rfc9009xml2.original.xml   rfc9009.xml 
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<rfc category="std" docName="draft-ietf-roll-efficient-npdao-18" ipr="trust20090
2">
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<front> <front>
<!-- The abbreviated title is used in the page header - it is only necessary
if the
full title is longer than 39 characters -->
<title abbrev="Efficient Route Invalidation">Efficient Route Invalidation</t itle> <title abbrev="Efficient Route Invalidation">Efficient Route Invalidation</t itle>
<seriesInfo name="RFC" value="9009"/>
<author fullname="Rahul Arvind Jadhav" initials="R.A." role="editor" surname ="Jadhav"> <author fullname="Rahul Arvind Jadhav" initials="R.A." role="editor" surname ="Jadhav">
<organization>Huawei</organization> <organization>Huawei</organization>
<address> <address>
<postal> <postal>
<street>Kundalahalli Village, Whitefield,</street> <street>Kundalahalli Village</street>
<extaddr>Whitefield</extaddr>
<city>Bangalore</city> <city>Bangalore</city>
<region>Karnataka</region> <region>Karnataka</region>
<code>560037</code> <code>560037</code>
<country>India</country> <country>India</country>
</postal> </postal>
<phone>+91-080-49160700</phone> <phone>+91-080-49160700</phone>
<email>rahul.ietf@gmail.com</email> <email>rahul.ietf@gmail.com</email>
</address> </address>
</author> </author>
<author initials="P" surname="Thubert" fullname="Pascal Thubert"> <author initials="P" surname="Thubert" fullname="Pascal Thubert">
<organization abbrev="Cisco">Cisco Systems, Inc</organization> <organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address> <address>
<postal> <postal>
<street>Building D</street> <extaddr>Building D</extaddr>
<street>45 Allee des Ormes - BP1200 </street> <street>45 Allee des Ormes - BP1200 </street>
<city>MOUGINS - Sophia Antipolis</city> <city>MOUGINS - Sophia Antipolis</city>
<code>06254</code> <code>06254</code>
<country>France</country> <country>France</country>
</postal> </postal>
<phone>+33 497 23 26 34</phone> <phone>+33-497-23-26-34</phone>
<email>pthubert@cisco.com</email> <email>pthubert@cisco.com</email>
</address> </address>
</author> </author>
<author fullname="Rabi Narayan Sahoo" initials="R.N." surname="Sahoo"> <author fullname="Rabi Narayan Sahoo" initials="R.N." surname="Sahoo">
<organization>Huawei</organization> <organization>Huawei</organization>
<address> <address>
<postal> <postal>
<street>Kundalahalli Village, Whitefield, </street> <extaddr>Whitefield</extaddr>
<street>Kundalahalli Village</street>
<city>Bangalore</city> <city>Bangalore</city>
<region>Karnataka</region> <region>Karnataka</region>
<code>560037</code> <code>560037</code>
<country>India</country> <country>India</country>
</postal> </postal>
<phone>+91-080-49160700</phone> <phone>+91-080-49160700</phone>
<email>rabinarayans@huawei.com</email> <email>rabinarayans0828@gmail.com</email>
</address> </address>
</author> </author>
<author initials="Z" surname="Cao" fullname="Zhen Cao"> <author initials="Z" surname="Cao" fullname="Zhen Cao">
<organization>Huawei</organization> <organization>Huawei</organization>
<address> <address>
<postal> <postal>
<street>W Chang'an Ave</street> <street>W Chang'an Ave</street>
<city>Beijing</city> <city>Beijing</city>
<country>P.R. China</country> <country>China</country>
</postal> </postal>
<email>zhencao.ietf@gmail.com</email> <email>zhencao.ietf@gmail.com</email>
</address> </address>
</author> </author>
<date year="2021" month="April" />
<date/> <keyword>NPDAO</keyword>
<keyword>DCO</keyword>
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<area>Routing</area>
<workgroup>ROLL</workgroup>
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<abstract> <abstract>
<t> <t>
This document explains the problems associated with the current use of This document explains the problems associated with the use of
NPDAO messaging and also discusses the requirements for an optimized No-Path Destination Advertisement Object (NPDAO) messaging in RFC 6550 a
route invalidation messaging scheme. Further a new proactive route nd also discusses the requirements for an optimized
invalidation message called as "Destination Cleanup Object" (DCO) is route invalidation messaging scheme. Further, this document specifies a
specified which fulfills requirements of an optimized route new proactive route
invalidation message called the "Destination Cleanup Object" (DCO),
which fulfills requirements for optimized route
invalidation messaging. invalidation messaging.
</t> </t>
</abstract> </abstract>
</front> </front>
<middle>
<middle> <section numbered="true" toc="default">
<section title="Introduction"> <name>Introduction</name>
<t> <t>
RPL <xref target="RFC6550"/> (Routing Protocol for Low power and RPL (the Routing Protocol for Low-Power and Lossy Networks) as defin
lossy networks) specifies a proactive distance-vector based routing ed in
<xref target="RFC6550" format="default"/>
specifies a proactive distance-vector-based routing
scheme. RPL has optional messaging in the form of DAO scheme. RPL has optional messaging in the form of DAO
(Destination Advertisement Object) messages, which the 6LBR (6Lo (Destination Advertisement Object) messages, which the 6LBR (6LoWPAN
Border Router) and 6LR (6Lo Router) can use to learn a route Border Router) and 6LR (6LoWPAN Router) can use to learn a route
towards the downstream nodes. In storing mode, DAO messages would towards the downstream nodes. ("6LoWPAN" stands for "IPv6 over Low-P
ower Wireless Personal Area Network".) In Storing mode, DAO messages would
result in routing entries being created on all intermediate 6LRs result in routing entries being created on all intermediate 6LRs
from the node's parent all the way towards the 6LBR. from a node's parent all the way towards the 6LBR.
</t> </t>
<t>
<t>
RPL allows the use of No-Path DAO (NPDAO) messaging to invalidate a RPL allows the use of No-Path DAO (NPDAO) messaging to invalidate a
routing path corresponding to the given target, thus releasing routing path corresponding to the given target, thus releasing
resources utilized on that path. A NPDAO is a DAO message with resources utilized on that path. An NPDAO is a DAO message with a
route lifetime of zero, originates at the target node and always route lifetime of zero. It originates at the target node and always
flows upstream towards the 6LBR. This document explains the flows upstream towards the 6LBR. This document explains the
problems associated with the current use of NPDAO messaging and problems associated with the use of NPDAO messaging in <xref target= "RFC6550"/> and
also discusses the requirements for an optimized route invalidation also discusses the requirements for an optimized route invalidation
messaging scheme. Further a new proactive route invalidation messaging scheme. Further, this document specifies a new proactive r
message called as "Destination Cleanup Object" (DCO) is specified oute invalidation
which fulfills requirements of an optimized route invalidation message called the "Destination Cleanup Object" (DCO),
which fulfills requirements for optimized route invalidation
messaging. messaging.
</t> </t>
<t>
This document only caters to RPL's Storing Mode of Operation
(MOP). The Non-Storing MOP does not require the use of an NPDAO for
route
invalidation, since routing entries are not maintained on 6LRs.
</t>
<section numbered="true" toc="default">
<name>Requirements Language and Terminology</name>
<t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
"<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>",
"<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>",
"<bcp14>SHOULD NOT</bcp14>",
"<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document
are to be interpreted as described in BCP&nbsp;14
<xref target="RFC2119"/> <xref target="RFC8174"/> when, and only
when, they appear in all capitals, as shown here.</t>
<t> <t>
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
invalidation since routing entries are not maintained on 6LRs.
</t>
<section title="Requirements Language and Terminology">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14 <xref target="RFC2119"/> <xref
target="RFC8174"/> when, and only when, they appear in all
capitals, as shown here.
</t>
<t>
This specification requires readers to be familiar with all the This specification requires readers to be familiar with all the
terms and concepts that are discussed in "RPL: IPv6 Routing terms and concepts that are discussed in "RPL: IPv6 Routing
Protocol for Low-Power and Lossy Networks" <xref Protocol for Low-Power and Lossy Networks" <xref target="RFC6550
target="RFC6550"/>. "/>.
</t> </t>
<dl newline="true" spacing="normal">
<t> <dt>Low-Power and Lossy Network (LLN):</dt>
<list style="hanging"> <dd>
<t hangText="Low Power and Lossy Networks (LLN):"> <vspace / A network in which both the routers and their
> interconnects are constrained. LLN routers typically
Network in which both the routers and their operate with constraints on processing power, memory,
interconnect are constrained. LLN routers typically and energy (battery power). Their interconnects are
operate with constraints on processing power, memory, characterized by high loss rates, low data rates, and
and energy (batter power). Their interconnects are instability.
characterized by high loss rates, low data rates, and </dd>
instability. <dt>6LoWPAN Router (6LR):</dt>
</t> <dd>
<t hangText="6LoWPAN Router (6LR):"> <vspace /> An intermediate router that is able to send and receive Router
An intermediate router that is able to send and receive Advertisements (RAs) and Router Solicitations (RSs) as well as
Router forward and route IPv6 packets.
Advertisements (RAs) and Router Solicitations (RSs) as w </dd>
ell as <dt>Directed Acyclic Graph (DAG):</dt>
forward and route IPv6 packets. <dd>
</t> A directed graph having the property that all edges are
<t hangText="Directed Acyclic Graph (DAG):"> <vspace /> oriented in such a way that no cycles exist.
A directed graph having the property that all edges are </dd>
oriented in such a way that no cycles exist. <dt>Destination-Oriented DAG (DODAG):</dt>
</t> <dd>
<t hangText="Destination-Oriented DAG (DODAG):"> <vspace /> A DAG rooted at a single destination, i.e., at a single
A DAG rooted at a single destination, i.e., at a single DAG root with no outgoing edges.
DAG root with no outgoing edges. </dd>
</t> <dt>6LoWPAN Border Router (6LBR):</dt>
<t hangText="6LoWPAN Border Router (6LBR):"> <vspace /> <dd>
A border router which is a DODAG root and is the edge A border router that is a DODAG root and is the edge
node for traffic flowing in and out of the 6LoWPAN node for traffic flowing in and out of the 6LoWPAN.
network. </dd>
</t> <dt>Destination Advertisement Object (DAO):</dt>
<t hangText="Destination Advertisement Object (DAO):"> <vspa <dd>
ce /> DAO messaging allows downstream routes to the nodes to
DAO messaging allows downstream routes to the nodes to be established.
be established. </dd>
</t> <dt>DODAG Information Object (DIO):</dt>
<t hangText="DODAG Information Object (DIO):"> <vspace /> <dd>
DIO messaging allows upstream routes to the 6LBR to be DIO messaging allows upstream routes to the 6LBR to be
established. DIO messaging is initiated at the DAO established. DIO messaging is initiated at the DAO
root. root.
</t> </dd>
<dt>Common ancestor node:</dt>
<t hangText="Common Ancestor node"> <vspace /> <dd>
6LR/6LBR node which is the first common node between A 6LR/6LBR node that is the first common node between
two paths of a target node. two paths of a target node.
</t> </dd>
<dt>No-Path DAO (NPDAO):</dt>
<t hangText="No-Path DAO (NPDAO):"> <vspace /> <dd>
A DAO message which has target with lifetime 0 used for A DAO message that has a target with a lifetime of 0. Used for
the purpose of route invalidation. the purpose of route invalidation.
</t> </dd>
<dt>Destination Cleanup Object (DCO):</dt>
<t hangText="Destination Cleanup Object (DCO):"> <vspace /> <dd>
A new RPL control message code defined by this A new RPL control message code defined by this
document. DCO messaging improves proactive route document. DCO messaging improves proactive route
invalidation in RPL. invalidation in RPL.
</t> </dd>
<dt>Regular DAO:</dt>
<t hangText="Regular DAO:"> <vspace /> <dd>
A DAO message with non-zero lifetime. Routing A DAO message with a non-zero lifetime. Routing
adjacencies are created or updated based on this adjacencies are created or updated based on this
message. message.
</t> </dd>
<dt>Target node:</dt>
<t hangText="Target node:"> <vspace /> <dd>
The node switching its parent whose routing adjacencies The node switching its parent whose routing adjacencies
are updated (created/removed). are updated (created/removed).
</t> </dd>
</list> </dl>
</t> </section>
</section> <section anchor="current_npdao" numbered="true" toc="default">
<name>RPL NPDAO Messaging</name>
<section anchor="current_npdao" title="Current NPDAO messaging"> <t>
<t> RPL uses NPDAO messaging in Storing mode so that the node
RPL uses NPDAO messaging in the storing mode so that the node
changing its routing adjacencies can invalidate the previous changing its routing adjacencies can invalidate the previous
route. This is needed so that nodes along the previous path can route. This is needed so that nodes along the previous path can
release any resources (such as the routing entry) they maintain release any resources (such as the routing entry) they maintain
on behalf of target node. on behalf of the target node.
</t> </t>
<t>
<t> Throughout this document, we will refer to the topology shown in <xref t
For the rest of this document consider the following topology: arget="sample_top"/>:
</t> </t>
<figure anchor="sample_top">
<t> <figure align="center" anchor="sample_top" title="Sample <name>Sample Topology</name>
topology"> <artwork align="center"><![CDATA[ <artwork align="center" name="" type="" alt=""><![CDATA[
(6LBR) (6LBR)
| |
| |
| |
(A) (A)
/ \
/ \
/ \
(G) (H)
| |
| |
| |
(B) (C)
\ ;
\ ;
\ ;
(D)
/ \ / \
/ \ / \
/ \ / \
(G) (H) (E) (F)]]></artwork>
| | </figure>
| | <t>
| | Node D is connected via preferred parent B. D has an
(B) (C) alternate 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 B to C, RPL allows sending an NPDAO to B
\ ; and a regular DAO to C.
(D) </t>
/ \ </section>
/ \ <section numbered="true" toc="default">
/ \ <name>Why Is NPDAO Messaging Important?</name>
(E) (F)
]]></artwork> </figure> </t>
<t>
Node (D) is connected via preferred parent (B). (D) has an
alternate 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 (B) to (C), RPL allows sending NPDAO to (B)
and regular DAO to (C).
</t>
</section>
<!--
<section title="Cases when No-Path DAO may be used">
<t> There are following cases in which a node switches its parent
and may employ No-Path DAO messaging:</t>
<t>Case I: Current parent becomes unavailable because of transient
or permanent link or parent node failure.</t>
<t>Case II: The node finds a better parent node i.e. the metrics of
another parent is better than its current parent.</t>
<t>Case III: The node switches to a new parent whom it "thinks" has
a better metric but does not in reality.</t>
<t>The usual steps of operation when the node switches the parent
is that the node sends a No-Path DAO message via its current par
ent
to invalidate its current route and subsequently it tries to
establish a new routing path by sending a new DAO via its new
parent.</t>
</section>
-->
<section title="Why Is NPDAO Important?"> <t>
<t> Resources in LLN nodes are typically constrained. There is limit
Nodes in LLNs may be resource constrained. There is limited ed
memory available and routing entry records are one of the memory available, and routing entry records are one of the
primary elements occupying dynamic memory in the nodes. Route primary elements occupying dynamic memory in the nodes. Route
invalidation helps 6LR nodes to decide which entries could be invalidation helps 6LR nodes to decide which routing entries can
discarded to better optimize resource utilization. Thus it be
discarded for better use of the limited resources. Thus, it
becomes necessary to have an efficient route invalidation becomes necessary to have an efficient route invalidation
mechanism. Also note that a single parent switch may result in mechanism. Also note that a single parent switch may result in
a "sub-tree" switching from one parent to another. Thus the a "subtree" switching from one parent to another. Thus, the
route invalidation needs to be done on behalf of the sub-tree route invalidation needs to be done on behalf of the subtree
and not the switching node alone. In the above example, when and not the switching node alone. In the above example, when
Node (D) switches parent, the route updates needs to be done Node D switches its parent, route updates need to be done
for the routing tables entries of (C),(H),(A),(G), and (B) with for the routing table entries of C, H, A, G, and B with
destination (D),(E) and (F). Without efficient route destinations D, E, and F. Without efficient route
invalidation, a 6LR may have to hold a lot of stale route invalidation, a 6LR may have to hold a lot of stale route
entries. entries.
</t> </t>
</section> </section>
</section> </section>
<section anchor="current_npdao_problems" numbered="true" toc="default">
<section anchor="current_npdao_problems" title="Problems with current NPDAO <name>Problems with the RPL NPDAO Messaging</name>
messaging"> <section numbered="true" toc="default">
<section title="Lost NPDAO due to link break to the previous parent"> <name>Lost NPDAO Due to Link Break to the Previous Parent</name>
<t> <t>
When a node switches its parent, the NPDAO is to be sent to 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 its previous parent and a regular DAO to its new parent. In
cases where the node switches its parent because of transient cases where the node switches its parent because of transient
or permanent parent link/node failure then the NPDAO message is or permanent parent link/node failure, the NPDAO message may
bound to fail. not be received by the parent.
</t> </t>
<!--
<t>
RPL allows use of route lifetime to remove unwanted routes in
case the routes could not be refreshed. But route lifetimes in
case of LLNs could be substantially high and thus the route
entries would be stuck for longer times.
</t>
-->
</section> </section>
<section numbered="true" toc="default">
<section title="Invalidate Routes of Dependent Nodes"> <name>Invalidating Routes of Dependent Nodes</name>
<t> <t>
RPL does not specify how route invalidation will work for RPL does not specify how route invalidation will work for
dependent nodes rooted at the switching node, resulting in dependent nodes in the switching node subDAG, resulting in
stale routing entries of the dependent nodes. The only way for stale routing entries of the dependent nodes. The only way for a
6LR to invalidate the route entries for dependent nodes would 6LR to invalidate the route entries for dependent nodes would
be to use route lifetime expiry which could be substantially be to use route lifetime expiry, which could be substantially
high for LLNs. high for LLNs.
</t> </t>
<t> <t>
In the example topology, when Node (D) switches its parent, In the example topology, when Node D switches its parent,
Node (D) generates an NPDAO on its behalf. There is no NPDAO Node D generates an NPDAO on its own behalf. There is no NPDAO
generated by the dependent child nodes (E) and (F), through the generated by the dependent child Nodes E and F, through the
previous path via (D) to (B) and (G), resulting in stale previous path via D to B and G, resulting in stale
entries on nodes (B) and (G) for nodes (E) and (F). entries on Nodes B and G for Nodes E and F.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Possible route downtime caused by asynchronous operation <name>Possible Route Downtime Caused by Asynchronous Operation of the NP
of NPDAO and DAO"> DAO and DAO</name>
<t> <t>
A switching node may generate both an NPDAO and DAO via two A switching node may generate both an NPDAO and a DAO via two
different paths at almost the same time. There is a possibility different paths at almost the same time. It is possible
that an NPDAO generated may invalidate the previous route and that the NPDAO may invalidate the previous route and
the regular DAO sent via the new path gets lost on the way. the regular DAO sent via the new path gets lost on the way.
This may result in route downtime impacting downward This may result in route downtime, impacting downward
traffic for the switching node. traffic for the switching node.
</t> </t>
<t> <t>
In the example topology, consider Node (D) switches from parent In the example topology, say that Node D switches from parent
(B) to (C). An NPDAO sent via the previous route may invalidate B to C. An NPDAO sent via the previous route may invalidate
the previous route whereas there is no way to determine whether the previous route, whereas there is no way to determine whether
the new DAO has successfully updated the route entries on the the new DAO has successfully updated the route entries on the
new path. new path.
</t> </t>
</section> </section>
</section> </section>
<section anchor="requirements" numbered="true" toc="default">
<section title="Requirements for the NPDAO Optimization" anchor="requirement <name>Requirements for NPDAO Optimization</name>
s"> <section numbered="true" toc="default">
<name>Req. #1: Remove Messaging Dependency on the Link to the Previous
<section title="Req#1: Remove messaging dependency on link to the previo Parent</name>
us parent"> <t>
<t>
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 parent, it is normal that the link to the previous parent is
prone to failure (that's why the node decided to switch). prone to failure (that's why the node decided to switch).
Therefore, it is required that the route invalidation does not Therefore, it is required that the route invalidation does not
depend on the previous link which is prone to failure. The depend on the previous link, which is prone to failure. The
previous link referred here represents the link between the previous link referred to here represents the link between the
node and its previous parent (from whom the node is now node and its previous parent (from which the node is now
disassociating). disassociating).
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Req#2: Dependent nodes route invalidation on parent <name>Req. #2: Route Invalidation for Dependent Nodes at the Parent Swit
switching"> ching Node</name>
<t> <t>
It should be possible to do route invalidation for dependent It should be possible to do route invalidation for dependent
nodes rooted at the switching node. nodes rooted at the switching node.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Req#3: Route invalidation should not impact data traffic <name>Req. #3: Route Invalidation Should Not Impact Data Traffic</name>
"> <t>
<t>
While sending the NPDAO and DAO messages, it is possible that While sending the NPDAO and DAO messages, it is possible that
the NPDAO successfully invalidates the previous path, while the the NPDAO successfully invalidates the previous path, while the
newly sent DAO gets lost (new path not set up successfully). newly sent DAO gets lost (new path not set up successfully).
This will result in downstream unreachability to the node This will result in downstream unreachability to the node
switching paths. Therefore, it is desirable that the route switching paths. Therefore, it is desirable that the route
invalidation is synchronized with the DAO to avoid the risk of invalidation is synchronized with the DAO to avoid the risk of
route downtime. route downtime.
</t> </t>
</section> </section>
</section>
<!-- Too Confusing section and may not be needed now... If required th
is can be added in Appendix.
<section title="Existing Solution">
<section title="NPDAO can be generated by the parent node who detects
link failure to the child">
<t>RPL states mechanisms which could be utilized to clear DAO
states in a sub-DODAG. [RFC6550] Section 11.2.2.3 states "With DAO
inconsistency loop recovery, a packet can be used to recursively
explore and clean up the obsolete DAO states along a
sub-DODAG".</t>
<t>Thus in the sample topology in Figure 1, when Node (B) detects
link failure to (D), (B) has an option of generating an NPDAO on
behalf of Node (D) and its sub-childs, (E) and (F).</t>
<t>This section explains why generation of an NPDAO in such cases
may not function as desired. Primarily the DAO state information in
the form of Path Sequence plays a major role here. Every target is
associated with a Path Sequence number which relates to the latest
state of the target. <xref target="RFC6550"/> Section 7.1 explains
the semantics of Path Sequence number. The target node increments
the Path Sequence number every time it generates a new DAO. The
router nodes en-route utilize this Path Sequence number to decide
the freshness of target information. If a non-target node has to
generate an NPDAO then it could use following two possibilities
with Path Sequence number: </t>
<t>Let the Path Sequence number of old regular DAO that flowed
through (B) be x. The subsequent regular DAO generated by Node (D)
will have sequence number x+1.</t>
<t>i. Node (B) uses the previous Path Sequence number from the
regular DAO i.e. NPDAO(pathseq=x)</t>
<t>ii. Node (B) increments the Path Sequence number i.e.
NPDAO(pathseq=x+1)</t>
<t>In case i, the NPDAO(pathseq=x) will be dropped by all the
intermediate nodes since the semantics of Path Sequence number
dictates that any DAO with an older Path Sequence number be
dropped.</t>
<t>In case ii, there is a risk that the NPDAO(pathseq=x+1)
traverses up the DODAG and invalidates all the routes till the root
and then the regular DAO(pathseq=x+1) from the target traverses
upwards. In this case the regular DAO(pathseq=x+1) will be dropped
from common ancestor node to the root. This will result in route
downtime.</t>
<t>Another problem with this scheme is its dependence on the
upstream neighbor to detect that the downstream neighbor is
unavailable. There are two possibilities by which such a detection
might be put to work:</t>
<t>i. There is P2P traffic from the previous sub-DODAG to any of
nodes in the sub-tree which has switched the path. In the above
example, lets consider that Node (G) has P2P traffic for either of
nodes (D), (E), or (F). In this case, Node (B) will detect
forwarding error while forwarding the packets from Node (B) to (D).
But dependence on P2P traffic may not be an optimal way to solve
this problem considering the reactive approach of the scheme. The
P2P traffic pattern might be sparse and thus such a detection might
kick-in too late.</t>
<t>ii. The other case is where Node (B) explicitly employs some
mechanism to probe directly attached downstream child nodes. Such
kind of schemes are seldom used.</t>
</section>
<section title="NPDAO can be generated once the link is restored to
the previous parent">
<t>This scheme solves a specific scenario of transient links. The
child node can detect that the connection to previous parent is
restored and then transmit an NPDAO to the previous parent to
invalidate the route. This scheme is stateful, thus requires more
memory and solves a specific scenario.</t>
</section>
</section> </section>
--> <section numbered="true" toc="default">
<section title="Changes to RPL signaling"> <name>Changes to RPL Signaling</name>
<section title="Change in RPL route invalidation semantics"> <section numbered="true" toc="default">
<t> <name>Change in RPL Route Invalidation Semantics</name>
As described in <xref target="current_npdao"/>, the NPDAO <t>
As described in <xref target="current_npdao" format="default"/>,
the NPDAO
originates at the node changing to a new parent and traverses originates at the node changing to a new parent and traverses
upstream towards the root. In order to solve the problems as upstream towards the root. In order to solve the problems
mentioned in <xref target="current_npdao_problems"/>, the discussed in <xref target="current_npdao_problems" format="defau
lt"/>, this
document adds a new proactive route invalidation message document adds a new proactive route invalidation message
called "Destination Cleanup Object" (DCO) that originates at a called the "Destination Cleanup Object" (DCO), which originates
common ancestor node and flows downstream between the new and at a
old path. The common ancestor node generates a DCO in response common ancestor node and flows downstream the
to the change in the next-hop on receiving a regular DAO with old path. The common ancestor node generates a DCO when removing
updated Path Sequence for the target. a next hop to a target -- for instance, as a delayed response to
</t> receiving a regular DAO from another child node with a Path
<t> Sequence for the target that is the same or newer, in which case
The 6LRs in the path for DCO take action such as route the DCO transmission is canceled.
</t>
<t>
The 6LRs in the path for the DCO take such action as route
invalidation based on the DCO information and subsequently send invalidation based on the DCO information and subsequently send
another DCO with the same information downstream to the next another DCO with the same information downstream to the next
hop. This operation is similar to how the DAOs are handled on hop(s). This operation is similar to how the DAOs are handled on
intermediate 6LRs in storing MOP in <xref target="RFC6550"/>. intermediate 6LRs in the Storing MOP <xref target="RFC6550" form
Just like DAO in storing MOP, the DCO is sent using link-local at="default"/>.
unicast source and destination IPv6 address. Unlike DAO, which Just like the DAO in the Storing MOP, the DCO is sent using link
-local
unicast source and destination IPv6 addresses. Unlike the DAO, w
hich
always travels upstream, the DCO always travels downstream. always travels upstream, the DCO always travels downstream.
</t> </t>
<t>
<t> In <xref target="sample_top" format="default"/>, when child Node
In <xref target="sample_top"/>, when node D decides to D decides to
switch the path from B to C, it sends a regular DAO to node C switch the path from parent B to parent C, it sends a regular DA
O to Node C
with reachability information containing the address of D as with reachability information containing the address of D as
the target and an incremented Path Sequence. Node C will update the target and an incremented Path Sequence. Node C will update
the routing table based on the reachability information in the the routing table based on the reachability information in the
DAO and in turn generate another DAO with the same reachability DAO and will in turn generate another DAO with the same reachabi
information and forward it to H. Node H also follows the same lity
procedure as Node C and forwards it to node A. When node A information and forward it to H. Node H recursively 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 receives the regular DAO, it finds that it already has a
routing table entry on behalf of the target address of node D. routing table entry on behalf of the Target Address of Node D.
It finds however that the next hop information for reaching It finds, however, that the next-hop information for reaching
node D has changed i.e., node D has decided to change the Node D has changed, i.e., Node D has decided to change the
paths. In this case, Node A which is the common ancestor node paths. In this case, Node A, which is the common ancestor node
for node D along the two paths (previous and new), should for Node D along the two paths (previous and new), can
generate a DCO which traverses downwards in the network. Node A generate a DCO that traverses the network downwards over the
handles normal DAO forwarding to 6LBR as required by <xref old path to the target. Node A handles normal DAO forwarding to
target="RFC6550"/>. the 6LBR as required by <xref target="RFC6550" format="default"/
</t> >.
</t>
</section> </section>
<section title="Transit Information Option changes" anchor="transit_opt_ <section anchor="transit_opt_changes" numbered="true" toc="default">
changes"> <name>Transit Information Option Changes</name>
<t> <t>
Every RPL message is divided into base message fields and Every RPL message is divided into base message fields and
additional Options as described in Section 6 of <xref additional options, as described in <xref target="RFC6550" secti
target="RFC6550"/>. The base fields apply to the message as a on="6" sectionFormat="of"/>. The base fields apply to the message as a
whole and options are appended to add message/use-case specific whole, and options are appended to add message-specific /
use-case-specific
attributes. As an example, a DAO message may be attributed by attributes. As an example, a DAO message may be attributed by
one or more "RPL Target" options which specify the reachability one or more "RPL Target" options that specify that the reachabil
information for the given targets. Similarly, a Transit ity
information is for the given targets. Similarly, a Transit
Information option may be associated with a set of RPL Target Information option may be associated with a set of RPL Target
options. options.
</t> </t>
<t>
<t> This document specifies a change in the Transit Information opti
This document specifies a change in the Transit Information Opti on to
on to
contain the "Invalidate previous route" (I) flag. This 'I' flag signals contain the "Invalidate previous route" (I) flag. This 'I' flag signals
the common ancestor node to generate a DCO on behalf of the the common ancestor node to generate a DCO on behalf of the
target node with a RPL Status of 195 indicating that the address target node with a RPL Status of 195, indicating that the addres s
has moved. The 'I' flag is carried in the Transit Information has moved. The 'I' flag is carried in the Transit Information
Option which augments the reachability information for a given option, which augments the reachability information for a given
set of RPL Target(s). Transit Information Option with 'I' flag set of one or more RPL Targets. A Transit Information option wit
h the 'I' flag
set should be carried in the DAO message when route set should be carried in the DAO message when route
invalidation is sought for the corresponding target(s). invalidation is sought for the corresponding target or targets.
</t> </t>
<t> <t>
Value 195 represents 'E' and 'A' bit in RPL Status to be set as Value 195 represents the 'U' and 'A' bits in RPL Status, to be s
per Figure 3 of <xref target="I-D.ietf-roll-unaware-leaves"/> et as
with the lower 6 bits with value 3 indicating 'Moved' as per per Figure 6 of <xref target="RFC9010" format="default"/>,
Table 1 of [RFC8505]. with the lower 6 bits set to the 6LoWPAN Neighbor Discovery (ND)
</t> Extended Address Registration Option (EARO) Status value of 3
<t> <figure align="center" anchor="transit_info_with_i" indicating 'Moved' as per Table 1 of <xref target="RFC8505"/>.
title="Updated Transit Information Option (New I flag </t>
added)"> <artwork align="center"><![CDATA[ <figure anchor="transit_info_with_i">
0 1 2 3 <name>Updated Transit Information Option (New &apos;I&apos; Flag Added
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 )</name>
<artwork align="center" name="" type="" alt=""><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
]]></artwork> </figure> </t> </figure>
<t>
I (Invalidate previous route) flag: The 'I' flag is set by the <dl>
<dt>I (Invalidate previous route) flag:</dt><dd>The 'I' flag is
set by the
target node to indicate to the common ancestor node that it target node to indicate to the common ancestor node that it
wishes to invalidate any previous route between the two paths. wishes to invalidate any previous route between the two paths.
</t> </dd>
<t> </dl>
<xref target="RFC6550"/> allows the parent address to be sent in <t>
the Transit Information Option depending on the mode of <xref target="RFC6550" format="default"/> allows the parent addr
operation. In case of storing mode of operation the field is ess to be sent in
usually not needed. In case of DCO, the parent address field the Transit Information option, depending on the MOP.
MUST NOT be included. In the case of the Storing MOP, the field is
</t> usually not needed. In the case of a DCO, the Parent Address fie
<t> ld
The common ancestor node SHOULD generate a DCO message in <bcp14>MUST NOT</bcp14> be included.
response to this 'I' flag when it sees that the routing </t>
adjacencies have changed for the target. The 'I' flag is <t>
Upon receiving a DAO message with a Transit Information option t
hat has the 'I' flag set,
and as a delayed response removing a routing adjacency to the ta
rget indicated in the Transit Information option,
the common ancestor node <bcp14>SHOULD</bcp14> generate a DCO me
ssage
to the next hop associated to that adjacency. The 'I' flag is
intended to give the target node control over its own route intended to give the target node control over its own route
invalidation, serving as a signal to request DCO generation. invalidation, serving as a signal to request DCO generation.
</t> </t>
</section> </section>
<section title="Destination Cleanup Object (DCO)"> <section numbered="true" toc="default">
<t> <name>Destination Cleanup Object (DCO)</name>
<t>
A new ICMPv6 RPL control message code is defined by this A new ICMPv6 RPL control message code is defined by this
specification and is referred to as "Destination Cleanup Object" specification and is referred to as the "Destination Cleanup Obj ect"
(DCO), which is used for proactive cleanup of state and routing (DCO), which is used for proactive cleanup of state and routing
information held on behalf of the target node by 6LRs. The DCO information held on behalf of the target node by 6LRs. The DCO
message always traverses downstream and cleans up route message always traverses downstream and cleans up route
information and other state information associated with the information and other state information associated with the
given target. given target. The format of the DCO message is shown in
</t> <xref target="dco_obj"/>.
</t>
<t> <figure align="center" anchor="dco_obj" <figure anchor="dco_obj">
title="DCO base object"> <name>DCO Base Object</name>
<artwork align="center"><![CDATA[ <artwork align="center" name="" type="" alt=""><![CDATA[
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID |K|D| Flags | RPL Status | DCOSequence | | RPLInstanceID |K|D| Flags | RPL Status | DCOSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ DODAGID(optional) + + DODAGID (optional) +
| | | |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)... | Option(s)...
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+]]></artwork>
]]></artwork> </figure> </t> </figure>
<dl>
<t> <dt> RPLInstanceID:</dt><dd>8-bit field indicating the topology i
RPLInstanceID: 8-bit field indicating the topology instance nstance
associated with the DODAG, as learned from the DIO. associated with the DODAG, as learned from the DIO.
</t> </dd>
<t> <dt>
K: The 'K' flag indicates that the recipient of DCO message is K:</dt><dd>The 'K' flag indicates that the recipient of a DCO me
ssage is
expected to send a DCO-ACK back. If the DCO-ACK is not received expected to send a DCO-ACK back. If the DCO-ACK is not received
even after setting the 'K' flag, an implementation may retry even after setting the 'K' flag, an implementation may retry
the DCO at a later time. The number of retries are the DCO at a later time. The number of retries is
implementation and deployment dependent and are expected to be implementation and deployment dependent and is expected to be
kept similar with those used in DAO retries in <xref kept similar to the number of DAO retries <xref target="RFC6550"
target="RFC6550"/>. <xref target="dco_retry"/> specifies format="default"/>. <xref target="dco_retry" format="default"/> specifies
the considerations for DCO retry. A node receiving a DCO the considerations for DCO retries. A node receiving a DCO
message without the 'K' flag set MAY respond with a DCO-ACK, message without the 'K' flag set <bcp14>MAY</bcp14> respond with
a DCO-ACK,
especially to report an error condition. An example error especially to report an error condition. An example error
condition could be that the node sending the DCO-ACK does not condition could be that the node sending the DCO-ACK does not
find the routing entry for the indicated target. When the find the routing entry for the indicated target. When the
sender does not set the 'K' flag it is an indication that the sender does not set the 'K' flag, it is an indication that the
sender does not expect a response, and the sender SHOULD NOT sender does not expect a response, and the sender <bcp14>SHOULD
NOT</bcp14>
retry the DCO. retry the DCO.
</t> </dd>
<t> <dt>
D: The 'D' flag indicates that the DODAGID field is present. D:</dt><dd>The 'D' flag indicates that the DODAGID field is pres
This flag MUST be set when a local RPLInstanceID is used. ent.
</t> This flag <bcp14>MUST</bcp14> be set when a local RPLInstanceID
<t> is used.
Flags: The 6 bits remaining unused in the Flags field are </dd>
reserved for future use. These bits MUST be initialized to zero <dt>
by Flags:</dt><dd>The 6 bits remaining unused in the Flags field ar
the sender and MUST be ignored by the receiver. e
</t> reserved for future use. These bits <bcp14>MUST</bcp14> be initi
<t> alized to zero by
RPL Status: As defined in <xref target="RFC6550"/> and updated the sender and <bcp14>MUST</bcp14> be ignored by the receiver.
in <xref target="I-D.ietf-roll-unaware-leaves"/>. The root or </dd>
<dt>
RPL Status:</dt><dd>As defined in <xref target="RFC6550" format=
"default"/> and updated
in <xref target="RFC9010" format="default"/>. The root or
common parent that generates a DCO is authoritative for setting common parent that generates a DCO is authoritative for setting
the status information and the information is unchanged as the status information, and the information is unchanged as
propagated down the DODAG. This document does not specify a propagated down the DODAG. This document does not specify a
differentiated action based on the RPL status. differentiated action based on the RPL Status.
</t> </dd>
<t> <dt>
DCOSequence: 8-bit field incremented at each unique DCO message DCOSequence:</dt><dd>8-bit field incremented at each unique DCO
message
from a node and echoed in the DCO-ACK message. The initial from a node and echoed in the DCO-ACK message. The initial
DCOSequence can be chosen randomly by the node. <xref DCOSequence can be chosen randomly by the node. <xref target="ba
target="base_rules"/> explains the handling of the se_rules" format="default"/> explains the handling of the
DCOSequence. DCOSequence.
</t> </dd>
<t> <dt>
DODAGID (optional): 128-bit unsigned integer set by a DODAG DODAGID (optional):</dt><dd>128-bit unsigned integer set by a DO
root that uniquely identifies a DODAG. This field MUST be DAG
present when the 'D' flag is set and MUST NOT be present if 'D' root that uniquely identifies a DODAG. This field <bcp14>MUST</b
flag is not set. DODAGID is used when a local RPLInstanceID is cp14> be
present when the 'D' flag is set and <bcp14>MUST NOT</bcp14> be
present if the 'D'
flag is not set. The DODAGID is used when a local RPLInstanceID
is
in use, in order to identify the DODAGID that is associated in use, in order to identify the DODAGID that is associated
with the RPLInstanceID. with the RPLInstanceID.
</t> </dd>
</dl>
<section title="Secure DCO"> <section numbered="true" toc="default">
<t> <name>Secure DCO</name>
A Secure DCO message follows the format in <xref <t>
target="RFC6550"/> Figure 7, where the base message A Secure DCO message follows the format shown in <xref target="RFC6550
format is the DCO message shown in <xref " format="default"/>, Figure 7, where the base message
target="dco_obj"/>. format is the DCO message shown in <xref target="dco_obj" format="defa
</t> ult"/>
</section> of this document.
</t>
<section title="DCO Options"> </section>
<t> <section numbered="true" toc="default">
The DCO message MUST carry at least one RPL Target and the <name>DCO Options</name>
Transit Information Option and MAY carry other valid <t>
options. This specification allows for the DCO message to The DCO message <bcp14>MUST</bcp14> carry at least one RPL Target and
carry the following options: the
<list> Transit Information option and <bcp14>MAY</bcp14> carry other valid
<t>0x00 Pad1</t> options. This specification allows for the DCO message to
<t>0x01 PadN</t> carry the following options:
<t>0x05 RPL Target</t> </t>
<t>0x06 Transit Information</t> <dl newline="false" spacing="compact">
<t>0x09 RPL Target Descriptor</t> <dt>0x00</dt><dd>Pad1</dd>
</list> <dt>0x01</dt><dd>PadN</dd>
Section 6.7 of <xref target="RFC6550"/> defines all the <dt>0x05</dt><dd>RPL Target</dd>
above mentioned options. The DCO carries an RPL Target <dt>0x06</dt><dd>Transit Information</dd>
Option and an associated Transit Information Option with a <dt>0x09</dt><dd>RPL Target Descriptor</dd>
lifetime of 0x00000000 to indicate a loss of reachability </dl>
to that Target. <t>
</t> <xref target="RFC6550" section="6.7" sectionFormat="of"/> defines all
</section> the
<section title="Path Sequence number in the DCO"> above-mentioned options. The DCO carries a RPL Target
<t> option and an associated Transit Information option with a
A DCO message may contain a Path Sequence in the Transit lifetime of 0x00000000 to indicate a loss of reachability
Information Option to identify the freshness of the DCO to that target.
message. The Path Sequence in the DCO MUST use the same </t>
Path Sequence number present in the regular DAO message </section>
when the DCO is generated in response to a DAO message. <section numbered="true" toc="default">
Thus if a DCO is received by a 6LR and subsequently a DAO <name>Path Sequence in the DCO</name>
is received with an old sequence number, then the DAO <t>
MUST be ignored. When the DCO is generated in response to a A DCO message includes a Transit Information option for each invalidat
DCO from upstream parent, the Path Sequence MUST be copied ed path.
from the received DCO. The value of the Path Sequence counter in the Transit Information opti
</t> on allows identification of the freshness of the DCO
</section> message versus the newest known to the 6LRs along the path being remov
ed.
<section title="Destination Cleanup Option Acknowledgment (DCO-ACK)" If the DCO is generated by a common parent in response to a DAO messag
> e, then the Transit Information option in
<t> the DCO <bcp14>MUST</bcp14> use the value of the Path Sequence as foun
The DCO-ACK message SHOULD be sent as a unicast packet by a d
DCO recipient in response to a unicast DCO message with 'K' in the newest Transit Information option that was received for that ta
flag set. If 'K' flag is not set then the receiver of the rget by the common parent.
DCO message MAY send a DCO-ACK, especially to report an erro If a 6LR down the path receives a DCO with a Path Sequence that is not
r newer than
condition. the Path Sequence as known from a Transit Information option in a DAO
</t> message, then the 6LR
<t> <figure align="center" anchor="dco_ack" title="DCO-ACK base <bcp14>MUST NOT</bcp14> remove its current routing state, and it <bcp1
object"> <artwork align="center"><![CDATA[ 4>MUST NOT</bcp14> forward the DCO
0 1 2 3 down a path where it is not newer. If the DCO is newer, the 6LR may
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 retain a temporary state to ensure that a DAO that is received later
with a Transit Information option with an older sequence number is ign
ored. A Transit Information option in a DAO message
that is as new as or newer than that in a DCO wins, meaning that the p
ath indicated in the DAO is installed and the DAO is propagated. When the DCO is
propagated upon a
DCO from an upstream parent, the Path Sequence <bcp14>MUST</bcp14> be
copied
from the received DCO.
</t>
</section>
<section numbered="true" toc="default">
<name>Destination Cleanup Option Acknowledgment (DCO-ACK)</name>
<t>
The DCO-ACK message <bcp14>SHOULD</bcp14> be sent as a unicast packet
by a
DCO recipient in response to a unicast DCO message with the 'K'
flag set. If the 'K' flag is not set, then the receiver of the
DCO message <bcp14>MAY</bcp14> send a DCO-ACK, especially to report an
error
condition. The format of the DCO-ACK message is shown in
<xref target="dco_ack"/>.
</t>
<figure anchor="dco_ack">
<name>DCO-ACK Base Object</name>
<artwork align="center" name="" type="" alt=""><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID |D| Flags | DCOSequence | DCO-ACK Status| | RPLInstanceID |D| Flags | DCOSequence | DCO-ACK Status|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ DODAGID(optional) + + DODAGID (optional) +
| | | |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
]]></artwork> </figure> </t> </figure>
<dl>
<t> <dt>
RPLInstanceID: 8-bit field indicating the topology instance RPLInstanceID:</dt><dd>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.
</t> </dd>
<t> <dt>
D: The 'D' flag indicates that the DODAGID field is present. D:</dt><dd>The 'D' flag indicates that the DODAGID field is present.
This flag MUST be set when a local RPLInstanceID is used. This flag <bcp14>MUST</bcp14> be set when a local RPLInstanceID is use
</t> d.
<t> </dd>
Flags: 7-bit unused field. The field MUST be initialized to <dt>
zero by the sender and MUST be ignored by the receiver. Flags:</dt><dd>7-bit unused field. The field <bcp14>MUST</bcp14> be in
</t> itialized to
<t> zero by the sender and <bcp14>MUST</bcp14> be ignored by the receiver.
DCOSequence: 8-bit field. The DCOSequence in DCO-ACK is </dd>
copied from the DCOSequence received in the DCO message. <dt>
</t> DCOSequence:</dt><dd>8-bit field. The DCOSequence in the DCO-ACK is
<t> copied from the DCOSequence received in the DCO message.
DCO-ACK Status: Indicates the completion. A value of 0 is </dd>
defined as <dt>
unqualified acceptance in this specification. A value of 1 DCO-ACK Status:</dt><dd>Indicates completion status. The DCO-ACK Statu
is s field is defined based on Figure 6 of <xref target="RFC9010" format="default"/
defined as "No routing-entry for the Target found". The > defining the RPL Status Format. A StatusValue of 0 along with the 'U' bit set
remaining status values are reserved as rejection codes. to 0 indicates Success / Unqualified acceptance as per Figure 6 of <xref target=
</t> "RFC9010" format="default"/>. A StatusValue of 1 with the 'U' bit set to 1 indic
<t> ates 'No routing entry' as defined in <xref target="rpl_reject_status" format="d
DODAGID (optional): 128-bit unsigned integer set by a DODAG efault"/> of this document.
root that uniquely identifies a DODAG. This field MUST be </dd>
present when the 'D' flag is set and MUST NOT be present <dt>
when 'D' flag is not set. DODAGID is used when a local DODAGID (optional):</dt><dd>128-bit unsigned integer set by a DODAG
RPLInstanceID is in use, in order to identify the DODAGID root that uniquely identifies a DODAG. This field <bcp14>MUST</bcp14>
that is associated with the RPLInstanceID. be
</t> present when the 'D' flag is set and <bcp14>MUST NOT</bcp14> be presen
</section> t
when the 'D' flag is not set. The DODAGID is used when a local
<section title="Secure DCO-ACK"> RPLInstanceID is in use, in order to identify the DODAGID
<t> that is associated with the RPLInstanceID.
A Secure DCO-ACK message follows the format in <xref </dd>
target="RFC6550"/> Figure 7, where the base message </dl>
format is the DCO-ACK message shown in <xref
target="dco_ack"/>.
</t>
</section>
</section> </section>
<section numbered="true" toc="default">
<section title="DCO Base Rules" anchor="base_rules"> <name>Secure DCO-ACK</name>
<t> <t>
<list style="numbers"> A Secure DCO-ACK message follows the format shown in <xref target="RFC
<t> 6550" format="default"/>, Figure 7, where the base message
If a node sends a DCO message with newer or different format is the DCO-ACK message shown in <xref target="dco_ack" format="
information than the prior DCO message transmission, it default"/> of this document.
MUST increment the DCOSequence field by at least one. </t>
A DCO message transmission that is identical to the
prior DCO message transmission MAY increment the
DCOSequence field. The DCOSequence counter follows the
sequence counter operation as defined in Section 7.2 of
<xref target="RFC6550"/>.
</t>
<t>
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.
</t>
<t>
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.
</t>
<t>
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.
</t>
<t>
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, newer than
the Path Sequence received in the DCO, then the DCO
MUST be dropped.
</t>
<t>
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.
</t>
<t>
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.
</t>
</list>
</t>
<t>
The scope of DCOSequence values is unique to the node which
generates it.
</t>
</section> </section>
</section>
<section title="Unsolicited DCO"> <section anchor="base_rules" numbered="true" toc="default">
<t> <name>DCO Base Rules</name>
A 6LR may generate an unsolicited DCO to unilaterally cleanup <ol spacing="normal" type="1"><li>
If a node sends a DCO message with newer or different
information than the prior DCO message transmission, it
<bcp14>MUST</bcp14> increment the DCOSequence field by at least on
e.
A DCO message transmission that is identical to the
prior DCO message transmission <bcp14>MAY</bcp14> increment the
DCOSequence field. The DCOSequence counter follows the
sequence counter operation as defined in
<xref target="RFC6550" section="7.2" sectionFormat="of"/>.
</li>
<li>
The RPLInstanceID and DODAGID fields of a DCO message
<bcp14>MUST</bcp14> have the same values as those contained in the
DAO message in
response to which the DCO is generated on the common
ancestor node.
</li>
<li>
A node <bcp14>MAY</bcp14> set the 'K' flag in a unicast DCO messag
e to
solicit a unicast DCO-ACK in response, in order to
confirm the attempt.
</li>
<li>
A node receiving a unicast DCO message with the 'K'
flag set <bcp14>SHOULD</bcp14> respond with a DCO-ACK. A node
receiving a DCO message without the 'K' flag set <bcp14>MAY</bcp14
>
respond with a DCO-ACK, especially to report an error
condition.
</li>
<li>
A node receiving a unicast DCO message <bcp14>MUST</bcp14> verify
the
stored Path Sequence in context to the given target. If
the stored Path Sequence is as new as or newer than
the Path Sequence received in the DCO, then the DCO
<bcp14>MUST</bcp14> be dropped.
</li>
<li>
A node that sets the 'K' flag in a unicast DCO message
but does not receive a DCO-ACK in response <bcp14>MAY</bcp14> resc
hedule
the DCO message transmission for another attempt, up
until an implementation-specific number of retries.
</li>
<li>
A node receiving a unicast DCO message with its own
address in the RPL Target option <bcp14>MUST</bcp14> strip off tha
t
Target option. If this Target option is the only one in
the DCO message, then the DCO message <bcp14>MUST</bcp14> be dropp
ed.
</li>
</ol>
<t>
The scope of DCOSequence values is unique to the node that
generates them.
</t>
</section>
<section numbered="true" toc="default">
<name>Unsolicited DCO</name>
<t>
A 6LR may generate an unsolicited DCO to unilaterally clean up
the path on behalf of the target entry. The 6LR has all the the path on behalf of the target entry. The 6LR has all the
state information, namely, the Target address and the Path state information, namely, the Target Address and the Path
Sequence, required for generating DCO in its routing table. Sequence, required for generating a DCO in its routing table.
The conditions why 6LR may generate an unsolicited DCO are The conditions under which a 6LR may generate an unsolicited DCO
beyond the scope of this document but some possible reasons are
could be: beyond the scope of this document, but possible reasons
<list style="numbers"> could be as follows:
<t> </t>
On route expiry of an entry, a 6LR may decide to <ol spacing="normal" type="1"><li>
graciously cleanup the entry by initiating DCO. On route expiry of an entry, a 6LR may decide to
</t> graciously clean up the entry by initiating a DCO.
<t> </li>
6LR needs to entertain higher priority entries in case <li>
the routing table is full, thus resulting in eviction A 6LR needs to entertain higher-priority entries in case
of an existing routing entry. In this case the eviction the routing table is full, thus resulting in eviction
can be handled graciously using DCO. of an existing routing entry. In this case, the eviction
</t> can be handled graciously by using a DCO.
</list> </li>
</t> </ol>
<t> <t>
Note that if the 6LR initiates a unilateral path cleanup using A DCO that is generated asynchronously to a DAO message and is meant t
DCO and if it has the latest state for the target then the DCO o
would finally reach the target node. Thus the target node would discard all state along the path regardless of the Path Sequence <bcp1
be informed of its invalidation. 4>MUST</bcp14>
</t> use a Path Sequence value of 240 (see <xref target="RFC6550" section="
7.2" sectionFormat="of"/>).
This value allows the DCO to win against any established DAO path but
to lose against a DAO path that is being installed.
Note that if an ancestor initiates a unilateral path cleanup on an
established path using a DCO with a Path Sequence value of 240, the
DCO will eventually reach the target node, which will thus be informed
of the path invalidation.
</t>
</section>
<section numbered="true" toc="default">
<name>Other Considerations</name>
<section numbered="true" toc="default">
<name>Invalidation of Dependent Nodes</name>
<t>
The RPL specification <xref target="RFC6550" format="default"/> does n
ot provide a
mechanism for route invalidation for dependent nodes. This
document allows the invalidation of dependent nodes. Dependent
nodes will generate their respective DAOs to update their
paths, and the previous route invalidation for those nodes
should work in a manner similar to what is described for a switching
node. The dependent node may set the 'I' flag in the Transit
Information option as part of a regular DAO so as to
request invalidation of the previous route from the common
ancestor node.
</t>
<t>
Dependent nodes do not have any indication regarding whether any
of their parents have in turn decided to switch their
parent. Thus, for route invalidation, the dependent nodes may
choose to always set the 'I' flag in all their DAO messages'
Transit Information options. Note that setting the 'I' flag is
not counterproductive even if there is no previous
route to be invalidated.
</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Other considerations"> <name>NPDAO and DCO in the Same Network</name>
<section title="Dependent Nodes invalidation"> <t>
<t> The NPDAO mechanism provided in <xref target="RFC6550" format="default
Current RPL <xref target="RFC6550"/> does not provide a "/> can
mechanism for route invalidation for dependent nodes. This still be used in the same network where a DCO is used.
document allows the dependent nodes invalidation. Dependent NPDAO messaging can be used, for example, on route lifetime
nodes will generate their respective DAOs to update their expiry of the target or when the node simply decides to
paths, and the previous route invalidation for those nodes gracefully terminate the RPL session on graceful node
should work in the similar manner described for switching shutdown. Moreover, a deployment can have a mix of nodes
node. The dependent node may set the 'I' flag in the Transit supporting the DCO and the existing NPDAO mechanism. It is
Information Option as part of regular DAO so as to also possible that the same node supports both NPDAO
request invalidation of previous route from the common and DCO signaling for route invalidation.
ancestor node. </t>
</t> <t>
<t> <xref target="RFC6550" section="9.8" sectionFormat="of"/> states, "Whe
Dependent nodes do not have any indication regarding if any n a
of their parents in turn have decided to switch their node removes a node from its DAO parent set, it <bcp14>SHOULD</bcp14>
parent. Thus for route invalidation the dependent nodes may send a No-Path DAO message (Section 6.4.3) to that removed DAO parent
choose to always set the 'I' flag in all its DAO message's to
Transit Information Option. Note that setting the 'I' flag i invalidate the existing route." This document introduces
s an alternative and more optimized way to perform route invalidation,
not counterproductive even if there is no previous but it also allows existing NPDAO messaging to work. Thus,
route to be invalidated. an implementation has two choices to make when a route
</t> invalidation is to be initiated:
</section> </t>
<section title="NPDAO and DCO in the same network"> <ol spacing="normal" type="1"><li>
<t> Use an NPDAO to invalidate the previous route, and
The current NPDAO mechanism in <xref target="RFC6550"/> can send a regular DAO on the new path.
still be used in the same network where DCO is used. The </li>
NPDAO messaging can be used, for example, on route lifetime <li>
expiry of the target or when the node simply decides to Send a regular DAO on the new path with the 'I'
gracefully terminate the RPL session on graceful node flag set in the Transit Information option such
shutdown. Moreover, a deployment can have a mix of nodes that the common ancestor node initiates the DCO
supporting the DCO and the existing NPDAO mechanism. It is message downstream to invalidate the previous
also possible that the same node supports both the NPDAO route.
and DCO signaling for route invalidation. </li>
</t> </ol>
<t> <t>
Section 9.8 of <xref target="RFC6550"/> states, "When a This document recommends using option 2, for the reasons
node removes a node from its DAO parent set, it SHOULD specified in <xref target="requirements" format="default"/>
send a No-Path DAO message to that removed DAO parent to of this document.
invalidate the existing router". This document introduces </t>
an alternative and more optimized way of route invalidation <t>
but it also allows existing NPDAO messaging to work. Thus This document assumes that all the 6LRs in the network
an implementation has two choices to make when a route support this specification. If there are 6LR nodes that do not support
invalidation is to be initiated: this document that are in the path of the DCO message transmission, then the
</t> route invalidation for the corresponding targets (targets that are in
<t> the DCO message) may not work
<list style="numbers"> or may work partially. Alternatively, a node
<t> could generate an NPDAO if it does not receive a DCO with
Use NPDAO to invalidate the previous route and itself as the target within a specified time limit. The specified
send regular DAO on the new path. time limit is deployment specific and depends upon the
</t> maximum depth of the network and per-hop average latency.
<t> Note that sending an NPDAO and a DCO for the same operation
Send regular DAO on the new path with the 'I' would not result in unwanted side effects because the
flag set in the Transit Information Option such acceptability of an NPDAO or a DCO depends upon the Path
that the common ancestor node initiates the DCO Sequence freshness.
message downstream to invalidate the previous </t>
route. </section>
</t> <section anchor="dco_retry" numbered="true" toc="default">
</list> <name>Considerations for DCO Retries</name>
</t> <t>
<t> A DCO message could be retried by a sender if it sets the
This document recommends using option 2 for reasons 'K' flag and does not receive a DCO-ACK. The DCO retry time
specified in <xref target="requirements"/> in this could be dependent on the maximum depth of the network and
document. average per-hop latency. This could range from 2 seconds to
</t> 120 seconds, depending on the deployment. If the
<t> latency limits are not known, an implementation <bcp14>MUST NOT</bcp14
This document assumes that all the 6LRs in the network >
support this specification. If there are 6LRs en-route DCO retry more than once in 3 seconds and <bcp14>MUST NOT</bcp14> retry mo
message path which do not support this document, then the re
route invalidation for corresponding targets may not work than three times.
or may work partially i.e., only part of the path </t>
supporting DCO may be invalidated. Alternatively, a node <t>
could generate an NPDAO if it does not receive a DCO with The number of retries could also be set depending on how
itself as target within specified time limit. The specified critical the route invalidation could be for the deployment
time limit is deployment specific and depends upon the and the link-layer retry configuration. For networks
maximum depth of the network and per hop average latency. supporting only Multi-Point to Point (MP2P) and Point-to-Multipoint (P
Note that sending NPDAO and DCO for the same operation 2MP) flows, such as in Advanced Metering Infrastructure (AMI) and
would not result in unwanted side-effects because the telemetry applications, the 6LRs may not be very keen to
acceptability of NPDAO or DCO depends upon the Path invalidate routes, unless they are highly
Sequence freshness. memory constrained. For home and building automation
</t> networks that may have substantial P2P traffic, the 6LRs
</section> might be keen to invalidate efficiently because it may
<section title="Considerations for DCO retry" anchor="dco_retry"> additionally impact forwarding efficiency.
<t> </t>
A DCO message could be retried by a sender if it sets the </section>
'K' flag and does not receive a DCO-ACK. The DCO retry time <section numbered="true" toc="default">
could be dependent on the maximum depth of the network and <name>DCO with Multiple Preferred Parents</name>
average per hop latency. This could range from 2 seconds to <t>
120 seconds depending on the deployment. In case the <xref target="RFC6550" format="default"/> allows a node to select mult
latency limits are not known, an implementation MUST NOT iple
retry more than once in 3 seconds and MUST NOT retry more preferred parents for route establishment.
than 3 times. <xref target="RFC6550" section="9.2.1" sectionFormat="of"/> specifies,
</t> "All DAOs generated
<t> at the same time for the same target <bcp14>MUST</bcp14> be sent with
The number of retries could also be set depending on how the
critical the route invalidation could be for the deployment same Path Sequence in the Transit Information."
and the link layer retry configuration. For networks Subsequently, when route invalidation has to be initiated,
supporting only MP2P and P2MP flows, such as in AMI and an NPDAO, which can be initiated with an
telemetry applications, the 6LRs may not be very keen to updated Path Sequence to all the parent nodes through which
invalidate routes, unless they are highly the route is to be invalidated, can be used; see <xref target="RFC6550
memory-constrained. For home and building automation "/>.
networks which may have substantial P2P traffic, the 6LRs </t>
might be keen to invalidate efficiently because it may <t>
additionally impact the forwarding efficiency. With a DCO, the target node itself does not initiate the
</t> route invalidation; this is left to the common ancestor
</section> node. A common ancestor node when it discovers an updated
<section title="DCO with multiple preferred parents"> DAO from a new next hop, it initiates a DCO. It is recommended
<t> that an implementation initiate a DCO after a time period (DelayDCO) s
<xref target="RFC6550"/> allows a node to select multiple uch that
preferred parents for route establishment. Section 9.2.1 the common ancestor node may receive updated DAOs from all
of <xref target="RFC6550"/> specifies, "All DAOs generated possible next hops. This will help to reduce DCO control
at the same time for the same Target MUST be sent with the overhead, i.e., the common ancestor can wait for updated
same Path Sequence in the Transit Information". DAOs from all possible directions before initiating a DCO
Subsequently when route invalidation has to be initiated, for route invalidation. After timeout, the DCO needs to be
RPL mentions use of NPDAO which can be initiated with an generated for all the next hops for which the route
updated Path Sequence to all the parent nodes through which invalidation needs to be done.
the route is to be invalidated. </t>
</t> <t>
<t> This document recommends using a DelayDCO timer value of
With DCO, the Target node itself does not initiate the 1 second. This value is inspired by the default DelayDAO timer value
route invalidation and it is left to the common ancestor of 1 second <xref target="RFC6550" format="default"/>. Here, the hypot
node. A common ancestor node when it discovers an updated hesis is
DAO from a new next-hop, it initiates a DCO. With multiple that the DAOs from all possible parent sets would be
preferred parents, this handling does not change. But in received on the common ancestor within this time period.
this case it is recommended that an implementation </t>
initiates a DCO after a time period (DelayDCO) such that <t>
the common ancestor node may receive updated DAOs from all It is still possible that a DCO is generated before all the
possible next-hops. This will help to reduce DCO control updated DAOs from all the paths are received. In this case,
overhead i.e., the common ancestor can wait for updated the ancestor node would start the invalidation procedure
DAOs from all possible directions before initiating a DCO for paths from which the updated DAO is not received. The
for route invalidation. After timeout, the DCO needs to be DCO generated in this case would start invalidating the
generated for all the next-hops for whom the route segments along these paths on which the updated DAOs are
invalidation needs to be done. not received. But once the DAO reaches these segments, the
</t> routing state would be updated along these segments; this
<t> should not lead to any inconsistent routing states.
This document recommends using a DelayDCO timer value of </t>
1sec. This value is inspired by the default DelayDAO value <t>
of 1sec in <xref target="RFC6550"/>. Here the hypothesis is Note that there is no requirement for synchronization
that the DAOs from all possible parent sets would be between a DCO and DAOs. The DelayDCO timer simply ensures
received on the common ancestor within this time period. that DCO control overhead can be reduced and is only
</t> needed when the network contains nodes using multiple
<t> preferred parents.
It is still possible that a DCO is generated before all the </t>
updated DAOs from all the paths are received. In this case,
the ancestor node would start the invalidation procedure
for paths from which the updated DAO is not received. The
DCO generated in this case would start invalidating the
segments along these paths on which the updated DAOs are
not received. But once the DAO reaches these segments, the
routing state would be updated along these segments and
should not lead to any inconsistent routing state.
</t>
<t>
Note that there is no requirement for 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.
</t>
</section>
</section> </section>
</section>
</section> </section>
<section anchor="IANA" numbered="true" toc="default">
<name>IANA Considerations</name>
<t>
IANA has allocated codes for the DCO and DCO-ACK
messages from the "RPL Control Codes" registry.
</t>
<table align="center">
<name>New Codes for DCO and DCO-ACK Messages</name>
<thead>
<tr>
<th align="center">Code</th>
<th align="center">Description</th>
<th align="center">Reference</th>
</tr>
</thead>
<tbody>
<tr>
<td align="center">0x07</td>
<td align="center">Destination Cleanup Object</td>
<td align="center">This document</td>
</tr>
<tr>
<td align="center">0x08</td>
<td align="center">Destination Cleanup Object Acknowledgment</td>
<td align="center">This document</td>
</tr>
<tr>
<td align="center">0x87</td>
<td align="center">Secure Destination Cleanup Object</td>
<td align="center">This document</td>
</tr>
<tr>
<td align="center">0x88</td>
<td align="center">Secure Destination Cleanup Object Acknowledgment<
/td>
<td align="center">This document</td>
</tr>
</tbody>
</table>
<section anchor="Acknowledgments" title="Acknowledgments"> <t>
IANA has allocated bit 1 from the "Transit Information
Option Flags" registry for the 'I' flag (Invalidate previous route;
see <xref target="transit_opt_changes" format="default"/>).
</t>
<section numbered="true" toc="default">
<name>New Registry for the Destination Cleanup Object (DCO) Flags</name>
<t> <t>
Many thanks to Alvaro Retana, Cenk Gundogan, Simon Duquennoy, Georgi IANA has created a registry for the 8-bit Destination Cleanup
os Object (DCO) Flags field. The "Destination Cleanup Object
Papadopoulous, Peter Van Der Stok for their review and comments. (DCO) Flags" registry is located in the "Routing Protocol for
Alvaro Retana helped shape this document's final version with Low Power and Lossy Networks (RPL)" registry.
critical review comments.
</t> </t>
</section>
<!-- Possibly a 'Contributors' section ... -->
<section anchor="IANA" title="IANA Considerations">
<t> <t>
IANA is requested to allocate new codes for the DCO and DCO-ACK New bit numbers may be allocated only by IETF Review
messages from the RPL Control Codes registry. <xref target="RFC8126"/>. Each
bit is tracked with the following qualities:
</t> </t>
<ul spacing="normal">
<texttable title=""> <li>Bit number (counting from bit 0 as the most significant bit)</li>
<ttcol align='center'>Code</ttcol> <li>Capability description</li>
<ttcol align='center'>Description</ttcol> <li>Defining RFC</li>
<ttcol align='center'>Reference</ttcol> </ul>
<c>TBD1</c>
<c>Destination Cleanup Object</c>
<c>This document</c>
<c>TBD2</c>
<c>Destination Cleanup Object Acknowledgment</c>
<c>This document</c>
<c>TBD3</c>
<c>Secure Destination Cleanup Object</c>
<c>This document</c>
<c>TBD4</c>
<c>Secure Destination Cleanup Object Acknowledgment</c>
<c>This document</c>
</texttable>
<t> <t>
IANA is requested to allocate bit 1 from the Transit Information
Option Flags registry for the 'I' flag (<xref target="transit_opt_ch
anges"/>)
</t>
<section title="New Registry for the Destination Cleanup Object (DCO) Fl
ags">
<t>
IANA is requested to create a registry for the 8-bit Destination
Cleanup
Object (DCO) Flags field. This registry should be located in
existing category of "Routing Protocol for Low Power and Lossy
Networks (RPL)".
</t>
<t>
New bit numbers may be allocated only by an IETF Review. Each
bit is tracked with the following qualities:
</t>
<t>
<list style="symbols">
<t>Bit number (counting from bit 0 as the most significant b
it)</t>
<t>Capability description</t>
<t>Defining RFC</t>
</list>
</t>
<t>
The following bits are currently defined: The following bits are currently defined:
</t> </t>
<texttable title="DCO Base Flags"> <table align="center">
<ttcol align='center'>Bit number</ttcol> <name>DCO Base Flags</name>
<ttcol align='center'>Description</ttcol> <thead>
<ttcol align='center'>Reference</ttcol> <tr>
<c>0</c> <th align="center">Bit number</th>
<c>DCO-ACK request (K)</c> <th align="center">Description</th>
<c>This document</c> <th align="center">Reference</th>
</tr>
<c>1</c> </thead>
<c>DODAGID field is present (D)</c> <tbody>
<c>This document</c> <tr>
</texttable> <td align="center">0</td>
</section> <td align="center">DCO-ACK request (K)</td>
<section title="New Registry for the Destination Cleanup Object Acknowle <td align="center">This document</td>
dgment (DCO-ACK) Status field"> </tr>
<t> <tr>
IANA is requested to create a registry for the 8-bit Destination <td align="center">1</td>
Cleanup <td align="center">DODAGID field is present (D)</td>
Object Acknowledgment (DCO-ACK) Status field. This registry <td align="center">This document</td>
should be located in existing category of "Routing Protocol for </tr>
Low Power and Lossy Networks (RPL)". </tbody>
</t> </table>
<t> </section>
New Status values may be allocated only by an IETF Review. Each <section numbered="true" toc="default">
value is tracked with the following qualities: <name>New Registry for the Destination Cleanup Object (DCO) Acknowledgme
</t> nt Flags</name>
<t> <t>
<list style="symbols"> IANA has created a registry for the 8-bit
<t>Status Code</t>
<t>Description</t>
<t>Defining RFC</t>
</list>
</t>
<t>
The following values are currently defined:
</t>
<texttable title="DCO-ACK Status Codes">
<ttcol align='center'>Status Code</ttcol>
<ttcol align='center'>Description</ttcol>
<ttcol align='center'>Reference</ttcol>
<c>0</c>
<c>Unqualified acceptance</c>
<c>This document</c>
<c>1</c>
<c>No routing-entry for the indicated Target found</c>
<c>This document</c>
</texttable>
</section>
<section title="New Registry for the Destination Cleanup Object (DCO)
Acknowledgment Flags">
<t>
IANA is requested to create a registry for the 8-bit
Destination Cleanup Object (DCO) Acknowledgment Flags field. Destination Cleanup Object (DCO) Acknowledgment Flags field.
This registry should be located in existing category of The "Destination Cleanup Object (DCO) Acknowledgment Flags" regi
"Routing Protocol for Low Power and Lossy Networks (RPL)". stry
</t> is located in the
<t> "Routing Protocol for Low Power and Lossy Networks (RPL)" regist
New bit numbers may be allocated only by an IETF Review. Each ry.
</t>
<t>
New bit numbers may be allocated only by IETF Review
<xref target="RFC8126"/>. Each
bit is tracked with the following qualities: bit is tracked with the following qualities:
</t> </t>
<t> <ul spacing="normal">
<list style="symbols"> <li>Bit number (counting from bit 0 as the most significant bit)</li>
<t>Bit number (counting from bit 0 as the most significant b <li>Capability description</li>
it)</t> <li>Defining RFC</li>
<t>Capability description</t> </ul>
<t>Defining RFC</t> <t>
</list> The following bit is currently defined:
</t> </t>
<t> <table align="center">
The following bits are currently defined: <name>DCO-ACK Base Flag</name>
</t> <thead>
<texttable title="DCO-ACK Base Flags"> <tr>
<ttcol align='center'>Bit number</ttcol> <th align="center">Bit number</th>
<ttcol align='center'>Description</ttcol> <th align="center">Description</th>
<ttcol align='center'>Reference</ttcol> <th align="center">Reference</th>
<c>0</c> </tr>
<c>DODAGID field is present (D)</c> </thead>
<c>This document</c> <tbody>
</texttable> <tr>
</section> <td align="center">0</td>
</section> <td align="center">DODAGID field is present (D)</td>
<td align="center">This document</td>
<section anchor="Security" title="Security Considerations"> </tr>
</tbody>
</table>
</section>
<section anchor="rpl_reject_status" numbered="true" toc="default">
<name>RPL Rejection Status Values</name>
<t> <t>
This document adds a new status value to the "RPL Rejection Status" s
ubregistry initially created per <xref target="RFC9010" sectionFormat="of" secti
on="12.6"/>.
</t>
<table align="center">
<name>Rejection Value of the RPL Status</name>
<thead>
<tr>
<th align="center">Value</th>
<th align="center">Meaning</th>
<th align="center">Reference</th>
</tr>
</thead>
<tbody>
<tr>
<td align="center">1</td>
<td align="center">No routing entry</td>
<td align="center">This document</td>
</tr>
</tbody>
</table>
</section>
</section>
<section anchor="Security" numbered="true" toc="default">
<name>Security Considerations</name>
<t>
This document introduces the ability for a common ancestor node to This document introduces the ability for a common ancestor node to
invalidate a route on behalf of the target node. The common invalidate a route on behalf of the target node. The common
ancestor node could be directed to do so by the target node using ancestor node could be directed to do so by the target node, using
the 'I' flag in DCO's Transit Information Option. However, the commo the 'I' flag in a DCO's Transit Information option. However, the com
n mon
ancestor node is in a position to unilaterally initiate the route ancestor node is in a position to unilaterally initiate the route
invalidation since it possesses all the required state information, invalidation, since it possesses all the required state information,
namely, the Target address and the corresponding Path Sequence. namely, the Target Address and the corresponding Path Sequence.
Thus a rogue common ancestor node could initiate such an Thus, a rogue common ancestor node could initiate such an
invalidation and impact the traffic to the target node. invalidation and impact the traffic to the target node.
</t> </t>
<t> The DCO carries a RPL Status value, which is informative. New Status <t> The DCO carries a RPL Status value, which is informative. New Status
values may be created over time and a node will ignore an unknown values may be created over time, and a node will ignore an unknown
Status value. This enables RPL Status field to be Status value. This enables the RPL Status field to be
used as a cover channel. But the channel only works once since the used as a cover channel. But the channel only works once, since the
message destroys its own medium, that is the existing route that it message destroys its own medium, i.e., the existing route that it
is removing. is removing.
</t> </t>
<t> <t>
This document also introduces an 'I' flag which is set by the target This document also introduces an 'I' flag, which is set by the targe
t
node and used by the ancestor node to initiate a DCO if the node and used by the ancestor node to initiate a DCO if the
ancestor sees an update in the route adjacency. However, ancestor sees an update in the routing adjacency. However,
this flag could be spoofed by a malicious 6LR in the path and can this flag could be spoofed by a malicious 6LR in the path and can
cause invalidation of an existing active path. Note that invalidatio n cause invalidation of an existing active path. Note that invalidatio n
will happen only if the other conditions such as Path Sequence will work only if the Path Sequence condition is also met for the
condition is also met. Having said that, such a malicious 6LR may target for which the invalidation is attempted. Having said that, su
ch a malicious 6LR may
spoof a DAO on behalf of the (sub) child with the 'I' flag set and spoof a DAO on behalf of the (sub) child with the 'I' flag set and
can cause route invalidation on behalf of the (sub) child node. can cause route invalidation on behalf of the (sub) child node.
Note that, using existing mechanisms offered by <xref Note that by using existing mechanisms offered by <xref target="RFC6
target="RFC6550"/>, a malicious 6LR might also spoof a DAO with 550" format="default"/>, a malicious 6LR might also spoof a DAO with a
lifetime of zero or otherwise cause denial of service by dropping lifetime of zero or otherwise cause denial of service by dropping
traffic entirely, so the new mechanism described in this document traffic entirely, so the new mechanism described in this document
does not present a substantially increased risk of disruption. does not present a substantially increased risk of disruption.
</t> </t>
<t> <t>
This document assumes that the security mechanisms as defined in This document assumes that the security mechanisms as defined in
<xref target="RFC6550"/> are followed, which means that the common <xref target="RFC6550" format="default"/> are followed, which means that the common
ancestor node and all the 6LRs are part of the RPL network because ancestor node and all the 6LRs are part of the RPL network because
they have the required credentials. A non-secure RPL network needs they have the required credentials. A non-secure RPL network needs
to take into consideration the risks highlighted in this section as to take into consideration the risks highlighted in this section as
well as those highlighted in <xref target="RFC6550"/>. well as those highlighted in <xref target="RFC6550" format="default"
</t> />.
<t> </t>
All RPL messages support a secure version of messages which allows <t>
integrity protection using either a MAC or a signature. Optionally, All RPL messages support a secure version of messages; this allows
integrity protection using either a Message Authentication Code (MAC
) or a signature. Optionally,
secured RPL messages also have encryption protection for secured RPL messages also have encryption protection for
confidentiality. confidentiality.
</t> </t>
<t> <t>
The document adds new messages (DCO, DCO-ACK) which are This document adds new messages (DCO and DCO-ACK) that are
syntactically similar to existing RPL messages such as DAO, syntactically similar to existing RPL messages such as DAO and
DAO-ACK. Secure versions of DCO and DCO-ACK are added similar to DAO-ACK. Secure versions of DCO and DCO-ACK messages are added in a
other RPL messages (such as DAO, DAO-ACK). way that is similar to the technique used for other RPL messages (such as DAO an
</t> d DAO-ACK).
<t> </t>
RPL supports three security modes as mentioned in Section 10.1 of <t>
<xref target="RFC6550"/>: RPL supports three security modes, as mentioned in
<list style="numbers"> <xref target="RFC6550" section="10.1" sectionFormat="of"/>:
<t> </t>
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.
Also note that unsecured mode does not imply that all
messages are sent without any protection.
</t>
<t>
Preinstalled: In this mode, RPL uses secure messages. Thus
secure versions of DCO, DCO-ACK MUST be used in this mode.
</t>
<t>
Authenticated: In this mode, RPL uses secure messages. Thus
secure versions of DCO, DCO-ACK MUST be used in this mode.
</t>
</list>
</t>
</section>
</middle>
<back>
<!-- References split into informative and normative -->
<!-- There are 2 ways to insert reference entries from the citation librarie <dl newline="false" spacing="normal">
s: <dt>Unsecured:</dt><dd>In this mode, it is expected that the RPL contr
1. define an ENTITY at the top, and use "ampersand character"RFC2629; here ol messages
(as shown) are secured by other security mechanisms, such as
2. simply use a PI "less than character"?rfc include="reference.RFC.2119.xm link-layer security. In this mode, the RPL control messages,
l"?> here including DCO and DCO-ACK messages, do not have Security sections.
(for I-Ds: include="reference.I-D.narten-iana-considerations-rfc2434bis. Also note that unsecured mode does not imply that all
xml") messages are sent without any protection.</dd>
<dt>Preinstalled:</dt><dd>In this mode, RPL uses secure messages. Thus
,
secure versions of DCO and DCO-ACK messages <bcp14>MUST</bcp14> be use
d in this mode.</dd>
<dt>Authenticated:</dt><dd>In this mode, RPL uses secure messages. Thu
s,
secure versions of DCO and DCO-ACK messages <bcp14>MUST</bcp14> be use
d in this mode.</dd>
</dl>
</section>
</middle>
<back>
<references>
<name>Normative References</name>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC
.6550.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC
.2119.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC
.8174.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC
.8505.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC
.8126.xml"/>
Both are cited textually in the same manner: by using xref elements. <!-- draft-ietf-roll-unaware-leaves (RFC 9010) -->
If you use the PI option, xml2rfc will, by default, try to find included fi <reference anchor='RFC9010' target="https://www.rfc-editor.org/info/rfc9010">
les in the same <front>
directory as the including file. You can also define the XML_LIBRARY enviro <title>Routing for RPL (Routing Protocol for Low-Power and Lossy Networks) Leave
nment variable s</title>
with a value containing a set of directories to search. These can be either <author initials='P' surname='Thubert' fullname='Pascal Thubert' role="editor">
in the local <organization />
filing system or remote ones accessed by http (http://domain/dir/... ).--> </author>
<author initials='M' surname='Richardson' fullname='Michael Richardson'>
<organization />
</author>
<date month='April' year='2021' />
</front>
<seriesInfo name="RFC" value="9010"/>
<seriesInfo name="DOI" value="10.17487/RFC9010"/>
</reference>
<references title="Normative References">
<!--?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RF
C.2119.xml"?-->
&RFC6550;
&RFC2119;
&RFC8174;
<?rfc include='reference.I-D.ietf-roll-unaware-leaves.xml'?>
</references> </references>
<section anchor="app-additional" numbered="true" toc="default">
<section anchor="app-additional" title="Example Messaging"> <name>Example Messaging</name>
<section title="Example DCO Messaging"> <section numbered="true" toc="default">
<name>Example DCO Messaging</name>
<t> <t>
In <xref target="sample_top"/>, node (D) switches its parent from In this example, Node D (<xref target="sample_top" format="default"/
(B) to (C). This example assumes that Node D has already >)
switches its parent from
B to C. This example assumes that Node D has already
established its own route via Node B-G-A-6LBR using pathseq=x. The established its own route via Node B-G-A-6LBR using pathseq=x. The
example uses DAO and DCO messaging convention and specifies only example uses DAO and DCO messaging conventions and specifies only
the required parameters to explain the example namely, the the required parameters to explain the example, namely, the
parameter 'tgt', which stands for Target Option and value of this parameter 'tgt', which stands for "Target option"; the value of this
parameter specifies the address of the target node. The parameter parameter specifies the address of the target node. The parameter
'pathseq', which specifies the Path Sequence value carried in the 'pathseq' specifies the Path Sequence value carried in the
Transit Information Option. The parameter 'I_flag' specifies the Transit Information option, and the parameter 'I_flag' specifies the
'I' flag in the Transit Information Option. 'I' flag in the Transit Information option. The
sequence of actions is as follows: sequence of actions is as follows:
<list style="numbers"> </t>
<t>Node D switches its parent from node B to node C</t> <ol spacing="normal" type="1"><li>Node D switches its parent from Node B
to Node C.</li>
<t>D sends a regular DAO(tgt=D,pathseq=x+1,I_flag=1) in the <li>D sends a regular DAO(tgt=D,pathseq=x+1,I_flag=1) in the
updated path to C</t> updated path to C.</li>
<li>C checks for a routing entry on behalf of D; since it cannot
<t>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
find an entry on behalf of D it creates a new routing entry and forwards the reachability information of the target D
and forwards the reachability information of the target D to H in a DAO(tgt=D,pathseq=x+1,I_flag=1).</li>
to H in a DAO(tgt=D,pathseq=x+1,I_flag=1).</t> <li>Similar to C, Node H checks for a routing entry on behalf of
D, cannot find an entry, and hence creates a new routing
<t>Similar to C, node H checks for a routing entry on behalf of entry and forwards the reachability information of the
D, cannot find an entry and hence creates a new routing target D to A in a DAO(tgt=D,pathseq=x+1,I_flag=1).</li>
entry and forwards the reachability information of the <li>
target D to A in a DAO(tgt=D,pathseq=x+1,I_flag=1).</t> Node A receives the DAO(tgt=D,pathseq=x+1,I_flag=1) and
checks for a routing entry on behalf of D. It finds a
<t> routing entry but checks that the next hop for target D is
Node A receives the DAO(tgt=D,pathseq=x+1,I_flag=1), and different (i.e., Node G). Node A checks the I_flag and
checks for a routing entry on behalf of D. It finds a generates the DCO(tgt=D,pathseq=x+1) to the previous next hop for
routing entry but checks that the next hop for target D is target D, which is G. Subsequently, Node A updates the
different (i.e., Node G). Node A checks the I_flag and routing entry and forwards the reachability information of
generates DCO(tgt=D,pathseq=x+1) to previous next hop for target D upstream using the DAO(tgt=D,pathseq=x+1,I_flag=1).
target D which is G. Subsequently, Node A updates the </li>
routing entry and forwards the reachability information of <li>
target D upstream DAO(tgt=D,pathseq=x+1,I_flag=1). Node G receives the DCO(tgt=D,pathseq=x+1). It checks to see if
</t> the received Path Sequence is later than the stored Path
Sequence. If it is later, Node G invalidates the routing entry
<t> of target D and forwards the (un)reachability information
Node G receives the DCO(tgt=D,pathseq=x+1). It checks if downstream to B in the DCO(tgt=D,pathseq=x+1).
the received path sequence is later than the stored path </li>
sequence. If it is later, Node G invalidates the routing ent <li>
ry Similarly, B processes the DCO(tgt=D,pathseq=x+1) by
of target D and forwards the (un)reachability information invalidating the routing entry of target D and forwards the
downstream to B in DCO(tgt=D,pathseq=x+1). (un)reachability information downstream to D.
</t> </li>
<li>
<t> D ignores the DCO(tgt=D,pathseq=x+1), since the target is
Similarly, B processes the DCO(tgt=D,pathseq=x+1) by itself.
invalidating the routing entry of target D and forwards the </li>
(un)reachability information downstream to D. <li>
</t> The propagation of the DCO will stop at any node where the
node does not have routing information associated with
<t> the target. If cached routing information is present and
D ignores the DCO(tgt=D,pathseq=x+1) since the target is the cached Path Sequence is higher than the value in the
itself. DCO, then the DCO is dropped.
</t> </li>
</ol>
<t> </section>
The propagation of the DCO will stop at any node where the <section numbered="true" toc="default">
node does not have an routing information associated with <name>Example DCO Messaging with Multiple Preferred Parents</name>
the target. If cached routing information is present and
the cached Path Sequence is higher than the value in the
DCO, then the DCO is dropped.
</t>
</list> <t>
</t> As shown in <xref target="sample_top_mpp" format="default"/>, no
</section> de (N41) selects multiple
<section title="Example DCO Messaging with multiple preferred parents">
<t> <figure align="center" anchor="sample_top_mpp" title="Sample
topology 2"> <artwork align="center"><![CDATA[
(6LBR)
|
|
|
(N11)
/ \
/ \
/ \
(N21) (N22)
/ / \
/ / \
/ / \
(N31) (N32) (N33)
: | /
: | /
: | /
(N41)
]]></artwork> </figure> </t>
<t>
In <xref target="sample_top_mpp"/>, node (N41) selects multiple
preferred parents (N32) and (N33). preferred parents (N32) and (N33).
The sequence of actions is as follows: The sequence of actions is listed below the figure.
<list style="numbers"> </t>
<t>
(N41) sends DAO(tgt=N41,PS=x,I_flag=1) to (N32) and (N33
).
Here I_flag refers to the Invalidation flag and PS refer
s to
Path Sequence in Transit Information option.
</t>
<t>
(N32) sends DAO(tgt=N41,PS=x,I_flag=1) to (N22). (N33) a
lso
sends DAO(tgt=N41,PS=x,I_flag=1) to (N22). (N22) learns
multiple routes for the same destination (N41) through
multiple next-hops. (N22) may receive the DAOs from
(N32) and (N33) in any order with the I_flag set. The
implementation should use the DelayDCO timer to wait to
initiate the DCO. If (N22) receives an updated DAO from
all the paths then the DCO need not be initiated in
this case. Thus the route table at N22 should contain
(Dst,NextHop,PS): { (N41,N32,x), (N41,N33,x) }.
</t>
<t>
(N22) sends DAO(tgt=N41,PS=x,I_flag=1) to (N11).
</t>
<t>
(N11) sends DAO(tgt=N41,PS=x,I_flag=1) to (6LBR). Thus t
he
complete path is established.
</t>
<t>
(N41) decides to change preferred parent set from {
N32, N33 } to { N31, N32 }.
</t>
<t>
(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).
</t>
<t>
(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 (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).
</t>
<t>
(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.
</t>
<t>
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).
</t>
<t>
(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.
</t>
<t>
(N11) forwards the DAO(tgt=N41,PS=x+1,I_flag=1) to 6LBR
and the full path is established.
</t>
</list></t> <figure anchor="sample_top_mpp">
</section> <name>Sample Topology 2</name>
<artwork align="center" name="" type="" alt=""><![CDATA[
(6LBR)
|
|
|
(N11)
/ \
/ \
/ \
(N21) (N22)
/ / \
/ / \
/ / \
(N31) (N32) (N33)
: | /
: | /
: | /
(N41)]]></artwork>
</figure>
<ol spacing="normal" type="1"><li>
(N41) sends a DAO(tgt=N41,PS=x,I_flag=1) to (N32) and (N33).
Here, 'I_flag' refers to the Invalidation flag, and 'PS' refers to
the Path Sequence in the Transit Information option.
</li>
<li>
(N32) sends the DAO(tgt=N41,PS=x,I_flag=1) to (N22). (N33) also
sends the DAO(tgt=N41,PS=x,I_flag=1) to (N22). (N22) learns
multiple routes for the same destination (N41) through
multiple next hops. (N22) may receive the DAOs from
(N32) and (N33) in any order with the I_flag set. The
implementation should use the DelayDCO timer to wait to
initiate the DCO. If (N22) receives an updated DAO from
all the paths, then the DCO need not be initiated in
this case. Thus, the routing table at N22 should contain
(Dst,NextHop,PS): { (N41,N32,x), (N41,N33,x) }.
</li>
<li>
(N22) sends the DAO(tgt=N41,PS=x,I_flag=1) to (N11).
</li>
<li>
(N11) sends the DAO(tgt=N41,PS=x,I_flag=1) to (6LBR). Thus, the
complete path is established.
</li>
<li>
(N41) decides to change the preferred parent set from
{&nbsp;N32,&nbsp;N33&nbsp;} to { N31, N32 }.
</li>
<li>
(N41) sends the DAO(tgt=N41,PS=x+1,I_flag=1) to (N32). (N41)
sends the DAO(tgt=N41,PS=x+1,I_flag=1) to (N31).
</li>
<li>
(N32) sends the 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 waits for a predetermined time period (the DelayDCO
time period) to invalidate another route
{ (N41),(N33),x }. &nbsp;After the time period, (N22) sends the
DCO(tgt=N41,PS=x+1) to (N33). Also (N22) sends the
regular DAO(tgt=N41,PS=x+1,I_flag=1) to (N11).
</li>
<li>
(N33) receives the DCO(tgt=N41,PS=x+1). The received Path
Sequence is the latest and thus invalidates the entry
associated with the target (N41). (N33) then sends the
DCO(tgt=N41,PS=x+1) to (N41). (N41) sees itself as the
target and drops the DCO.
</li>
<li>
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).
</li>
<li>
(N11) receives the DAO(tgt=N41,PS=x+1,I_flag=1) from (N21).
It waits for the DelayDCO timer, since it has multiple
routes to (N41). (N41) will receive the
DAO(tgt=N41,PS=x+1,I_flag=1) from (N22) from Step 7
above. Thus, (N11) has received the regular
DAO(tgt=N41,PS=x+1,I_flag=1) from all paths and thus
does not initiate the DCO.
</li>
<li>
(N11) forwards the DAO(tgt=N41,PS=x+1,I_flag=1) to (6LBR),
and the full path is established.
</li>
</ol>
</section>
</section> </section>
<section anchor="Acknowledgments" numbered="false" toc="default">
</back> <name>Acknowledgments</name>
<t>
Many thanks to <contact fullname="Alvaro Retana"/>, <contact fullname="Cen
k Gundogan"/>, <contact fullname="Simon Duquennoy"/>, <contact fullname="Georgio
s Papadopoulos"/>, and <contact fullname="Peter van der Stok"/> for their review
and comments.
<contact fullname="Alvaro Retana"/> helped shape this document's fin
al version with
critical review comments.
</t>
</section>
</back>
</rfc> </rfc>
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