draft-ietf-roll-efficient-npdao-18.txt   rfc9009.txt 
ROLL R. Jadhav, Ed. Internet Engineering Task Force (IETF) R.A. Jadhav, Ed.
Internet-Draft Huawei Request for Comments: 9009 Huawei
Intended status: Standards Track P. Thubert Category: Standards Track P. Thubert
Expires: October 17, 2020 Cisco ISSN: 2070-1721 Cisco
R. Sahoo R.N. Sahoo
Z. Cao Z. Cao
Huawei Huawei
April 15, 2020 April 2021
Efficient Route Invalidation Efficient Route Invalidation
draft-ietf-roll-efficient-npdao-18
Abstract Abstract
This document explains the problems associated with the current use This document explains the problems associated with the use of No-
of NPDAO messaging and also discusses the requirements for an Path Destination Advertisement Object (NPDAO) messaging in RFC 6550
optimized route invalidation messaging scheme. Further a new and also discusses the requirements for an optimized route
proactive route invalidation message called as "Destination Cleanup invalidation messaging scheme. Further, this document specifies a
Object" (DCO) is specified which fulfills requirements of an new proactive route invalidation message called the "Destination
optimized route invalidation messaging. Cleanup Object" (DCO), which fulfills requirements for optimized
route invalidation messaging.
Status of This Memo Status of This Memo
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and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9009.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
1.1. Requirements Language and Terminology . . . . . . . . . . 3 1.1. Requirements Language and Terminology
1.2. Current NPDAO messaging . . . . . . . . . . . . . . . . . 4 1.2. RPL NPDAO Messaging
1.3. Why Is NPDAO Important? . . . . . . . . . . . . . . . . . 5 1.3. Why Is NPDAO Messaging Important?
2. Problems with current NPDAO messaging . . . . . . . . . . . . 6 2. Problems with the RPL NPDAO Messaging
2.1. Lost NPDAO due to link break to the previous parent . . . 6 2.1. Lost NPDAO Due to Link Break to the Previous Parent
2.2. Invalidate Routes of Dependent Nodes . . . . . . . . . . 6 2.2. Invalidating Routes of Dependent Nodes
2.3. Possible route downtime caused by asynchronous operation 2.3. Possible Route Downtime Caused by Asynchronous Operation of
of NPDAO and DAO . . . . . . . . . . . . . . . . . . . . 6 the NPDAO and DAO
3. Requirements for the NPDAO Optimization . . . . . . . . . . . 6 3. Requirements for NPDAO Optimization
3.1. Req#1: Remove messaging dependency on link to the 3.1. Req. #1: Remove Messaging Dependency on the Link to the
previous parent . . . . . . . . . . . . . . . . . . . . . 6 Previous Parent
3.2. Req#2: Dependent nodes route invalidation on parent 3.2. Req. #2: Route Invalidation for Dependent Nodes at the
switching . . . . . . . . . . . . . . . . . . . . . . . . 7 Parent Switching Node
3.3. Req#3: Route invalidation should not impact data traffic 7 3.3. Req. #3: Route Invalidation Should Not Impact Data Traffic
4. Changes to RPL signaling . . . . . . . . . . . . . . . . . . 7 4. Changes to RPL Signaling
4.1. Change in RPL route invalidation semantics . . . . . . . 7 4.1. Change in RPL Route Invalidation Semantics
4.2. Transit Information Option changes . . . . . . . . . . . 8 4.2. Transit Information Option Changes
4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 9 4.3. Destination Cleanup Object (DCO)
4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 10 4.3.1. Secure DCO
4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 10 4.3.2. DCO Options
4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 11 4.3.3. Path Sequence in the DCO
4.3.4. Destination Cleanup Option Acknowledgment (DCO-ACK) . 11 4.3.4. Destination Cleanup Option Acknowledgment (DCO-ACK)
4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 12 4.3.5. Secure DCO-ACK
4.4. DCO Base Rules . . . . . . . . . . . . . . . . . . . . . 12 4.4. DCO Base Rules
4.5. Unsolicited DCO . . . . . . . . . . . . . . . . . . . . . 13 4.5. Unsolicited DCO
4.6. Other considerations . . . . . . . . . . . . . . . . . . 13 4.6. Other Considerations
4.6.1. Dependent Nodes invalidation . . . . . . . . . . . . 13 4.6.1. Invalidation of Dependent Nodes
4.6.2. NPDAO and DCO in the same network . . . . . . . . . . 14 4.6.2. NPDAO and DCO in the Same Network
4.6.3. Considerations for DCO retry . . . . . . . . . . . . 14 4.6.3. Considerations for DCO Retries
4.6.4. DCO with multiple preferred parents . . . . . . . . . 15 4.6.4. DCO with Multiple Preferred Parents
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 5. IANA Considerations
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 5.1. New Registry for the Destination Cleanup Object (DCO) Flags
6.1. New Registry for the Destination Cleanup Object (DCO) 5.2. New Registry for the Destination Cleanup Object (DCO)
Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Acknowledgment Flags
6.2. New Registry for the Destination Cleanup Object 5.3. RPL Rejection Status Values
Acknowledgment (DCO-ACK) Status field . . . . . . . . . . 17 6. Security Considerations
6.3. New Registry for the Destination Cleanup Object (DCO) 7. Normative References
Acknowledgment Flags . . . . . . . . . . . . . . . . . . 17 Appendix A. Example Messaging
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18 A.1. Example DCO Messaging
8. Normative References . . . . . . . . . . . . . . . . . . . . 19 A.2. Example DCO Messaging with Multiple Preferred Parents
Appendix A. Example Messaging . . . . . . . . . . . . . . . . . 20 Acknowledgments
A.1. Example DCO Messaging . . . . . . . . . . . . . . . . . . 20 Authors' Addresses
A.2. Example DCO Messaging with multiple preferred parents . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction 1. Introduction
RPL [RFC6550] (Routing Protocol for Low power and lossy networks) RPL (the Routing Protocol for Low-Power and Lossy Networks) as
specifies a proactive distance-vector based routing scheme. RPL has defined in [RFC6550] specifies a proactive distance-vector-based
optional messaging in the form of DAO (Destination Advertisement routing scheme. RPL has optional messaging in the form of DAO
Object) messages, which the 6LBR (6Lo Border Router) and 6LR (6Lo (Destination Advertisement Object) messages, which the 6LBR (6LoWPAN
Router) can use to learn a route towards the downstream nodes. In Border Router) and 6LR (6LoWPAN Router) can use to learn a route
storing mode, DAO messages would result in routing entries being towards the downstream nodes. ("6LoWPAN" stands for "IPv6 over Low-
created on all intermediate 6LRs from the node's parent all the way Power Wireless Personal Area Network".) In Storing mode, DAO
towards the 6LBR. messages would result in routing entries being created on all
intermediate 6LRs from a node's parent all the way towards the 6LBR.
RPL allows the use of No-Path DAO (NPDAO) messaging to invalidate a RPL allows the use of No-Path DAO (NPDAO) messaging to invalidate a
routing path corresponding to the given target, thus releasing routing path corresponding to the given target, thus releasing
resources utilized on that path. A NPDAO is a DAO message with route resources utilized on that path. An NPDAO is a DAO message with a
lifetime of zero, originates at the target node and always flows route lifetime of zero. It originates at the target node and always
upstream towards the 6LBR. This document explains the problems flows upstream towards the 6LBR. This document explains the problems
associated with the current use of NPDAO messaging and also discusses associated with the use of NPDAO messaging in [RFC6550] and also
the requirements for an optimized route invalidation messaging discusses the requirements for an optimized route invalidation
scheme. Further a new proactive route invalidation message called as messaging scheme. Further, this document specifies a new proactive
"Destination Cleanup Object" (DCO) is specified which fulfills route invalidation message called the "Destination Cleanup Object"
requirements of an optimized route invalidation messaging. (DCO), which fulfills requirements for optimized route invalidation
messaging.
The document only caters to the RPL's storing mode of operation This document only caters to RPL's Storing Mode of Operation (MOP).
(MOP). The non-storing MOP does not require use of NPDAO for route The Non-Storing MOP does not require the use of an NPDAO for route
invalidation since routing entries are not maintained on 6LRs. invalidation, since routing entries are not maintained on 6LRs.
1.1. Requirements Language and Terminology 1.1. Requirements Language and 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 BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This specification requires readers to be familiar with all the terms This specification requires readers to be familiar with all the terms
and concepts that are discussed in "RPL: IPv6 Routing Protocol for and concepts that are discussed in "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks" [RFC6550]. Low-Power and Lossy Networks" [RFC6550].
Low Power and Lossy Networks (LLN): Low-Power and Lossy Network (LLN):
Network in which both the routers and their interconnect are A network in which both the routers and their interconnects are
constrained. LLN routers typically operate with constraints on constrained. LLN routers typically operate with constraints on
processing power, memory, and energy (batter power). Their processing power, memory, and energy (battery power). Their
interconnects are characterized by high loss rates, low data interconnects are characterized by high loss rates, low data
rates, and instability. rates, and instability.
6LoWPAN Router (6LR): 6LoWPAN Router (6LR):
An intermediate router that is able to send and receive Router An intermediate router that is able to send and receive Router
Advertisements (RAs) and Router Solicitations (RSs) as well as Advertisements (RAs) and Router Solicitations (RSs) as well as
forward and route IPv6 packets. forward and route IPv6 packets.
Directed Acyclic Graph (DAG): Directed Acyclic Graph (DAG):
A directed graph having the property that all edges are oriented A directed graph having the property that all edges are oriented
in such a way that no cycles exist. in such a way that no cycles exist.
Destination-Oriented DAG (DODAG): Destination-Oriented DAG (DODAG):
A DAG rooted at a single destination, i.e., at a single DAG root A DAG rooted at a single destination, i.e., at a single DAG root
with no outgoing edges. with no outgoing edges.
6LoWPAN Border Router (6LBR): 6LoWPAN Border Router (6LBR):
A border router which is a DODAG root and is the edge node for A border router that is a DODAG root and is the edge node for
traffic flowing in and out of the 6LoWPAN network. traffic flowing in and out of the 6LoWPAN.
Destination Advertisement Object (DAO): Destination Advertisement Object (DAO):
DAO messaging allows downstream routes to the nodes to be DAO messaging allows downstream routes to the nodes to be
established. established.
DODAG Information Object (DIO): DODAG Information Object (DIO):
DIO messaging allows upstream routes to the 6LBR to be DIO messaging allows upstream routes to the 6LBR to be
established. DIO messaging is initiated at the DAO root. established. DIO messaging is initiated at the DAO root.
Common Ancestor node
6LR/6LBR node which is the first common node between two paths of Common ancestor node:
A 6LR/6LBR node that is the first common node between two paths of
a target node. a target node.
No-Path DAO (NPDAO): No-Path DAO (NPDAO):
A DAO message which has target with lifetime 0 used for the A DAO message that has a target with a lifetime of 0. Used for
purpose of route invalidation. the purpose of route invalidation.
Destination Cleanup Object (DCO): Destination Cleanup Object (DCO):
A new RPL control message code defined by this document. DCO A new RPL control message code defined by this document. DCO
messaging improves proactive route invalidation in RPL. messaging improves proactive route invalidation in RPL.
Regular DAO: Regular DAO:
A DAO message with non-zero lifetime. Routing adjacencies are A DAO message with a non-zero lifetime. Routing adjacencies are
created or updated based on this message. created or updated based on this message.
Target node: Target node:
The node switching its parent whose routing adjacencies are The node switching its parent whose routing adjacencies are
updated (created/removed). updated (created/removed).
1.2. Current NPDAO messaging 1.2. RPL NPDAO Messaging
RPL uses NPDAO messaging in the storing mode so that the node RPL uses NPDAO messaging in Storing mode so that the node changing
changing its routing adjacencies can invalidate the previous route. its routing adjacencies can invalidate the previous route. This is
This is needed so that nodes along the previous path can release any needed so that nodes along the previous path can release any
resources (such as the routing entry) they maintain on behalf of resources (such as the routing entry) they maintain on behalf of the
target node. target node.
For the rest of this document consider the following topology: Throughout this document, we will refer to the topology shown in
Figure 1:
(6LBR) (6LBR)
| |
| |
| |
(A) (A)
/ \
/ \
/ \
(G) (H)
| |
| |
| |
(B) (C)
\ ;
\ ;
\ ;
(D)
/ \ / \
/ \ / \
/ \ / \
(G) (H) (E) (F)
| |
| |
| |
(B) (C)
\ ;
\ ;
\ ;
(D)
/ \
/ \
/ \
(E) (F)
Figure 1: Sample topology Figure 1: Sample Topology
Node (D) is connected via preferred parent (B). (D) has an alternate Node D is connected via preferred parent B. D has an alternate path
path via (C) towards the 6LBR. Node (A) is the common ancestor for via C towards the 6LBR. Node A is the common ancestor for D for
(D) for paths through (B)-(G) and (C)-(H). When (D) switches from paths through B-G and C-H. When D switches from B to C, RPL allows
(B) to (C), RPL allows sending NPDAO to (B) and regular DAO to (C). sending an NPDAO to B and a regular DAO to C.
1.3. Why Is NPDAO Important? 1.3. Why Is NPDAO Messaging Important?
Nodes in LLNs may be resource constrained. There is limited memory Resources in LLN nodes are typically constrained. There is limited
available and routing entry records are one of the primary elements memory available, and routing entry records are one of the primary
occupying dynamic memory in the nodes. Route invalidation helps 6LR elements occupying dynamic memory in the nodes. Route invalidation
nodes to decide which entries could be discarded to better optimize helps 6LR nodes to decide which routing entries can be discarded for
resource utilization. Thus it becomes necessary to have an efficient better use of the limited resources. Thus, it becomes necessary to
route invalidation mechanism. Also note that a single parent switch have an efficient route invalidation mechanism. Also note that a
may result in a "sub-tree" switching from one parent to another. single parent switch may result in a "subtree" switching from one
Thus the route invalidation needs to be done on behalf of the sub- parent to another. Thus, the route invalidation needs to be done on
tree and not the switching node alone. In the above example, when behalf of the subtree and not the switching node alone. In the above
Node (D) switches parent, the route updates needs to be done for the example, when Node D switches its parent, route updates need to be
routing tables entries of (C),(H),(A),(G), and (B) with destination done for the routing table entries of C, H, A, G, and B with
(D),(E) and (F). Without efficient route invalidation, a 6LR may destinations D, E, and F. Without efficient route invalidation, a
have to hold a lot of stale route entries. 6LR may have to hold a lot of stale route entries.
2. Problems with current NPDAO messaging 2. Problems with the RPL NPDAO Messaging
2.1. Lost NPDAO due to link break to the previous parent 2.1. Lost NPDAO Due to Link Break to the Previous Parent
When a node switches its parent, the NPDAO is to be sent to its When a node switches its parent, the NPDAO is to be sent to its
previous parent and a regular DAO to its new parent. In cases where previous parent and a regular DAO to its new parent. In cases where
the node switches its parent because of transient or permanent parent the node switches its parent because of transient or permanent parent
link/node failure then the NPDAO message is bound to fail. link/node failure, the NPDAO message may not be received by the
parent.
2.2. Invalidate Routes of Dependent Nodes 2.2. Invalidating Routes of Dependent Nodes
RPL does not specify how route invalidation will work for dependent RPL does not specify how route invalidation will work for dependent
nodes rooted at the switching node, resulting in stale routing nodes in the switching node subDAG, resulting in stale routing
entries of the dependent nodes. The only way for 6LR to invalidate entries of the dependent nodes. The only way for a 6LR to invalidate
the route entries for dependent nodes would be to use route lifetime the route entries for dependent nodes would be to use route lifetime
expiry which could be substantially high for LLNs. expiry, which could be substantially high for LLNs.
In the example topology, when Node (D) switches its parent, Node (D) In the example topology, when Node D switches its parent, Node D
generates an NPDAO on its behalf. There is no NPDAO generated by the generates an NPDAO on its own behalf. There is no NPDAO generated by
dependent child nodes (E) and (F), through the previous path via (D) the dependent child Nodes E and F, through the previous path via D to
to (B) and (G), resulting in stale entries on nodes (B) and (G) for B and G, resulting in stale entries on Nodes B and G for Nodes E and
nodes (E) and (F). F.
2.3. Possible route downtime caused by asynchronous operation of NPDAO 2.3. Possible Route Downtime Caused by Asynchronous Operation of the
and DAO NPDAO and DAO
A switching node may generate both an NPDAO and DAO via two different A switching node may generate both an NPDAO and a DAO via two
paths at almost the same time. There is a possibility that an NPDAO different paths at almost the same time. It is possible that the
generated may invalidate the previous route and the regular DAO sent NPDAO may invalidate the previous route and the regular DAO sent via
via the new path gets lost on the way. This may result in route the new path gets lost on the way. This may result in route
downtime impacting downward traffic for the switching node. downtime, impacting downward traffic for the switching node.
In the example topology, consider Node (D) switches from parent (B) In the example topology, say that Node D switches from parent B to C.
to (C). An NPDAO sent via the previous route may invalidate the An NPDAO sent via the previous route may invalidate the previous
previous route whereas there is no way to determine whether the new route, whereas there is no way to determine whether the new DAO has
DAO has successfully updated the route entries on the new path. successfully updated the route entries on the new path.
3. Requirements for the NPDAO Optimization 3. Requirements for NPDAO Optimization
3.1. Req#1: Remove messaging dependency on link to the previous parent 3.1. Req. #1: Remove Messaging Dependency on the Link to the Previous
Parent
When the switching node sends the NPDAO message to the previous When the switching node sends the NPDAO message to the previous
parent, it is normal that the link to the previous parent is prone to parent, it is normal that the link to the previous parent is prone to
failure (that's why the node decided to switch). Therefore, it is failure (that's why the node decided to switch). Therefore, it is
required that the route invalidation does not depend on the previous required that the route invalidation does not depend on the previous
link which is prone to failure. The previous link referred here link, which is prone to failure. The previous link referred to here
represents the link between the node and its previous parent (from represents the link between the node and its previous parent (from
whom the node is now disassociating). which the node is now disassociating).
3.2. Req#2: Dependent nodes route invalidation on parent switching 3.2. Req. #2: Route Invalidation for Dependent Nodes at the Parent
Switching Node
It should be possible to do route invalidation for dependent nodes It should be possible to do route invalidation for dependent nodes
rooted at the switching node. rooted at the switching node.
3.3. Req#3: Route invalidation should not impact data traffic 3.3. Req. #3: Route Invalidation Should Not Impact Data Traffic
While sending the NPDAO and DAO messages, it is possible that the While sending the NPDAO and DAO messages, it is possible that the
NPDAO successfully invalidates the previous path, while the newly NPDAO successfully invalidates the previous path, while the newly
sent DAO gets lost (new path not set up successfully). This will sent DAO gets lost (new path not set up successfully). This will
result in downstream unreachability to the node switching paths. result in downstream unreachability to the node switching paths.
Therefore, it is desirable that the route invalidation is Therefore, it is desirable that the route invalidation is
synchronized with the DAO to avoid the risk of route downtime. synchronized with the DAO to avoid the risk of route downtime.
4. Changes to RPL signaling 4. Changes to RPL Signaling
4.1. Change in RPL route invalidation semantics 4.1. Change in RPL Route Invalidation Semantics
As described in Section 1.2, the NPDAO originates at the node As described in Section 1.2, the NPDAO originates at the node
changing to a new parent and traverses upstream towards the root. In changing to a new parent and traverses upstream towards the root. In
order to solve the problems as mentioned in Section 2, the document order to solve the problems discussed in Section 2, this document
adds a new proactive route invalidation message called "Destination adds a new proactive route invalidation message called the
Cleanup Object" (DCO) that originates at a common ancestor node and "Destination Cleanup Object" (DCO), which originates at a common
flows downstream between the new and old path. The common ancestor ancestor node and flows downstream the old path. The common ancestor
node generates a DCO in response to the change in the next-hop on node generates a DCO when removing a next hop to a target -- for
receiving a regular DAO with updated Path Sequence for the target. instance, as a delayed response to receiving a regular DAO from
another child node with a Path Sequence for the target that is the
same or newer, in which case the DCO transmission is canceled.
The 6LRs in the path for DCO take action such as route invalidation The 6LRs in the path for the DCO take such action as route
based on the DCO information and subsequently send another DCO with invalidation based on the DCO information and subsequently send
the same information downstream to the next hop. This operation is another DCO with the same information downstream to the next hop(s).
similar to how the DAOs are handled on intermediate 6LRs in storing This operation is similar to how the DAOs are handled on intermediate
MOP in [RFC6550]. Just like DAO in storing MOP, the DCO is sent 6LRs in the Storing MOP [RFC6550]. Just like the DAO in the Storing
using link-local unicast source and destination IPv6 address. Unlike MOP, the DCO is sent using link-local unicast source and destination
DAO, which always travels upstream, the DCO always travels IPv6 addresses. Unlike the DAO, which always travels upstream, the
downstream. DCO always travels downstream.
In Figure 1, when node D decides to switch the path from B to C, it In Figure 1, when child Node D decides to switch the path from parent
sends a regular DAO to node C with reachability information B to parent C, it sends a regular DAO to Node C with reachability
containing the address of D as the target and an incremented Path information containing the address of D as the target and an
Sequence. Node C will update the routing table based on the incremented Path Sequence. Node C will update the routing table
reachability information in the DAO and in turn generate another DAO based on the reachability information in the DAO and will in turn
with the same reachability information and forward it to H. Node H generate another DAO with the same reachability information and
also follows the same procedure as Node C and forwards it to node A. forward it to H. Node H recursively follows the same procedure as
When node A receives the regular DAO, it finds that it already has a Node C and forwards it to Node A. When Node A receives the regular
routing table entry on behalf of the target address of node D. It DAO, it finds that it already has a routing table entry on behalf of
finds however that the next hop information for reaching node D has the Target Address of Node D. It finds, however, that the next-hop
changed i.e., node D has decided to change the paths. In this case, information for reaching Node D has changed, i.e., Node D has decided
Node A which is the common ancestor node for node D along the two to change the paths. In this case, Node A, which is the common
paths (previous and new), should generate a DCO which traverses ancestor node for Node D along the two paths (previous and new), can
downwards in the network. Node A handles normal DAO forwarding to generate a DCO that traverses the network downwards over the old path
6LBR as required by [RFC6550]. to the target. Node A handles normal DAO forwarding to the 6LBR as
required by [RFC6550].
4.2. Transit Information Option changes 4.2. Transit Information Option Changes
Every RPL message is divided into base message fields and additional Every RPL message is divided into base message fields and additional
Options as described in Section 6 of [RFC6550]. The base fields options, as described in Section 6 of [RFC6550]. The base fields
apply to the message as a whole and options are appended to add apply to the message as a whole, and options are appended to add
message/use-case specific attributes. As an example, a DAO message message-specific / use-case-specific attributes. As an example, a
may be attributed by one or more "RPL Target" options which specify DAO message may be attributed by one or more "RPL Target" options
the reachability information for the given targets. Similarly, a that specify that the reachability information is for the given
Transit Information option may be associated with a set of RPL Target targets. Similarly, a Transit Information option may be associated
options. with a set of RPL Target options.
This document specifies a change in the Transit Information Option to This document specifies a change in the Transit Information option to
contain the "Invalidate previous route" (I) flag. This 'I' flag contain the "Invalidate previous route" (I) flag. This 'I' flag
signals the common ancestor node to generate a DCO on behalf of the signals the common ancestor node to generate a DCO on behalf of the
target node with a RPL Status of 195 indicating that the address has target node with a RPL Status of 195, indicating that the address has
moved. The 'I' flag is carried in the Transit Information Option moved. The 'I' flag is carried in the Transit Information option,
which augments the reachability information for a given set of RPL which augments the reachability information for a given set of one or
Target(s). Transit Information Option with 'I' flag set should be more RPL Targets. A Transit Information option with the 'I' flag set
carried in the DAO message when route invalidation is sought for the should be carried in the DAO message when route invalidation is
corresponding target(s). sought for the corresponding target or targets.
Value 195 represents 'E' and 'A' bit in RPL Status to be set as per Value 195 represents the 'U' and 'A' bits in RPL Status, to be set as
Figure 3 of [I-D.ietf-roll-unaware-leaves] with the lower 6 bits with per Figure 6 of [RFC9010], with the lower 6 bits set to the 6LoWPAN
value 3 indicating 'Moved' as per Table 1 of [RFC8505]. Neighbor Discovery (ND) Extended Address Registration Option (EARO)
Status value of 3 indicating 'Moved' as per Table 1 of [RFC8505].
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 = 0x06 | Option Length |E|I| Flags | Path Control | | Type = 0x06 | Option Length |E|I| Flags | Path Control |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Sequence | Path Lifetime | | Path Sequence | Path Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Updated Transit Information Option (New I flag added) Figure 2: Updated Transit Information Option (New 'I' Flag Added)
I (Invalidate previous route) flag: The 'I' flag is set by the target I (Invalidate previous route) flag: The 'I' flag is set by the
node to indicate to the common ancestor node that it wishes to target node to indicate to the common ancestor node that it wishes
invalidate any previous route between the two paths. to invalidate any previous route between the two paths.
[RFC6550] allows the parent address to be sent in the Transit [RFC6550] allows the parent address to be sent in the Transit
Information Option depending on the mode of operation. In case of Information option, depending on the MOP. In the case of the Storing
storing mode of operation the field is usually not needed. In case MOP, the field is usually not needed. In the case of a DCO, the
of DCO, the parent address field MUST NOT be included. Parent Address field MUST NOT be included.
The common ancestor node SHOULD generate a DCO message in response to Upon receiving a DAO message with a Transit Information option that
this 'I' flag when it sees that the routing adjacencies have changed has the 'I' flag set, and as a delayed response removing a routing
for the target. The 'I' flag is intended to give the target node adjacency to the target indicated in the Transit Information option,
control over its own route invalidation, serving as a signal to the common ancestor node SHOULD generate a DCO message to the next
request DCO generation. hop associated to that adjacency. The 'I' flag is intended to give
the target node control over its own route invalidation, serving as a
signal to request DCO generation.
4.3. Destination Cleanup Object (DCO) 4.3. Destination Cleanup Object (DCO)
A new ICMPv6 RPL control message code is defined by this A new ICMPv6 RPL control message code is defined by this
specification and is referred to as "Destination Cleanup Object" specification and is referred to as the "Destination Cleanup Object"
(DCO), which is used for proactive cleanup of state and routing (DCO), which is used for proactive cleanup of state and routing
information held on behalf of the target node by 6LRs. The DCO information held on behalf of the target node by 6LRs. The DCO
message always traverses downstream and cleans up route information message always traverses downstream and cleans up route information
and other state information associated with the given target. and other state information associated with the given target. The
format of the DCO message is shown in Figure 3.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID |K|D| Flags | RPL Status | DCOSequence | | RPLInstanceID |K|D| Flags | RPL Status | DCOSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ DODAGID(optional) + + DODAGID (optional) +
| | | |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)... | Option(s)...
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 3: DCO base object Figure 3: DCO Base Object
RPLInstanceID: 8-bit field indicating the topology instance RPLInstanceID: 8-bit field indicating the topology instance
associated with the DODAG, as learned from the DIO. associated with the DODAG, as learned from the DIO.
K: The 'K' flag indicates that the recipient of DCO message is K: The 'K' flag indicates that the recipient of a DCO message is
expected to send a DCO-ACK back. If the DCO-ACK is not received even expected to send a DCO-ACK back. If the DCO-ACK is not received
after setting the 'K' flag, an implementation may retry the DCO at a even after setting the 'K' flag, an implementation may retry the
later time. The number of retries are implementation and deployment DCO at a later time. The number of retries is implementation and
dependent and are expected to be kept similar with those used in DAO deployment dependent and is expected to be kept similar to the
retries in [RFC6550]. Section 4.6.3 specifies the considerations for number of DAO retries [RFC6550]. Section 4.6.3 specifies the
DCO retry. A node receiving a DCO message without the 'K' flag set considerations for DCO retries. A node receiving a DCO message
MAY respond with a DCO-ACK, especially to report an error condition. without the 'K' flag set MAY respond with a DCO-ACK, especially to
An example error condition could be that the node sending the DCO-ACK report an error condition. An example error condition could be
does not find the routing entry for the indicated target. When the that the node sending the DCO-ACK does not find the routing entry
sender does not set the 'K' flag it is an indication that the sender for the indicated target. When the sender does not set the 'K'
does not expect a response, and the sender SHOULD NOT retry the DCO. flag, it is an indication that the sender does not expect a
response, and the sender SHOULD NOT retry the DCO.
D: The 'D' flag indicates that the DODAGID field is present. This D: The 'D' flag indicates that the DODAGID field is present. This
flag MUST be set when a local RPLInstanceID is used. flag MUST be set when a local RPLInstanceID is used.
Flags: The 6 bits remaining unused in the Flags field are reserved Flags: The 6 bits remaining unused in the Flags field are reserved
for future use. These bits MUST be initialized to zero by the sender for future use. These bits MUST be initialized to zero by the
and MUST be ignored by the receiver. sender and MUST be ignored by the receiver.
RPL Status: As defined in [RFC6550] and updated in RPL Status: As defined in [RFC6550] and updated in [RFC9010]. The
[I-D.ietf-roll-unaware-leaves]. The root or common parent that root or common parent that generates a DCO is authoritative for
generates a DCO is authoritative for setting the status information setting the status information, and the information is unchanged
and the information is unchanged as propagated down the DODAG. This as propagated down the DODAG. This document does not specify a
document does not specify a differentiated action based on the RPL differentiated action based on the RPL Status.
status.
DCOSequence: 8-bit field incremented at each unique DCO message from DCOSequence: 8-bit field incremented at each unique DCO message from
a node and echoed in the DCO-ACK message. The initial DCOSequence a node and echoed in the DCO-ACK message. The initial DCOSequence
can be chosen randomly by the node. Section 4.4 explains the can be chosen randomly by the node. Section 4.4 explains the
handling of the DCOSequence. handling of the DCOSequence.
DODAGID (optional): 128-bit unsigned integer set by a DODAG root that DODAGID (optional): 128-bit unsigned integer set by a DODAG root
uniquely identifies a DODAG. This field MUST be present when the 'D' that uniquely identifies a DODAG. This field MUST be present when
flag is set and MUST NOT be present if 'D' flag is not set. DODAGID the 'D' flag is set and MUST NOT be present if the 'D' flag is not
is used when a local RPLInstanceID is in use, in order to identify set. The DODAGID is used when a local RPLInstanceID is in use, in
the DODAGID that is associated with the RPLInstanceID. order to identify the DODAGID that is associated with the
RPLInstanceID.
4.3.1. Secure DCO 4.3.1. Secure DCO
A Secure DCO message follows the format in [RFC6550] Figure 7, where A Secure DCO message follows the format shown in [RFC6550], Figure 7,
the base message format is the DCO message shown in Figure 3. where the base message format is the DCO message shown in Figure 3 of
this document.
4.3.2. DCO Options 4.3.2. DCO Options
The DCO message MUST carry at least one RPL Target and the Transit The DCO message MUST carry at least one RPL Target and the Transit
Information Option and MAY carry other valid options. This Information option and MAY carry other valid options. This
specification allows for the DCO message to carry the following specification allows for the DCO message to carry the following
options: options:
0x00 Pad1 0x00 Pad1
0x01 PadN 0x01 PadN
0x05 RPL Target 0x05 RPL Target
0x06 Transit Information 0x06 Transit Information
0x09 RPL Target Descriptor 0x09 RPL Target Descriptor
Section 6.7 of [RFC6550] defines all the above mentioned options. Section 6.7 of [RFC6550] defines all the above-mentioned options.
The DCO carries an RPL Target Option and an associated Transit The DCO carries a RPL Target option and an associated Transit
Information Option with a lifetime of 0x00000000 to indicate a loss Information option with a lifetime of 0x00000000 to indicate a loss
of reachability to that Target. of reachability to that target.
4.3.3. Path Sequence number in the DCO 4.3.3. Path Sequence in the DCO
A DCO message may contain a Path Sequence in the Transit Information A DCO message includes a Transit Information option for each
Option to identify the freshness of the DCO message. The Path invalidated path. The value of the Path Sequence counter in the
Sequence in the DCO MUST use the same Path Sequence number present in Transit Information option allows identification of the freshness of
the regular DAO message when the DCO is generated in response to a the DCO message versus the newest known to the 6LRs along the path
DAO message. Thus if a DCO is received by a 6LR and subsequently a being removed. If the DCO is generated by a common parent in
DAO is received with an old sequence number, then the DAO MUST be response to a DAO message, then the Transit Information option in the
ignored. When the DCO is generated in response to a DCO from DCO MUST use the value of the Path Sequence as found in the newest
upstream parent, the Path Sequence MUST be copied from the received Transit Information option that was received for that target by the
DCO. common parent. If a 6LR down the path receives a DCO with a Path
Sequence that is not newer than the Path Sequence as known from a
Transit Information option in a DAO message, then the 6LR MUST NOT
remove its current routing state, and it MUST NOT forward the DCO
down a path where it is not newer. If the DCO is newer, the 6LR may
retain a temporary state to ensure that a DAO that is received later
with a Transit Information option with an older sequence number is
ignored. A Transit Information option in a DAO message that is as
new as or newer than that in a DCO wins, meaning that the path
indicated in the DAO is installed and the DAO is propagated. When
the DCO is propagated upon a DCO from an upstream parent, the Path
Sequence MUST be copied from the received DCO.
4.3.4. Destination Cleanup Option Acknowledgment (DCO-ACK) 4.3.4. Destination Cleanup Option Acknowledgment (DCO-ACK)
The DCO-ACK message SHOULD be sent as a unicast packet by a DCO The DCO-ACK message SHOULD be sent as a unicast packet by a DCO
recipient in response to a unicast DCO message with 'K' flag set. If recipient in response to a unicast DCO message with the 'K' flag set.
'K' flag is not set then the receiver of the DCO message MAY send a If the 'K' flag is not set, then the receiver of the DCO message MAY
DCO-ACK, especially to report an error condition. send a DCO-ACK, especially to report an error condition. The format
of the DCO-ACK message is shown in Figure 4.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID |D| Flags | DCOSequence | DCO-ACK Status| | RPLInstanceID |D| Flags | DCOSequence | DCO-ACK Status|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ DODAGID(optional) + + DODAGID (optional) +
| | | |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: DCO-ACK base object Figure 4: DCO-ACK Base Object
RPLInstanceID: 8-bit field indicating the topology instance RPLInstanceID: 8-bit field indicating the topology instance
associated with the DODAG, as learned from the DIO. associated with the DODAG, as learned from the DIO.
D: The 'D' flag indicates that the DODAGID field is present. This D: The 'D' flag indicates that the DODAGID field is present. This
flag MUST be set when a local RPLInstanceID is used. flag MUST be set when a local RPLInstanceID is used.
Flags: 7-bit unused field. The field MUST be initialized to zero by Flags: 7-bit unused field. The field MUST be initialized to zero by
the sender and MUST be ignored by the receiver. the sender and MUST be ignored by the receiver.
DCOSequence: 8-bit field. The DCOSequence in DCO-ACK is copied from DCOSequence: 8-bit field. The DCOSequence in the DCO-ACK is copied
the DCOSequence received in the DCO message. from the DCOSequence received in the DCO message.
DCO-ACK Status: Indicates the completion. A value of 0 is defined as DCO-ACK Status: Indicates completion status. The DCO-ACK Status
unqualified acceptance in this specification. A value of 1 is field is defined based on Figure 6 of [RFC9010] defining the RPL
defined as "No routing-entry for the Target found". The remaining Status Format. A StatusValue of 0 along with the 'U' bit set to 0
status values are reserved as rejection codes. indicates Success / Unqualified acceptance as per Figure 6 of
[RFC9010]. A StatusValue of 1 with the 'U' bit set to 1 indicates
'No routing entry' as defined in Section 5.3 of this document.
DODAGID (optional): 128-bit unsigned integer set by a DODAG root that DODAGID (optional): 128-bit unsigned integer set by a DODAG root
uniquely identifies a DODAG. This field MUST be present when the 'D' that uniquely identifies a DODAG. This field MUST be present when
flag is set and MUST NOT be present when 'D' flag is not set. the 'D' flag is set and MUST NOT be present when the 'D' flag is
DODAGID is used when a local RPLInstanceID is in use, in order to not set. The DODAGID is used when a local RPLInstanceID is in
identify the DODAGID that is associated with the RPLInstanceID. use, in order to identify the DODAGID that is associated with the
RPLInstanceID.
4.3.5. Secure DCO-ACK 4.3.5. Secure DCO-ACK
A Secure DCO-ACK message follows the format in [RFC6550] Figure 7, A Secure DCO-ACK message follows the format shown in [RFC6550],
where the base message format is the DCO-ACK message shown in Figure 7, where the base message format is the DCO-ACK message shown
Figure 4. in Figure 4 of this document.
4.4. DCO Base Rules 4.4. DCO Base Rules
1. If a node sends a DCO message with newer or different information 1. If a node sends a DCO message with newer or different information
than the prior DCO message transmission, it MUST increment the than the prior DCO message transmission, it MUST increment the
DCOSequence field by at least one. A DCO message transmission DCOSequence field by at least one. A DCO message transmission
that is identical to the prior DCO message transmission MAY that is identical to the prior DCO message transmission MAY
increment the DCOSequence field. The DCOSequence counter follows increment the DCOSequence field. The DCOSequence counter follows
the sequence counter operation as defined in Section 7.2 of the sequence counter operation as defined in Section 7.2 of
[RFC6550]. [RFC6550].
2. The RPLInstanceID and DODAGID fields of a DCO message MUST be the
same value as that of the DAO message in response to which the 2. The RPLInstanceID and DODAGID fields of a DCO message MUST have
DCO is generated on the common ancestor node. the same values as those contained in the DAO message in response
to which the DCO is generated on the common ancestor node.
3. A node MAY set the 'K' flag in a unicast DCO message to solicit a 3. A node MAY set the 'K' flag in a unicast DCO message to solicit a
unicast DCO-ACK in response in order to confirm the attempt. unicast DCO-ACK in response, in order to confirm the attempt.
4. A node receiving a unicast DCO message with the 'K' flag set 4. A node receiving a unicast DCO message with the 'K' flag set
SHOULD respond with a DCO-ACK. A node receiving a DCO message SHOULD respond with a DCO-ACK. A node receiving a DCO message
without the 'K' flag set MAY respond with a DCO-ACK, especially without the 'K' flag set MAY respond with a DCO-ACK, especially
to report an error condition. to report an error condition.
5. A node receiving a unicast DCO message MUST verify the stored 5. A node receiving a unicast DCO message MUST verify the stored
Path Sequence in context to the given target. If the stored Path Path Sequence in context to the given target. If the stored Path
Sequence is more fresh, newer than the Path Sequence received in Sequence is as new as or newer than the Path Sequence received in
the DCO, then the DCO MUST be dropped. the DCO, then the DCO MUST be dropped.
6. A node that sets the 'K' flag in a unicast DCO message but does 6. A node that sets the 'K' flag in a unicast DCO message but does
not receive DCO-ACK in response MAY reschedule the DCO message not receive a DCO-ACK in response MAY reschedule the DCO message
transmission for another attempt, up until an implementation transmission for another attempt, up until an implementation-
specific number of retries. specific number of retries.
7. A node receiving a unicast DCO message with its own address in 7. A node receiving a unicast DCO message with its own address in
the RPL Target Option MUST strip-off that Target Option. If this the RPL Target option MUST strip off that Target option. If this
Target Option is the only one in the DCO message then the DCO Target option is the only one in the DCO message, then the DCO
message MUST be dropped. message MUST be dropped.
The scope of DCOSequence values is unique to the node which generates The scope of DCOSequence values is unique to the node that generates
it. them.
4.5. Unsolicited DCO 4.5. Unsolicited DCO
A 6LR may generate an unsolicited DCO to unilaterally cleanup the A 6LR may generate an unsolicited DCO to unilaterally clean up the
path on behalf of the target entry. The 6LR has all the state path on behalf of the target entry. The 6LR has all the state
information, namely, the Target address and the Path Sequence, information, namely, the Target Address and the Path Sequence,
required for generating DCO in its routing table. The conditions why required for generating a DCO in its routing table. The conditions
6LR may generate an unsolicited DCO are beyond the scope of this under which a 6LR may generate an unsolicited DCO are beyond the
document but some possible reasons could be: scope of this document, but possible reasons could be as follows:
1. On route expiry of an entry, a 6LR may decide to graciously 1. On route expiry of an entry, a 6LR may decide to graciously clean
cleanup the entry by initiating DCO. up the entry by initiating a DCO.
2. 6LR needs to entertain higher priority entries in case the
2. A 6LR needs to entertain higher-priority entries in case the
routing table is full, thus resulting in eviction of an existing routing table is full, thus resulting in eviction of an existing
routing entry. In this case the eviction can be handled routing entry. In this case, the eviction can be handled
graciously using DCO. graciously by using a DCO.
Note that if the 6LR initiates a unilateral path cleanup using DCO A DCO that is generated asynchronously to a DAO message and is meant
and if it has the latest state for the target then the DCO would to discard all state along the path regardless of the Path Sequence
finally reach the target node. Thus the target node would be MUST use a Path Sequence value of 240 (see Section 7.2 of [RFC6550]).
informed of its invalidation. This value allows the DCO to win against any established DAO path but
to lose against a DAO path that is being installed. Note that if an
ancestor initiates a unilateral path cleanup on an established path
using a DCO with a Path Sequence value of 240, the DCO will
eventually reach the target node, which will thus be informed of the
path invalidation.
4.6. Other considerations 4.6. Other Considerations
4.6.1. Dependent Nodes invalidation 4.6.1. Invalidation of Dependent Nodes
Current RPL [RFC6550] does not provide a mechanism for route The RPL specification [RFC6550] does not provide a mechanism for
invalidation for dependent nodes. This document allows the dependent route invalidation for dependent nodes. This document allows the
nodes invalidation. Dependent nodes will generate their respective invalidation of dependent nodes. Dependent nodes will generate their
DAOs to update their paths, and the previous route invalidation for respective DAOs to update their paths, and the previous route
those nodes should work in the similar manner described for switching invalidation for those nodes should work in a manner similar to what
node. The dependent node may set the 'I' flag in the Transit is described for a switching node. The dependent node may set the
Information Option as part of regular DAO so as to request 'I' flag in the Transit Information option as part of a regular DAO
invalidation of previous route from the common ancestor node. so as to request invalidation of the previous route from the common
ancestor node.
Dependent nodes do not have any indication regarding if any of their Dependent nodes do not have any indication regarding whether any of
parents in turn have decided to switch their parent. Thus for route their parents have in turn decided to switch their parent. Thus, for
invalidation the dependent nodes may choose to always set the 'I' route invalidation, the dependent nodes may choose to always set the
flag in all its DAO message's Transit Information Option. Note that 'I' flag in all their DAO messages' Transit Information options.
setting the 'I' flag is not counterproductive even if there is no Note that setting the 'I' flag is not counterproductive even if there
previous route to be invalidated. is no previous route to be invalidated.
4.6.2. NPDAO and DCO in the same network 4.6.2. NPDAO and DCO in the Same Network
The current NPDAO mechanism in [RFC6550] can still be used in the The NPDAO mechanism provided in [RFC6550] can still be used in the
same network where DCO is used. The NPDAO messaging can be used, for same network where a DCO is used. NPDAO messaging can be used, for
example, on route lifetime expiry of the target or when the node example, on route lifetime expiry of the target or when the node
simply decides to gracefully terminate the RPL session on graceful simply decides to gracefully terminate the RPL session on graceful
node shutdown. Moreover, a deployment can have a mix of nodes node shutdown. Moreover, a deployment can have a mix of nodes
supporting the DCO and the existing NPDAO mechanism. It is also supporting the DCO and the existing NPDAO mechanism. It is also
possible that the same node supports both the NPDAO and DCO signaling possible that the same node supports both NPDAO and DCO signaling for
for route invalidation. route invalidation.
Section 9.8 of [RFC6550] states, "When a node removes a node from its Section 9.8 of [RFC6550] states, "When a node removes a node from its
DAO parent set, it SHOULD send a No-Path DAO message to that removed DAO parent set, it SHOULD send a No-Path DAO message (Section 6.4.3)
DAO parent to invalidate the existing router". This document to that removed DAO parent to invalidate the existing route." This
introduces an alternative and more optimized way of route document introduces an alternative and more optimized way to perform
invalidation but it also allows existing NPDAO messaging to work. route invalidation, but it also allows existing NPDAO messaging to
Thus an implementation has two choices to make when a route work. Thus, an implementation has two choices to make when a route
invalidation is to be initiated: invalidation is to be initiated:
1. Use NPDAO to invalidate the previous route and send regular DAO 1. Use an NPDAO to invalidate the previous route, and send a regular
on the new path. DAO on the new path.
2. Send regular DAO on the new path with the 'I' flag set in the
Transit Information Option such that the common ancestor node 2. Send a regular DAO on the new path with the 'I' flag set in the
Transit Information option such that the common ancestor node
initiates the DCO message downstream to invalidate the previous initiates the DCO message downstream to invalidate the previous
route. route.
This document recommends using option 2 for reasons specified in This document recommends using option 2, for the reasons specified in
Section 3 in this document. Section 3 of this document.
This document assumes that all the 6LRs in the network support this This document assumes that all the 6LRs in the network support this
specification. If there are 6LRs en-route DCO message path which do specification. If there are 6LR nodes that do not support this
not support this document, then the route invalidation for document that are in the path of the DCO message transmission, then
corresponding targets may not work or may work partially i.e., only the route invalidation for the corresponding targets (targets that
part of the path supporting DCO may be invalidated. Alternatively, a are in the DCO message) may not work or may work partially.
node could generate an NPDAO if it does not receive a DCO with itself Alternatively, a node could generate an NPDAO if it does not receive
as target within specified time limit. The specified time limit is a DCO with itself as the target within a specified time limit. The
deployment specific and depends upon the maximum depth of the network specified time limit is deployment specific and depends upon the
and per hop average latency. Note that sending NPDAO and DCO for the maximum depth of the network and per-hop average latency. Note that
same operation would not result in unwanted side-effects because the sending an NPDAO and a DCO for the same operation would not result in
acceptability of NPDAO or DCO depends upon the Path Sequence unwanted side effects because the acceptability of an NPDAO or a DCO
freshness. depends upon the Path Sequence freshness.
4.6.3. Considerations for DCO retry 4.6.3. Considerations for DCO Retries
A DCO message could be retried by a sender if it sets the 'K' flag A DCO message could be retried by a sender if it sets the 'K' flag
and does not receive a DCO-ACK. The DCO retry time could be and does not receive a DCO-ACK. The DCO retry time could be
dependent on the maximum depth of the network and average per hop dependent on the maximum depth of the network and average per-hop
latency. This could range from 2 seconds to 120 seconds depending on latency. This could range from 2 seconds to 120 seconds, depending
the deployment. In case the latency limits are not known, an on the deployment. If the latency limits are not known, an
implementation MUST NOT retry more than once in 3 seconds and MUST implementation MUST NOT retry more than once in 3 seconds and MUST
NOT retry more than 3 times. NOT retry more than three times.
The number of retries could also be set depending on how critical the The number of retries could also be set depending on how critical the
route invalidation could be for the deployment and the link layer route invalidation could be for the deployment and the link-layer
retry configuration. For networks supporting only MP2P and P2MP retry configuration. For networks supporting only Multi-Point to
flows, such as in AMI and telemetry applications, the 6LRs may not be Point (MP2P) and Point-to-Multipoint (P2MP) flows, such as in
very keen to invalidate routes, unless they are highly memory- Advanced Metering Infrastructure (AMI) and telemetry applications,
constrained. For home and building automation networks which may the 6LRs may not be very keen to invalidate routes, unless they are
have substantial P2P traffic, the 6LRs might be keen to invalidate highly memory constrained. For home and building automation networks
efficiently because it may additionally impact the forwarding that may have substantial P2P traffic, the 6LRs might be keen to
invalidate efficiently because it may additionally impact forwarding
efficiency. efficiency.
4.6.4. DCO with multiple preferred parents 4.6.4. DCO with Multiple Preferred Parents
[RFC6550] allows a node to select multiple preferred parents for [RFC6550] allows a node to select multiple preferred parents for
route establishment. Section 9.2.1 of [RFC6550] specifies, "All DAOs route establishment. Section 9.2.1 of [RFC6550] specifies, "All DAOs
generated at the same time for the same Target MUST be sent with the generated at the same time for the same target MUST be sent with the
same Path Sequence in the Transit Information". Subsequently when same Path Sequence in the Transit Information." Subsequently, when
route invalidation has to be initiated, RPL mentions use of NPDAO route invalidation has to be initiated, an NPDAO, which can be
which can be initiated with an updated Path Sequence to all the initiated with an updated Path Sequence to all the parent nodes
parent nodes through which the route is to be invalidated. through which the route is to be invalidated, can be used; see
[RFC6550].
With DCO, the Target node itself does not initiate the route With a DCO, the target node itself does not initiate the route
invalidation and it is left to the common ancestor node. A common invalidation; this is left to the common ancestor node. A common
ancestor node when it discovers an updated DAO from a new next-hop, ancestor node when it discovers an updated DAO from a new next hop,
it initiates a DCO. With multiple preferred parents, this handling it initiates a DCO. It is recommended that an implementation
does not change. But in this case it is recommended that an initiate a DCO after a time period (DelayDCO) such that the common
implementation initiates a DCO after a time period (DelayDCO) such ancestor node may receive updated DAOs from all possible next hops.
that the common ancestor node may receive updated DAOs from all This will help to reduce DCO control overhead, i.e., the common
possible next-hops. This will help to reduce DCO control overhead ancestor can wait for updated DAOs from all possible directions
i.e., the common ancestor can wait for updated DAOs from all possible before initiating a DCO for route invalidation. After timeout, the
directions before initiating a DCO for route invalidation. After DCO needs to be generated for all the next hops for which the route
timeout, the DCO needs to be generated for all the next-hops for whom invalidation needs to be done.
the route invalidation needs to be done.
This document recommends using a DelayDCO timer value of 1sec. This This document recommends using a DelayDCO timer value of 1 second.
value is inspired by the default DelayDAO value of 1sec in [RFC6550]. This value is inspired by the default DelayDAO timer value of 1
Here the hypothesis is that the DAOs from all possible parent sets second [RFC6550]. Here, the hypothesis is that the DAOs from all
would be received on the common ancestor within this time period. possible parent sets would be received on the common ancestor within
this time period.
It is still possible that a DCO is generated before all the updated It is still possible that a DCO is generated before all the updated
DAOs from all the paths are received. In this case, the ancestor DAOs from all the paths are received. In this case, the ancestor
node would start the invalidation procedure for paths from which the node would start the invalidation procedure for paths from which the
updated DAO is not received. The DCO generated in this case would updated DAO is not received. The DCO generated in this case would
start invalidating the segments along these paths on which the start invalidating the segments along these paths on which the
updated DAOs are not received. But once the DAO reaches these updated DAOs are not received. But once the DAO reaches these
segments, the routing state would be updated along these segments and segments, the routing state would be updated along these segments;
should not lead to any inconsistent routing state. this should not lead to any inconsistent routing states.
Note that there is no requirement for synchronization between DCO and Note that there is no requirement for synchronization between a DCO
DAOs. The DelayDCO timer simply ensures that the DCO control and DAOs. The DelayDCO timer simply ensures that DCO control
overhead can be reduced and is only needed when the network contains overhead can be reduced and is only needed when the network contains
nodes using multiple preferred parent. nodes using multiple preferred parents.
5. Acknowledgments 5. IANA Considerations
Many thanks to Alvaro Retana, Cenk Gundogan, Simon Duquennoy, IANA has allocated codes for the DCO and DCO-ACK messages from the
Georgios Papadopoulous, Peter Van Der Stok for their review and "RPL Control Codes" registry.
comments. Alvaro Retana helped shape this document's final version
with critical review comments.
6. IANA Considerations +======+===========================================+===============+
| Code | Description | Reference |
+======+===========================================+===============+
| 0x07 | Destination Cleanup Object | This document |
+------+-------------------------------------------+---------------+
| 0x08 | Destination Cleanup Object Acknowledgment | This document |
+------+-------------------------------------------+---------------+
| 0x87 | Secure Destination Cleanup Object | This document |
+------+-------------------------------------------+---------------+
| 0x88 | Secure Destination Cleanup Object | This document |
| | Acknowledgment | |
+------+-------------------------------------------+---------------+
IANA is requested to allocate new codes for the DCO and DCO-ACK Table 1: New Codes for DCO and DCO-ACK Messages
messages from the RPL Control Codes registry.
+------+---------------------------------------------+--------------+ IANA has allocated bit 1 from the "Transit Information Option Flags"
| Code | Description | Reference | registry for the 'I' flag (Invalidate previous route; see
+------+---------------------------------------------+--------------+ Section 4.2).
| TBD1 | Destination Cleanup Object | This |
| | | document |
| TBD2 | Destination Cleanup Object Acknowledgment | This |
| | | document |
| TBD3 | Secure Destination Cleanup Object | This |
| | | document |
| TBD4 | Secure Destination Cleanup Object | This |
| | Acknowledgment | document |
+------+---------------------------------------------+--------------+
IANA is requested to allocate bit 1 from the Transit Information 5.1. New Registry for the Destination Cleanup Object (DCO) Flags
Option Flags registry for the 'I' flag (Section 4.2)
6.1. New Registry for the Destination Cleanup Object (DCO) Flags IANA has created a registry for the 8-bit Destination Cleanup Object
(DCO) Flags field. The "Destination Cleanup Object (DCO) Flags"
registry is located in the "Routing Protocol for Low Power and Lossy
Networks (RPL)" registry.
IANA is requested to create a registry for the 8-bit Destination New bit numbers may be allocated only by IETF Review [RFC8126]. Each
Cleanup Object (DCO) Flags field. This registry should be located in bit is tracked with the following qualities:
existing category of "Routing Protocol for Low Power and Lossy
Networks (RPL)".
New bit numbers may be allocated only by an IETF Review. Each bit is * Bit number (counting from bit 0 as the most significant bit)
tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit) * Capability description
o Capability description
o Defining RFC * Defining RFC
The following bits are currently defined: The following bits are currently defined:
+------------+------------------------------+---------------+ +============+==============================+===============+
| Bit number | Description | Reference | | Bit number | Description | Reference |
+------------+------------------------------+---------------+ +============+==============================+===============+
| 0 | DCO-ACK request (K) | This document | | 0 | DCO-ACK request (K) | This document |
+------------+------------------------------+---------------+
| 1 | DODAGID field is present (D) | This document | | 1 | DODAGID field is present (D) | This document |
+------------+------------------------------+---------------+ +------------+------------------------------+---------------+
DCO Base Flags Table 2: DCO Base Flags
6.2. New Registry for the Destination Cleanup Object Acknowledgment
(DCO-ACK) Status field
IANA is requested to create a registry for the 8-bit Destination 5.2. New Registry for the Destination Cleanup Object (DCO)
Cleanup Object Acknowledgment (DCO-ACK) Status field. This registry Acknowledgment Flags
should be located in existing category of "Routing Protocol for Low
Power and Lossy Networks (RPL)".
New Status values may be allocated only by an IETF Review. Each IANA has created a registry for the 8-bit Destination Cleanup Object
value is tracked with the following qualities: (DCO) Acknowledgment Flags field. The "Destination Cleanup Object
(DCO) Acknowledgment Flags" registry is located in the "Routing
Protocol for Low Power and Lossy Networks (RPL)" registry.
o Status Code New bit numbers may be allocated only by IETF Review [RFC8126]. Each
o Description bit is tracked with the following qualities:
o Defining RFC
The following values are currently defined: * Bit number (counting from bit 0 as the most significant bit)
+------------+----------------------------------------+-------------+ * Capability description
| Status | Description | Reference |
| Code | | |
+------------+----------------------------------------+-------------+
| 0 | Unqualified acceptance | This |
| | | document |
| 1 | No routing-entry for the indicated | This |
| | Target found | document |
+------------+----------------------------------------+-------------+
DCO-ACK Status Codes * Defining RFC
6.3. New Registry for the Destination Cleanup Object (DCO) The following bit is currently defined:
Acknowledgment Flags
IANA is requested to create a registry for the 8-bit Destination +============+==============================+===============+
Cleanup Object (DCO) Acknowledgment Flags field. This registry | Bit number | Description | Reference |
should be located in existing category of "Routing Protocol for Low +============+==============================+===============+
Power and Lossy Networks (RPL)". | 0 | DODAGID field is present (D) | This document |
+------------+------------------------------+---------------+
New bit numbers may be allocated only by an IETF Review. Each bit is Table 3: DCO-ACK Base Flag
tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit) 5.3. RPL Rejection Status Values
o Capability description
o Defining RFC
The following bits are currently defined: This document adds a new status value to the "RPL Rejection Status"
subregistry initially created per Section 12.6 of [RFC9010].
+------------+------------------------------+---------------+ +=======+==================+===============+
| Bit number | Description | Reference | | Value | Meaning | Reference |
+------------+------------------------------+---------------+ +=======+==================+===============+
| 0 | DODAGID field is present (D) | This document | | 1 | No routing entry | This document |
+------------+------------------------------+---------------+ +-------+------------------+---------------+
DCO-ACK Base Flags Table 4: Rejection Value of the RPL Status
7. Security Considerations 6. Security Considerations
This document introduces the ability for a common ancestor node to This document introduces the ability for a common ancestor node to
invalidate a route on behalf of the target node. The common ancestor invalidate a route on behalf of the target node. The common ancestor
node could be directed to do so by the target node using the 'I' flag node could be directed to do so by the target node, using the 'I'
in DCO's Transit Information Option. However, the common ancestor flag in a DCO's Transit Information option. However, the common
node is in a position to unilaterally initiate the route invalidation ancestor node is in a position to unilaterally initiate the route
since it possesses all the required state information, namely, the invalidation, since it possesses all the required state information,
Target address and the corresponding Path Sequence. Thus a rogue namely, the Target Address and the corresponding Path Sequence.
common ancestor node could initiate such an invalidation and impact Thus, a rogue common ancestor node could initiate such an
the traffic to the target node. invalidation and impact the traffic to the target node.
The DCO carries a RPL Status value, which is informative. New Status The DCO carries a RPL Status value, which is informative. New Status
values may be created over time and a node will ignore an unknown values may be created over time, and a node will ignore an unknown
Status value. This enables RPL Status field to be used as a cover Status value. This enables the RPL Status field to be used as a
channel. But the channel only works once since the message destroys cover channel. But the channel only works once, since the message
its own medium, that is the existing route that it is removing. destroys its own medium, i.e., the existing route that it is
removing.
This document also introduces an 'I' flag which is set by the target This document also introduces an 'I' flag, which is set by the target
node and used by the ancestor node to initiate a DCO if the ancestor node and used by the ancestor node to initiate a DCO if the ancestor
sees an update in the route adjacency. However, this flag could be sees an update in the routing adjacency. However, this flag could be
spoofed by a malicious 6LR in the path and can cause invalidation of spoofed by a malicious 6LR in the path and can cause invalidation of
an existing active path. Note that invalidation will happen only if an existing active path. Note that invalidation will work only if
the other conditions such as Path Sequence condition is also met. the Path Sequence condition is also met for the target for which the
Having said that, such a malicious 6LR may spoof a DAO on behalf of invalidation is attempted. Having said that, such a malicious 6LR
the (sub) child with the 'I' flag set and can cause route may spoof a DAO on behalf of the (sub) child with the 'I' flag set
invalidation on behalf of the (sub) child node. Note that, using and can cause route invalidation on behalf of the (sub) child node.
existing mechanisms offered by [RFC6550], a malicious 6LR might also Note that by using existing mechanisms offered by [RFC6550], a
spoof a DAO with lifetime of zero or otherwise cause denial of malicious 6LR might also spoof a DAO with a lifetime of zero or
service by dropping traffic entirely, so the new mechanism described otherwise cause denial of service by dropping traffic entirely, so
in this document does not present a substantially increased risk of the new mechanism described in this document does not present a
disruption. substantially increased risk of disruption.
This document assumes that the security mechanisms as defined in This document assumes that the security mechanisms as defined in
[RFC6550] are followed, which means that the common ancestor node and [RFC6550] are followed, which means that the common ancestor node and
all the 6LRs are part of the RPL network because they have the all the 6LRs are part of the RPL network because they have the
required credentials. A non-secure RPL network needs to take into required credentials. A non-secure RPL network needs to take into
consideration the risks highlighted in this section as well as those consideration the risks highlighted in this section as well as those
highlighted in [RFC6550]. highlighted in [RFC6550].
All RPL messages support a secure version of messages which allows All RPL messages support a secure version of messages; this allows
integrity protection using either a MAC or a signature. Optionally, integrity protection using either a Message Authentication Code (MAC)
secured RPL messages also have encryption protection for or a signature. Optionally, secured RPL messages also have
confidentiality. encryption protection for confidentiality.
The document adds new messages (DCO, DCO-ACK) which are syntactically This document adds new messages (DCO and DCO-ACK) that are
similar to existing RPL messages such as DAO, DAO-ACK. Secure syntactically similar to existing RPL messages such as DAO and DAO-
versions of DCO and DCO-ACK are added similar to other RPL messages ACK. Secure versions of DCO and DCO-ACK messages are added in a way
(such as DAO, DAO-ACK). that is similar to the technique used for other RPL messages (such as
DAO and DAO-ACK).
RPL supports three security modes as mentioned in Section 10.1 of RPL supports three security modes, as mentioned in Section 10.1 of
[RFC6550]: [RFC6550]:
1. Unsecured: In this mode, it is expected that the RPL control Unsecured: In this mode, it is expected that the RPL control
messages are secured by other security mechanisms, such as link- messages are secured by other security mechanisms, such as link-
layer security. In this mode, the RPL control messages, layer security. In this mode, the RPL control messages, including
including DCO, DCO-ACK, do not have Security sections. Also note DCO and DCO-ACK messages, do not have Security sections. Also
that unsecured mode does not imply that all messages are sent note that unsecured mode does not imply that all messages are sent
without any protection. without any protection.
2. Preinstalled: In this mode, RPL uses secure messages. Thus
secure versions of DCO, DCO-ACK MUST be used in this mode.
3. Authenticated: In this mode, RPL uses secure messages. Thus
secure versions of DCO, DCO-ACK MUST be used in this mode.
8. Normative References Preinstalled: In this mode, RPL uses secure messages. Thus, secure
versions of DCO and DCO-ACK messages MUST be used in this mode.
[I-D.ietf-roll-unaware-leaves] Authenticated: In this mode, RPL uses secure messages. Thus, secure
Thubert, P. and M. Richardson, "Routing for RPL Leaves", versions of DCO and DCO-ACK messages MUST be used in this mode.
draft-ietf-roll-unaware-leaves-14 (work in progress),
April 2020. 7. 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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550, Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012, DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>. <https://www.rfc-editor.org/info/rfc6550>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
<https://www.rfc-editor.org/info/rfc8505>.
[RFC9010] Thubert, P., Ed. and M. Richardson, "Routing for RPL
(Routing Protocol for Low-Power and Lossy Networks)
Leaves", RFC 9010, DOI 10.17487/RFC9010, April 2021,
<https://www.rfc-editor.org/info/rfc9010>.
Appendix A. Example Messaging Appendix A. Example Messaging
A.1. Example DCO Messaging A.1. Example DCO Messaging
In Figure 1, node (D) switches its parent from (B) to (C). This In this example, Node D (Figure 1) switches its parent from B to C.
example assumes that Node D has already established its own route via This example assumes that Node D has already established its own
Node B-G-A-6LBR using pathseq=x. The example uses DAO and DCO route via Node B-G-A-6LBR using pathseq=x. The example uses DAO and
messaging convention and specifies only the required parameters to DCO messaging conventions and specifies only the required parameters
explain the example namely, the parameter 'tgt', which stands for to explain the example, namely, the parameter 'tgt', which stands for
Target Option and value of this parameter specifies the address of "Target option"; the value of this parameter specifies the address of
the target node. The parameter 'pathseq', which specifies the Path the target node. The parameter 'pathseq' specifies the Path Sequence
Sequence value carried in the Transit Information Option. The value carried in the Transit Information option, and the parameter
parameter 'I_flag' specifies the 'I' flag in the Transit Information 'I_flag' specifies the 'I' flag in the Transit Information option.
Option. sequence of actions is as follows: The sequence of actions is as follows:
1. Node D switches its parent from Node B to Node C.
1. Node D switches its parent from node B to node C
2. D sends a regular DAO(tgt=D,pathseq=x+1,I_flag=1) in the updated 2. D sends a regular DAO(tgt=D,pathseq=x+1,I_flag=1) in the updated
path to C path to C.
3. C checks for a routing entry on behalf of D, since it cannot find
an entry on behalf of D it creates a new routing entry and 3. C checks for a routing entry on behalf of D; since it cannot find
an entry on behalf of D, it creates a new routing entry and
forwards the reachability information of the target D to H in a forwards the reachability information of the target D to H in a
DAO(tgt=D,pathseq=x+1,I_flag=1). DAO(tgt=D,pathseq=x+1,I_flag=1).
4. Similar to C, node H checks for a routing entry on behalf of D,
cannot find an entry and hence creates a new routing entry and 4. Similar to C, Node H checks for a routing entry on behalf of D,
cannot find an entry, and hence creates a new routing entry and
forwards the reachability information of the target D to A in a forwards the reachability information of the target D to A in a
DAO(tgt=D,pathseq=x+1,I_flag=1). DAO(tgt=D,pathseq=x+1,I_flag=1).
5. Node A receives the DAO(tgt=D,pathseq=x+1,I_flag=1), and checks
5. Node A receives the DAO(tgt=D,pathseq=x+1,I_flag=1) and checks
for a routing entry on behalf of D. It finds a routing entry but for a routing entry on behalf of D. It finds a routing entry but
checks that the next hop for target D is different (i.e., Node checks that the next hop for target D is different (i.e., Node
G). Node A checks the I_flag and generates G). Node A checks the I_flag and generates the
DCO(tgt=D,pathseq=x+1) to previous next hop for target D which is DCO(tgt=D,pathseq=x+1) to the previous next hop for target D,
G. Subsequently, Node A updates the routing entry and forwards which is G. Subsequently, Node A updates the routing entry and
the reachability information of target D upstream forwards the reachability information of target D upstream using
DAO(tgt=D,pathseq=x+1,I_flag=1). the DAO(tgt=D,pathseq=x+1,I_flag=1).
6. Node G receives the DCO(tgt=D,pathseq=x+1). It checks if the
received path sequence is later than the stored path sequence. 6. Node G receives the DCO(tgt=D,pathseq=x+1). It checks to see if
If it is later, Node G invalidates the routing entry of target D the received Path Sequence is later than the stored Path
and forwards the (un)reachability information downstream to B in Sequence. If it is later, Node G invalidates the routing entry
DCO(tgt=D,pathseq=x+1). of target D and forwards the (un)reachability information
downstream to B in the DCO(tgt=D,pathseq=x+1).
7. Similarly, B processes the DCO(tgt=D,pathseq=x+1) by invalidating 7. Similarly, B processes the DCO(tgt=D,pathseq=x+1) by invalidating
the routing entry of target D and forwards the (un)reachability the routing entry of target D and forwards the (un)reachability
information downstream to D. information downstream to D.
8. D ignores the DCO(tgt=D,pathseq=x+1) since the target is itself.
8. D ignores the DCO(tgt=D,pathseq=x+1), since the target is itself.
9. The propagation of the DCO will stop at any node where the node 9. The propagation of the DCO will stop at any node where the node
does not have an routing information associated with the target. does not have routing information associated with the target. If
If cached routing information is present and the cached Path cached routing information is present and the cached Path
Sequence is higher than the value in the DCO, then the DCO is Sequence is higher than the value in the DCO, then the DCO is
dropped. dropped.
A.2. Example DCO Messaging with multiple preferred parents A.2. Example DCO Messaging with Multiple Preferred Parents
As shown in Figure 5, node (N41) selects multiple preferred parents
(N32) and (N33). The sequence of actions is listed below the figure.
(6LBR) (6LBR)
| |
| |
| |
(N11) (N11)
/ \ / \
/ \ / \
/ \ / \
(N21) (N22) (N21) (N22)
/ / \ / / \
/ / \ / / \
/ / \ / / \
(N31) (N32) (N33) (N31) (N32) (N33)
: | / : | /
: | / : | /
: | / : | /
(N41) (N41)
Figure 5: Sample topology 2 Figure 5: Sample Topology 2
In Figure 5, node (N41) selects multiple preferred parents (N32) and 1. (N41) sends a DAO(tgt=N41,PS=x,I_flag=1) to (N32) and (N33).
(N33). The sequence of actions is as follows: Here, 'I_flag' refers to the Invalidation flag, and 'PS' refers
to the Path Sequence in the Transit Information option.
1. (N41) sends DAO(tgt=N41,PS=x,I_flag=1) to (N32) and (N33). Here 2. (N32) sends the DAO(tgt=N41,PS=x,I_flag=1) to (N22). (N33) also
I_flag refers to the Invalidation flag and PS refers to Path sends the DAO(tgt=N41,PS=x,I_flag=1) to (N22). (N22) learns
Sequence in Transit Information option.
2. (N32) sends DAO(tgt=N41,PS=x,I_flag=1) to (N22). (N33) also
sends DAO(tgt=N41,PS=x,I_flag=1) to (N22). (N22) learns
multiple routes for the same destination (N41) through multiple multiple routes for the same destination (N41) through multiple
next-hops. (N22) may receive the DAOs from (N32) and (N33) in next hops. (N22) may receive the DAOs from (N32) and (N33) in
any order with the I_flag set. The implementation should use any order with the I_flag set. The implementation should use
the DelayDCO timer to wait to initiate the DCO. If (N22) the DelayDCO timer to wait to initiate the DCO. If (N22)
receives an updated DAO from all the paths then the DCO need not receives an updated DAO from all the paths, then the DCO need
be initiated in this case. Thus the route table at N22 should not be initiated in this case. Thus, the routing table at N22
contain (Dst,NextHop,PS): { (N41,N32,x), (N41,N33,x) }. should contain (Dst,NextHop,PS): { (N41,N32,x), (N41,N33,x) }.
3. (N22) sends DAO(tgt=N41,PS=x,I_flag=1) to (N11).
4. (N11) sends DAO(tgt=N41,PS=x,I_flag=1) to (6LBR). Thus the 3. (N22) sends the DAO(tgt=N41,PS=x,I_flag=1) to (N11).
4. (N11) sends the DAO(tgt=N41,PS=x,I_flag=1) to (6LBR). Thus, the
complete path is established. complete path is established.
5. (N41) decides to change preferred parent set from { N32, N33 }
to { N31, N32 }. 5. (N41) decides to change the preferred parent set from
6. (N41) sends DAO(tgt=N41,PS=x+1,I_flag=1) to (N32). (N41) sends { N32, N33 } to { N31, N32 }.
DAO(tgt=N41,PS=x+1,I_flag=1) to (N31).
7. (N32) sends DAO(tgt=N41,PS=x+1,I_flag=1) to (N22). (N22) has 6. (N41) sends the DAO(tgt=N41,PS=x+1,I_flag=1) to (N32). (N41)
multiple routes to destination (N41). It sees that a new Path sends the DAO(tgt=N41,PS=x+1,I_flag=1) to (N31).
Sequence for Target=N41 is received and thus it waits for pre-
determined time period (DelayDCO time period) to invalidate 7. (N32) sends the DAO(tgt=N41,PS=x+1,I_flag=1) to (N22). (N22)
another route {(N41),(N33),x}. After time period, (N22) sends has multiple routes to destination (N41). It sees that a new
DCO(tgt=N41,PS=x+1) to (N33). Also (N22) sends the regular Path Sequence for Target=N41 is received and thus waits for a
DAO(tgt=N41,PS=x+1,I_flag=1) to (N11). predetermined time period (the DelayDCO time period) to
8. (N33) receives DCO(tgt=N41,PS=x+1). The received Path Sequence invalidate another route { (N41),(N33),x }. After the time
is latest and thus it invalidates the entry associated with period, (N22) sends the DCO(tgt=N41,PS=x+1) to (N33). Also
target (N41). (N33) then sends the DCO(tgt=N41,PS=x+1) to (N22) sends the regular DAO(tgt=N41,PS=x+1,I_flag=1) to (N11).
(N41). (N41) sees itself as the target and drops the DCO.
8. (N33) receives the DCO(tgt=N41,PS=x+1). The received Path
Sequence is the latest and thus invalidates the entry associated
with the target (N41). (N33) then sends the DCO(tgt=N41,PS=x+1)
to (N41). (N41) sees itself as the target and drops the DCO.
9. From Step 6 above, (N31) receives the 9. From Step 6 above, (N31) receives the
DAO(tgt=N41,PS=x+1,I_flag=1). It creates a routing entry and DAO(tgt=N41,PS=x+1,I_flag=1). It creates a routing entry and
sends the DAO(tgt=N41,PS=x+1,I_flag=1) to (N21). Similarly sends the DAO(tgt=N41,PS=x+1,I_flag=1) to (N21). Similarly,
(N21) receives the DAO and subsequently sends the (N21) receives the DAO and subsequently sends the
DAO(tgt=N41,PS=x+1,I_flag=1) to (N11). DAO(tgt=N41,PS=x+1,I_flag=1) to (N11).
10. (N11) receives DAO(tgt=N41,PS=x+1,I_flag=1) from (N21). It
waits for DelayDCO timer since it has multiple routes to (N41). 10. (N11) receives the DAO(tgt=N41,PS=x+1,I_flag=1) from (N21). It
(N41) will receive DAO(tgt=N41,PS=x+1,I_flag=1) from (N22) from waits for the DelayDCO timer, since it has multiple routes to
Step 7 above. Thus (N11) has received regular (N41). (N41) will receive the DAO(tgt=N41,PS=x+1,I_flag=1) from
(N22) from Step 7 above. Thus, (N11) has received the regular
DAO(tgt=N41,PS=x+1,I_flag=1) from all paths and thus does not DAO(tgt=N41,PS=x+1,I_flag=1) from all paths and thus does not
initiate DCO. initiate the DCO.
11. (N11) forwards the DAO(tgt=N41,PS=x+1,I_flag=1) to 6LBR and the
full path is established. 11. (N11) forwards the DAO(tgt=N41,PS=x+1,I_flag=1) to (6LBR), and
the full path is established.
Acknowledgments
Many thanks to Alvaro Retana, Cenk Gundogan, Simon Duquennoy,
Georgios Papadopoulos, and Peter van der Stok for their review and
comments. Alvaro Retana helped shape this document's final version
with critical review comments.
Authors' Addresses Authors' Addresses
Rahul Arvind Jadhav (editor) Rahul Arvind Jadhav (editor)
Huawei Huawei
Kundalahalli Village, Whitefield, Whitefield
Bangalore, Karnataka 560037 Kundalahalli Village
Bangalore 560037
Karnataka
India India
Phone: +91-080-49160700 Phone: +91-080-49160700
Email: rahul.ietf@gmail.com Email: rahul.ietf@gmail.com
Pascal Thubert Pascal Thubert
Cisco Systems, Inc Cisco Systems, Inc.
Building D Building D
45 Allee des Ormes - BP1200 45 Allee des Ormes - BP1200
MOUGINS - Sophia Antipolis 06254 06254 MOUGINS - Sophia Antipolis
France France
Phone: +33 497 23 26 34 Phone: +33-497-23-26-34
Email: pthubert@cisco.com Email: pthubert@cisco.com
Rabi Narayan Sahoo Rabi Narayan Sahoo
Huawei Huawei
Kundalahalli Village, Whitefield, Whitefield
Bangalore, Karnataka 560037 Kundalahalli Village
Bangalore 560037
Karnataka
India India
Phone: +91-080-49160700 Phone: +91-080-49160700
Email: rabinarayans@huawei.com Email: rabinarayans0828@gmail.com
Zhen Cao Zhen Cao
Huawei Huawei
W Chang'an Ave W Chang'an Ave
Beijing Beijing
P.R. China China
Email: zhencao.ietf@gmail.com Email: zhencao.ietf@gmail.com
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