draft-ietf-roll-efficient-npdao-07.txt   draft-ietf-roll-efficient-npdao-08.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: March 31, 2019 Cisco Expires: April 3, 2019 Cisco
R. Sahoo R. Sahoo
Z. Cao Z. Cao
Huawei Huawei
September 27, 2018 September 30, 2018
Efficient Route Invalidation Efficient Route Invalidation
draft-ietf-roll-efficient-npdao-07 draft-ietf-roll-efficient-npdao-08
Abstract Abstract
This document describes the problems associated with the use of NPDAO This document describes the problems associated with NPDAO messaging
messaging in RPL and signaling changes to improve route invalidation used in RPL for route invalidation and signaling changes to improve
efficiency. route invalidation efficiency.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 31, 2019. This Internet-Draft will expire on April 3, 2019.
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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? . . . . . . . . . . . . . . . . . 4 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 to 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 . . . . . . . . . . . . . . . . . . . . . . 5 NPDAO and DAO . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements for the NPDAO Optimization . . . . . . . . . . . 5 3. Requirements for the NPDAO Optimization . . . . . . . . . . . 6
3.1. Req#1: Tolerant to link failures to the previous 3.1. Req#1: Remove messaging dependency on link to the
parents . . . . . . . . . . . . . . . . . . . . . . . . . 5 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. Proposed 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 . . . . . . . . . . . 7
4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 8 4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 8
4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 9 4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 10
4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 9 4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 10
4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 9 4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 10
4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 9 4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 10
4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 10 4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 11
4.4. Other considerations . . . . . . . . . . . . . . . . . . 11 4.4. Other considerations . . . . . . . . . . . . . . . . . . 12
4.4.1. Dependent Nodes invalidation . . . . . . . . . . . . 11 4.4.1. Dependent Nodes invalidation . . . . . . . . . . . . 12
4.4.2. NPDAO and DCO in the same network . . . . . . . . . . 11 4.4.2. NPDAO and DCO in the same network . . . . . . . . . . 12
4.4.3. DCO with multiple preferred parents . . . . . . . . . 11 4.4.3. DCO with multiple preferred parents . . . . . . . . . 12
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . 12 8.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Example DCO Messaging . . . . . . . . . . . . . . . 13 Appendix A. Example Messaging . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 A.1. Example DCO Messaging . . . . . . . . . . . . . . . . . . 14
A.2. Example DCO Messaging with multiple preferred parents . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
RPL [RFC6550] specifies a proactive distance-vector based routing RPL [RFC6550] (Routing Protocol for Low power and lossy networks)
scheme. RPL has an optional messaging in the form of DAO specifies a proactive distance-vector based routing scheme. RPL has
(Destination Advertisement Object) messages using which the 6LBR can an optional messaging in the form of DAO (Destination Advertisement
learn route towards the nodes. In storing mode, DAO messages would Object) messages using which the 6LBR (6Lo Border Router) and 6LR
result in routing entries been created on all intermediate hops from (6Lo Router) can learn route towards the downstream nodes. In
the node's parent all the way towards the 6LBR. storing mode, DAO messages would result in routing entries been
created on all intermediate 6LRs from the node's parent all the way
towards the 6LBR.
RPL allows use of No-Path DAO (NPDAO) messaging to invalidate a RPL allows 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
skipping to change at page 3, line 28 skipping to change at page 3, line 37
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", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
DAO: Destination Advertisement Object 6LR: 6LoWPAN Router. This is an intermediate 6lowpan router which
allows traffic routing through itself in a multihop 6lo network.
DIO: DODAG Information Object DAG: Directed Acyclic Graph. A directed graph having the property
that all edges are oriented in such a way that no cycles exist.
Common Ancestor node: 6LR node which is the first common node on the DODAG: Destination-oriented DAG. A DAG rooted at a single
old and new path for the child node. 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. NPDAO: No-Path DAO. A DAO message which has target with lifetime 0.
DCO: Destination Cleanup Object, A new RPL control message type DCO: Destination Cleanup Object, A new RPL control message type
defined by this draft. defined by this draft. DCO messaging improves proactive route
invalidation in RPL.
Regular DAO: A DAO message with non-zero lifetime. Regular DAO: A DAO message with non-zero lifetime.
LLN: Low Power and Lossy Networks. LLN: Low Power and Lossy Networks.
Target Node: The node switching its parent whose routing adjacencies Target Node: The node switching its parent whose routing adjacencies
are updated (created/removed). are updated (created/removed).
This document also uses terminology described in [RFC6550]. This document also uses terminology described in [RFC6550].
skipping to change at page 4, line 40 skipping to change at page 5, line 30
\ ; \ ;
(D) (D)
/ \ / \
/ \ / \
/ \ / \
(E) (F) (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 via (C) towards the BR. Node (A) is the common ancestor for (D) path via (C) towards the 6LBR. Node (A) is the common ancestor for
for paths through (B)-(G) and (C)-(H). When (D) switches from (B) to (D) for paths through (B)-(G) and (C)-(H). When (D) switches from
(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 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.
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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 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 invalidation needs to be done for Node (D) switches parent, the route updates needs to be done for the
(D), (E) and (F). Thus without efficient route invalidation, a 6LR routing tables entries of (C),(H),(A),(G), and (B) with destination
may have to hold a lot of stale route entries. (D),(E) and (F). Without efficient route invalidation, a 6LR may
have to hold a lot of stale route entries.
2. Problems with current NPDAO messaging 2. Problems with current 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 then the NPDAO message is bound to fail.
2.2. Invalidate routes to 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 switching node, resulting in stale routing entries of
the dependent nodes. The only way for 6LR to invalidate the route the dependent nodes. The only way for 6LR to invalidate the route
entries for dependent nodes would be to use route lifetime expiry entries for dependent nodes would be to use route lifetime expiry
which could be substantially high for LLNs. 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 generates an NPDAO on its behalf. There is no NPDAO generated by the
these child nodes through the previous path resulting in stale dependent child nodes (E) and (F), through the previous path via (D)
entries on nodes (B) and (G) for nodes (E) and (F). to (B) and (G), resulting in stale entries on nodes (B) and (G) for
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 from previous route may invalidate the to (C). An NPDAO sent via previous route may invalidate the previous
existing 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 the NPDAO Optimization
3.1. Req#1: Tolerant to link failures to the previous parents 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. Therefore, it is required that the route invalidation does failure (thats why the node decided to switch). Therefore, it is
not depend on the previous link which is prone to failure. The required that the route invalidation does not depend on the previous
previous link referred here represents the link between the node and link which is prone to failure. The previous link referred here
its previous parent (from whom the node is now disassociating). represents the link between the node and its previous parent (from
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
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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 switching the 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 draft adds
new pro-active route invalidation message called as "Destination new pro-active route invalidation message called as "Destination
Cleanup Object" (DCO) that originates at a common ancestor node Cleanup Object" (DCO) that originates at a common ancestor node
between the new and old path. The common ancestor node generates a between the new and old path. The common ancestor node generates a
DCO in response to the change in the next-hop on receiving a regular DCO in response to the change in the next-hop on receiving a regular
DAO for the target. DAO with updated path sequence for the target.
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 a incremented path sequence
number. Node C will update the routing table based on the number. Node C will update the routing table based on the
reachability information in DAO and in turn generate another DAO with reachability information in DAO and in turn generate another DAO with
the same reachability information and forward it to H. Node H also the same reachability information and forward it to H. Node H also
follows the same procedure as Node C and forwards it to node A. When follows the same procedure as Node C and forwards it to node A. When
node A receives the regular DAO, it finds that it already has a node A receives the regular DAO, it finds that it already has a
routing table entry on behalf of the target address of node D. It routing table entry on behalf of the target address of node D. It
finds however that the next hop information for reaching node D has finds however that the next hop information for reaching node D has
changed i.e. the node D has decided to change the paths. In this changed i.e. the node D has decided to change the paths. In this
case, Node A which is the common ancestor node for node D along the case, Node A which is the common ancestor node for node D along the
two paths (previous and new), may generate a DCO which traverses two paths (previous and new), should generate a DCO which traverses
downwards in the network. The document in the subsequent section downwards in the network.
will explain the message format changes to handle this downward flow
of NPDAO.
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. The base fields apply to the message as a whole and options
are appended to add message/use-case specific attributes. As an are appended to add message/use-case specific attributes. As an
example, a DAO message may be attributed by one or more "RPL Target" example, a DAO message may be attributed by one or more "RPL Target"
options which specifies the reachability information for the given options which specify the reachability information for the given
targets. Similarly, a Transit Information option may be associated targets. Similarly, a Transit Information option may be associated
with a set of RPL Target options. with a set of RPL Target options.
The draft proposes a change in Transit Information option to contain The draft proposes a change in Transit Information option to contain
"Invalidate previous route" (I) bit. This I-bit signals the common "Invalidate previous route" (I) bit. This I-bit signals the common
ancestor node to generate a DCO on behalf of the target node. The ancestor node to generate a DCO on behalf of the target node. The
I-bit is carried in the transit information option which augments the I-bit is carried in the transit information option which augments the
reachability information for a given set of RPL Target(s). Transit reachability information for a given set of RPL Target(s). Transit
information option should be carried in the DAO message with I-bit information option should be carried in the DAO message with I-bit
set in case route invalidation is sought for the correspondig set in case route invalidation is sought for the correspondig
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 is expected to send a
DCO-ACK back. DCO-ACK back. If the DCO-ACK is not received even after setting the
'K', an implementation may choose to retry the DCO at a later time.
The number of retries are implementation and deployment dependent.
This document recommends using retries similar to what will be set
for DAO-ACK handling.
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. echoed in the DCO-ACK message. The initial DCOSequence can be chosen
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 is only present when the 'D'
flag is set. This field is typically only present when a local flag is set. This field is typically only present when a local
RPLInstanceID is in use, in order to identify the DODAGID that is RPLInstanceID is in use, in order to identify the DODAGID that is
associated with the RPLInstanceID. When a global RPLInstanceID is in associated with the RPLInstanceID. When a global RPLInstanceID is in
use, this field need not be present. Unassigned bits of the DCO Base 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 are reserved. They MUST be set to zero on transmission and MUST be
ignored on reception. ignored on reception.
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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.
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: Incremented at each unique DCO message from a node and DCOSequence: The DCOSequence in DCO-ACK is copied from the
echoed in the DCO-ACK 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. 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 is only present when the 'D'
flag is set. This field is typically only present when a local flag is set. This field is typically only present when a local
RPLInstanceID is in use, in order to identify the DODAGID that is RPLInstanceID is in use, in order to identify the DODAGID that is
associated with the RPLInstanceID. When a global RPLInstanceID is in associated with the RPLInstanceID. When a global RPLInstanceID is in
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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 proposed
DCO and the existing NPDAO mechanism. DCO and the existing NPDAO mechanism.
4.4.3. DCO with multiple preferred parents 4.4.3. 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. DCO can be used for route invalidation in such route establishment. Section 9.2.1 of [RFC6550] specifies, "All DAOs
cases as well. There are no changes required in the DCO messaging to generated at the same time for the same Target MUST be sent with the
support multiple preferred parents and DCO should work seemlessly in same Path Sequence in the Transit Information". Thus a DAO message
such scenarios. with the same path sequence MUST be sent to all the parents.
Subsequently when route invalidation has to be initiated, RPL
mentions that an NPDAO must be initiated with updated path sequence
to all the routes to be invalidated.
With DCO, the Target node itself does not initiate the route
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,
it initiates a DCO. With multiple preferred parents, this handling
does not change. But in this case it is recommended that an
implementation initiates a DCO after a time period such that the
common ancestor node may receive updated DAOs from all possible next-
hops. This will help to reduce DCO control overhead i.e., the common
ancestor can wait for updated DAOs from all possible directions
before initiating a DCO for route invalidation. The time period for
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
the route invalidation needs to be done.
5. Acknowledgements 5. Acknowledgements
Many thanks to Cenk Gundogan, Simon Duquennoy, Georgios Many thanks to Cenk Gundogan, Simon Duquennoy, Georgios
Papadopoulous, Peter Van Der Stok for their review and comments. Papadopoulous, Peter Van Der Stok for their review and 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 ICMPv6 RPL control codes in RPL
[RFC6550] for DCO and DCO-ACK messages. [RFC6550] for DCO and DCO-ACK messages.
skipping to change at page 12, line 24 skipping to change at page 13, line 34
| 0x85 | Secure Destination Cleanup Object | This | | 0x85 | Secure Destination Cleanup Object | This |
| | Acknowledgement | document | | | Acknowledgement | document |
+------+---------------------------------------------+--------------+ +------+---------------------------------------------+--------------+
IANA is requested to allocate bit 18 in the Transit Information IANA is requested to allocate bit 18 in the Transit Information
Option defined in RPL [RFC6550] section 6.7.8 for Invalidate route Option defined in RPL [RFC6550] section 6.7.8 for Invalidate route
'I' flag. 'I' flag.
7. Security Considerations 7. Security Considerations
The document adds new messages (DCO, DCO-ACK) which are similar to All RPL messages support a secure version of messages which allows
existing RPL messages such as DAO, DAO-ACK. Secure versions of DCO integrity protection using either a MAC or a signature. Optionally,
and DCO-ACK are added similar to other RPL messages (such as DAO, secured RPL messages also have encryption protection for
DAO-ACK). For general RPL security considerations, see [RFC6550]. confidentiality.
The document adds new messages (DCO, DCO-ACK) which are syntactically
similar to existing RPL messages such as DAO, DAO-ACK. Secure
versions of DCO and DCO-ACK are added similar to other RPL messages
(such as DAO, DAO-ACK).
RPL supports three security modes as mentioned in Section 10.1 of
[RFC6550]:
1. Unsecured: In this mode, it is expected that the RPL control
messages are secured by other security mechanisms, such as link-
layer security. In this mode, the RPL control messages,
including DCO, DCO-ACK, do not have Security sections.
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. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, 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>.
skipping to change at page 13, line 5 skipping to change at page 14, line 31
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>.
8.2. Informative References 8.2. Informative References
[I-D.ietf-6tisch-architecture] [I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-14 (work of IEEE 802.15.4", draft-ietf-6tisch-architecture-14 (work
in progress), April 2018. in progress), April 2018.
Appendix A. Example DCO Messaging Appendix A. Example 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). The
sequence of actions is as follows: 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 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
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and forwards the (un)reachability information downstream to B. and forwards the (un)reachability information downstream to B.
7. Similarly, B processes the DCO by invalidating the routing entry 7. Similarly, B processes the DCO by invalidating the routing entry
of target D and forwards the (un)reachability information of target D and forwards the (un)reachability information
downstream to D. downstream to D.
8. D ignores the DCO since the target is itself. 8. D ignores the DCO 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 the pathseq associated
is not older, then still the DCO is dropped. is not older, then still the DCO is dropped.
A.2. Example DCO Messaging with multiple preferred parents
(6LBR)
|
|
|
(N11)
/ \
/ \
/ \
(N21) (N22)
/ / \
/ / \
/ / \
(N31) (N32) (N33)
: | /
: | /
: | /
(N41)
Figure 5: Sample topology 2
In Figure 5, node (N41) selects multiple preferred parents (N32) and
(N33). The sequence of actions is as follows:
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
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 next-hops.
The route table at N22 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
complete path is established.
5. (N41) decides to change preferred parent set from { N32, N33 } to
{ N31, N32 }.
6. (N41) sends DAO(tgt=N41,PS=x+1,I_flag=1) to (N32). (N41) sends
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
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 to invalidate another route
{(N41),(N33),x}. After time period, (N22) sends
DCO(tgt=N41,PS=x+1) to (N33).
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
Email: rahul.ietf@gmail.com Email: rahul.ietf@gmail.com
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