< draft-ietf-roll-efficient-npdao-09.txt   draft-ietf-roll-efficient-npdao-10.txt >
ROLL R. Jadhav, Ed. ROLL R. Jadhav, Ed.
Internet-Draft Huawei Internet-Draft Huawei
Intended status: Standards Track P. Thubert Intended status: Standards Track P. Thubert
Expires: April 17, 2019 Cisco Expires: October 29, 2019 Cisco
R. Sahoo R. Sahoo
Z. Cao Z. Cao
Huawei Huawei
October 14, 2018 April 27, 2019
Efficient Route Invalidation Efficient Route Invalidation
draft-ietf-roll-efficient-npdao-09 draft-ietf-roll-efficient-npdao-10
Abstract Abstract
This document describes the problems associated with NPDAO messaging This document describes the problems associated with No-Path
used in RPL for route invalidation and signaling changes to improve Destination Advertisement Object (NPDAO) messaging used in Routing
route invalidation efficiency. Protocol for Low power and lossy networks (RPL) for route
invalidation and signaling changes to improve route invalidation
efficiency.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 17, 2019. This Internet-Draft will expire on October 29, 2019.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language and Terminology . . . . . . . . . . 3 1.1. Requirements Language and Terminology . . . . . . . . . . 3
1.2. Current NPDAO messaging . . . . . . . . . . . . . . . . . 4 1.2. Current NPDAO messaging . . . . . . . . . . . . . . . . . 4
1.3. Why NPDAO is important? . . . . . . . . . . . . . . . . . 5 1.3. Why NPDAO is important? . . . . . . . . . . . . . . . . . 5
2. Problems with current NPDAO messaging . . . . . . . . 5 2. Problems with current NPDAO messaging . . . . . . . . 6
2.1. Lost NPDAO due to link break to the previous parent . . . 5 2.1. Lost NPDAO due to link break to the previous parent . . . 6
2.2. Invalidate routes of dependent nodes . . . . . . . . . . 5 2.2. Invalidate routes of dependent nodes . . . . . . . . . . 6
2.3. Possible route downtime caused by async operation of 2.3. Possible route downtime caused by async operation of
NPDAO and DAO . . . . . . . . . . . . . . . . . . . . . . 6 NPDAO and DAO . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements for the NPDAO Optimization . . . . . . . . . . . 6 3. Requirements for the NPDAO Optimization . . . . . . . . . . . 6
3.1. Req#1: Remove messaging dependency on link to the 3.1. Req#1: Remove messaging dependency on link to the
previous parent . . . . . . . . . . . . . . . 6 previous parent . . . . . . . . . . . . . . . 6
3.2. Req#2: Dependent nodes route invalidation on parent 3.2. Req#2: Dependent nodes route invalidation on parent
switching . . . . . . . . . . . . . . . . . . . . . . . . 6 switching . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Req#3: Route invalidation should not impact data traffic 6 3.3. Req#3: Route invalidation should not impact data traffic 7
4. Proposed changes to RPL signaling . . . . . . . . . . . . . . 6 4. Changes to RPL signaling . . . . . . . . . . . . . . . . . . 7
4.1. Change in RPL route invalidation semantics . . . . . . . 6 4.1. Change in RPL route invalidation semantics . . . . . . . 7
4.2. Transit Information Option changes . . . . . . . . . . . 7 4.2. Transit Information Option changes . . . . . . . . . . . 8
4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 8 4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 9
4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 10 4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 10
4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 10 4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 10
4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 10 4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 10
4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 10 4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 11
4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 11 4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 12
4.4. Other considerations . . . . . . . . . . . . . . . . . . 12 4.4. DCO Base Rules . . . . . . . . . . . . . . . . . . . . . 12
4.4.1. Dependent Nodes invalidation . . . . . . . . . . . . 12 4.5. Other considerations . . . . . . . . . . . . . . . . . . 12
4.4.2. NPDAO and DCO in the same network . . . . . . . . . . 12 4.5.1. Dependent Nodes invalidation . . . . . . . . . . . . 12
4.4.3. DCO with multiple preferred parents . . . . . . . . . 12 4.5.2. NPDAO and DCO in the same network . . . . . . . . . . 13
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 4.5.3. DCO with multiple preferred parents . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Normative References . . . . . . . . . . . . . . . . . . . . 14 6.1. New Registry for the Destination Cleanup Object (DCO)
Appendix A. Example Messaging . . . . . . . . . . . . . . . . . 14 Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 15
A.1. Example DCO Messaging . . . . . . . . . . . . . . . . . . 14 6.2. New Registry for the Destination Cleanup Object
A.2. Example DCO Messaging with multiple preferred parents . . 15 Acknowledgement (DCO-ACK) Status field . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 6.3. New Registry for the Destination Cleanup Object (DCO)
Acknowledgement Flags . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. Normative References . . . . . . . . . . . . . . . . . . . . 17
Appendix A. Example Messaging . . . . . . . . . . . . . . . . . 18
A.1. Example DCO Messaging . . . . . . . . . . . . . . . . . . 18
A.2. Example DCO Messaging with multiple preferred parents . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
RPL [RFC6550] (Routing Protocol for Low power and lossy networks) RPL [RFC6550] (Routing Protocol for Low power and lossy networks)
specifies a proactive distance-vector based routing scheme. RPL has specifies a proactive distance-vector based routing scheme. RPL has
an optional messaging in the form of DAO (Destination Advertisement an optional messaging in the form of DAO (Destination Advertisement
Object) messages using which the 6LBR (6Lo Border Router) and 6LR Object) messages, which the 6LBR (6Lo Border Router) and 6LR (6Lo
(6Lo Router) can learn route towards the downstream nodes. In Router) can use to learn a route towards the downstream nodes. In
storing mode, DAO messages would result in routing entries been storing mode, DAO messages would result in routing entries being
created on all intermediate 6LRs from the node's parent all the way created on all intermediate 6LRs from the node's parent all the way
towards the 6LBR. towards the 6LBR.
RPL allows 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. A NPDAO is a DAO message with route
lifetime of zero, originates at the target node and always flows lifetime of zero, originates at the target node and always flows
upstream towards the 6LBR. This document explains the problems upstream towards the 6LBR. This document explains the problems
associated with the current use of NPDAO messaging and also discusses associated with the current use of NPDAO messaging and also discusses
the requirements for an optimized route invalidation messaging the requirements for an optimized route invalidation messaging
scheme. Further a new pro-active route invalidation message called scheme. Further a new pro-active route invalidation message called
as "Destination Cleanup Object (DCO)" is specified which fulfills as "Destination Cleanup Object" (DCO) is specified which fulfills
requirements of an optimized route invalidation messaging. requirements of an optimized route invalidation messaging.
The document only caters to the RPL's storing mode of operation The document only caters to the RPL's storing mode of operation
(MOP). The non-storing MOP does not require use of NPDAO for route (MOP). The non-storing MOP does not require use of 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", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
6LR: 6LoWPAN Router. This is an intermediate 6lowpan router which capitals, as shown here.
allows traffic routing through itself in a multihop 6lo network.
DAG: Directed Acyclic Graph. A directed graph having the property
that all edges are oriented in such a way that no cycles exist.
DODAG: Destination-oriented DAG. A DAG rooted at a single
destination, i.e., at a single DAG root with no outgoing edges.
6LBR: 6LoWPAN Border Router. A border router which is a DODAG root
and is the edge node for traffic flowing in and out of the 6lo
network.
DAO: Destination Advertisement Object. DAO messaging allows
downstream routes to the nodes to be established.
DIO: DODAG Information Object. DIO messaging allows upstream routes
to the 6LBR to be 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 a target node.
NPDAO: No-Path DAO. A DAO message which has target with lifetime 0.
DCO: Destination Cleanup Object, A new RPL control message type
defined by this draft. DCO messaging improves proactive route
invalidation in RPL.
Regular DAO: A DAO message with non-zero lifetime.
LLN: Low Power and Lossy Networks. This specification requires readers to be familiar with all the terms
and concepts that are discussed in "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks" [RFC6550].
Target Node: The node switching its parent whose routing adjacencies 6LoWPAN Router (6LR):
are updated (created/removed). An intermediate router that is able to send and receive Router
Advertisements (RAs) and Router Solicitations (RSs) as well as
forward and route IPv6 packets.
Directed Acyclic Graph (DAG):
A directed graph having the property that all edges are oriented
in such a way that no cycles exist.
This document also uses terminology described in [RFC6550]. Destination-Oriented DAG (DODAG):
A DAG rooted at a single destination, i.e., at a single DAG root
with no outgoing edges.
6LoWPAN Border Router (6LBR):
A border router which is a DODAG root and is the edge node for
traffic flowing in and out of the 6LoWPAN network.
Destination Advertisement Object (DAO):
DAO messaging allows downstream routes to the nodes to be
established.
DODAG Information Object (DIO):
DIO messaging allows upstream routes to the 6LBR to be
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
a target node.
No-Path DAO (NPDAO):
A DAO message which has target with lifetime 0 used for the
purpose of route invalidation.
Destination Cleanup Object (DCO):
A new RPL control message type defined by this document. DCO
messaging improves proactive route invalidation in RPL.
Regular DAO:
A DAO message with non-zero lifetime. Routing adjacencies are
created or updated based on this message.
Target node:
The node switching its parent whose routing adjacencies are
updated (created/removed).
1.2. Current NPDAO messaging 1.2. Current NPDAO messaging
RPL uses NPDAO messaging in the storing mode so that the node RPL uses NPDAO messaging in the storing mode so that the node
changing it routing adjacencies can invalidate the previous route. changing it routing adjacencies can invalidate the previous route.
This is needed so that nodes along previous path can release any This is needed so that nodes along the previous path can release any
resources (such as the routing entry) it maintains on behalf of resources (such as the routing entry) it maintains on behalf of
target node. target node.
For the rest of this document consider the following topology: For the rest of this document consider the following topology:
(6LBR) (6LBR)
| |
| |
| |
(A) (A)
skipping to change at page 5, line 16 skipping to change at page 5, line 40
path via (C) towards the 6LBR. Node (A) is the common ancestor for path via (C) towards the 6LBR. Node (A) is the common ancestor for
(D) for paths through (B)-(G) and (C)-(H). When (D) switches from (D) for paths through (B)-(G) and (C)-(H). When (D) switches from
(B) to (C), RPL allows sending NPDAO to (B) and regular DAO to (C). (B) to (C), RPL allows sending NPDAO to (B) and regular DAO to (C).
1.3. Why NPDAO is important? 1.3. Why NPDAO is important?
Nodes in LLNs may be resource constrained. There is limited memory Nodes in LLNs may be resource constrained. There is limited memory
available and routing entry records are one of the primary elements available and routing entry records are one of the primary elements
occupying dynamic memory in the nodes. Route invalidation helps 6LR occupying dynamic memory in the nodes. Route invalidation helps 6LR
nodes to decide which entries could be discarded to better achieve nodes to decide which entries could be discarded to better achieve
resource utilization. Thus it becomes necessary to have efficient resource utilization. Thus it becomes necessary to have an efficient
route invalidation mechanism. Also note that a single parent switch route invalidation mechanism. Also note that a single parent switch
may result in a "sub-tree" switching from one parent to another. may result in a "sub-tree" switching from one parent to another.
Thus the route invalidation needs to be done on behalf of the sub- Thus the route invalidation needs to be done on behalf of the sub-
tree and not the switching node alone. In the above example, when tree and not the switching node alone. In the above example, when
Node (D) switches parent, the route updates needs to be done for the Node (D) switches parent, the route updates needs to be done for the
routing tables entries of (C),(H),(A),(G), and (B) with destination routing tables entries of (C),(H),(A),(G), and (B) with destination
(D),(E) and (F). Without efficient route invalidation, a 6LR may (D),(E) and (F). Without efficient route invalidation, a 6LR may
have to hold a lot of stale route entries. have to hold a lot of stale route entries.
2. Problems with current NPDAO messaging 2. Problems with current NPDAO messaging
skipping to change at page 5, line 38 skipping to change at page 6, line 17
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 then the NPDAO message is bound to fail.
2.2. Invalidate routes of dependent nodes 2.2. Invalidate 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 switching node, resulting in stale routing entries of nodes rooted at the switching node, resulting in stale routing
the dependent nodes. The only way for 6LR to invalidate the route entries of the dependent nodes. The only way for 6LR to invalidate
entries for dependent nodes would be to use route lifetime expiry the route entries for dependent nodes would be to use route lifetime
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 behalf. There is no NPDAO generated by the
dependent child nodes (E) and (F), through the previous path via (D) dependent child nodes (E) and (F), through the previous path via (D)
to (B) and (G), resulting in stale entries on nodes (B) and (G) for to (B) and (G), resulting in stale entries on nodes (B) and (G) for
nodes (E) and (F). nodes (E) and (F).
2.3. Possible route downtime caused by async operation of NPDAO and DAO 2.3. Possible route downtime caused by async operation of 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 DAO via two different
paths at almost the same time. There is a possibility that an NPDAO paths at almost the same time. There is a possibility that an NPDAO
generated may invalidate the previous route and the regular DAO sent generated may invalidate the previous route and the regular DAO sent
via the new path gets lost on the way. This may result in route via 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, consider Node (D) switches from parent (B)
to (C). An NPDAO sent via previous route may invalidate the previous to (C). An NPDAO sent via the previous route may invalidate the
route whereas there is no way to determine whether the new DAO has previous route whereas there is no way to determine whether the new
successfully updated the route entries on the new path. DAO has successfully updated the route entries on the new path.
3. Requirements for the NPDAO Optimization 3. Requirements for the NPDAO Optimization
3.1. Req#1: Remove messaging dependency on link to the previous parent 3.1. Req#1: Remove messaging dependency on 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 (thats 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 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). whom the node is now disassociating).
3.2. Req#2: Dependent nodes route invalidation on parent switching 3.2. Req#2: Dependent nodes route invalidation on parent switching
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. Proposed 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
switching the 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 draft adds order to solve the problems as mentioned in Section 2, the document
new pro-active route invalidation message called as "Destination adds a new pro-active route invalidation message called "Destination
Cleanup Object" (DCO) that originates at a common ancestor node Cleanup Object" (DCO) that originates at a common ancestor node and
between the new and old path. The common ancestor node generates a flows downstream between the new and old path. The common ancestor
DCO in response to the change in the next-hop on receiving a regular node generates a DCO in response to the change in the next-hop on
DAO with updated path sequence for the target. receiving a regular DAO with updated Path Sequence for the target.
The 6LRs in the path for DCO take action such as route invalidation
based on the DCO information and subsequently send another DCO with
the same information downstream to the next hop. This operation is
similar to how the DAOs are handled on intermediate 6LRs in storing
MOP in [RFC6550]. Just like DAO in storing MOP, the DCO is sent
using link-local unicast source and destination IPv6 address. Unlike
DAO, which always travels upstream, the DCO always travels
downstream.
In Figure 1, when node D decides to switch the path from B to C, it In Figure 1, when node D decides to switch the path from B to C, it
sends a regular DAO to node C with reachability information sends a regular DAO to node C with reachability information
containing target as address of D and a incremented path sequence containing target as address of D and an incremented Path Sequence.
number. Node C will update the routing table based on the Node C will update the routing table based on the reachability
reachability information in DAO and in turn generate another DAO with information in the DAO and in turn generate another DAO with the same
the same reachability information and forward it to H. Node H also reachability information and forward it to H. Node H also follows
follows the same procedure as Node C and forwards it to node A. When the same procedure as Node C and forwards it to node A. When node A
node A receives the regular DAO, it finds that it already has a receives the regular DAO, it finds that it already has a routing
routing table entry on behalf of the target address of node D. It table entry on behalf of the target address of node D. It finds
finds however that the next hop information for reaching node D has however that the next hop information for reaching node D has changed
changed i.e. the node D has decided to change the paths. In this i.e. node D has decided to change the paths. In this case, Node A
case, Node A which is the common ancestor node for node D along the which is the common ancestor node for node D along the two paths
two paths (previous and new), should generate a DCO which traverses (previous and new), should generate a DCO which traverses downwards
downwards in the network. in the network.
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. The base fields apply to the message as a whole and options Options as described in Section 6 of [RFC6550]. The base fields
are appended to add message/use-case specific attributes. As an apply to the message as a whole and options are appended to add
example, a DAO message may be attributed by one or more "RPL Target" message/use-case specific attributes. As an example, a DAO message
options which specify the reachability information for the given may be attributed by one or more "RPL Target" options which specify
targets. Similarly, a Transit Information option may be associated the reachability information for the given targets. Similarly, a
with a set of RPL Target options. Transit Information option may be associated with a set of RPL Target
options.
The draft proposes a change in Transit Information option to contain This document specifies a change in the Transit Information Option to
"Invalidate previous route" (I) bit. This I-bit signals the common contain the "Invalidate previous route" (I) bit. This I-bit signals
ancestor node to generate a DCO on behalf of the target node. The the common ancestor node to generate a DCO on behalf of the target
I-bit is carried in the transit information option which augments the node. The I-bit is carried in the Transit Information Option which
reachability information for a given set of RPL Target(s). Transit augments the reachability information for a given set of RPL
information option should be carried in the DAO message with I-bit Target(s). Transit Information Option should be carried in the DAO
set in case route invalidation is sought for the correspondig message with I-bit set in case route invalidation is sought for the
target(s). corresponding target(s).
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 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| | | |
+ + + +
| | | |
+ Parent Address* + + Parent Address +
| | | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Updated Transit Information Option (New I flag added) Figure 2: Updated Transit Information Option (New I flag added)
I (Invalidate previous route) bit: 1 bit flag. The 'I' flag is set I (Invalidate previous route) bit: The 'I' flag is set by the target
by the target node to indicate that it wishes to invalidate the node to indicate to the common ancestor node that it wishes to
previous route by a common ancestor node between the two paths. invalidate any previous route between the two paths.
The common ancestor node SHOULD generate a DCO message in response to The common ancestor node SHOULD generate a DCO message in response to
this I-bit when it sees that the routing adjacencies have changed for this I-bit when it sees that the routing adjacencies have changed for
the target. I-bit governs the ownership of the DCO message in a way the target. I-bit governs the ownership of the DCO message in a way
that the target node is still in control of its own route that the target node is still in control of its own route
invalidation. invalidation.
4.3. Destination Cleanup Object (DCO) 4.3. Destination Cleanup Object (DCO)
A new ICMPv6 RPL control message type is defined by this A new ICMPv6 RPL control message type is defined by this
skipping to change at page 9, line 26 skipping to change at page 9, line 37
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 is expected to send a K: The 'K' flag indicates that the recipient of DCO message is
DCO-ACK back. If the DCO-ACK is not received even after setting the expected to send a DCO-ACK back. If the DCO-ACK is not received even
'K', an implementation may choose to retry the DCO at a later time. after setting the 'K' flag, an implementation may retry the DCO at a
The number of retries are implementation and deployment dependent. later time. The number of retries are implementation and deployment
This document recommends using retries similar to what will be set dependent. A node receiving a DCO message without the 'K' flag set
for DAO-ACK handling. MAY respond with a DCO-ACK, especially to report an error condition.
An example error condition could be that the node sending the DCO-ACK
does not find the routing entry for the indicated target.
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 sender
and MUST be ignored by the receiver. and MUST be ignored by the receiver.
Reserved: 8-bit unused field. The field MUST be initialized to zero Reserved: 8-bit unused field. The field MUST be initialized to zero
by the sender and MUST be ignored by the receiver. by the sender and MUST be ignored by the receiver.
DCOSequence: Incremented at each unique DCO message from a node and DCOSequence: Incremented at each unique DCO message from a node and
echoed in the DCO-ACK message. The initial DCOSequence can be chosen echoed in the DCO-ACK message. The initial DCOSequence can be chosen
randomly by the node. randomly by the node.
DODAGID (optional): 128-bit unsigned integer set by a DODAG root that DODAGID (optional): 128-bit unsigned integer set by a DODAG root that
uniquely identifies a DODAG. This field is only present when the 'D' uniquely identifies a DODAG. This field MUST be present when the 'D'
flag is set. This field is typically only present when a local flag is set. DODAGID is used when a local RPLInstanceID is in use,
RPLInstanceID is in use, in order to identify the DODAGID that is in order to identify the DODAGID that is associated with the
associated with the RPLInstanceID. When a global RPLInstanceID is in RPLInstanceID.
use, this field need not be present. Unassigned bits of the DCO Base
are reserved. They MUST be set to zero on transmission and MUST be
ignored on reception.
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 in [RFC6550] Figure 7, where
the base message format is the DCO message shown in Figure 3. the base message format is the DCO message shown in Figure 3.
4.3.2. DCO Options 4.3.2. DCO Options
The DCO message MAY carry valid options. This specification allows The DCO message MUST carry atleast one RPL Target and the Transit
for the DCO message to carry the following options: Information Option and MAY carry other valid options. This
specification allows for the DCO message to carry the following
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
The DCO carries a Target option and an associated Transit Information The DCO carries an RPL Target Option and an associated Transit
option with a lifetime of 0x00000000 to indicate a loss of Information Option with a lifetime of 0x00000000 to indicate a loss
reachability to that Target. of reachability to that Target. The lifetime indicated in the
Transit Information Option of the DCO message MUST be set to
0x00000000.
4.3.3. Path Sequence number in the DCO 4.3.3. Path Sequence number in the DCO
A DCO message may contain a Path Sequence in the transit information A DCO message may contain a Path Sequence in the Transit Information
option to identify the freshness of the DCO message. The Path Option to identify the freshness of the DCO message. The Path
Sequence in the DCO MUST use the same Path Sequence number present in Sequence in the DCO MUST use the same Path Sequence number present in
the regular DAO message when the DCO is generated in response to DAO the regular DAO message when the DCO is generated in response to a
message. The DAO and DCO path sequence are picked from the same DAO message. The Path Sequence present in the Transit Information
sequence number set. Thus if a DCO is received by a 6LR and Option of the DAO and the correspondingly triggered DCO MUST be same.
subsequently a DAO is received with old seqeunce number, then the DAO Thus if a DCO is received by a 6LR and subsequently a DAO is received
should be ignored. with an old seqeunce number, then the DAO MUST be ignored.
4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK)
The DCO-ACK message may 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. recipient in response to a unicast DCO message with 'K' flag set. If
'K' flag is not set then the receiver of the DCO message MAY send a
DCO-ACK to signal an error condition.
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| Reserved | DCOSequence | Status | | RPLInstanceID |D| Reserved | DCOSequence | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ DODAGID(optional) + + DODAGID(optional) +
skipping to change at page 11, line 34 skipping to change at page 11, line 41
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.
Reserved: 7-bit unused field. The field MUST be initialized to zero Reserved: 7-bit unused field. The field MUST be initialized to zero
by the sender and MUST be ignored by the receiver. by the sender and MUST be ignored by the receiver.
DCOSequence: The DCOSequence in DCO-ACK is copied from the DCOSequence: The DCOSequence in DCO-ACK is copied from the
DCOSequence received in the DCO message. DCOSequence received in the DCO message.
Status: Indicates the completion. Status 0 is defined as unqualified Status: Indicates the completion. Status 0 is defined as unqualified
acceptance in this specification. The remaining status values are acceptance in this specification. Status 1 is defined as "No
routing-entry for the Target found". The remaining status values are
reserved as rejection codes. reserved as rejection codes.
DODAGID (optional): 128-bit unsigned integer set by a DODAG root that DODAGID (optional): 128-bit unsigned integer set by a DODAG root that
uniquely identifies a DODAG. This field is only present when the 'D' uniquely identifies a DODAG. This field MUST be present when the 'D'
flag is set. This field is typically only present when a local flag is set. DODAGID is used when a local RPLInstanceID is in use,
RPLInstanceID is in use, in order to identify the DODAGID that is in order to identify the DODAGID that is associated with the
associated with the RPLInstanceID. When a global RPLInstanceID is in RPLInstanceID.
use, this field need not be present. Unassigned bits of the DCO-Ack
Base are reserved. They MUST be set to zero on transmission and MUST
be ignored on reception.
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 in [RFC6550] Figure 7,
where the base message format is the DCO-ACK message shown in where the base message format is the DCO-ACK message shown in
Figure 4. Figure 4.
4.4. Other considerations 4.4. DCO Base Rules
4.4.1. Dependent Nodes invalidation 1. If a node sends a DCO message with newer or different information
than the prior DCO message transmission, it MUST increment the
DCOSequence field by at least one. A DCO message transmission
that is identical to the prior DCO message transmission MAY
increment the DCOSequence field.
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
DCO is generated on the common ancestor node.
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.
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
without the 'K' flag set MAY respond with a DCO-ACK, especially
to report an error condition.
5. A node receiving a unicast DCO message MUST verify the stored
Path Sequence in context to the given target. If the stored Path
Sequence is more fresh i.e. newer than the Path Sequence received
in the DCO, then the DCO MUST be dropped.
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
transmission for another attempt, up until an implementation
specific number of retries.
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
Target Option is the only one in the DCO message then the DCO
message MUST be dropped.
The scope of DCOSequence values is unique to each node.
4.5. Other considerations
4.5.1. Dependent Nodes invalidation
Current RPL [RFC6550] does not provide a mechanism for route Current RPL [RFC6550] does not provide a mechanism for route
invalidation for dependent nodes. This document allows the dependent invalidation for dependent nodes. This document allows the dependent
nodes invalidation. Dependent nodes will generate their respective nodes invalidation. Dependent nodes will generate their respective
DAOs to update their paths, and the previous route invalidation for DAOs to update their paths, and the previous route invalidation for
those nodes should work in the similar manner described for switching those nodes should work in the similar manner described for switching
node. The dependent node may set the I-bit in the transit node. The dependent node may set the I-bit in the Transit
information option as part of regular DAO so as to request Information Option as part of regular DAO so as to request
invalidation of previous route from the common ancestor node. invalidation of previous route from the common ancestor node.
4.4.2. NPDAO and DCO in the same network Dependent nodes do not have any indication regarding if any of its
parent nodes in turn have decided to switch their parent. Thus for
route invalidation the dependent nodes may choose to always set the
'I' bit in all its DAO message's Transit Information Option. Note
that setting the I-bit is not counter productive even if there is no
previous route to be invalidated.
4.5.2. NPDAO and DCO in the same network
Even with the changed semantics, the current NPDAO mechanism in Even with the changed semantics, the current NPDAO mechanism in
[RFC6550] can still be used, for example, when the route lifetime [RFC6550] can still be used, for example, when the route lifetime
expiry of the target happens or when the node simply decides to expiry of the target happens or when the node simply decides to
gracefully terminate the RPL session on graceful node shutdown. gracefully terminate the RPL session on graceful node shutdown.
Moreover a deployment can have a mix of nodes supporting the proposed Moreover a deployment can have a mix of nodes supporting the DCO and
DCO and the existing NPDAO mechanism. the existing NPDAO mechanism. It is also possible that the same node
supports both the NPDAO and DCO signalling.
4.4.3. DCO with multiple preferred parents 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 to invalidate the existing router". This document
introduces an alternate and more optimized way of route invalidation
but it also allows existing NPDAO messaging to work. Thus an
implementation has two choices to make when a route invalidation is
to be initiated:
1. Use NPDAO to invalidate the previous route and send regular DAO
on the new path.
2. Send regular DAO on the new path with the 'I' bit set in the
Transit Information Option such that the common ancestor node
initiates the DCO message downstream to invalidate the previous
route.
This document recommends using option 2 for reasons specified in
Section 3 in this document.
4.5.3. 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". Thus a DAO message same Path Sequence in the Transit Information". Subsequently when
with the same path sequence MUST be sent to all the parents. route invalidation has to be initiated, RPL mentions use of NPDAO
Subsequently when route invalidation has to be initiated, RPL which can be initiated with an updated Path Sequence to all the
mentions that an NPDAO must be initiated with updated path sequence parent nodes through which the route is to be invalidated.
to all the routes to be invalidated.
With DCO, the Target node itself does not initiate the route With DCO, the Target node itself does not initiate the route
invalidation and it is left to the common ancestor node. A common invalidation and it 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. With multiple preferred parents, this handling
does not change. But in this case it is recommended that an does not change. But in this case it is recommended that an
implementation initiates a DCO after a time period such that the implementation initiates a DCO after a time period (DelayDCO) such
common ancestor node may receive updated DAOs from all possible next- that the common ancestor node may receive updated DAOs from all
hops. 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. The time period for directions before initiating a DCO for route invalidation. After
initiating a DCO could be based on the depth of the network. After
timeout, the DCO needs to be generated for all the next-hops for whom timeout, the DCO needs to be generated for all the next-hops for whom
the route invalidation needs to be done. the route invalidation needs to be done.
This documents recommends using a DelayDCO timer value of 1sec. This
value is inspired by the default DelayDAO value of 1sec in [RFC6550].
Here the hypothesis is that the DAOs from all possible parent set
would be received on the common ancestor within this time period.
Note that there is no requirement of synchronization between DCO and
DAOs. The DelayDCO timer simply ensures that the DCO control
overhead can be reduced and is only needed when the network contains
nodes using multiple preferred parent.
5. Acknowledgements 5. Acknowledgements
Many thanks to Cenk Gundogan, Simon Duquennoy, Georgios Many thanks to Alvaro Retana, Cenk Gundogan, Simon Duquennoy,
Papadopoulous, Peter Van Der Stok for their review and comments. Georgios Papadopoulous, Peter Van Der Stok for their review and
comments. Alvaro Retana helped shape this document's final version
with critical review comments.
6. IANA Considerations 6. IANA Considerations
IANA is requested to allocate new ICMPv6 RPL control codes in RPL IANA is requested to allocate new codes for the DCO and DCO-ACK
[RFC6550] for DCO and DCO-ACK messages. messages from the RPL Control Codes registry.
+------+---------------------------------------------+--------------+ +------+---------------------------------------------+--------------+
| Code | Description | Reference | | Code | Description | Reference |
+------+---------------------------------------------+--------------+ +------+---------------------------------------------+--------------+
| 0x04 | Destination Cleanup Object | This | | TBD1 | Destination Cleanup Object | This |
| | | document | | | | document |
| 0x05 | Destination Cleanup Object Acknowledgement | This | | TBD2 | Destination Cleanup Object Acknowledgement | This |
| | | document | | | | document |
| 0x84 | Secure Destination Cleanup Object | This | | TBD3 | Secure Destination Cleanup Object | This |
| | | document | | | | document |
| 0x85 | Secure Destination Cleanup Object | This | | TBD4 | Secure Destination Cleanup Object | This |
| | Acknowledgement | document | | | Acknowledgement | document |
+------+---------------------------------------------+--------------+ +------+---------------------------------------------+--------------+
IANA is requested to allocate bit 1 from the Transit Information
Option Flags registry for the I-bit (Section 4.2)
IANA is requested to allocate bit 18 in the Transit Information 6.1. New Registry for the Destination Cleanup Object (DCO) Flags
Option defined in RPL [RFC6550] section 6.7.8 for Invalidate route
'I' flag. IANA has created a registry for the 8-bit Destination Cleanup Object
(DCO) Flags field.
New bit numbers may be allocated only by an IETF Review. Each bit is
tracked with the following qualities:
oBit number (counting from bit 0 as the most significant bit)
oCapability description
oDefining RFC
The following bits are currently defined:
+------------+------------------------------+---------------+
| Bit number | Description | Reference |
+------------+------------------------------+---------------+
| 0 | DCO-ACK request (K) | This document |
| 1 | DODAGID field is present (D) | This document |
+------------+------------------------------+---------------+
DCO Base Flags
6.2. New Registry for the Destination Cleanup Object Acknowledgement
(DCO-ACK) Status field
IANA has created a registry for the 8-bit Destination Cleanup Object
Acknowledgement (DCO-ACK) Status field.
New Status values may be allocated only by an IETF Review. Each
value is tracked with the following qualities:
oStatus Code
oDescription
oDefining RFC
The following bits are currently defined:
+------------+----------------------------------------+-------------+
| Status | Description | Reference |
| Code | | |
+------------+----------------------------------------+-------------+
| 0 | Unqualified acceptance | This |
| | | document |
| 1 | No routing-entry for the indicated | This |
| | Target found | document |
+------------+----------------------------------------+-------------+
DCO Status Codes
6.3. New Registry for the Destination Cleanup Object (DCO)
Acknowledgement Flags
IANA has created a registry for the 8-bit Destination Cleanup Object
(DCO) Acknowledgement Flags field.
New bit numbers may be allocated only by an IETF Review. Each bit is
tracked with the following qualities:
oBit number (counting from bit 0 as the most significant bit)
oCapability description
oDefining RFC
The following bits are currently defined:
+------------+------------------------------+---------------+
| Bit number | Description | Reference |
+------------+------------------------------+---------------+
| 0 | DODAGID field is present (D) | This document |
+------------+------------------------------+---------------+
DCO-ACK Base Flags
7. Security Considerations 7. Security Considerations
This document introduces the ability for a common ancestor node to
invalidate a route on behalf of the target node. The common ancestor
node is directed to do so by the target node using the 'I' bit in
DCO's Transit Information Option. However, the common ancestor node
is in a position to unilaterally initiate the route invalidation
since it possesses all the required state information namely, the
Target address and the correspond Path Sequence. Thus a rogue common
ancestor node could initiate such an invalidation and impact the
traffic to the target node. This document assumes that the security
mechanisms as defined in [RFC6550] are followed, which means that the
common ancestor node is part of the RPL network because it has the
required credentials.
All RPL messages support a secure version of messages which allows All RPL messages support a secure version of messages which allows
integrity protection using either a MAC or a signature. Optionally, integrity protection using either a MAC or a signature. Optionally,
secured RPL messages also have encryption protection for secured RPL messages also have encryption protection for
confidentiality. confidentiality.
The document adds new messages (DCO, DCO-ACK) which are syntactically The document adds new messages (DCO, DCO-ACK) which are syntactically
similar to existing RPL messages such as DAO, DAO-ACK. Secure similar to existing RPL messages such as DAO, DAO-ACK. Secure
versions of DCO and DCO-ACK are added similar to other RPL messages versions of DCO and DCO-ACK are added similar to other RPL messages
(such as DAO, DAO-ACK). (such as DAO, 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 1. 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 DCO, DCO-ACK, do not have Security sections. including DCO, DCO-ACK, do not have Security sections. A DCO and
DCO-ACK message which is not encrypted at link-layer MUST not be
handled by the RPL layer. Also all the DCO and DCO-ACK messages
that are transmitted MUST be link-layer encrypted.
2. Preinstalled: In this mode, RPL uses secure messages. Thus 2. Preinstalled: In this mode, RPL uses secure messages. Thus
secure versions of DCO, DCO-ACK MUST be used in this mode. secure versions of DCO, DCO-ACK MUST be used in this mode.
3. Authenticated: In this mode, RPL uses secure messages. Thus 3. Authenticated: In this mode, RPL uses secure messages. Thus
secure versions of DCO, DCO-ACK MUST be used in this mode. secure versions of DCO, DCO-ACK MUST be used in this mode.
8. Normative References 8. 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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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). The In Figure 1, node (D) switches its parent from (B) to (C). This
sequence of actions is as follows: example assumes that Node D has already established its own route via
Node B-G-A-6LBR using pathseq=x. The example uses DAO and DCO
messaging convention and specifies only the required parameters to
explain the example namely, the parameter 'tgt', which stands for
Target Option and value of this parameter specifies the address of
the target node. The parameter 'pathseq', which specifies the Path
Sequence value carried in the Transit Information Option. The
parameter 'I_flag' specifies the 'I' bit in the Transit Information
Option. 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 routing entry on behalf of D, since it cannot find 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 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. DAO(tgt=D,pathseq=x+1,I_flag=1).
4. Similar to C, node H checks for routing entry on behalf of D, 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 cannot find an entry and hence 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 A in a
DAO. DAO(tgt=D,pathseq=x+1,I_flag=1).
5. Node A receives the DAO, and checks for routing entry on behalf 5. Node A receives the DAO(tgt=D,pathseq=x+1,I_flag=1), and checks
of D. It finds a routing entry but checks that the next hop for for a routing entry on behalf of D. It finds a routing entry but
target D is now changed. Node A checks the I_flag and generates checks that the next hop for target D is different (i.e. Node
DCO(tgt=D,pathseq=pathseq(DAO)) to previous next hop for target D G). Node A checks the I_flag and generates
which is G. Subsequently, A updates the routing entry and DCO(tgt=D,pathseq=x+1) to previous next hop for target D which is
forwards the reachability information of target D upstream G. Subsequently, Node A updates the routing entry and forwards
DAO(tgt=D,pathseq=x+1,I_flag=x) (the I_flag carries no the reachability information of target D upstream
significance henceforth). DAO(tgt=D,pathseq=x+1,I_flag=1).
6. Node G receives the DCO and invalidates routing entry of target D 6. Node G receives the DCO(tgt=D,pathseq=x+1). It checks if the
and forwards the (un)reachability information downstream to B. received path sequence is latest as compared to the stored path
7. Similarly, B processes the DCO by invalidating the routing entry sequence. If it is latest, Node G invalidates routing entry of
of target D and forwards the (un)reachability information target D and forwards the (un)reachability information downstream
downstream to D. to B in DCO(tgt=D,pathseq=x+1).
7. Similarly, B processes the DCO(tgt=D,pathseq=x+1) by invalidating
8. D ignores the DCO since the target is itself. the routing entry of target D and forwards the (un)reachability
information downstream to D.
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 an routing information associated with the target.
If the routing information is present and the pathseq associated If the routing information is present and its Path Sequence is
is not older, then still the DCO is dropped. higher, then still the DCO is dropped.
A.2. Example DCO Messaging with multiple preferred parents A.2. Example DCO Messaging with multiple preferred parents
(6LBR) (6LBR)
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(N11) (N11)
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/ \ / \
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(N41) (N41)
Figure 5: Sample topology 2 Figure 5: Sample topology 2
In Figure 5, node (N41) selects multiple preferred parents (N32) and In Figure 5, node (N41) selects multiple preferred parents (N32) and
(N33). The sequence of actions is as follows: (N33). The sequence of actions is as follows:
1. (N41) sends DAO(tgt=N41,PS=x,I_flag=1) to (N32) and (N33). Here 1. (N41) sends DAO(tgt=N41,PS=x,I_flag=1) to (N32) and (N33). Here
I_flag refers to the Invalidation flag and PS refers to Path I_flag refers to the Invalidation flag and PS refers to Path
Sequence in Transit Information option. Sequence in Transit Information option.
2. (N32) sends DAO(tgt=N41,PS=x,I_flag=1) to (N22). (N33) also 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 sends DAO(tgt=N41,PS=x,I_flag=1) to (N22). (N22) learns
routes for the same destination (N41) through multiple next-hops. multiple routes for the same destination (N41) through multiple
The route table at N22 should contain (Dst,NextHop,PS): { next-hops. (N22) may receive the DAOs from (N32) and (N33) in
(N41,N32,x), (N41,N33,x) }. any order with the I_flag set. The implementation should use
3. (N22) sends DAO(tgt=N41,PS=x,I_flag=1) to (N11). the DelayDCO timer to wait to initiate the DCO. If (N22)
4. (N11) sends DAO(tgt=N41,PS=x,I_flag=1) to (6LBR). Thus the receives an updated DAO from all the paths then the DCO need not
complete path is established. be initiated in this case. Thus the route table at N22 should
5. (N41) decides to change preferred parent set from { N32, N33 } to contain (Dst,NextHop,PS): { (N41,N32,x), (N41,N33,x) }.
{ N31, N32 }. 3. (N22) sends DAO(tgt=N41,PS=x,I_flag=1) to (N11).
6. (N41) sends DAO(tgt=N41,PS=x+1,I_flag=1) to (N32). (N41) sends 4. (N11) sends DAO(tgt=N41,PS=x,I_flag=1) to (6LBR). Thus the
DAO(tgt=N41,PS=x+1,I_flag=1) to (N31). complete path is established.
7. (N32) sends DAO(tgt=N41,PS=x+1,I_flag=1) to (N22). (N22) has 5. (N41) decides to change preferred parent set from { N32, N33 }
multiple routes to destination (N41). It sees that a new path to { N31, N32 }.
sequence for Target=N41 is received and thus it waits for pre- 6. (N41) sends DAO(tgt=N41,PS=x+1,I_flag=1) to (N32). (N41) sends
determined time period to invalidate another route DAO(tgt=N41,PS=x+1,I_flag=1) to (N31).
{(N41),(N33),x}. After time period, (N22) sends 7. (N32) sends DAO(tgt=N41,PS=x+1,I_flag=1) to (N22). (N22) has
DCO(tgt=N41,PS=x+1) to (N33). multiple routes to destination (N41). It sees that a new Path
Sequence for Target=N41 is received and thus it waits for pre-
determined time period (DelayDCO time period) to invalidate
another route {(N41),(N33),x}. After time period, (N22) sends
DCO(tgt=N41,PS=x+1) to (N33). Also (N22) sends the regular
DAO(tgt=N41,PS=x+1,I_flag=1) to (N11).
8. (N33) receives DCO(tgt=N41,PS=x+1). The received Path Sequence
is latest and thus it invalidates the entry associated with
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
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
(N21) receives the DAO and subsequently sends the
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).
(N41) will receive DAO(tgt=N41,PS=x+1,I_flag=1) from (N22) from
Step 7 above. Thus (N11) has received regular
DAO(tgt=N41,PS=x+1,I_flag=1) from all paths and thus does not
initiate DCO.
11. (N11) forwards the DAO(tgt=N41,PS=x+1,I_flag=1) to 6LBR and the
full path is established.
Authors' Addresses Authors' Addresses
Rahul Arvind Jadhav (editor) Rahul Arvind Jadhav (editor)
Huawei Huawei
Kundalahalli Village, Whitefield, Kundalahalli Village, Whitefield,
Bangalore, Karnataka 560037 Bangalore, Karnataka 560037
India India
Phone: +91-080-49160700 Phone: +91-080-49160700
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