defined for use in the DAG Information Object. are currently defined for use in the DAG Information Object.
Implementations MUST silently ignore any DIO message suboptions When processing a DIO message containing a suboption for which the
options that they do not understand. Suboption Type value is not recognized by the receiver, the receiver
MUST silently ignore the unrecognized option and continue to process
the following suboption, correctly handling any remaining options in
the message.
DIO message suboptions may have alignment requirements. Following DIO message suboptions may have alignment requirements. Following
the convention in IPv6, these options are aligned in a packet such the convention in IPv6, these options are aligned in a packet such
that multi-octet values within the Option Data field of each option that multi-octet values within the Option Data field of each option
fall on natural boundaries (i.e., fields of width n octets are placed fall on natural boundaries (i.e., fields of width n octets are placed
at an integer multiple of n octets from the start of the header, for at an integer multiple of n octets from the start of the header, for
n = 1, 2, 4, or 8). n = 1, 2, 4, or 8).
6.1.3.1.1.2. Pad1 5.1.3.2. Pad1
The Pad1 suboption does not have any alignment requirements. Its The Pad1 suboption does not have any alignment requirements. Its
format is as follows: 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 6: Pad 1
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 The Pad1 option is used to insert one or two octets of padding in the
DIO message to enable suboptions alignment. If more than two octets DIO message to enable suboptions alignment. If more than two octets
of padding is required, the PadN option, described next, should be of padding is required, the PadN option, described next, should be
used rather than multiple Pad1 options. used rather than multiple Pad1 options.
6.1.3.1.1.3. PadN 5.1.3.3. PadN
The PadN option does not have any alignment requirements. Its format The PadN option does not have any alignment requirements. Its format
is as follows: 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 | Subopt Length | Subopt Data | Type = 1 | Subopt Length | Subopt Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 7: Pad N Figure 7: Pad N
The PadN option is used to insert three or more octets of padding in The PadN option is used to insert three or more octets of padding in
the DIO message to enable suboptions alignment. For N (N > 2) octets the DIO message to enable suboptions alignment. For N (N > 2) octets
of padding, the Option Length field contains the value N-3, and the of padding, the Option Length field contains the value N-3, and the
Option Data consists of N-3 zero-valued octets. PadN Option data Option Data consists of N-3 zero-valued octets. PadN Option data
MUST be ignored by the receiver. MUST be ignored by the receiver.
6.1.3.1.1.4. DAG Metric Container 5.1.3.4. Metric Container
The DAG Metric Container suboption may be aligned as necessary to The Metric Container suboption may be aligned as necessary to support
support its contents. Its format is as follows: its contents. 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 | Container Length | DAG Metric Data | Type = 2 | Subopt Length | Metric Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 8: DAG Metric Container Figure 8: Metric Container
The DAG Metric Container is used to report aggregated path metrics
along the DODAG. The DAG Metric Container may contain a number of
discrete node, link, and aggregate path metrics as chosen by the
implementer. The Container Length field contains the length in
octets of the DAG Metric Data. The order, content, and coding of the
DAG Metric Container data is as specified in
[I-D.ietf-roll-routing-metrics].
The DAG Metric Container MUST include the value for the DAG Objective The Metric Container is used to report aggregated path metrics along
Code Point. the DODAG. The Metric Container may contain a number of discrete
node, link, and aggregate path metrics as chosen by the implementer.
The Suboption Length field contains the length in octets of the
Metric Data. The 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 DAG Metric Container is The processing and propagation of the Metric Container is governed by
governed by implementation specific policy functions. implementation specific policy functions.
6.1.3.1.1.5. Destination Prefix 5.1.3.5. Destination Prefix
The Destination Prefix suboption does not have any alignment The Destination Prefix suboption does not have any alignment
requirements. Its format is as follows: requirements. 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 = 3 | Length |Resvd|Prf|Resvd| | Type = 3 | Subopt Length |Resvd|Prf|Resvd|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Lifetime | | Prefix Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | | | Prefix Length | |
+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+ |
| Destination Prefix (Variable Length) | | Destination Prefix (Variable Length) |
. . . .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 25, line 44 skipping to change at page 28, line 12
The Destination Prefix suboption is used when the DODAG root, or The Destination Prefix suboption is used when the DODAG root, or
another node located upwards along the DODAG on the path to the DODAG another node located upwards along the DODAG on the path to the DODAG
root, needs to indicate that it offers connectivity to destination root, needs to indicate that it offers connectivity to destination
prefixes other than the default. This may be useful in cases where prefixes other than the default. This may be useful in cases where
more than one LBR is operating within the LLN and offering more than one LBR is operating within the LLN and offering
connectivity to different administrative domains, e.g. a home network connectivity to different administrative domains, e.g. a home network
and a utility network. In such cases, upon observing the Destination and a utility network. In such cases, upon observing the Destination
Prefixes offered by a particular DODAG, a node MAY decide to join Prefixes offered by a particular DODAG, a node MAY decide to join
multiple DODAGs in support of a particular application. multiple DODAGs in support of a particular application.
The Length is coded as the length of the suboption in octets, The Suboption Length is coded as the length of the suboption in
excluding the Type and Length fields. octets, excluding the Type and Length fields.
Prf is the Route Preference as in [RFC4191]. The reserved fields Prf is the Route Preference as in [RFC4191]. The reserved fields
MUST be set to zero on transmission and MUST be ignored on receipt. MUST be set to zero on transmission and MUST be ignored on receipt.
The Prefix Lifetime is a 32-bit unsigned integer representing the The Prefix Lifetime is a 32-bit unsigned integer representing the
length of time in seconds (relative to the time the packet is sent) length of time in seconds (relative to the time the packet is sent)
that the Destination Prefix is valid for route determination. The that the Destination Prefix is valid for route determination. The
lifetime is initially set by the node that owns the prefix and lifetime is initially set by the node that owns the prefix and
denotes the valid lifetime for that prefix (similar to denotes the valid lifetime for that prefix (similar to
AdvValidLifetime [RFC4861]). The value might be reduced by the AdvValidLifetime [RFC4861]). The value might be reduced by the
skipping to change at page 26, line 24 skipping to change at page 28, line 40
number of leading bits in the destination prefix. number of leading bits in the destination prefix.
The Destination Prefix contains Prefix Length significant bits of the The Destination Prefix contains Prefix Length significant bits of the
destination prefix. The remaining bits of the Destination Prefix, as destination prefix. The remaining bits of the Destination Prefix, as
required to complete the trailing octet, are set to 0. required to complete the trailing octet, are set to 0.
In the event that a DIO message may need to specify connectivity to In the event that a DIO message may need to specify connectivity to
more than one destination, the Destination Prefix suboption may be more than one destination, the Destination Prefix suboption may be
repeated. repeated.
6.1.3.1.1.6. DAG Configuration 5.1.3.6. DODAG Configuration
The DAG Configuration suboption does not have any alignment The DODAG Configuration suboption does not have any alignment
requirements. Its format is as follows: requirements. 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 = 4 | Length | DIOIntDoubl. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DIOIntMin. | DIORedun. | MaxRankInc | | DIOIntMin. | DIORedun. | MaxRankInc | MinHopRankInc |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: DAG Configuration Figure 10: DODAG Configuration
The DAG Configuration suboption is used to distribute configuration The DODAG Configuration suboption is used to distribute configuration
information for DAG Operation through the DODAG. The information information for DODAG Operation through the DODAG. The information
communicated in this suboption is generally static and unchanging communicated in this suboption is generally static and unchanging
within the DODAG, therefore it is not necessary to include in every within the DODAG, therefore it is not necessary to include in every
DIO. This suboption MAY be included occasionally by the DODAG Root, DIO. This suboption MAY be included occasionally by the DODAG Root,
and MUST be included in response to a unicast request, e.g. a DAG and MUST be included in response to a unicast request, e.g. a DODAG
Information Solicitation (DIS) message. Information Solicitation (DIS) message.
The Length is coded as 5. The Length is coded as 5.
DIOIntervalDoublings is an 8-bit unsigned integer, configured on the DIOIntervalDoublings is an 8-bit unsigned integer, configured on the
DODAG root and used to configure the trickle timer governing when DIO 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 message should be sent within the DODAG. DIOIntervalDoublings is the
number of times that the DIOIntervalMin is allowed to be doubled number of times that the DIOIntervalMin is allowed to be doubled
during the trickle timer operation. during the trickle timer operation.
DIOIntervalMin is an 8-bit unsigned integer, configured on the DODAG DIOIntervalMin is an 8-bit unsigned integer, configured on the DODAG
root and used to configure the trickle timer governing when DIO root and used to configure the trickle timer governing when DIO
message should be sent within the DODAG. The minimum configured message should be sent within the DODAG. The minimum configured
interval for the DIO trickle timer in units of ms is interval for the DIO trickle timer in units of ms is
2^DIOIntervalMin. For example, a DIOIntervalMin value of 16ms is 2^DIOIntervalMin. For example, a DIOIntervalMin value of 16ms is
expressed as 4. expressed as 4.
skipping to change at page 27, line 25 skipping to change at page 29, line 49
DIORedundancyConstant is an 8-bit unsigned integer used to configure DIORedundancyConstant is an 8-bit unsigned integer used to configure
suppression of DIO transmissions. DIORedundancyConstant is the suppression of DIO transmissions. DIORedundancyConstant is the
minimum number of relevant incoming DIOs required to suppress a DIO minimum number of relevant incoming DIOs required to suppress a DIO
transmission. If the value is 0xFF then the suppression mechanism is transmission. If the value is 0xFF then the suppression mechanism is
disabled. disabled.
MaxRankInc, 8-bit unsigned integer, is the DAGMaxRankIncrease. This MaxRankInc, 8-bit unsigned integer, is the DAGMaxRankIncrease. This
is the allowable increase in rank in support of local repair. If is the allowable increase in rank in support of local repair. If
DAGMaxRankIncrease is 0 then this mechanism is disabled. DAGMaxRankIncrease is 0 then this mechanism is disabled.
6.1.4. Destination Advertisement Object (DAO) MinHopRankInc, 8-bit unsigned integer, is the MinHopRankIncrease as
described in Section 3.6.2.1.
The Destination Advertisement Object (DAO) is used to propagate
destination information upwards along the DODAG. The RPL use of the
DAO allows the nodes in the DODAG to provision routing state for
nodes contained in the sub-DAG in support of traffic flowing down
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 | InstanceID | DAO Rank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DAO Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | RRCount | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Prefix (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Route Stack (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: The Destination Advertisement Object (DAO)
DAO Sequence: Incremented by the node that owns the prefix for each
new DAO message for that prefix.
InstanceID: 8-bit field indicating the topology instance associated
with the DODAG, as learned from the DIO.
DAO Rank: Set by the node that owns the prefix and first issues the
DAO message to its rank.
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.
Route Tag: 32-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.
Prefix: Variable-length field containing an IPv6 address or a prefix
of an IPv6 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 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.
6.2. Protocol Elements
6.2.1. Topological Elements
RPL uses four identifiers to track and control the routing topology
o The first is an InstanceID. An InstanceID defines what OF a DAG
uses and may also indicate what destinations are offered. A
network may have multiple InstanceIDs, each of which defines an
independent DAG optimized for a different OF and/or application.
The DAG defined by an InstanceID is called a DAG Instance.
o The second is a DAGID. The scope of a DAGID is a DAG Instance. A
combination of InstanceID and DAGID defines a DODAG. A DAG
Instance may have multiple DODAGs.
o The third value is a DAG Sequence Number. The scope of a DAG
Sequence Number is a DODAG. A DODAG is sometimes reconstructed
from the root, by incrementing the DAGSequenceNumber. A
combination of InstanceID, DAGID, and DAG Sequence Number defines
a DODAG Iteration.
o The fourth value is rank. The scope of rank is a DODAG Iteration.
Rank establishes a partial order over a DODAG Iteration, defining
individual node positions.
6.2.2. Neighbors, Parents, and Siblings
1. A node that is not a DODAG root MAY maintain multiple DAG parents
for a single DAG Instance.
2. The set of DAG parents MUST be a conceptual subset of the set of
candidate neighbors. (This does not dictate implementation,
e.g., to use a certain data structure).
3. If Neighbor Unreachability Detection (NUD), or an equivalent
mechanism, determines that a neighbor is no longer reachable,
then a RPL node MUST NOT consider this node in the neighbor set
when calculating and advertising routes until the node determines
it is reachable again.
4. Routes via that unreachable neighbor MUST be eliminated from the
routing table, and the node SHOULD poison using no-DAO all DAO
routes that it has advertised via DAO and that it can reach only
via that neighbor.
A node's neighbor set is an unconstrained subset of the nodes that it
can reach with a link-local multicast.
The OF guides in the selection and maintains a number of neighbors to
interact with, which neighbors being qualified as statistically
stable and presenting adequate properties as per the the OF logic,
for instance following mechanisms discussed in
[I-D.ietf-roll-routing-metrics]. Those neighbors are referred to as
candidate neighbors.
Candidate neighbors may take the role of Parent or Siblings, in part
as determined by rank.
For the purpose of inheriting metrics and computing rank, the OF
might select one preferred parent. In that case, the rank of this
node is computed as the rank of the preferred parent plus a rank
increment as determined by the OF.
6.2.3. DODAG Information
For each DODAG that a node is, or may become, a member of, the
implementation should conceptually keep track of the following
information for each DODAG. 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 InstanceID
o DAGID
o DAGSequenceNumber
o DAG Metric Container, including DAGObjectiveCodePoint
o A set of Destination Prefixes offered upwards along the DODAG
o A set of DAG parents
o A set of DAG siblings 5.2. DODAG Information Solicitation (DIS)
o A timer to govern the sending of DIO messages 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; 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.
When the DAG parent set is depleted on a node that is not a root, 5.3. Upward Route Discovery and Maintenance
(i.e. the last parent is removed), then the DAG information should
not be suppressed until after the expiration of an implementation-
specific local timer in order to observe that the DAGSequenceNumber
has incremented should any new parents appear for the DODAG.
6.2.3.1. DAG Parents/Siblings Structure Upward route discovery allows a node to join a DODAG by discovering
neighbors that are members of the DODAG and identifying a set of
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.
When the DODAG is self-rooted, the set of DAG parents is empty. 5.3.1. RPL Instance
For each node in a DAG parent/sibling set, the implementation should A RPLInstanceID MUST be unique across an LLN.
conceptually keep track of:
o a reference to the neighboring device which is the DAG parent/ A node MAY belong to multiple RPL Instances.
sibling
o a record of most recent information taken from the DAG Information Within a given LLN, there may be multiple, logically independent RPL
Object last processed in the case where the neighboring device is instances. This document describes how a single instance behaves.
a DAG parent
DAG parents may be ordered, according to the OF. When ordering DAG 5.3.2. Neighbors and Parents within a DODAG Iteration
parents, in consultation with the OF, the most preferred DAG parent
may be identified. All current DAG parents must have a rank less
than self. All current DAG siblings must have a rank equal to self.
When nodes are added to or removed from the DAG parent/sibling sets RPL's upward route discovery algorithms and processing are in terms
the most preferred DAG parent may have changed. The role of all the of three logical sets of link-local nodes. First, the candidate
nodes in the list should be reevaluated. In particular, any nodes neighbor set is a subset of the nodes that can be reached via link-
having a rank greater than self after such a change must be evicted local multicast. The selection of this set is implementation-
from the set. dependent and OF-dependent. Second, the parent set is a restricted
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
preferred next hop in upward routes.
6.3. DAG Discovery and Maintenance More precisely:
DAG discovery allows a node to join a DODAG rooted at a DODAG root by 1. The DODAG parent set MUST be a subset of the candidate neighbor
discovering neighbors that are members of the DODAG, and identifying set.
a set of parents. DAG discovery also identifies siblings, which may
be used later to provide additional path diversity towards the DODAG
root.
DODAG discovery may avoid loops by constraining how and when nodes 2. A DODAG root MUST have a DODAG parent set of size zero.
can increase their rank, and by statistically poisoning the nodes
that present the highest risk.
DAG discovery enables nodes to implement different policies for 3. A node that is not a DODAG root MAY maintain a DODAG parent set
selecting their DAG parents in the DODAG by using implementation of size greater than or equal to one.
specific policy functions. DAG discovery specifies a set of rules to
be followed by all implementations to enable interoperation.
6.3.1. DAG Discovery Rules 4. A node's preferred DODAG parent MUST be a member of its DODAG
parent set.
The following rules define the RPL DAG Discovery procedures: 5. A node's rank MUST be greater than all elements of its DODAG
parent set.
6.3.1.1. DODAG Iteration 6. When Neighbor Unreachability Detection (NUD), or an equivalent
mechanism, determines that a neighbor is no longer reachable, a
RPL node MUST NOT consider this node in the candidate neighbor
set when calculating and advertising routes until it determines
that it is again reachable. Routes through an unreachable
neighbor MUST be eliminated from the routing table.
1. An InstanceID SHOULD be administratively provisioned on a DODAG These rules ensure that there is a consistent partial order on nodes
root that is significant RPL objective. The InstanceID MUST be within the DODAG. As long as node ranks do not change, following the
unique to that purpose across the scope of the LLN. 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
candidate neighbor set and parent set selection, as discussed in
[I-D.ietf-roll-routing-metrics].
2. A DAGID MUST be unique within the scope of the InstanceID. It 5.3.3. Neighbors and Parents across DODAG Iterations
MAY be derived from the IPv6 address of the DODAG root.
3. A node MAY belong to multiple DAG instances. The related The above rules govern a single DODAG iteration. The rules in this
details of operation are outside the scope of this section define how RPL operates when there are multiple DODAG
specification. iterations:
4. DODAG roots MAY increment the DAGSequenceNumber that they 5.3.3.1. DODAG Iteration
advertise.
5. When a DODAG root increments its DAGSequenceNumber, it MUST 1. The tuple (RPLInstanceID, DODAGID, DODAGSequenceNumber) uniquely
follow the conventions of Serial Number Arithmetic as described defines a DODAG Iteration. Every element of a node's DODAG
in [RFC1982]. parent set, as conveyed by the last heard DIO from each DODAG
parent, MUST belong to the same DODAG iteration. Elements of a
node's candidate neighbor set MAY belong to different DODAG
Iterations.
6. The tuple (InstanceID, DAGID, DAGSequenceNumber) uniquely 2. A node is a member of a DODAG iteration if every element of its
defines a DODAG Iteration. All of a node's parents within a DODAG parent set belongs to that DODAG iteration, or if that node
DODAG MUST belong to the same DODAG iteration, as conveyed by is the root of the corresponding DODAG.
the last heard DIO from each parent.
7. A node MUST NOT propagate DIOs for a DODAG Iteration unless it 3. A node MUST NOT send DIOs for DODAG iterations of which it is not
is the DODAG root of the DODAG iteration or has selected DODAG a member.
parents in that DODAG iteration.
8. A node acting as a leaf SHOULD NOT propagate DIOs for a DODAG 4. DODAG roots MAY increment the DODAGSequenceNumber that they
Iteration. advertise and thus move to a new DODAG iteration. When a DODAG
root increments its DODAGSequenceNumber, it MUST follow the
conventions of Serial Number Arithmetic as described in
[RFC1982].
9. A node MUST belong at most to one DODAG Iteration per 5. Within a given DODAG, a node that is a not a root MUST NOT
InstanceID. advertise a DODAGSequenceNumber higher than the highest
DODAGSequenceNumber it has heard. Higher is defined as the
greater-than operator in [RFC1982].
10. Within a given DODAG, a node that is a not a root MUST NOT 6. Once a node has advertised a DODAG iteration by sending a DIO, it
advertise a DAGSequenceNumber higher than the highest MUST NOT be member of a previous DODAG iteration of the same
DAGSequenceNumber it has heard. DODAG (i.e. with the same DODAGID and a lower
DODAGSequenceNumber). Lower is defined as the less-than operator
in [RFC1982].
Within a particular implementation, a DODAG root may increment the Within a particular implementation, a DODAG root may increment the
DAGSequenceNumber periodically, at a rate that depends on the DODAGSequenceNumber periodically, at a rate that depends on the
deployment. In other implementations loop detection may be deployment. In other implementations, loop detection may be
considered sufficient to solve the routing issues, and the DODAG root considered sufficient to solve routing issues, and the DODAG root may
may increment the DAGSequenceNumber only upon administrative increment the DODAGSequenceNumber only upon administrative
intervention. Another possibility is that nodes within the LLN have intervention. Another possibility is that nodes within the LLN have
some means to signal the DODAG root in order to request an on-demand some means by which they can signal detected routing inconsistencies
increment when routing issues are detected. or suboptimalities to the DODAG root, in order to request an on-
demand DODAGSequenceNumber increment (i.e. request a global repair of
the DODAG).
As the DAGSequenceNumber is incremented, a new DODAG Iteration When the DODAG parent set is depleted on a node that is not a root,
(i.e. the last parent is removed), then the DODAG information should
not be suppressed until after the expiration of an implementation-
specific local timer in order to observe if the DODAGSequenceNumber
has been incremented, should any new parents appear for the DODAG.
As the DODAGSequenceNumber is incremented, a new DODAG Iteration
spreads outward from the DODAG root. Thus a parent that advertises spreads outward from the DODAG root. Thus a parent that advertises
the new DAGSequenceNumber can not possibly belong to the sub-DAG of a the new DODAGSequenceNumber can not possibly belong to the sub-DODAG
node that still advertises an older DAGSequenceNumber. A node may of a node that still advertises an older DODAGSequenceNumber. A node
safely add such a parent, without risk of forming a loop, without may safely add such a parent, without risk of forming a loop, without
regard to its relative rank in the prior DODAG Iteration. This is regard to its relative rank in the prior DODAG Iteration. This is
equivalent to jumping to a different DODAG. equivalent to jumping to a different DODAG.
As a node transitions to new DODAG Iterations as a consequence of As a node transitions to new DODAG Iterations 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 DAGSequenceNumber) once it has previous DODAG Iteration (prior DODAGSequenceNumber) once it has
committed to advertising the new DODAG Iteration. committed to advertising the new DODAG Iteration.
During a transition to a new DODAG Iteration, a node may decide to During transition to a new DODAG Iteration, 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 InstanceID and DAGID), but are observed to advertise a more (same RPLInstanceID and DODAGID), but are observed to advertise a
recent (incremented) DAGSequenceNumber. more recent (incremented) DODAGSequenceNumber.
6.3.1.2. DODAG Roots 5.3.3.2. DODAG Roots
1. A DODAG root that does not have connectivity to a network outside 1. A DODAG root that does not have connectivity to the set of
of the LLN MUST NOT set the Grounded bit. addresses described as application-level goals, MUST NOT set the
Grounded bit.
2. A DODAG root MUST advertise a rank of ROOT_RANK. 2. A DODAG root MUST advertise a rank of ROOT_RANK.
3. A node that does not have any DODAG parent MAY become the DODAG 3. A node whose DODAG parent set is empty MAY become the DODAG root
root of a floating DODAG. It MAY also set its DAGPreference such of a floating DODAG. It MAY also set its DAGPreference such that
that it is less preferred. This behavior may be a desired it is less preferred.
alternate to poisoning.
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 the backbone and use one router roots, it is possible to run RPL over that backbone and use one
as a backbone root. The backbone root is the virtual root of the router as a "backbone root". The backbone root is the virtual root
DODAG and exposes a rank of BASE_RANK over the backbone. All the LLN of the DODAG, and exposes a rank of BASE_RANK over the backbone. All
roots that are parented to that backbone root, including the backbone the LLN roots that are parented to that backbone root, including the
root if it also serves as LLN root, expose a rank of ROOT_RANK over backbone root if it also serves as LLN root itself, expose a rank of
the LLN and are part of the same DODAG, coordinated with the virtual ROOT_RANK to the LLN, and are part of the same DODAG, coordinating
root over the backbone. DODAGSequenceNumber and other DODAG root determined parameters with
the virtual root over the backbone.
6.3.1.3. Rank and Movement within a DODAG Iteration 5.3.3.3. DODAG Selection
The DODAGPreference (Prf) provides an administrative mechanism to
engineer the self-organization of the LLN, for example indicating the
most preferred LBR. If a node has the option to join a more
preferred DODAG while still meeting other optimization objectives,
then the node will generally seek to join the more preferred DODAG as
determined by the OF.
5.3.3.4. Rank and Movement within a DODAG Iteration
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 Iteration.
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. (This corresponds to a node moving within the DODAG Iteration.
up within the DODAG Iteration).
3. Let L be the lowest rank within a DODAG iteration that a given 3. Let L be the lowest rank within a DODAG iteration that a given
node has advertised. Within a DODAG Iteration, that node MUST node has advertised. Within the same DODAG Iteration, that node
NOT advertise an effective rank deeper than L + MUST 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
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 Iteration.)
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 DAG 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 that the node has been that different DODAG is a DODAG Iteration of which that node has
a prior member of, in which case the rule of the previous bullet previously been a member, in which case the rule of the previous
(3) must be observed. Until a node transmits a DIO indicating bullet (3) must be observed. Until a node transmits a DIO
its new DODAG membership, it MUST forward packets along the indicating its new DODAG membership, it MUST forward packets
previous DODAG. along the previous DODAG.
5. A node MAY, at any time after hearing the next DAGSequenceNumber 5. A node MAY, at any time after hearing the next
Iteration advertised from suitable parents, choose to migrate up DODAGSequenceNumber Iteration advertised from suitable DODAG
to the next DODAG Iteration within the DODAG. parents, choose to migrate to the next DODAG Iteration within the
DODAG.
Conceptually, an implementation is maintaining a parent set within Conceptually, an implementation is maintaining a DODAG parent set
the DODAG Iteration. Movement entails changes to the parent set. within the DODAG Iteration. Movement entails changes to the DODAG
Moving up does not present the risk to create a loop but moving down parent set. Moving up does not present the risk to create a loop but
might, so that operation is subject to additional constraints. moving down might, so that operation is subject to additional
constraints.
When a node migrates into the next DODAG Iteration, the parent and When a node migrates to the next DODAG Iteration, the DODAG parent
sibling sets need to be rebuilt for the new iteration. An and sibling sets need to be rebuilt for the new iteration. An
implementation could defer to migrate until for some reasonable time implementation could defer to migrate for some reasonable amount of
to see if some other neighbors with potentially better metrics but time, to see if some other neighbors with potentially better metrics
higher rank announce themselves. Similarly, when a node jumps into a but higher rank announce themselves. Similarly, when a node jumps
new DODAG it needs to construct new parent/sibling sets for the new into a new DODAG it needs to construct new DODAG parent/sibling sets
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 parents and siblings with a rank larger than itself. As abandon all DODAG parents and siblings with a rank larger than
a consequence of the movement it may also add new siblings. Such a itself. As a consequence of the movement it may also add new
movement may occur at any time to decrease the rank, as per the siblings. Such a movement may occur at any time to decrease the
calculation indicated by the OF. Maintenance of the parent and rank, as per the calculation indicated by the OF. Maintenance of the
sibling sets occurs as the rank of candidate neighbors is observed as parent and sibling sets occurs as the rank of candidate neighbors is
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 DAG rank to increase, then it MAY poison its routes and delay the rank to increase, then it MAY poison its routes and delay before
before moving as described in Section 6.3.1.4. moving as described in Section 5.3.3.5.
6.3.1.4. Poisoning a Broken Path 5.3.3.5. 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-DAG, 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 the 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 6.3.1.3, the node MUST advertise INFINITE_RANK 3. As per Section 5.3.3.4, the node MUST advertise INFINITE_RANK
within the DODAG iteration if its revised rank would exceed the within the DODAG iteration in which it participates, if its
maximum DAG rank increase. revised 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 that loses all of its current parents, i.e. the set of DAG a node loses all of its current parents, i.e. the set of DODAG
parents becomes depleted, and it can not jump onto 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
develop an accurate assessment of its new rank. Such gains are develop an accurate assessment of its new rank. Such gains are
obtained at the expense of potentially increasing the delay before obtained at the expense of potentially increasing the delay before
lower portions of the network are able to re-establish up routes. portions of the network are able to re-establish upwards routes.
Path redundancy in the DAG reduces the significance of either effect, Path redundancy in the DODAG reduces the significance of either
since children with alternate parents should be able to utilize those effect, since children with alternate parents should be able to
alternates and retain rank while the detached parent re-establishes utilize those alternates and retain their rank while the detached
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).
6.3.1.5. Detaching 5.3.3.6. Detaching
1. A node that does not have a solution to stay connected to a DODAG 1. A node unable to stay connected to a DODAG within a given DODAG
within a given iteration MAY detach from its current DODAG iteration MAY detach from this DODAG iteration. A node that
iteration. A node that detaches becomes root of its own floating detaches becomes root of its own floating DODAG and SHOULD
DODAG and SHOULD immediately advertise its new situation in a DIO immediately advertise this new situation in a DIO as an alternate
as an alternate to poisoning. to poisoning.
6.3.1.6. Following a Parent 5.3.3.7. Following a Parent
1. If a node receives a DIO from one of its parents indicating that 1. If a node receives a DIO from one of its DODAG parents,
the parent has left the DODAG, it SHOULD stay in its current indicating that the parent has left the DODAG, that node SHOULD
DODAG through an alternate DAG parent if that is possible. It stay in its current DODAG through an alternative DODAG parent, if
MAY follow that parent. possible. It MAY follow the leaving parent.
A DAG parent may have moved, migrated forward into the next DODAG A DODAG parent may have moved, migrated to the next DODAG Iteration,
Iteration, or jumped to a different DODAG. A node should give some or jumped to a different DODAG. A node should give some preference
preference to remaining in the current DODAG if possible, but ought to remaining in the current DODAG, if possible, but ought to follow
to follow the parent if there are no other options. the parent if there are no other options.
6.3.2. DIO Message Communication 5.3.4. DIO Message Communication
When an DIO message is received from a source device named SRC, the When an DIO message is received, the receiving node must first
receiving node must first determine whether or not the DIO message determine whether or not the DIO message should be accepted for
should be accepted for further processing, and subsequently present further processing, and subsequently present the DIO message for
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 is silently discarded. A RPL
implementation MAY log the reception of a malformed DIO message. implementation MAY log the reception of a malformed DIO message.
2. If SRC is a member of the candidate neighbor set, then the DIO is 2. If the sender of the DIO message is a member of the candidate
eligible for further processing. neighbor set, then the DIO is eligible for further processing.
6.3.2.1. DIO Message Processing
If the node has sent an DIO message within the risk window as
described in Section 6.7 then a collision has occurred; do not
process the DIO message any further.
Process the DIO message as per the rules in Section 6.3 5.3.4.1. 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 DAG parents by following the rules of DAG may be promoted to DODAG parents by following the rules of DODAG
discovery as described in Section 6.3. When a node places a neighbor discovery as described in Section 5.3. When a node places a neighbor
into the DAG Parent set, the node becomes attached to the DODAG into the DODAG parent set, the node becomes attached to the DODAG
through the new parent node. through the new DODAG parent node.
In the DAG discovery implementation, the most preferred parent should The most preferred parent should be used to restrict which other
be used to restrict which other nodes may become DAG parents. Some nodes may become DODAG parents. Some nodes in the DODAG parent set
nodes in the DAG parent set may be of a rank less than or equal to may be of a rank less than or equal to the most preferred DODAG
the most preferred DAG parent. (This case may occur, for example, if parent. (This case may occur, for example, if an energy constrained
an energy constrained device is at a lesser rank but should be device is at a lesser rank but should be avoided as per an
avoided as per an optimization objective, resulting in a more optimization objective, resulting in a more preferred parent at a
preferred parent at a greater rank). greater rank).
6.3.3. DIO Transmission 5.3.5. DIO Transmission
Each node maintains a timer that governs when to multicast DIO Each node maintains a timer, that governs when to multicast DIO
messages. This timer is a trickle timer, as detailed in messages. This timer is a trickle timer, as detailed in
Section 6.3.4. The DIO Configuration Option includes the Section 5.3.5.1. The DIO Configuration Option includes the
configuration of a DAG Instance's trickle timer. configuration of a RPL Instance's trickle timer.
o When a node detects or causes an inconsistency, it MUST reset the o When a node detects or causes an inconsistency, it MUST reset the
interval of the trickle timer to a minimum value. interval of the trickle timer to its minimum value.
o When a node migrates to a new DODAG Iteration it MUST reset the o When a node migrates to a new DODAG Iteration it MUST reset the
trickle timer to its minimum value trickle timer to its minimum value
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 6.9, the node MUST reset the trickle timer to detailed in Section 7.2, the node MUST reset the trickle timer to
its minimum value. its minimum value.
o When a node receives a multicast DIS message, it MUST reset the o When a node receives a multicast DIS message, it MUST reset the
trickle timer to the minimum value. trickle timer to its minimum value.
o When a node receives a unicast DIS message, it MUST unicast a DIO o When a node receives a unicast DIS message, it MUST unicast a DIO
message in response, and include the DAG Configuration Object. In message in response, and MUST include the DODAG Configuration
this case the node SHOULD NOT reset the trickle timer. Object. 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 o If a node is not a member of a DODAG, it MUST suppress
transmitting DIO messages. transmission of DIO messages.
o When a node is initialized, it MAY be configured to remain silent o When a node is initialized, it MAY be configured to remain silent
and not multicast any DIO messages until it has encountered and and not multicast any DIO messages until it has encountered and
joined a DODAG (perhaps initially probing for a nearby DODAG with joined a DODAG (perhaps initially probing for a nearby DODAG with
an DIS message). Alternately, it may choose to root its own an DIS message). Alternately, it MAY choose to root its own
floating DODAG and begin multicasting DIO messages using a default floating DODAG and begin multicasting DIO messages using a default
trickle configuration. The second case may be advantageous if it trickle configuration. The second case may be advantageous if it
is desired for independent nodes to begin aggregating into is desired for independent nodes to begin aggregating into
scattered floating DODAGs in the absence of a grounded node, for scattered floating DODAGs, in the absence of a grounded node, for
example in support of LLN installation and commissioning. example in support of LLN installation and commissioning.
6.3.4. Trickle Timer for DIO Transmission 5.3.5.1. Trickle Timer for DIO Transmission
RPL treats the construction of a DODAG as a consistency problem, and RPL treats the construction of a DODAG as a consistency problem, and
uses a trickle timer [Levis08] to control the rate of control uses a trickle timer [Levis08] to control the rate of control
broadcasts. broadcasts.
For each DODAG that a node is part of, the node must maintain a For each DODAG that a node is part of (i.e. one DODAG per RPL
single trickle timer. The required state contains the following Instance), the node must maintain a single trickle timer. The
conceptual items: required state contains the following conceptual items:
I: The current length of the communication interval I: The current length of the communication interval
T: A timer with a duration set to a random value in the range T: A timer with a duration set to a random value in the range
[I/2, I] [I/2, I]
C: Redundancy Counter C: Redundancy Counter
I_min: The smallest communication interval in milliseconds. This I_min: The smallest communication interval in milliseconds. This
value is learned from the DIO message as (2^DIOIntervalMin)ms. value is learned from the DIO message as (2^DIOIntervalMin)ms.
The default value 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 I_doublings: The number of times I_min should be doubled before
maintaining a constant rate, i.e. I_max = I_min * maintaining a constant rate, i.e. I_max = I_min *
2^I_doublings. This value is learned from the DIO message as 2^I_doublings. This value is learned from the DIO message as
DIOIntervalDoublings. The default value is DIOIntervalDoublings. The default value is
DEFAULT_DIO_INTERVAL_DOUBLINGS. DEFAULT_DIO_INTERVAL_DOUBLINGS.
6.3.4.1. Resetting the Trickle Timer 5.3.5.1.1. Resetting the Trickle Timer
The trickle timer for a DODAG is reset by: The trickle timer for a DODAG is reset by:
1. Setting I_min and I_doublings to the values learned from the DIO 1. Setting I_min and I_doublings to the values learned from the
message. DODAG root via a received DIO message.
2. Setting C to zero. 2. Setting C to zero.
3. Setting I to I_min. 3. Setting I to I_min.
4. Setting T to a random value as described above. 4. Setting T to a random value as described above.
5. Restarting the trickle timer to expire after a duration T 5. Restarting the trickle timer to expire after a duration T
When a node learns about a DODAG through a DIO message and makes the When a node learns about a DODAG through a DIO message, and makes the
decision to join it, it initializes the state of the trickle timer by decision to join this DODAG, it initializes the state of the trickle
resetting the trickle timer and listening. Each time it hears a timer by resetting the trickle timer and listening. Each time it
redundant DIO message for this DODAG, it MAY increment C. The exact hears a redundant DIO message for this DODAG, it MAY increment C. The
determination of redundant is left to an implementation; it could exact determination of what constitutes a redundant DIO message is
include DIOs that advertise the same rank. 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 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 constant, DIORedundancyConstant. If C is less than that value, or if
the DIORedundancyConstant value is 0xFF, the node generates a new DIO the DIORedundancyConstant value is 0xFF, the node generates a new DIO
message and multicasts it. When the communication interval I message and multicasts it. When the communication interval I
expires, the node doubles the interval I so long as it has previously 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 doubled it fewer than I_doubling times, resets C, and chooses a new T
value. value.
6.3.4.2. Determination of Inconsistency 5.3.5.1.2. Determination of Inconsistency
The trickle timer is reset whenever an inconsistency is detected The trickle timer is reset whenever an inconsistency is detected
within the DODAG, for example: within the DODAG, for example:
o The node joins a new DODAG o The node joins a new DODAG
o The node moves within a DODAG o The node moves within a DODAG
o The node receives a modified DIO message from a DAG parent o The node receives a modified DIO message from a DODAG parent
o A DAG parent forwards a packet intended to move up, indicating an o A DODAG parent forwards a packet intended to move up, indicating
inconsistency and possible loop. an inconsistency and possible loop.
o A metric communicated in the DIO message is determined to be o A metric communicated in the DIO message is determined to be
inconsistent, as according to a implementation specific path inconsistent, as according to a implementation specific path
metric selection engine. metric selection engine.
o The rank of a DAG parent has changed. o The rank of a DODAG parent has changed.
6.4. DAG Selection 5.3.6. DODAG Selection
The DAG selection is implementation and algorithm dependent. Nodes The DODAG selection is implementation and algorithm dependent. Nodes
SHOULD prefer to join DODAGs for InstanceIDs advertising OCPs and SHOULD 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 fixed network 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 DAG parent. considers that candidate as a DODAG parent.
6.5. Operation as a Leaf Node
In some cases it a RPL node may attach to a DODAG for DAG Instance as 5.4. Operation as a Leaf Node
a leaf node only; the node in this case is not to extend connectivity
to the DODAG to other nodes under any circumstances. Such a case may
occur, for example, when a node is attaching to a DODAG that is using
an unknown Objective Function. When operating as a leaf node, a
node:
1. MAY receive and process DIOs for that DODAG 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
Instance's OF. A leaf node does not extend DODAG connectivity but
still needs to advertise its presence using DIOs. A node operating
as a leaf node must obey the following rules:
2. SHOULD NOT transmit DIOs for that DODAG 1. It MUST NOT transmit DIOs containing the DAG Metric Container.
3. MUST NOT transmit DIOs containing the DAG Metric Container for 2. Its DIOs must advertise a DAGRank of INFINITE_RANK.
that DODAG
4. MAY transmit unicast DAOs to the chosen parents for that DODAG 3. It MAY transmit unicast DAOs as described in Section 6.2.
5. MAY transmit multicast DAOs to the `1 hop' neighborhood. 4. It MAY transmit multicast DAOs to the '1 hop' neighborhood as
described in Section 6.2.9.
6.6. Administrative rank 5.5. Administrative Rank
When the DODAG is formed under a common administration, or when a In some cases it might be beneficial to adjust the rank advertised by
node performs a certain role within a community, it might be a node beyond that computed by the OF based on some implementation
beneficial to associate a range of acceptable rank with that node. specific policy and properties of the node. For example, a node that
For instance, a node that has limited battery should be a leaf unless has limited battery should be a leaf unless there is no other choice,
there is no other choice, and may then augment the rank computation and may then augment the rank computation specified by the OF in
specified by the OF in order to expose an exaggerated rank. order to expose an exaggerated rank.
6.7. Collision 5.6. Collision
A race condition occurs if 2 nodes send DIO messages at the same time 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, and then attempt to join each other. This might happen, for example,
between nodes which act as DAG root of their own DODAGs. In order to between nodes which act as DODAG root of their own DODAGs. In order
detect the situation, LLN Nodes time stamp the sending of DIO to detect the situation, LLN Nodes time stamp the sending of DIO
message. Any DIO message received within a short link-layer- message. Any DIO message received within a short link-layer-
dependent period introduces a risk. It left to the implementation to dependent period introduces a risk. It left to the implementation to
define the duration of the risk window. define the duration of the risk window.
There is risk of a collision when a node receives and processes a DIO 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 within the risk window. For example, it may occur that two nodes are
associated with different DODAGs and near-simultaneously send DIO associated with different DODAGs and near-simultaneously send DIO
messages, which are received and processed by both, and possibly messages, which are received and processed by both, and possibly
result in both nodes simultaneously deciding to attach to each other. result in both nodes simultaneously deciding to attach to each other.
As a remedy, in the face of a potential collision, as determined by 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 receiving a DIO within the risk window, the DIO message is not
processed. It is expected that subsequent DIOs would not cross. processed. It is expected that subsequent DIOs would not cross.
6.8. Establishing Routing State Down the DODAG 6. Downward Routes
The destination advertisement mechanism supports the dissemination of This section describes how RPL discovers and maintains downward
routing state required to support traffic flows down along the DODAG, routes. Messages containing the Destination Advertisement Object
from the DODAG root toward nodes. (DAO), used to construct downward routes, are described. The
downward routes are necessary in support of P2MP flows, from the
DODAG roots toward the leaves. It specifies non-storing and storing
behavior of nodes with respect to DAO messaging and DAO routing table
entries. Nodes, as according to their resources and the
implementation, may selectively store routing table entries learned
from DAO messages, or may instead propagate the DAO information
upwards while adding source routing information. A further
optimization is described whereby DAO messages may be used to
populate routing table entries for the '1-hop' neighbors, which may
be useful in some cases as a shortcut for P2P flows.
As a result of destination advertisement operation: 6.1. Destination Advertisement Object (DAO)
o Destination advertisement establishes down routes along the DODAG. The Destination Advertisement Object (DAO) is used to propagate
Such paths consist of: destination information upwards along the DODAG.
* Hop-By-Hop routing state within islands of `stateful' nodes.
* Source Routing `bridges' across nodes that do not retain state.
Destinations disseminated with the destination advertisement 0 1 2 3
mechanism may be prefixes, individual hosts, or multicast listeners. 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
The mechanism supports nodes of varying capabilities as follows: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DAO Sequence | DAO Rank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID | Route Tag | Prefix Length | RRCount |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DAO Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Prefix (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Route Stack (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-option(s)...
+-+-+-+-+-+-+-+-+
o When nodes are capable of storing routing state, they may inspect Figure 11: The Destination Advertisement Object (DAO)
destination advertisements and learn hop-by-hop routing state
toward destinations by populating their routing tables with the
routes learned from nodes in their sub-DAG. In this process they
may also learn necessary piecewise source routes to traverse
regions of the LLN that do not maintain routing state. They may
perform route aggregation on known destinations before emitting
Destination Advertisements.
o When nodes are incapable of storing routing state, they may DAO Sequence: 16-bit unsigned integer. Incremented by the node that
forward destination advertisements, recording the reverse route as owns the prefix for each new DAO message for that prefix.
the go in order to support the construction of piecewise source
routes.
Nodes that are capable of storing routing state, and finally the DAO Rank: 16-bit unsigned integer indicating the DAO Rank associated
DODAG roots, are able to learn which destinations are contained in with the advertised Destination Prefix. The DAO Rank is
the sub-DAG below the node, and via which next-hop neighbors. The analogous to the Rank in the DIO message in that it may be used
dissemination and installation of this routing state into nodes to convey a relative distance to the Destination Prefix as
allows for Hop-By-Hop routing from the DODAG root down the DODAG. computed by the Objective Function in use over the DODAG. It
The mechanism is further enhance by supporting the construction of serves as a mechanism by which an ancestor node may order
source routes across stateless `gaps' in the DODAG, where nodes are alternate DAO paths.
incapable of storing additional routing state. An adaptation of this
mechanism allows for the implementation of loose-source routing.
A special case, the reception of a destination advertisement RPLInstanceID: 8-bit field indicating the topology instance
addressed to a link-local multicast address, allows for a node to associated with the DODAG, as learned from the DIO.
learn destinations directly available from its one-hop neighbors.
A design choice behind advertising routes via destination Route Tag: 8-bit unsigned integer. The Route Tag may be used to
advertisements is not to synchronize the parent and children give a priority to prefixes that should be stored. This may be
databases along the DODAG, but instead to update them regularly to useful in cases where intermediate nodes are capable of storing
recover from the loss of packets. The rationale for that choice is a limited amount of routing state. The further specification
time variations in connectivity across unreliable links. If the of this field and its use is under investigation.
topology can be expected to change frequently, synchronization might
be an excessive goal in terms of exchanges and protocol complexity.
The approach used here results in a simple protocol with no real
peering. The destination advertisement mechanism hence provides for
periodic updates of the routing state, similarly to other protocols
such as RIP [RFC2453].
6.8.1. Destination Advertisement Operation Prefix Length: 8-bit unsigned integer. Number of valid leading bits
in the IPv6 Prefix.
6.8.1.1. Overview 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.
According to implementation specific policy, a subset or all of the DAO Lifetime: 32-bit unsigned integer. The length of time in
feasible parents in the DODAG may be selected to receive prefix seconds (relative to the time the packet is sent) that the
information from the destination advertisement mechanism. This prefix is valid for route determination. A value of all one
subset of DAG parents shall be designated the set of DA parents. bits (0xFFFFFFFF) represents infinity. A value of all zero
bits (0x00000000) indicates a loss of reachability.
As DAO messages for particular destinations move up the DODAG, a Destination Prefix: Variable-length field identifying an IPv6
sequence counter is used to guarantee their freshness. The sequence destination address, prefix, or multicast group. The Prefix
counter is incremented by the source of the DAO message (the node Length field contains the number of valid leading bits in the
that owns the prefix, or learned the prefix via some other means), prefix. The bits in the prefix after the prefix length (if
each time it issues a DAO message for its prefix. Nodes that receive any) are reserved and MUST be set to zero on transmission and
the DAO message and, if scope allows, will be forwarding a DAO MUST be ignored on receipt.
message for the unmodified destination up the DODAG, will leave the
sequence number unchanged. Intermediate nodes will check the
sequence counter before processing a DAO message, and if the DAO is
unchanged (the sequence counter has not changed), then the DAO
message will be discarded without additional processing. Further, if
the DAO message appears to be out of synch (the sequence counter is 2
or more behind the present value) then the DAO state is considered to
be stale and may be purged, and the DAO message is discarded. The
rank is also added for tracking purposes; nodes that are storing
routing state may use it to determine which possible next-hops for
the destination are more optimal.
If destination advertisements are activated in the DIO message as Reverse Route Stack: Variable-length field containing a sequence of
indicated by the `D' bit, the node sends unicast destination RRCount (possibly compressed) IPv6 addresses. A node that adds
advertisements to one of its DA parents, that is selected as most on to the Reverse Route Stack will append to the list and
favored for incoming down traffic. The node only accepts unicast increment the RRCount.
destination advertisements from any nodes but those contained in the
DA parent subset.
Receiving a DIO message with the `D' destination advertisement bit 6.1.1. DAO Suboptions
set from a DAG parent stimulates the sending of a delayed destination
advertisement back, with the collection of all known prefixes (that
is the prefixes learned via destination advertisements for nodes
lower in the DODAG, and any connected prefixes). If the Destination
Advertisement Supported (A) bit is set in the DIO message for the
DODAG, then a destination advertisement is also sent to a DAG parent
once it has been added to the DA parent set after a movement, or when
the list of advertised prefixes has changed.
A node that modifies its DAG Parent set may set the `D' bit in The DAO message may optionally include a number of suboptions.
subsequent DIO propagation in order to trigger destination
advertisements to be updated to its DAG Parents and other ancestors
on the DODAG. Additional recommendations and guidelines regarding
the use of this mechanism are still under consideration and will be
elaborated in a future revision of this specification.
Destination advertisements may advertise positive (prefix is present) The DAO suboptions are in the same format as the DIO Suboptions
or negative (removed) DAO messages, termed as no-DAOs. A no-DAO is described in Section 6.1.1.
stimulated by the disappearance of a prefix below. This is
discovered by timing out after a request (a DIO message) or by
receiving a no-DAO. A no-DAO is a conveyed as a DAO message with a
DAO Lifetime of ZERO_LIFETIME.
A node that is capable of recording the state information conveyed in In particular, a DAO message may include a DAG Metric Container
a unicast DAO message will do so upon receiving and processing the suboption as described in Section 5.1.3.4. This suboption may be
DAO message, thus provisioning routing state concerning destinations present in implementations where the DAO Rank is insufficient to
located downwards along the DODAG. If a node capable of recording optimize a path to the DAO Destination Prefix.
state information receives a DAO message containing a Reverse Route
Stack, then the node knows that the DAO message has traversed one or
more nodes that did not retain any routing state as it traversed the
path from the DAO source to the node. The node may then extract the
Reverse Route Stack and retain the included state in order to specify
Source Routing instructions along the return path towards the
destination. The node MUST set the RRCount back to zero and clear
the Reverse Route Stack prior to passing the DAO message information
on.
A node that is unable to record the state information conveyed in the 6.2. Downward Route Discovery and Maintenance
DAO message will append the next-hop address to the Reverse Route
Stack, increment the RRCount, and then pass the destination
advertisement on without recording any additional state. In this way
the Reverse Route Stack will contain a vector of next hops that must
be traversed along the reverse path that the DAO message has
traveled. The vector will be ordered such that the node closest to
the destination will appear first in the list. In such cases, if it
is useful to the implementation to try and provision redundant paths,
the node may choose to convey the destination advertisement to one or
more DAG parents in order of preference as guided by an
implementation specific policy.
In certain cases (called hybrid cases), some nodes along the path a 6.2.1. Overview
destination advertisement follows up the DODAG may store state and
some may not. The destination advertisement mechanism allows for the
provisioning of routing state such that when a packet is traversing
down the DODAG, some nodes may be able to directly forward to the
next hop, and other nodes may be able to specify a piecewise source
route in order to bridge spans of stateless nodes within the path on
the way to the desired destination.
In the case where no node is able to store any routing state as Destination Advertisement operation produces DAO messages that flow
destination advertisements pass by, and the DAG root ends up with DAO up the DODAG, provisioning downward routing state for destination
messages that contain a completely specified route back to the prefixes available in the sub-DODAG of the DODAG root, and possibly
originating node in the form of the inverted Reverse Route Stack. A other nodes. The routing state provisioned with this mechanism is in
DAG root should not request (Destination Advertisement Trigger) nor the form of soft-state routing table entries. DAO messages are able
indicate support (Destination Advertisement Supported) for to record loose source routing information as by propagate up the
destination advertisements if it is not able to store the Reverse DODAG. This mechanism is flexible to support the provisioning of
Route Stack information in this case. 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.
The destination advertisement mechanism requires stateful nodes to Destination Advertisement may or may not be enabled over a DODAG
maintain lists of known prefixes. A prefix entry contains the rooted at a DODAG root. This is an a priori configuration determined
following abstract information: by the implementation/deployment and not generally changed during the
operation of the RPL LLN.
o A reference to the ND entry that was created for the advertising When Destination Advertisement is enabled:
neighbor.
o The IPv6 address and interface for the advertising neighbor. 1. Some nodes in the LLN MAY store at least one routing table entry
for a particular destination learned from a DAO. Such a node is
termed a 'storing node', with respect to that particular
destination.
o The logical equivalent of the full destination advertisement 2. Some nodes are capable to store at least one routing table entry
information (including the prefixes, depth, and Reverse Route for every unique destination observed from all DAOs that pass
Stack, if any). through. Such a node is termed a 'fully storing node'.
o A 'reported' Boolean to keep track whether this prefix was 3. DODAG roots nodes SHOULD be fully-storing nodes.
reported already, and to which of the DA parents.
o A counter of retries to count how many DIO messages were sent on 4. Other nodes in the DODAG are not required to store routing table
the interface to the advertising neighbor without reachability entries for any particular destinations observed in DAOs. Nodes
confirmation for the prefix. that do not store routing table entries from DAOs are termed
'non-storing nodes', with respect to a particular destination.
Note that nodes may receive multiple information from different 5. Non-storing nodes MUST participate in the construction of
neighbors for a specific destination, as different paths through the piecewise source routes as they propagate the DAO message, as
DODAG may be propagating information up the DODAG for the same described in Section 6.2.5.
destination. A node that is recording routing state will keep track
of the information from each neighbor independently, and when it
comes time to propagate the DAO message for a particular prefix to
the DA parents, then the DAO information will be selected from among
the advertising neighbors who offer the least depth to the
destination.
When a node loses connectivity to a child that is used as next hop 6. Storing nodes MUST store any source route information received
for a route learned from a DAO, the node should cleanup all routes from the DAO (RRStack) in the routing table entry entry. If a
and DAO states that are related to that child. If the lost child was node is not capable to do this then it must act as a non-storing
the only adjacency leading to the DAO prefix, the node should poison node with respect to that particular destination.
the route by sending no-DAOs to the parents to which it has
advertised the DAO prefixes.
The destination advertisement mechanism stores the prefix entries in 7. Storing nodes MUST use piecewise source routes in order to
one of 3 abstract lists; the Connected, the Reachable and the forward data across a non-storing region of the LLN. The source
Unreachable lists. 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).
The Connected list corresponds to the prefixes owned and managed by 6.2.2. Mode of Operation
the local node.
The Reachable list contains prefixes for which the node keeps o DAO Operation may not be required for all use cases.
receiving DAO messages, and for those prefixes which have not yet
timed out.
The Unreachable list keeps track of prefixes which are no longer o Some applications may only need support for collection/upward/MP2P
valid and in the process of being deleted, in order to send DAO flow with no acknowledgement/reciprocal traffic.
messages with zero lifetime (also called no-DAO) to the DA parents.
6.8.1.1.1. Destination Advertisement Timers o Some DODAGs may not support DAO Operation, which could mean that
DAO Operation is wasteful overhead.
The destination advertisement mechanism requires 2 timers; the o As a special case, multicast DAO operation may be used to populate
DelayDAO timer and the RemoveTimer. 'one-hop' neighborhood routing table entries, and is distinct from
the unicast DAO operation used to establish downward routes along
the DODAG.
o The DelayDAO timer is armed upon a stimulation to send a 1. The 'A' flag in the DIO as conveyed from the DODAG root serves to
destination advertisement (such as a DIO message from a DA enable/disable DAO operation over the entire DODAG. This flag
parent). When the timer is armed, all entries in the Reachable should be administratively provisioned a priori at the DODAG root
list as well as all entries for Connected list are set to not be as a function of the implementation/deployment and not tend to
reported yet for that particular DA parent. change.
o For a root, the DIO timer has a duration of DEF_DAO_LATENCY. For 2. When DAO Operation is disabled, a node SHOULD NOT emit DAOs.
a node in a DODAG iteration, the DelayDAO timer has a duration
that is randomized between (DEF_DAO_LATENCY divided by the Rank of
the node) and (DEF_DAO_LATENCY divided by the Rank of the parent).
The intention is that nodes located deeper in the DODAG iteration
should have a shorter DelayDAO timer, allowing DAO messages a
chance to be reported from deeper in the DODAG and potentially
aggregated along sub-DAGs before propagating further up.
o The RemoveTimer is used to clean up entries for which DAO messages 3. When DAO Operation is disabled, a node MAY ignore received DAOs.
are no longer being received from the sub-DAG.
* When a DIO message is sent that is requesting destination 6.2.3. Destination Advertisement Parents
advertisements, a flag is set for all DAO entries in the
routing table.
* If the flag has already been set for a DAO entry, the retry o Nodes will select a subset of their DODAG Parents to whom DAOs
count is incremented. will be sent
* If a DAO message is received to confirm the entry, the entry is * This subset is the set of 'DAO Parents'
refreshed and the flag and count may be cleared.
* If at least one entry has reached a threshold value and the * Each DAO parent MUST be a DODAG Parent. (Not all DODAG parents
RemoveTimer is not running, the entry is considered to be need to be DAO parents).
probably gone and the RemoveTimer is started.
* When the RemoveTimer elapse, DAO messages with lifetime 0, i.e. * Operation with more than DAO Parent requires consideration of
no-DAOs, are sent to explicitly inform DA parents that the such issues as DAO fan-out and path diversity, to be elaborated
entries which have reached the threshold are no longer in a future version of this specification.
available, and the related routing states may be propagated and
cleaned up.
o The RemoveTimer has a duration of min (MAX_DESTROY_INTERVAL, o The selection of DAO parents is implementation specific and may be
TBD(DIO Trickle Timer Interval)). based on selecting the DODAG Parents that offer the best upwards
cost (as opposed to downwards or mixed), as determined by the
metrics in use and the Objective Function.
6.8.1.2. Multicast Destination Advertisement Messages o When DAO messages are unicast to the DAO Parent, the identity of
the DAO Parent (DODAGID x DAGSequenceNumber) combined with the
RPLInstanceID in the DAO message unambiguously associates the DAO
message, and thus the particular destination prefix, with a DODAG
Iteration.
It is also possible for a node to multicast a DAO message to the o When DAO messages are unicast to the DAO Parent, the DAO Rank may
link-local scope all-nodes multicast address FF02::1. This message be updated as according to the implementation and Objective
will be received by all node listening in range of the emitting node. Function in use to reflect the relative (aggregated) cost of
The objective is to enable direct P2P communication, between reaching the Destination Prefix through that DAO parent. As a
destinations directly supported by neighboring nodes, without needing further extension, a DAO Suboption for the Metric Container may be
the RPL routing structure to relay the packets. included.
A multicast DAO message MUST be used only to advertise information 6.2.4. Operation of DAO Storing Nodes
about self, i.e. prefixes in the Connected list or addresses owned by
this node. This would typically be a multicast group that this node
is listening to or a global address owned by this node, though it can
be used to advertise any prefix owned by this node as well. A
multicast DAO message is not used for routing and does not presume
any DODAG relationship between the emitter and the receiver; it MUST
NOT be used to relay information learned (e.g. information in the
Reachable list) from another node; information obtained from a
multicast DAO MAY be installed in the routing table and MAY be
propagated by a router in unicast DAOs.
A node receiving a multicast DAO message addressed to FF02::1 MAY 6.2.4.1. DAO Routing Table Entry
install prefixes contained in the DAO message in the routing table
for local use. Such a node MUST NOT perform any other processing on
the DAO message (i.e. such a node does not presume it is a DA
parent).
6.8.1.3. Unicast Destination Advertisement Messages from Child to A DAO Routing Table Entry conceptually contains the following
Parent elements:
When sending a destination advertisement to a DA parent, a node o Advertising Neighbor Information
includes the DAOs for prefix entries not already reported (since the * IPv6 Addr
last DA Trigger from an DIO message) in the Reachable and Connected * Interface ID
lists, as well as no-DAOs for all the entries in the Unreachable o To which DAO Parents has this entry been reported
list. Depending on its policy and ability to retain routing state, o Retry Counter
the receiving node SHOULD keep a record of the reported DAO message. o Logical equivalent of DAO Content:
If the DAO message offers the best route to the prefix as determined * DAO Sequence
by policy and other prefix records, the node SHOULD install a route * DAO Rank
to the prefix reported in the DAO message via the link local address * DAO Lifetime
of the reporting neighbor and it SHOULD further propagate the * Route tag (used to prioritize which destination entries should
information in a DAO message. be stored)
* Destination Prefix (or Address or Mcast Group)
* RR Stack*
The DIO message from the DODAG root is used to synchronize the whole The DAO Routing Table Entry is logically associated with the
DODAG iteration, including the periodic reporting of destination following states:
advertisements back up the DODAG. Its period is expected to vary,
depending on the configuration of the DIO trickle timer.
When a node receives a DIO message over an LLN interface from a DA CONNECTED This entry is 'owned' by the node - it is manually
parent, the DelayDAO is armed to force a full update. configured and is considered as a 'self' entry for DAO
Operation
When the node broadcasts a DIO message on an LLN interface, for all REACHABLE This entry has been reported from a neighbor of the node.
entries on that interface: This state includes the following substates:
o If the entry is CONFIRMED, it goes PENDING with the retry count CONFIRMED This entry is active, newly validated, and
set to 0. usable
o If the entry is PENDING, the retry count is incremented. If it PENDING This entry is active, awaiting validation, and
reaches a maximum threshold, the entry goes ELAPSED If at least usable. A Retry Counter is associated with
one entry is ELAPSED at the end of the process: if the RemoveTimer this substate
is not running then it is armed with a jitter.
Since the DelayDAO timer has a duration that decreases with the UNREACHABLE This entry is being cleaned up. This entry may be
depth, it is expected to receive all DAO messages from all children suppressed when the cleanup process is complete.
before the timer elapses and the full update is sent to the DA
parents.
Once the RemoveTimer is elapsed, the prefix entry is scheduled to be When an attempt is to be made to report the DAO entry to DAO Parents,
removed and moved to the Unreachable list if there are any DA parents the DAO Entry record is logically marked to indicate that an attempt
that need to be informed of the change in status for the prefix, has not yet been made for parent. As the unicast attempts are
otherwise the prefix entry is cleaned up right away. The prefix completed for each parent, this mark may be cleared. This mechanism
entry is removed from the Unreachable list when no more DA parents may serve to limit DAO entry updates for each parent to a subset that
need to be informed. This condition may be satisfied when a no-DAO needs to be reported.
is sent to all current DA parents indicating the loss of the prefix,
and noting that in some cases parents may have been removed from the
set of DA parents.
6.8.1.4. Other Events 6.2.4.1.1. DAO Routing Table Entry Management
Finally, the destination advertisement mechanism responds to a series +---------------------------------+
of events, such as: | |
| REACHABLE | +-------------+
| | | |
| +-----------+ | | CONNECTED |
(*)----------->| |-------+ | | |
| | Confirmed | | | +-------------+
| +-->| |---+ | |
| | +-----------+ | | |
| | | | |
| | | | |
| | | | |
| | +-----------+ | | | +-------------+
| | | |<--+ +-------->| |
| +---| Pending | | | UNREACHABLE |
| | |---------------->| |--->(*)
| +-----------+ | +-------------+
| |
+---------------------------------+
o Destination advertisement operation stopped: All entries in the DAO Routing Table Entry FSM
abstract lists are freed. All the routes learned from DAO
messages are removed.
o Interface going down: for all entries in the Reachable list on 6.2.4.1.1.1. Operation in the CONNECTED state
that interface, the associated route is removed, and the entry is
scheduled to be removed.
o Loss of routing adjacency: When the routing adjacency for a 1. CONNECTED DAO entries are to be provisioned outside of the
neighbor is lost, as per the procedures described in Section 6.11, context of RPL, e.g. through a management API. An implementation
and if the associated entries are in the Reachable list, the SHOULD provide a means to provision/manage CONNECTED DAO entries,
associated routes are removed, and the entries are scheduled to be including whether they are to be redistributed in RPL.
destroyed.
o Changes to DA parent set: all entries in the Reachable list are 6.2.4.1.1.2. Operation in the REACHABLE state
set to not 'reported' and DelayDAO is armed.
6.8.1.5. Aggregation of Prefixes by a Node 1. When a REACHABLE(*) entry times out, the entry MUST be placed
into the UNREACHABLE state and no-DAO SHOULD be scheduled to send
to the node's DAO Parents. (TBD MUST?)
There may be number of cases where a aggregation may be shared within 2. When a no-DAO for a REACHABLE(*) entry is received with a newer
a group of nodes. In such a case, it is possible to use aggregation DAO Sequence Number, the entry MUST be placed into the
techniques with destination advertisements and improve scalability. UNREACHABLE state and no-DAO SHOULD be scheduled to send to the
node's DAO Parents.
Other cases might occur for which additional support is required: 3. When a REACHABLE(*) entry is to be removed because NUD or
equivalent has determined that the next-hop neighbor is no longer
reachable, the entry MUST be placed into the UNREACHABLE state
and no-DAO SHOULD be scheduled to send to the node's DAO Parents.
1. The aggregating node is attached within the sub-DAG of the nodes 4. When a REACHABLE(*) entry is to be removed because an associated
it is aggregating for. Forwarding Error has been returned by the next-hop neighbor, the
entry MUST be placed into the UNREACHABLE state and no-DAO SHOULD
be scheduled to send to the node's DAO Parents.
2. A node that is to be aggregated for is located somewhere else 5. When a DAO (or no-DAO) for a REACHABLE(*) entry is received with
within the DODAG iteration, not in the sub-DAG of the aggregating an older or unchanged DAO Sequence Number, then the DAO (or no-
node. DAO) SHOULD be ignored and the associated entry MUST NOT be
updated with the stale information.
3. A node that is to be aggregated for is located somewhere else in 6.2.4.1.1.2.1. REACHABLE(Confirmed)
the LLN.
Consider a node M that is performing an aggregation, and a node N 1. When a DAO for a previously unknown (or UNREACHABLE) destination
that is to be a member of the aggregation group. A node Z situated is received and is to be stored, it MUST be entered into the
above the node M in the DODAG, but not above node N, will see the routing table in the REACHABLE(Confirmed) state. Alternately the
advertisements for the aggregation owned by M but not that of the node may behave as a non-storing node with respect to this
individual prefix for N. Such a node Z will route all the packets for destination.
node N towards node M, but node M will have no route to the node N
and will fail to forward.
Additional protocols may be applied beyond the scope of this 2. When a DAO for a REACHABLE(Confirmed) entry is received with a
specification to dynamically elect/provision an aggregating node and newer DAO Sequence Number the entry MUST be updated with the
groups of nodes eligible to be aggregated in order to provide route logical equivalent of the DAO contents.
summarization for a sub-DAG.
6.9. Loop Detection 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
entry MUST be placed in the REACHABLE(Pending) state and the
associated Retry Counter MUST be set to 0.
6.2.4.1.1.2.2. REACHABLE(Pending)
1. When a DAO for a REACHABLE(Pending) entry is received with a
newer DAO Sequence Number, the entry MUST be updated with the
logical equivalent of the DAO contents and the entry MUST be
placed in the REACHABLE(Confirmed) state.
2. When a DAO for a REACHABLE(Pending) entry is expected, e.g.
because DAO has (again) been triggered with respect to that
neighbor, then the associated Retry Counter MUST be incremented.
3. When a the associated Retry Counter for a REACHABLE(Pending)
entry reaches a maximum threshold, the entry MUST be placed into
the UNREACHABLE state and no-DAO SHOULD be scheduled to send to
the node's DAO Parents.
6.2.4.1.1.3. Operation in the UNREACHABLE state
1. An implementation SHOULD bound the time that the entry is
allocated in the UNREACHABLE state. Upon the equivalent expiry
of the related timer (RemoveTimer), the entry SHOULD be
suppressed.
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.
3. When the node has completed an attempt to report a no-DAO to each
of the DAO parents, the entry SHOULD be suppressed.
6.2.5. Operation of DAO Non-storing Nodes
1. When a DAO is received from a child by a node who will not store
a routing table entry for the DAO, the node MUST schedule to pass
the DAO contents along to its DAO parents. Prior to passing the
DAO along, the node MUST process the DAO as follows, in order
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')
is investigated to determine if the node already has a route
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
waypoint, then the node MUST append the address of the child
to the RRStack, and increment RRCount.
6.2.6. Scheduling to Send DAO (or no-DAO)
1. An implementation SHOULD arrange to rate-limit the sending of
DAOs.
2. When scheduling to send a DAO, an implementation SHOULD
equivalently start a timer (DelayDAO) to delay sending the DAO.
If the timer has already been armed then the DAO may be
considered as already scheduled, and implementation SHOULD leave
the timer running at its present duration.
o In order to increase the effectiveness of aggregation, an
implementation MAY allow time to receive no-DAOs from its sub-
DODAG prior to emitting DAOs to its DAO Parents.
* The scheduled delay in such cases may be, for example, such
that DAO_LATENCY/f(self_rank) <= delay < DAO_LATENCY/
f(parent_rank), where f(rank) is floor(rank/
MinHopRankIncrease), such that nodes deeper in the DODAG may
tend to report DAO messages first before their parent nodes
will report DAO messages. Note that this suggestion is
intended as an optimization to allow efficient aggregation --
it is not required for correct operation in the general case.
6.2.7. Triggering DAO Message from the Sub-DODAG
Note: The DIO is modified to add a 'S' flag, which is used to
indicate if a non-root ancestor storing routing table entries learned
from DAOs. This allows an optimization in the case where ONLY the
root node is storing such routing table entries, then it is not
necessary for an intermediate node to trigger DAO messages from its
sub-DODAG when it changes its DAO Parent.
1. The DODAG root MUST clear the 'S' flag when it emits DIO
messages.
2. Non-root nodes that store routing table entries learned from
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 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. (TBD A change to DTSN does not indicate
DAG inconsistency?).
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
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,
it SHOULD increment its DTSN as if the 'T' flag has been set.
12. DAO Transmission SHOULD be scheduled when a new parent is added
to the DAO Parent set.
13. A node that receives a newly incremented DTSN from a DAO Parent
MUST schedule a DAO transmission.
o When a node that is not fully-storing sees a DTSN increment, it
will increment its own DTSN. This will cause the DTSN increment
to extend down the DODAG to the first fully-storing node, which
will send its DAOs back up, rebuilding source routes information
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
reissue its entire set of routing table entries learned from DAOs
(or an aggregated subset thereof), but will not need to increment
its own DTSN. The 'DTSN increment wave' stops when it encounters
fully-storing nodes.
o When a fully-storing node sees a DTSN increment AND the 'T' flag
is set, it does increment its own DTSN as well. The 'T' flag
'punches through' all nodes, causing all routing tables in the
entire sub-DODAG to be refreshed.
6.2.8. Sending DAO Messages to DAO Parents
1. When storing nodes send DAO messages for stored entries the
RRStack SHOULD be cleared in the DAO message.
2. DAO Messages sent to DAO Parents MUST be unicast.
* The IPv6 Source Address is the node sending the DAO message.
* The IPv6 Destination Address is DAO parent.
3. When the appointed time arrives (DelayDAO) for the transmission
of DAO messages (with jitter as appropriate) for the requested
entries, the implementation MAY aggregate the the entries into a
reduced numbers of DAOs to be reported to each parent, and
perform compression if possible.
4. Note: it is NOT RECOMMENDED that a DAO Transmission (No-DAO) be
scheduled when a DAO Parent is removed from the DAO Parent set.
6.2.9. Multicast Destination Advertisement Messages
A special case of DAO operation, distinct from unicast DAO operation,
is multicast DAO operation which may be used to populate '1-hop'
routing table entries.
1. A node MAY multicast a DAO message to the link-local scope all-
nodes multicast address FF02::1.
2. A multicast DAO message MUST be used only to advertise
information about self, i.e. prefixes directly connected to or
owned by this node, such as a multicast group that the node is
subscribed to or a global address owned by the node.
3. A multicast DAO message MUST NOT be used to relay connectivity
information learned (e.g. through unicast DAO) from another node.
4. Information obtained from a multicast DAO MAY be installed in the
routing table and MAY be propagated by a node in unicast DAOs.
5. A node MUST NOT perform any other DAO related processing on a
received multicast DAO, in particular a node MUST NOT perform the
actions of a DAO parent upon receipt of a multicast DAO.
o The multicast DAO may be used to enable direct P2P communication,
without needing the RPL routing structure to relay the packets.
o The multicast DAO does not presume any DODAG relationship between
the emitter and the receiver.
7. Packet Forwarding and Loop Avoidance/Detection
7.1. Suggestions for Packet Forwarding
When forwarding a packet to a destination, precedence is given to
selection of a next-hop successor as follows:
1. In the scope of this specification, it is preferred to select a
successor from a DODAG iteration that matches the RPLInstanceID
marked in the IPv6 header of the packet being forwarded.
2. If a local administrative preference favors a route that has been
learned from a different routing protocol than RPL, then use that
successor.
3. If there is an entry in the routing table matching the
destination that has been learned from a multicast destination
advertisement (e.g. the destination is a one-hop neighbor), then
use that successor.
4. If there is an entry in the routing table matching the
destination that has been learned from a unicast destination
advertisement (e.g. the destination is located down the sub-
DODAG), then use that successor.
5. If there is a DODAG iteration offering a route to a prefix
matching the destination, then select one of those DODAG parents
as a successor.
6. If there is a DODAG parent offering a default route then select
that DODAG parent as a successor.
7. If there is a DODAG iteration offering a route to a prefix
matching the destination, but all DODAG parents have been tried
and are temporarily unavailable (as determined by the forwarding
procedure), then select a DODAG sibling as a successor.
8. Finally, if no DODAG siblings are available, the packet is
dropped. ICMP Destination Unreachable may be invoked. An
inconsistency is detected.
TTL MUST be decremented when forwarding. If the packet is being
forwarded via a sibling, then the TTL MAY be decremented more
aggressively (by more than one) to limit the impact of possible
loops.
Note that the chosen successor MUST NOT be the neighbor that was the
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,
such as switching from DIO routes to DAO routes as the destination is
neared.
7.2. 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 in
the IPv6 flow label. The IPv6 flow label is defined in [RFC2460] and the IPv6 flow label. The IPv6 flow label is defined in [RFC2460] and
its operation is further specified in [RFC3697]. For the purpose of its operation is further specified in [RFC3697]. For the purpose of
RPL operations, the flow label is constructed as follows: RPL operations, the flow label is constructed 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|O|S|R|F| SenderRank | InstanceID | |O|S|R|F| SenderRank | RPLInstanceID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: RPL Flow Label Figure 12: RPL Flow Label
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. iteration. A host MUST set the bit to 0.
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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 MUST set the bit to 0.
SenderRank: 8-bit field set to zero by the source and to its rank by SenderRank: 8-bit field set to zero by the source and to its rank by
a router that forwards inside the RPL network. a router that forwards inside the RPL network.
InstanceID: 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.
6.9.1. Source Node Operation 7.2.1. Source Node Operation
A packet that is sourced at a node connected to a RPL network or A packet that is sourced at a node connected to a RPL network or
destined to a node connected to a RPL network MUST be issued with the destined to a node connected to a RPL network MUST be issued with the
flow label zeroed out, but for the InstanceID field. flow label zeroed out, but for the RPLInstanceID field.
If the source is aware of the InstanceID that is preferred for the If the source is aware of the RPLInstanceID that is preferred for the
flow, then it MUST set the InstanceID field in the flow label flow, then it MUST set the RPLInstanceID field in the flow label
accordingly, otherwise it MUST set it to the RPL_DEFAULT_INSTANCE. accordingly, otherwise it MUST set it to the RPL_DEFAULT_INSTANCE.
If a compression mechanism such as 6LoWPAN is applied to the packet, 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 the flow label MUST NOT be compressed even if it is set to all
zeroes. zeroes.
6.9.2. Router Operation 7.2.2. Router Operation
6.9.2.1. Conformance to RFC 3697 7.2.2.1. Conformance to RFC 3697
[RFC3697] mandates that the Flow Label value set by the source MUST [RFC3697] mandates that the Flow Label value set by the source MUST
be delivered unchanged to the destination node(s). be delivered unchanged to the destination node(s).
In order to restore the flow label to its original value, an RPL In order to restore the flow label to its original value, an RPL
router that delivers a packet to a destination connected to a RPL 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 network or that routes a packet outside the RPL network MUST zero out
all the fields but the InstanceID field that must be delivered all the fields but the RPLInstanceID field that must be delivered
without a change. without a change.
6.9.2.2. Instance Forwarding 7.2.2.2. 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 InstanceID is placed by the source in the flow label. This The RPLInstanceID is placed by the source in the flow label. This
InstanceID MUST match the DODAG 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.
When a router receives a packet that is flagged with a given When a router receives a packet that is flagged with a given
InstanceID and the node can forward the packet along the DODAG RPLInstanceID and the node can forward the packet along the DODAG
associated to that instance, then the router MUST do so and leave the associated to that instance, then the router MUST do so and leave the
InstanceID flag unchanged. RPLInstanceID flag 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 InstanceID in the flow label, then the node SHOULD discard the the RPLInstanceID in the flow label, then the node SHOULD discard the
packet. packet.
6.9.2.3. DAG Inconsistency Loop Detection 7.2.2.3. 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 DAG Sequence Number a temporary When the DODAG root increments the DODAGSequenceNumber a temporary
rank discontinuity may form between the next iteration and the prior rank discontinuity may form between the next iteration and the prior
iteration, in particular if nodes are adjusting their rank in the iteration, in particular if nodes are adjusting their rank in the
next iteration and deferring their migration into the next iteration. next iteration and deferring their migration into the next iteration.
A router that is still a member of the prior iteration may choose to A router that is still a member of the prior iteration 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 iteration.
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 iteration is not necessarily
the same as in the next iteration and the packet may be judged to not the same as in the next iteration and the packet may be judged to not
be making forward progress. If the sending router is aware that the be 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 iteration, then the
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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 in the Flow Label.
When an inconsistency, is detected on a packet, if the Rank-Error bit When an inconsistency, is detected on a packet, if the Rank-Error bit
was not set then the Rank-Error bit is set. If it was set the packet was not set then the Rank-Error bit is set. If it was set the packet
is discarded and the trickle timer is reset. is discarded and the trickle timer is reset.
6.9.2.4. Sibling Loop Avoidance 7.2.2.4. 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 but 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.
6.9.2.5. DAO Inconsistency Loop Detection and Recovery 7.2.2.5. 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-DAG. 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. So rather than routing up a packet with the down bit set, the again. So rather than routing up a packet with the down bit set, the
router MUST discard the packet. If DAO inconsistency loop recovery router MUST discard the packet. If DAO inconsistency loop recovery
is applied, then the router SHOULD send the packet to the parent that is applied, then the router SHOULD send the packet to the parent that
passed it with the Forwarding-Error 'F' bit set. passed it with the Forwarding-Error 'F' bit set.
6.9.2.6. Forward Path Recovery 7.2.2.6. 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 its way 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.
6.10. Multicast Operation 8. 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
MLD, one can read MLDv2 or v3. MLD, one can read MLDv2 or v3.
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.
A router might select to pass a listener registration DAO message to A router might select to pass a listener registration DAO message to
its preferred parent only, in which case multicast packets coming its preferred parent only, in which case multicast packets coming
back might be lost for all of its sub-DAG if the transmission fails back might be lost for all of its sub-DODAG if the transmission fails
over that link. Alternatively the router might select to copy over that link. Alternatively the router might select to copy
additional parents as it would do for DAO messages advertising additional parents as it would do for DAO messages advertising
unicast destinations, in which case there might be duplicates that unicast destinations, in which case there might be duplicates that
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.
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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.
6.11. Maintenance of Routing Adjacency 9. 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.
7. Suggestions for Packet Forwarding 10. Guidelines for Objective Functions
When forwarding a packet to a destination, precedence is given to
selection of a next-hop successor as follows:
1. In the scope of this specification, it is preferred to select a
successor from a DODAG iteration that matches the InstanceID
marked in the IPv6 header of the packet being forwarded.
2. If a local administrative preference favors a route that has been
learned from a different routing protocol than RPL, then use that
successor.
3. If there is an entry in the routing table matching the
destination that has been learned from a multicast destination
advertisement (e.g. the destination is a one-hop neighbor), then
use that successor.
4. If there is an entry in the routing table matching the
destination that has been learned from a unicast destination
advertisement (e.g. the destination is located down the sub-DAG),
then use that successor.
5. If there is a DODAG iteration offering a route to a prefix
matching the destination, then select one of those DODAG parents
as a successor.
6. If there is a DAG parent offering a default route then select
that DAG parent as a successor.
7. If there is a DODAG iteration offering a route to a prefix
matching the destination, but all DAG parents have been tried and
are temporarily unavailable (as determined by the forwarding
procedure), then select a DAG sibling as a successor.
8. Finally, if no DAG siblings are available, the packet is dropped.
ICMP Destination Unreachable may be invoked. An inconsistency is
detected.
TTL MUST be decremented when forwarding. If the packet is being
forwarded via a sibling, then the TTL MAY be decremented more
aggressively (by more than one) to limit the impact of possible
loops.
Note that the chosen successor MUST NOT be the neighbor that was the
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,
such as switching from DIO routes to DAO routes as the destination is
neared.
8. 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 DAG 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 iteration.
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 compute the DODAG (e.g. "minimize the path cost using the be used to compute the DODAG (e.g. "minimize the path cost using the
ETX metric and avoid `Blue' links"). The Objective Code Points are ETX metric and avoid 'Blue' links"). The Objective Code Points are
specified in [I-D.ietf-roll-routing-metrics] and related companion specified in [I-D.ietf-roll-routing-metrics], [I-D.ietf-roll-of0],
specifications. and related companion specifications.
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, or a
trigger indicating that the state of a candidate neighbor has trigger indicating that the state of a candidate neighbor has
changed. changed.
skipping to change at page 56, line 25 skipping to change at page 59, line 14
completely excluded from the computation, while others might be completely excluded from the computation, while others might be
more or less preferred. more or less preferred.
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 the step of rank to that o An OF computes self's rank by adding to the rank of the candidate
candidate to the rank of that candidate. The step of rank is a value representing the relative locations of self and the
computed by estimating the link as follows: candidate in the DODAG iteration.
* The step of rank might vary from 1 to 16.
+ 1 indicates a unusually good link, for instance a link
between powered devices in a mostly battery operated
environment.
+ 4 indicates a `normal'/typical link, as qualified by the * The increase in rank must be at least MinHopRankIncrease.
implementation. (This prevents the creation of a path of sibling links
connecting a child with its parent.)
+ 16 indicates a link that can hardly be used to forward any * To keep loop avoidance and metric optimization in alignment,
packet, for instance a radio link with quality indicator or the increase in rank should reflect any increase in the metric
expected transmission count that is close to the acceptable value. For example, with a purely additive metric such as ETX,
threshold. the increase in rank can be made proportional to the increase
in the metric.
* Candidate neighbors that would cause self's rank to increase * Candidate neighbors that would cause self's rank to increase
are ignored are ignored
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
skipping to change at page 57, line 34 skipping to change at page 60, line 19
* 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 ignored
* Candidate neighbors of a lesser rank than self (non-siblings) * Candidate neighbors of a lesser rank than self (non-siblings)
are preferred are preferred
9. RPL Constants and Variables 11. RPL Constants and Variables
Following is a summary of RPL constants and variables. Some default Following is a summary of RPL constants and variables. Some default
values are to be determined in companion applicability statements. values are to be determined in companion applicability statements.
ZERO_LIFETIME This is the special value of a lifetime that indicates ZERO_LIFETIME This is the special value of a lifetime that indicates
immediate death and removal. ZERO_LIFETIME has a value of 0. immediate death and removal. ZERO_LIFETIME has a value of 0.
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 DAG root. ROOT_RANK has a value of ROOT_RANK This is the rank for a DODAG root. ROOT_RANK has a value
1. of 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 0xFF. INFINITE_RANK has a value of 0xFF.
RPL_DEFAULT_INSTANCE This is the InstanceID 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_DIO_INTERVAL_MIN To be determined DEFAULT_DIO_INTERVAL_MIN To be determined
DEFAULT_DIO_INTERVAL_DOUBLINGS To be determined DEFAULT_DIO_INTERVAL_DOUBLINGS To be determined
DEFAULT_DIO_REDUNDANCY_CONSTANT To be determined DEFAULT_DIO_REDUNDANCY_CONSTANT To be determined
DEF_DAO_LATENCY To be determined DEF_DAO_LATENCY To be determined
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DEFAULT_DIO_INTERVAL_MIN To be determined DEFAULT_DIO_INTERVAL_MIN To be determined
DEFAULT_DIO_INTERVAL_DOUBLINGS To be determined DEFAULT_DIO_INTERVAL_DOUBLINGS To be determined
DEFAULT_DIO_REDUNDANCY_CONSTANT To be determined DEFAULT_DIO_REDUNDANCY_CONSTANT To be determined
DEF_DAO_LATENCY To be determined DEF_DAO_LATENCY To be determined
MAX_DESTROY_INTERVAL To be determined MAX_DESTROY_INTERVAL 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 6.3.4 Section 5.3.5.1
DAG Sequence Number Increment Timer Up to one instance per DODAG DAG Sequence Number Increment Timer Up to one instance per DODAG
that the node is acting as DAG root of. May not be supported that the node is acting as DODAG root of. May not be supported
in all implementations. Expiry triggers revision of in all implementations. Expiry triggers revision of
DAGSequenceNumber, causing a new series of updated DIO message DODAGSequenceNumber, causing a new series of updated DIO
to be sent. Interval should be chosen appropriate to message 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 DA parent (the subset of DAG DelayDAO Timer Up to one instance per DAO parent (the subset of
parents chosen to receive destination advertisements) per DODAG parents chosen to receive destination advertisements) per
DODAG. Expiry triggers sending of DAO message to the DA DODAG. Expiry triggers sending of DAO message to the DAO
parent. The interval is to be proportional to DEF_DAO_LATENCY/ parent. See Section 6.2.6
(node rank), such that nodes of greater rank (further down
along the DODAG) expire first, coordinating the sending of DAO
messages to allow for a chance of aggregation. See
Section 6.8.1.1.1
RemoveTimer Up to one instance per DA entry per neighbor (i.e. those RemoveTimer Up to one instance per DAO entry per neighbor (i.e.
neighbors that have given DAO messages to this node as a DAG those neighbors that have given DAO messages to this node as a
parent) Expiry triggers a change in state for the DA entry, DODAG parent) Expiry triggers a change in state for the DAO
setting up to do unreachable (No-DAO) advertisements or entry, setting up to do unreachable (No-DAO) advertisements or
immediately deallocating the DA entry if there are no DA immediately deallocating the DAO entry if there are no DAO
parents. The interval is min(MAX_DESTROY_INTERVAL, TBD(DIO parents. See Section 6.2.4.1.1.3
Trickle Timer Interval)). See Section 6.8.1.1.1
10. Manageability Considerations 12. 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.
10.1. Control of Function and Policy 12.1. Control of Function and Policy
10.1.1. Initialization Mode 12.1.1. 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.
10.1.2. DIO Base option 12.1.2. 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 6.1.3.1: protocol parameters, which are further described in Section 5.1.1:
DAGPreference DAGPreference
InstanceID RPLInstanceID
DAGObjectiveCodePoint DAGObjectiveCodePoint
DAGID DODAGID
Destination Prefixes Destination Prefixes
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 DAG 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 DAG 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 DAG root for a configured period of time. act as a DODAG root for a configured period of time.
DAG Table Entry Suppression A RPL implementation SHOULD provide the DODAG Table Entry Suppression A RPL implementation SHOULD provide
ability to configure a timer after the expiration of which the the ability to configure a timer after the expiration of which
DAG table that contains all the records about a DAG is logical equivalent of the DODAG table that contains all the
suppressed, to be invoked if the DAG parent set becomes empty. records about a DODAG is suppressed, to be invoked if the DODAG
parent set becomes empty.
10.1.3. Trickle Timers 12.1.3. 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 DAG 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 6.3.4: the following parameters, further described in Section 5.3.5.1:
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.
10.1.4. DAG Sequence Number Increment 12.1.4. DAG Sequence Number Increment
A RPL implementation may allow by configuration at the DAG root to A RPL implementation may allow by configuration at the DODAG root to
refresh the DODAG states by updating the DAGSequenceNumber. A RPL refresh the DODAG states by updating the DODAGSequenceNumber. 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 DAG root to control event triggered mechanism are used by the DODAG root to control
DAGSequenceNumber change. DODAGSequenceNumber change.
10.1.5. Destination Advertisement Timers 12.1.5. 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
10.1.6. Policy Control 12.1.6. Policy Control
DAG discovery enables nodes to implement different policies for DAG discovery enables nodes to implement different policies for
selecting their DAG 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 A RPL implementation SHOULD allow for the configuration of the "Route
Tag" field of the DAO messages according to a set of rules defined by Tag" field of the DAO messages according to a set of rules defined by
policy. policy.
10.1.7. Data Structures 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.
10.2. Information and Data Models 12.2. 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.
10.3. Liveness Detection and Monitoring 12.3. 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 6.2, 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 DAG 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 DAG parents * A set of DODAG parents
10.3.1. Candidate Neighbor Data Structure 12.3.1. 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.
10.3.2. Directed Acyclic Graph (DAG) Table 12.3.2. 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 DAGID o DODAGID
o DAGObjectiveCodePoint o DAGObjectiveCodePoint
o A set of Destination Prefixes offered upwards along the DODAG o A set of Destination Prefixes offered upwards along the DODAG
o A set of DAG 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 DAGSequenceNumber The set of DODAG parents structure is itself a table with the
following entries:
The set of DAG parents structure is itself a table with the 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 DAG Parent Object last processed from the DODAG Parent
o A flag reporting if the Parent is a DA Parent as described in o A flag reporting if the Parent is a DAO Parent as described in
Section 6.8 Section 6
10.3.3. Routing Table 12.3.3. 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 Destination Prefix
o Destination Prefix Length o Destination Prefix Length
o Lifetime Timer o Lifetime Timer
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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
10.3.4. Other RPL Monitoring Parameters 12.3.4. 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 DAG a times the node has detected an inconsistency with respect to a
parent, e.g. if the DAGID 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.
10.3.5. RPL Trickle Timers 12.3.5. RPL Trickle Timers
A RPL implementation operating on a DAG 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).
10.4. Verifying Correct Operation 12.4. 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.
10.5. Requirements on Other Protocols and Functional Components 12.5. 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.
10.6. Impact on Network Operation 12.6. Impact on Network Operation
To be completed. To be completed.
11. Security Considerations 13. Security Considerations
Security Considerations for RPL are to be developed in accordance Security Considerations for RPL are to be developed in accordance
with recommendations laid out in, for example, with recommendations laid out in, for example,
[I-D.tsao-roll-security-framework]. [I-D.tsao-roll-security-framework].
12. IANA Considerations 14. IANA Considerations
12.1. RPL Control Message 14.1. RPL Control Message
The RPL Control Message is an ICMP information message type that is The RPL Control Message is an ICMP information message type that is
to be used carry DAG Information Objects, DAG Information to be used carry DAG Information Objects, DAG Information
Solicitations, and Destination Advertisement Objects in support of Solicitations, and Destination Advertisement Objects in support of
RPL operation. RPL operation.
IANA has defined a ICMPv6 Type Number Registry. The suggested type IANA has defined a ICMPv6 Type Number Registry. The suggested type
value for the RPL Control Message is 155, to be confirmed by IANA. value for the RPL Control Message is 155, to be confirmed by IANA.
12.2. New Registry for RPL Control Codes 14.2. New Registry for RPL Control Codes
IANA is requested to create a registry, RPL Control Codes, for the IANA is requested to create a registry, RPL Control Codes, for the
Code field of the ICMPv6 RPL Control Message. Code field of the ICMPv6 RPL Control Message.
New codes may be allocated only by an IETF Consensus action. Each New codes may be allocated only by an IETF Consensus action. Each
code should be tracked with the following qualities: code should be tracked with the following qualities:
o Code o Code
o Description o Description
skipping to change at page 65, line 15 skipping to change at page 67, line 31
+------+----------------------------------+---------------+ +------+----------------------------------+---------------+
| Code | Description | Reference | | Code | Description | Reference |
+------+----------------------------------+---------------+ +------+----------------------------------+---------------+
| 0x01 | DAG Information Solicitation | This document | | 0x01 | DAG Information Solicitation | This document |
| 0x02 | DAG Information Object | This document | | 0x02 | DAG Information Object | This document |
| 0x04 | Destination Advertisement Object | This document | | 0x04 | Destination Advertisement Object | This document |
+------+----------------------------------+---------------+ +------+----------------------------------+---------------+
RPL Control Codes RPL Control Codes
12.3. New Registry for the Control Field of the DIO Base 14.3. New Registry for the Control Field of the DIO Base
IANA is requested to create a registry for the Control field of the IANA is requested to create a registry for the Control field of the
DIO Base. DIO Base.
New bit numbers may be allocated only by an IETF Consensus action. New fields may be allocated only by an IETF Consensus action. Each
Each bit should be tracked with the following qualities: field should be tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit) o Bit number (counting from bit 0 as the most significant bit)
o Capability description o Capability description
o Defining RFC o Defining RFC
Four groups are currently defined: Four groups are currently defined:
+-------+-------------------------------------+---------------+ +-------+-----------------------------------------+---------------+
| Bit | Description | Reference | | Bit | Description | Reference |
+-------+-------------------------------------+---------------+ +-------+-----------------------------------------+---------------+
| 0 | Grounded DODAG | This document | | 0 | Grounded DODAG (G) | This document |
| 1 | Destination Advertisement Trigger | This document | | 1 | Destination Advertisement Supported (A) | This document |
| 2 | Destination Advertisement Supported | This document | | 2 | Destination Advertisement Trigger (T) | This document |
| 5,6,7 | DAG Preference | This document | | 3 | Destination Advertisements Stored (S) | This document |
+-------+-------------------------------------+---------------+ | 5,6,7 | DODAG Preference (Prf) | This document |
+-------+-----------------------------------------+---------------+
DIO Base Flags DIO Base Flags
12.4. DAG Information Object (DIO) Suboption 14.4. DAG Information Object (DIO) Suboption
IANA is requested to create a registry for the DIO Base Suboptions IANA is requested to create a registry for the DIO Base Suboptions
+-------+------------------------------+---------------+ +-------+------------------------------+---------------+
| Value | Meaning | Reference | | Value | Meaning | Reference |
+-------+------------------------------+---------------+ +-------+------------------------------+---------------+
| 0 | Pad1 - DIO Padding | This document | | 0 | Pad1 - DIO Padding | This document |
| 1 | PadN - DIO suboption padding | This document | | 1 | PadN - DIO suboption padding | This document |
| 2 | DAG Metric Container | This Document | | 2 | DAG Metric Container | This Document |
| 3 | Destination Prefix | This Document | | 3 | Destination Prefix | This Document |
| 4 | DAG Timer Configuration | This Document | | 4 | DAG Timer Configuration | This Document |
+-------+------------------------------+---------------+ +-------+------------------------------+---------------+
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+-------+------------------------------+---------------+ +-------+------------------------------+---------------+
| 0 | Pad1 - DIO Padding | This document | | 0 | Pad1 - DIO Padding | This document |
| 1 | PadN - DIO suboption padding | This document | | 1 | PadN - DIO suboption padding | This document |
| 2 | DAG Metric Container | This Document | | 2 | DAG Metric Container | This Document |
| 3 | Destination Prefix | This Document | | 3 | Destination Prefix | This Document |
| 4 | DAG Timer Configuration | This Document | | 4 | DAG Timer Configuration | This Document |
+-------+------------------------------+---------------+ +-------+------------------------------+---------------+
DAG Information Option (DIO) Base Suboptions DAG Information Option (DIO) Base Suboptions
13. Acknowledgements 15. Acknowledgements
The authors would like to acknowledge the review, feedback, and The authors would like to acknowledge the review, feedback, and
comments from Emmanuel Baccelli, Dominique Barthel, Yusuf Bashir, comments from Emmanuel Baccelli, Dominique Barthel, Yusuf Bashir,
Mathilde Durvy, Manhar Goindi, Mukul Goyal, Anders Jagd, Quentin Mathilde Durvy, Manhar Goindi, Mukul Goyal, Anders Jagd, Quentin
Lampin, Jerry Martocci, Alexandru Petrescu, and Don Sturek. Lampin, Jerry Martocci, Alexandru Petrescu, and Don Sturek.
The authors would like to acknowledge the guidance and input provided The authors would like to acknowledge the guidance and input provided
by the ROLL Chairs, David Culler and JP Vasseur. by the ROLL Chairs, David Culler and JP Vasseur.
The authors would like to acknowledge prior contributions of Robert The authors would like to acknowledge prior contributions of Robert
Assimiti, Mischa Dohler, Julien Abeille, Ryuji Wakikawa, Teco Boot, Assimiti, Mischa Dohler, Julien Abeille, Ryuji Wakikawa, Teco Boot,
Patrick Wetterwald, Bryan Mclaughlin, Carlos J. Bernardos, Thomas Patrick Wetterwald, Bryan Mclaughlin, Carlos J. Bernardos, Thomas
Watteyne, Zach Shelby, Caroline Bontoux, Marco Molteni, Billy Moon, Watteyne, Zach Shelby, Caroline Bontoux, Marco Molteni, Billy Moon,
and Arsalan Tavakoli, which have provided useful design and Arsalan Tavakoli, which have provided useful design
considerations to RPL. considerations to RPL.
14. Contributors 16. Contributors
RPL is the result of the contribution of the following members of the RPL is the result of the contribution of the following members of the
ROLL Design Team, including the editors, and additional contributors ROLL Design Team, including the editors, and additional contributors
as listed below: as listed below:
JP Vasseur JP Vasseur
Cisco Systems, Inc Cisco Systems, Inc
11, Rue Camille Desmoulins 11, Rue Camille Desmoulins
Issy Les Moulineaux, 92782 Issy Les Moulineaux, 92782
France France
Email: jpv@cisco.com Email: jpv@cisco.com
Jonathan W. Hui
Arch Rock Corporation
501 2nd St. Ste. 410
San Francisco, CA 94107
USA
Email: jhui@archrock.com
Thomas Heide Clausen Thomas Heide Clausen
LIX, Ecole Polytechnique, France LIX, Ecole Polytechnique, France
Phone: +33 6 6058 9349 Phone: +33 6 6058 9349
EMail: T.Clausen@computer.org EMail: T.Clausen@computer.org
URI: http://www.ThomasClausen.org/ URI: http://www.ThomasClausen.org/
Philip Levis Philip Levis
Stanford University Stanford University
358 Gates Hall, Stanford University 358 Gates Hall, Stanford University
skipping to change at page 67, line 33 skipping to change at page 69, line 42
Email: pal@cs.stanford.edu Email: pal@cs.stanford.edu
Richard Kelsey Richard Kelsey
Ember Corporation Ember Corporation
Boston, MA Boston, MA
USA USA
Phone: +1 617 951 1225 Phone: +1 617 951 1225
Email: kelsey@ember.com Email: kelsey@ember.com
Stephen Dawson-Haggerty Jonathan W. Hui
UC Berkeley Arch Rock Corporation
Soda Hall, UC Berkeley 501 2nd St. Ste. 410
Berkeley, CA 94720 San Francisco, CA 94107
USA USA
Email: stevedh@cs.berkeley.edu Email: jhui@archrock.com
Kris Pister Kris Pister
Dust Networks Dust Networks
30695 Huntwood Ave. 30695 Huntwood Ave.
Hayward, 94544 Hayward, 94544
USA USA
Email: kpister@dustnetworks.com Email: kpister@dustnetworks.com
Anders Brandt Anders Brandt
Zensys, Inc. Zensys, Inc.
Emdrupvej 26 Emdrupvej 26
Copenhagen, DK-2100 Copenhagen, DK-2100
Denmark Denmark
Email: abr@zen-sys.com Email: abr@zen-sys.com
skipping to change at page 68, line 14 skipping to change at page 70, line 20
Email: kpister@dustnetworks.com Email: kpister@dustnetworks.com
Anders Brandt Anders Brandt
Zensys, Inc. Zensys, Inc.
Emdrupvej 26 Emdrupvej 26
Copenhagen, DK-2100 Copenhagen, DK-2100
Denmark Denmark
Email: abr@zen-sys.com Email: abr@zen-sys.com
15. References Stephen Dawson-Haggerty
UC Berkeley
Soda Hall, UC Berkeley
Berkeley, CA 94720
USA
15.1. Normative References Email: stevedh@cs.berkeley.edu
17. References
17.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998. (IPv6) Specification", RFC 2460, December 1998.
15.2. Informative References 17.2. Informative References
[I-D.ietf-bfd-base] [I-D.ietf-bfd-base]
Katz, D. and D. Ward, "Bidirectional Forwarding Katz, D. and D. Ward, "Bidirectional Forwarding
Detection", draft-ietf-bfd-base-09 (work in progress), Detection", draft-ietf-bfd-base-11 (work in progress),
February 2009. January 2010.
[I-D.ietf-manet-nhdp] [I-D.ietf-manet-nhdp]
Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)", Network (MANET) Neighborhood Discovery Protocol (NHDP)",
draft-ietf-manet-nhdp-11 (work in progress), October 2009. draft-ietf-manet-nhdp-11 (work in progress), October 2009.
[I-D.ietf-roll-building-routing-reqs] [I-D.ietf-roll-building-routing-reqs]
Martocci, J., Riou, N., Mil, P., and W. Vermeylen, Martocci, J., Riou, N., Mil, P., and W. Vermeylen,
"Building Automation Routing Requirements in Low Power and "Building Automation Routing Requirements in Low Power and
Lossy Networks", draft-ietf-roll-building-routing-reqs-08 Lossy Networks", draft-ietf-roll-building-routing-reqs-09
(work in progress), December 2009. (work in progress), January 2010.
[I-D.ietf-roll-home-routing-reqs] [I-D.ietf-roll-home-routing-reqs]
Brandt, A. and J. Buron, "Home Automation Routing Brandt, A. and J. Buron, "Home Automation Routing
Requirements in Low Power and Lossy Networks", Requirements in Low Power and Lossy Networks",
draft-ietf-roll-home-routing-reqs-09 (work in progress), draft-ietf-roll-home-routing-reqs-11 (work in progress),
November 2009. January 2010.
[I-D.ietf-roll-of0]
Thubert, P., "RPL Objective Function 0",
draft-ietf-roll-of0-00 (work in progress), December 2009.
[I-D.ietf-roll-routing-metrics] [I-D.ietf-roll-routing-metrics]
Vasseur, J. and D. Networks, "Routing Metrics used for Vasseur, J. and D. Networks, "Routing Metrics used for
Path Calculation in Low Power and Lossy Networks", Path Calculation in Low Power and Lossy Networks",
draft-ietf-roll-routing-metrics-04 (work in progress), draft-ietf-roll-routing-metrics-04 (work in progress),
December 2009. December 2009.
[I-D.ietf-roll-terminology] [I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-02 (work in Networks", draft-ietf-roll-terminology-02 (work in
skipping to change at page 69, line 29 skipping to change at page 71, line 50
[Levis08] Levis, P., Brewer, E., Culler, D., Gay, D., Madden, S., [Levis08] Levis, P., Brewer, E., Culler, D., Gay, D., Madden, S.,
Patel, N., Polastre, J., Shenker, S., Szewczyk, R., and A. Patel, N., Polastre, J., Shenker, S., Szewczyk, R., and A.
Woo, "The Emergence of a Networking Primitive in Wireless Woo, "The Emergence of a Networking Primitive in Wireless
Sensor Networks", Communications of the ACM, v.51 n.7, Sensor Networks", Communications of the ACM, v.51 n.7,
July 2008, July 2008,
<http://portal.acm.org/citation.cfm?id=1364804>. <http://portal.acm.org/citation.cfm?id=1364804>.
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
August 1996. August 1996.
[RFC2453] Malkin, G., "RIP Version 2", STD 56, RFC 2453,
November 1998.
[RFC3697] Rajahalme, J., Conta, A., Carpenter, B., and S. Deering, [RFC3697] Rajahalme, J., Conta, A., Carpenter, B., and S. Deering,
"IPv6 Flow Label Specification", RFC 3697, March 2004. "IPv6 Flow Label Specification", RFC 3697, March 2004.
[RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D., [RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89, Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, July 2004. RFC 3819, July 2004.
[RFC4101] Rescorla, E. and IAB, "Writing Protocol Models", RFC 4101, [RFC4101] Rescorla, E. and IAB, "Writing Protocol Models", RFC 4101,
June 2005. June 2005.
skipping to change at page 71, line 43 skipping to change at page 74, line 11
NOTE: RPL is still a work in progress. At this time there remain NOTE: RPL is still a work in progress. At this time there remain
several unsatisfied application requirements, but these are to be several unsatisfied application requirements, but these are to be
addressed as RPL is further specified. addressed as RPL is further specified.
Appendix B. Examples Appendix B. Examples
Consider the example LLN physical topology in Figure 13. In this Consider the example LLN physical topology in Figure 13. In this
example the links depicted are all usable L2 links. Suppose that all example the links depicted are all usable L2 links. Suppose that all
links are equally usable, and that the implementation specific policy links are equally usable, and that the implementation specific policy
function is simply to minimize hops. This LLN physical topology then function is simply to minimize hops. This LLN physical topology then
yields the DAG depicted in Figure 14, where the links depicted are yields the DODAG depicted in Figure 14, where the links depicted are
the edges toward DAG parents. This topology includes one DAG, rooted the edges toward DODAG parents. This topology includes one DAG,
by an LBR node (LBR) at rank 1. The LBR node will issue DIO rooted by an LBR node (LBR) at rank 1. The LBR node will issue DIO
messages, as governed by a trickle timer. Nodes (11), (12), (13), messages, as governed by a trickle timer. Nodes (11), (12), (13),
have selected (LBR) as their only parent, attached to the DAG at rank have selected (LBR) as their only parent, attached to the DODAG at
2, and periodically multicast DIOs. Node (22) has selected (11) and rank 2, and periodically multicast DIOs. Node (22) has selected (11)
(12) in its DAG parent set, and advertises itself at rank 3. Node and (12) in its DODAG parent set, and advertises itself at rank 3.
(22) thus has a set of DAG parents {(11), (12)} and siblings {((21), Node (22) thus has a set of DODAG parents {(11), (12)} and siblings
(23)}. {((21), (23)}.
(LBR) (LBR)
/ | \ / | \
.---` | `----. .---' | `----.
/ | \ / | \
(11)------(12)------(13) (11)------(12)------(13)
| \ | \ | \ | \ | \ | \
| `----. | `----. | `----. | `----. | `----. | `----.
| \| \| \ | \| \| \
(21)------(22)------(23) (24) (21)------(22)------(23) (24)
| /| /| | | /| /| |
| .----` | .----` | | | .----' | .----' | |
| / | / | | | / | / | |
(31)------(32)------(33)------(34) (31)------(32)------(33)------(34)
| /| \ | \ | \ | /| \ | \ | \
| .----` | `----. | `----. | `----. | .----' | `----. | `----. | `----.
| / | \| \| \ | / | \| \| \
.--------(41) (42) (43)------(44)------(45) .--------(41) (42) (43)------(44)------(45)
/ / /| \ | \ / / /| \ | \
.----` .----` .----` | `----. | `----. .----' .----' .----' | `----. | `----.
/ / / | \| \ / / / | \| \
(51)------(52)------(53)------(54)------(55)------(56) (51)------(52)------(53)------(54)------(55)------(56)
Note that the links depicted represent the usable L2 connectivity Note that the links depicted represent the usable L2 connectivity
available in the LLN. For example, Node (31) can communicate available in the LLN. For example, Node (31) can communicate
directly with its neighbors, Nodes (21), (22), (32), and (41). Node directly with its neighbors, Nodes (21), (22), (32), and (41). Node
(31) cannot communicate directly with any other nodes, e.g. (33), (31) cannot communicate directly with any other nodes, e.g. (33),
(23), (42). In this example these links offer bidirectional (23), (42). In this example these links offer bidirectional
communication, and `bad' links are not depicted. communication, and 'bad' links are not depicted.
Figure 13: Example LLN Topology Figure 13: Example LLN Topology
(LBR) (LBR)
/ | \ / | \
.---` | `----. .---' | `----.
/ | \ / | \
(11) (12) (13) (11) (12) (13)
| \ | \ | \ | \ | \ | \
| `----. | `----. | `----. | `----. | `----. | `----.
| \| \| \ | \| \| \
(21) (22) (23) (24) (21) (22) (23) (24)
| /| /| | | /| /| |
| .----` | .----` | | | .----' | .----' | |
| / | / | | | / | / | |
(31) (32) (33) (34) (31) (32) (33) (34)
| /| \ | \ | \ | /| \ | \ | \
| .----` | `----. | `----. | `----. | .----' | `----. | `----. | `----.
| / | \| \| \ | / | \| \| \
.--------(41) (42) (43) (44) (45) .--------(41) (42) (43) (44) (45)
/ / /| \ | \ / / /| \ | \
.----` .----` .----` | `----. | `----. .----' .----' .----' | `----. | `----.
/ / / | \| \ / / / | \| \
(51) (52) (53) (54) (55) (56) (51) (52) (53) (54) (55) (56)
Note that the links depicted represent directed links in the DAG Note that the links depicted represent directed links in the DODAG
overlaid on top of the physical topology depicted in Figure 13. As overlaid on top of the physical topology depicted in Figure 13. As
such, the depicted edges represent the relationship between nodes and such, the depicted edges represent the relationship between nodes and
their DAG parents, wherein all depicted edges are directed and their DODAG parents, wherein all depicted edges are directed and
oriented `up' on the page toward the DAG root (LBR). The DAG may oriented 'up' on the page toward the DODAG root (LBR). The DODAG may
provide default routes within the LLN, and serves as the foundation provide default routes within the LLN, and serves as the foundation
on which RPL builds further routing structure, e.g. through the on which RPL builds further routing structure, e.g. through the
destination advertisement mechanism. destination advertisement mechanism.
Figure 14: Example DAG Figure 14: Example DAG
B.1. Destination Advertisement B.1. Destination Advertisement
Consider the example DAG depicted in Figure 14. Suppose that Nodes Consider the example DODAG depicted in Figure 14. Suppose that Nodes
(22) and (32) are unable to record routing state. Suppose that Node (22) and (32) are unable to record routing state. Suppose that Node
(42) is able to perform prefix aggregation on behalf of Nodes (53), (42) is able to perform prefix aggregation on behalf of Nodes (53),
(54), and (55). (54), and (55).
o Node (53) would send a DAO message to Node (42), indicating the o Node (53) would send a DAO message to Node (42), indicating the
availability of destination (53). availability of destination (53).
o Node (54) and Node (55) would similarly send DAO messages to Node o Node (54) and Node (55) would similarly send DAO messages to Node
(42) indicating their own destinations. (42) indicating their own destinations.
skipping to change at page 74, line 40 skipping to change at page 76, line 40
source route to (32) source route to (32)
* Destination (42') is available via Node (22) and the piecewise * Destination (42') is available via Node (22) and the piecewise
source route to (32), (42'). source route to (32), (42').
o Node (12) sends DAO messages to (LBR), allowing (LBR) to learn o Node (12) sends DAO messages to (LBR), allowing (LBR) to learn
routes to the destinations (12), (22), (32), and (42'). (42), routes to the destinations (12), (22), (32), and (42'). (42),
(53), (54), and (55) are available via the aggregation (42'). It (53), (54), and (55) are available via the aggregation (42'). It
is not necessary for Node (12) to propagate the piecewise source is not necessary for Node (12) to propagate the piecewise source
routes to (LBR). routes to (LBR).
B.2. Example: DAG Parent Selection B.2. Example: DODAG Parent Selection
For example, suppose that a node (N) is not attached to any DAG, and For example, suppose that a node (N) is not attached to any DAG, and
that it is in range of nodes (A), (B), (C), (D), and (E). Let all that it is in range of nodes (A), (B), (C), (D), and (E). Let all
nodes be configured to use an OCP which defines a policy such that nodes be configured to use an OCP which defines a policy such that
ETX is to be minimized and paths with the attribute `Blue' should be ETX is to be minimized and paths with the attribute 'Blue' should be
avoided. Let the rank computation indicated by the OCP simply avoided. Let the rank computation indicated by the OCP simply
reflect the ETX aggregated along the path. Let the links between reflect the ETX aggregated along the path. Let the links between
node (N) and its neighbors (A-E) all have an ETX of 1 (which is node (N) and its neighbors (A-E) all have an ETX of 1 (which is
learned by node (N) through some implementation specific method). learned by node (N) through some implementation specific method).
Let node (N) be configured to send RPL DIS messages to probe for Let node (N) be configured to send RPL DIS messages to probe for
nearby DAGs. nearby DAGs.
o Node (N) transmits a RPL DIS message. o Node (N) transmits a RPL DIS message.
o Node (B) responds. Node (N) investigates the DIO message, and o Node (B) responds. Node (N) investigates the DIO message, and
learns that Node (B) is a member of DAGID 1 at rank 4, and not learns that Node (B) is a member of DODAGID 1 at rank 4, and not
`Blue'. Node (N) takes note of this, but is not yet confident. 'Blue'. Node (N) takes note of this, but is not yet confident.
o Similarly, Node (N) hears from Node (A) at rank 9, Node (C) at o Similarly, Node (N) hears from Node (A) at rank 9, Node (C) at
rank 5, and Node (E) at rank 4. rank 5, and Node (E) at rank 4.
o Node (D) responds. Node (D) has a DIO message that indicates that o Node (D) responds. Node (D) has a DIO message that indicates that
it is a member of DAGID 1 at rank 2, but it carries the attribute it is a member of DODAGID 1 at rank 2, but it carries the
`Blue'. Node (N)'s policy function rejects Node (D), and no attribute 'Blue'. Node (N)'s policy function rejects Node (D),
further consideration is given. and no further consideration is given.
o This process continues until Node (N), based on implementation o This process continues until Node (N), based on implementation
specific policy, builds enough confidence to trigger a decision to specific policy, builds enough confidence to trigger a decision to
join DAGID 1. Let Node (N) determine its most preferred parent to join DODAGID 1. Let Node (N) determine its most preferred parent
be Node (E). to be Node (E).
o Node (N) adds Node (E) (rank 4) to its set of DAG parents for o Node (N) adds Node (E) (rank 4) to its set of DODAG parents for
DAGID 1. Following the mechanisms specified by the OCP, and given DODAGID 1. Following the mechanisms specified by the OCP, and
that the ETX is 1 for the link between (N) and (E), Node (N) is given that the ETX is 1 for the link between (N) and (E), Node (N)
now at rank 5 in DAGID 1. is now at rank 5 in DODAGID 1.
o Node (N) adds Node (B) (rank 4) to its set of DAG parents for o Node (N) adds Node (B) (rank 4) to its set of DODAG parents for
DAGID 1. DODAGID 1.
o Node (N) is a sibling of Node (C), both are at rank 5. o Node (N) is a sibling of Node (C), both are at rank 5.
o Node (N) may now forward traffic intended for the default o Node (N) may now forward traffic intended for the default
destination upwards along DAGID 1 via nodes (B) and (E). In some destination upwards along DODAGID 1 via nodes (B) and (E). In
cases, e.g. if nodes (B) and (E) are tried and fail, node (N) may some cases, e.g. if nodes (B) and (E) are tried and fail, node (N)
also choose to forward traffic to its sibling node (C), without may also choose to forward traffic to its sibling node (C),
making upwards progress but with the intention that node (C) or a without making upwards progress but with the intention that node
following successor can make upwards progress. Should Node (C) (C) or a following successor can make upwards progress. Should
not have a viable parent, it should never send the packet back to Node (C) not have a viable parent, it should never send the packet
Node (N) (to avoid a 2-node loop). back to Node (N) (to avoid a 2-node loop).
B.3. Example: DAG Maintenance B.3. Example: DODAG Maintenance
: : : : : :
: : : : : :
(A) (A) (A) (A) (A) (A)
|\ | | |\ | |
| `-----. | | | `-----. | |
| \ | | | \ | |
(B) (C) (B) (C) (B) (B) (C) (B) (C) (B)
| | \ | | \
| | `-----. | | `-----.
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| |
| |
| |
(D) (D)
-1- -2- -3- -1- -2- -3-
Figure 15: DAG Maintenance Figure 15: DAG Maintenance
Consider the example depicted in Figure 15-1. In this example, Node Consider the example depicted in Figure 15-1. In this example, Node
(A) is attached to a DAG at some rank d. Node (A) is a DAG parent of (A) is attached to a DODAG at some rank d. Node (A) is a DODAG
Nodes (B) and (C). Node (C) is a DAG parent of Node (D). There is parent of Nodes (B) and (C). Node (C) is a DODAG parent of Node (D).
also an undirected sibling link between Nodes (B) and (C). There is also an undirected sibling link between Nodes (B) and (C).
In this example, Node (C) may safely forward to Node (A) without In this example, Node (C) may safely forward to Node (A) without
creating a loop. Node (C) may not safely forward to Node (D), creating a loop. Node (C) may not safely forward to Node (D),
contained within it's own sub-DAG, without creating a loop. Node (C) contained within it's own sub-DODAG, without creating a loop. Node
may forward to Node (B) in some cases, e.g. the link (C)->(A) is (C) may forward to Node (B) in some cases, e.g. the link (C)->(A) is
temporarily unavailable, but with some chance of creating a loop temporarily unavailable, but with some chance of creating a loop
(e.g. if multiple nodes in a set of siblings start forwarding (e.g. if multiple nodes in a set of siblings start forwarding
`sideways' in a cycle) and requiring the intervention of additional 'sideways' in a cycle) and requiring the intervention of additional
mechanisms to detect and break the loop. mechanisms to detect and break the loop.
Consider the case where Node (C) hears a DIO message from a Node (Z) Consider the case where Node (C) hears a DIO message from a Node (Z)
at a lesser rank and superior position in the DAG than node (A). at a lesser rank and superior position in the DODAG than node (A).
Node (C) may safely undergo the process to evict node (A) from its Node (C) may safely undergo the process to evict node (A) from its
DAG parent set and attach directly to Node (Z) without creating a DAG parent set and attach directly to Node (Z) without creating a
loop, because its rank will decrease. loop, because its rank will decrease.
Now consider the case where the link (C)->(A) becomes nonviable, and Now consider the case where the link (C)->(A) becomes nonviable, and
node (C) must move to a deeper rank within the DAG: node (C) must move to a deeper rank within the DAG:
o Node (C) must first detach from the DAG by removing Node (A) from o Node (C) must first detach from the DODAG by removing Node (A)
its DAG parent set, leaving an empty DAG parent set. Node (C) may from its DODAG parent set, leaving an empty DODAG parent set.
become the root of its own floating, less preferred, DAG. Node (C) may become the root of its own floating, less preferred,
DAG.
o Node (D), hearing a modified DIO message from Node (C), follows o Node (D), hearing a modified DIO message from Node (C), follows
Node (C) into the floating DAG. This is depicted in Figure 15-2. Node (C) into the floating DAG. This is depicted in Figure 15-2.
In general, any node with no other options in the sub-DAG of Node In general, any node with no other options in the sub-DODAG of
(C) will follow Node (C) into the floating DAG, maintaining the Node (C) will follow Node (C) into the floating DAG, maintaining
structure of the sub-DAG. the structure of the sub-DODAG.
o Node (C) hears a DIO message with an incremented DAGSequenceNumber o Node (C) hears a DIO message with an incremented
from Node (B) and determines it is able to rejoin the grounded DAG DODAGSequenceNumber from Node (B) and determines it is able to
by reattaching at a deeper rank to Node (B). Node (C) adds Node rejoin the grounded DODAG by reattaching at a deeper rank to Node
(B) to its DAG parent set. Node (C) has now safely moved deeper (B). Node (C) adds Node (B) to its DODAG parent set. Node (C)
within the grounded DAG without creating any loops. has now safely moved deeper within the grounded DODAG without
creating any loops.
o Node (D), and any other sub-DAG of Node (C), will hear the o Node (D), and any other sub-DODAG of Node (C), will hear the
modified DIO message sourced from Node (C) and follow Node (C) in modified DIO message sourced from Node (C) and follow Node (C) in
a coordinated manner to reattach to the grounded DAG. The final a coordinated manner to reattach to the grounded DAG. The final
DAG is depicted in Figure 15-3 DODAG is depicted in Figure 15-3
B.4. Example: Greedy Parent Selection and Instability B.4. Example: Greedy Parent Selection and Instability
(A) (A) (A) (A) (A) (A)
|\ |\ |\ |\ |\ |\
| `-----. | `-----. | `-----. | `-----. | `-----. | `-----.
| \ | \ | \ | \ | \ | \
(B) (C) (B) \ | (C) (B) (C) (B) \ | (C)
\ | | / \ | | /
`-----. | | .-----` `-----. | | .-----'
\| |/ \| |/
(C) (B) (C) (B)
-1- -2- -3- -1- -2- -3-
Figure 16: Greedy DAG Parent Selection Figure 16: Greedy DODAG Parent Selection
Consider the example depicted in Figure 16. A DAG is depicted in 3 Consider the example depicted in Figure 16. A DODAG is depicted in 3
different configurations. A usable link between (B) and (C) exists different configurations. A usable link between (B) and (C) exists
in all 3 configurations. In Figure 16-1, Node (A) is a DAG parent in all 3 configurations. In Figure 16-1, Node (A) is a DODAG parent
for Nodes (B) and (C), and (B)--(C) is a sibling link. In for Nodes (B) and (C), and (B)--(C) is a sibling link. In
Figure 16-2, Node (A) is a DAG parent for Nodes (B) and (C), and Node Figure 16-2, Node (A) is a DODAG parent for Nodes (B) and (C), and
(B) is also a DAG parent for Node (C). In Figure 16-3, Node (A) is a Node (B) is also a DODAG parent for Node (C). In Figure 16-3, Node
DAG parent for Nodes (B) and (C), and Node (C) is also a DAG parent (A) is a DODAG parent for Nodes (B) and (C), and Node (C) is also a
for Node (B). DODAG parent for Node (B).
If a RPL node is too greedy, in that it attempts to optimize for an If a RPL node is too greedy, in that it attempts to optimize for an
additional number of parents beyond its preferred parent, then an additional number of parents beyond its preferred parent, then an
instability can result. Consider the DAG illustrated in Figure 16-1. instability can result. Consider the DODAG illustrated in
In this example, Nodes (B) and (C) may most prefer Node (A) as a DAG Figure 16-1. In this example, Nodes (B) and (C) may most prefer Node
parent, but are operating under the greedy condition that will try to (A) as a DODAG parent, but are operating under the greedy condition
optimize for 2 parents. that will try to optimize for 2 parents.
When the preferred parent selection causes a node to have only one When the preferred parent selection causes a node to have only one
parent and no siblings, the node may decide to insert itself at a parent and no siblings, the node may decide to insert itself at a
slightly higher rank in order to have at least one sibling and thus slightly higher rank in order to have at least one sibling and thus
an alternate forwarding solution. This does not deprive other nodes an alternate forwarding solution. This does not deprive other nodes
of a forwarding solution and this is considered acceptable of a forwarding solution and this is considered acceptable
greediness. greediness.
o Let Figure 16-1 be the initial condition. o Let Figure 16-1 be the initial condition.
o Suppose Node (C) first is able to leave the DAG and rejoin at a o Suppose Node (C) first is able to leave the DODAG and rejoin at a
lower rank, taking both Nodes (A) and (B) as DAG parents as lower rank, taking both Nodes (A) and (B) as DODAG parents as
depicted in Figure 16-2. Now Node (C) is deeper than both Nodes depicted in Figure 16-2. Now Node (C) is deeper than both Nodes
(A) and (B), and Node (C) is satisfied to have 2 DAG parents. (A) and (B), and Node (C) is satisfied to have 2 DODAG parents.
o Suppose Node (B), in its greediness, is willing to receive and o Suppose Node (B), in its greediness, is willing to receive and
process a DIO message from Node (C) (against the rules of RPL), process a DIO message from Node (C) (against the rules of RPL),
and then Node (B) leaves the DAG and rejoins at a lower rank, and then Node (B) leaves the DODAG and rejoins at a lower rank,
taking both Nodes (A) and (C) as DAG parents. Now Node (B) is taking both Nodes (A) and (C) as DODAG parents. Now Node (B) is
deeper than both Nodes (A) and (C) and is satisfied with 2 DAG deeper than both Nodes (A) and (C) and is satisfied with 2 DAG
parents. parents.
o Then Node (C), because it is also greedy, will leave and rejoin o Then Node (C), because it is also greedy, will leave and rejoin
deeper, to again get 2 parents and have a lower rank then both of deeper, to again get 2 parents and have a lower rank then both of
them. them.
o Next Node (B) will again leave and rejoin deeper, to again get 2 o Next Node (B) will again leave and rejoin deeper, to again get 2
parents parents
o And again Node (C) leaves and rejoins deeper... o And again Node (C) leaves and rejoins deeper...
o The process will repeat, and the DAG will oscillate between o The process will repeat, and the DODAG will oscillate between
Figure 16-2 and Figure 16-3 until the nodes count to infinity and Figure 16-2 and Figure 16-3 until the nodes count to infinity and
restart the cycle again. restart the cycle again.
o This cycle can be averted through mechanisms in RPL: o This cycle can be averted through mechanisms in RPL:
* Nodes (B) and (C) stay at a rank sufficient to attach to their * Nodes (B) and (C) stay at a rank sufficient to attach to their
most preferred parent (A) and don't go for any deeper (worse) most preferred parent (A) and don't go for any deeper (worse)
alternate parents (Nodes are not greedy) alternate parents (Nodes are not greedy)
* Nodes (B) and (C) do not process DIO messages from nodes deeper * Nodes (B) and (C) do not process DIO messages from nodes deeper
than themselves (because such nodes are possibly in their own than themselves (because such nodes are possibly in their own
sub-DAGs) sub-DODAGs)
Appendix C. Outstanding Issues Appendix C. Outstanding Issues
This section enumerates some outstanding issues that are to be This section enumerates some outstanding issues that are to be
addressed in future revisions of the RPL specification. addressed in future revisions of the RPL specification.
C.1. Additional Support for P2P Routing C.1. Additional Support for P2P Routing
In some situations the baseline mechanism to support arbitrary P2P In some situations the baseline mechanism to support arbitrary P2P
traffic, by flowing upwards along the DAG until a common ancestor is traffic, by flowing upwards along the DODAG until a common ancestor
reached and then flowing down, may not be suitable for all is reached and then flowing down, may not be suitable for all
application scenarios. A related scenario may occur when the down application scenarios. A related scenario may occur when the down
paths setup along the DAG by the destination advertisement mechanism paths setup along the DODAG by the destination advertisement
are not be the most desirable downward paths for the specific mechanism are not be the most desirable downward paths for the
application scenario (in part because the DAG links may not be specific application scenario (in part because the DODAG links may
symmetric). It may be desired to support within RPL the discovery not be symmetric). It may be desired to support within RPL the
and installation of more direct routes `across' the DAG. Such discovery and installation of more direct routes 'across' the DAG.
mechanisms need to be investigated. Such mechanisms need to be investigated.
C.2. Loop Detection
It is under investigation to complement the loop avoidance strategies
provided by RPL with a loop detection mechanism that may be employed
when traffic is forwarded.
C.3. Destination Advertisement / DAO Fan-out C.2. Destination Advertisement / DAO Fan-out
When DAO messages are relayed to more than one DAG parent, in some When DAO messages are relayed to more than one DODAG parent, in some
cases a situation may be created where a large number of DAO messages cases a situation may be created where a large number of DAO messages
conveying information about the same destination flow upwards along conveying information about the same destination flow upwards along
the DAG. It is desirable to bound/limit the multiplication/fan-out the DAG. It is desirable to bound/limit the multiplication/fan-out
of DAO messages in this manner. Some aspects of the Destination of DAO messages in this manner. Some aspects of the Destination
Advertisement mechanism remain under investigation, such as behavior Advertisement mechanism remain under investigation, such as behavior
in the face of links that may not be symmetric. in the face of links that may not be symmetric.
In general, the utility of providing redundancy along downwards In general, the utility of providing redundancy along downwards
routes by sending DAO messages to more than one parent is under routes by sending DAO messages to more than one parent is under
investigation. investigation.
The use of suitable triggers, such as the `D' bit, to trigger DA The use of suitable triggers, such as the 'T' flag, to trigger DA
operation within an affected sub-DAG, is under investigation. operation within an affected sub-DODAG, is under investigation.
Further, the ability to limit scope of the affected depth within the Further, the ability to limit scope of the affected depth within the
sub-DAG is under investigation (e.g. if a stateful node can proxy for sub-DODAG is under investigation (e.g. if a stateful node can proxy
all nodes `behind' it, then there may be no need to propagate the for all nodes 'behind' it, then there may be no need to propagate the
triggered `D' bit further). triggered 'T' flag further).
C.4. Source Routing C.3. Source Routing
In support of nodes that maintain minimal routing state, and to make In support of nodes that maintain minimal routing state, and to make
use of the collection of piecewise source routes from the destination use of the collection of piecewise source routes from the destination
advertisement mechanism, there needs to be some investigation of a advertisement mechanism, there needs to be some investigation of a
mechanism to specify, attach, and follow source routes for packets mechanism to specify, attach, and follow source routes for packets
traversing the LLN. traversing the LLN.
C.5. Address / Header Compression C.4. Address / Header Compression
In order to minimize overhead within the LLN it is desirable to In order to minimize overhead within the LLN it is desirable to
perform some sort of address and/or header compression, perhaps via perform some sort of address and/or header compression, perhaps via
labels, addresses aggregation, or some other means. This is still labels, addresses aggregation, or some other means. This is still
under investigation. under investigation.
C.5. Managing Multiple Instances
A network may run multiple instances of RPL concurrently. Such a
network will require methods for assigning and otherwise managing
RPLInstanceIDs. This will likely be addressed in a separate
document.
Authors' Addresses Authors' Addresses
Tim Winter (editor) Tim Winter (editor)
Email: wintert@acm.org Email: wintert@acm.org
Pascal Thubert (editor) Pascal Thubert (editor)
Cisco Systems Cisco Systems
Village d'Entreprises Green Side Village d'Entreprises Green Side
400, Avenue de Roumanille 400, Avenue de Roumanille
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