draft-ietf-roll-efficient-npdao-05.txt		draft-ietf-roll-efficient-npdao-06.txt
	ROLL R. Jadhav, Ed.		ROLL R. Jadhav, Ed.
	Internet-Draft Huawei		Internet-Draft Huawei
	Intended status: Standards Track P. Thubert		Intended status: Standards Track P. Thubert
	Expires: February 25, 2019 Cisco		Expires: March 30, 2019 Cisco
	R. Sahoo		R. Sahoo
	Z. Cao		Z. Cao
	Huawei		Huawei
	August 24, 2018		September 26, 2018
	Efficient Route Invalidation		Efficient Route Invalidation
	draft-ietf-roll-efficient-npdao-05		draft-ietf-roll-efficient-npdao-06
	Abstract		Abstract
	This document describes the problems associated with the use of No-		This document describes the problems associated with the use of NPDAO
	Path DAO messaging in RPL and signaling changes to improve route		messaging in RPL and signaling changes to improve route invalidation
	invalidation efficiency.		efficiency.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on February 25, 2019.		This Internet-Draft will expire on March 30, 2019.
	Copyright Notice		Copyright Notice
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	document authors. All rights reserved.		document authors. All rights reserved.
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	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Requirements Language and Terminology . . . . . . . . . . 3		1.1. Requirements Language and Terminology . . . . . . . . . . 3
	1.2. Current No-Path DAO messaging . . . . . . . . . . . . . . 4		1.2. Current NPDAO messaging . . . . . . . . . . . . . . . . . 3
	1.3. Cases when No-Path DAO may be used . . . . . . . . . . . 4		1.3. Why NPDAO is important? . . . . . . . . . . . . . . . . . 4
	1.4. Why No-Path DAO is important? . . . . . . . . . . . . . . 5		2. Problems with current NPDAO messaging . . . . . . . . 5
	2. Problems with current No-Path DAO messaging . . . . . 5
	2.1. Lost NPDAO due to link break to the previous parent . . . 5		2.1. Lost NPDAO due to link break to the previous parent . . . 5
	2.2. Invalidate routes to dependent nodes of the switching		2.2. Invalidate routes to dependent nodes . . . . . . . . . . 5
	node . . . . . . . . . . . . . . . . . . . . . . . . . . 6		2.3. Possible route downtime caused by async operation of
	2.3. Route downtime caused by asynchronous operation of		NPDAO and DAO . . . . . . . . . . . . . . . . . . . . . . 5
	NPDAO and DAO . . . . . . . . . . . . . . . . . . . . . . 6		3. Requirements for the NPDAO Optimization . . . . . . . . . . . 5
	3. Requirements for the No-Path DAO Optimization . . . . . . . . 6
	3.1. Req#1: Tolerant to link failures to the previous		3.1. Req#1: Tolerant to link failures to the previous
	parents . . . . . . . . . . . . . . . . . . . . . . . . . 6		parents . . . . . . . . . . . . . . . . . . . . . . . . . 5
	3.2. Req#2: Dependent nodes route invalidation on parent		3.2. Req#2: Dependent nodes route invalidation on parent
	switching . . . . . . . . . . . . . . . . . . . . . . . . 7		switching . . . . . . . . . . . . . . . . . . . . . . . . 6
	3.3. Req#3: No impact on traffic while NPDAO operation in		3.3. Req#3: Route invalidation should not impact data traffic 6
	progress . . . . . . . . . . . . . . . . . . . . . . . . 7		4. Proposed changes to RPL signaling . . . . . . . . . . . . . . 6
	4. Proposed changes to RPL signaling . . . . . . . . . . . . . . 7		4.1. Change in RPL route invalidation semantics . . . . . . . 6
	4.1. Change in RPL route invalidation semantics . . . . . . . 7		4.2. Transit Information Option changes . . . . . . . . . . . 7
	4.2. Transit Information Option format change . . . . . . . . 8		4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 8
	4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 9		4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 9
	4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 10		4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 9
	4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 10		4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 9
	4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 10		4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 9
	4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 10		4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 10
	4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 11		4.4. Other considerations . . . . . . . . . . . . . . . . . . 11
	4.4. Other considerations . . . . . . . . . . . . . . . . . . 12		4.4.1. Dependent Nodes invalidation . . . . . . . . . . . . 11
	4.4.1. Dependent Nodes invalidation . . . . . . . . . . . . 12		4.4.2. NPDAO and DCO in the same network . . . . . . . . . . 11
	4.4.2. NPDAO and DCO in the same network . . . . . . . . . . 12		5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
	5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12		7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 13		8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13		8.1. Normative References . . . . . . . . . . . . . . . . . . 12
	8.1. Normative References . . . . . . . . . . . . . . . . . . 13		8.2. Informative References . . . . . . . . . . . . . . . . . 12
	8.2. Informative References . . . . . . . . . . . . . . . . . 13		Appendix A. Example DCO Messaging . . . . . . . . . . . . . . . 12
	Appendix A. Example DCO Messaging . . . . . . . . . . . . . . . 13		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
	1. Introduction		1. Introduction
	RPL [RFC6550] specifies a proactive distance-vector based routing		RPL [RFC6550] specifies a proactive distance-vector based routing
	scheme. The specification has an optional messaging in the form of		scheme. RPL has an optional messaging in the form of DAO messages
	DAO messages using which the 6LBR can learn route towards any of the		using which the 6LBR can learn route towards the nodes. In storing
	nodes. In storing mode, DAO messages would result in routing entries		mode, DAO messages would result in routing entries been created on
	been created on all intermediate hops from the node's parent all the		all intermediate hops from the node's parent all the way towards the
	way towards the 6LBR.		6LBR.
	RPL allows use of No-Path DAO (NPDAO) messaging to invalidate a		RPL allows use of No-Path DAO (NPDAO) messaging to invalidate a
	routing path corresponding to the given target, thus releasing		routing path corresponding to the given target, thus releasing
	resources utilized on that path. A No-Path DAO is a DAO message with		resources utilized on that path. A NPDAO is a DAO message with route
	route lifetime of zero, originates at the target node and always		lifetime of zero, originates at the target node and always flows
	flows upstream towards the 6LBR, signaling route invalidation for the		upstream towards the 6LBR. This document explains the problems
	given target. This document explains the problems associated with		associated with the current use of NPDAO messaging and also discusses
	the current use of NPDAO messaging and also discusses the		the requirements for an optimized route invalidation messaging
	requirements for an optimized No-Path DAO messaging scheme. Further		scheme. Further a new pro-active route invalidation message called
	a new pro-active route invalidation message called as "Destination		as "Destination Cleanup Object (DCO)" is specified which fulfills
	Cleanup Object (DCO)" is specified which fulfills all mentioned
	requirements of an optimized route invalidation messaging.		requirements of an optimized route invalidation messaging.
	6TiSCH architecture [I-D.ietf-6tisch-architecture] leverages RPL and
	specifies use of non-storing and storing MOP for its routing
	operation. Thus an improvement in route invalidation will help
	optimize 6TiSCH based networks.
	1.1. Requirements Language and Terminology		1.1. Requirements Language and Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in RFC 2119 [RFC2119].		document are to be interpreted as described in RFC 2119 [RFC2119].
	The document only caters to the RPL's storing mode of operation		The document only caters to the RPL's storing mode of operation
	(MOP). The non-storing MOP does not require use of NPDAO for route		(MOP). The non-storing MOP does not require use of NPDAO for route
	invalidation since routing entries are not maintained on 6LRs.		invalidation since routing entries are not maintained on 6LRs.
	Common Ancestor node: 6LR node which is the first common node on the		Common Ancestor node: 6LR node which is the first common node on the
	old and new path for the child node.		old and new path for the child node.
	NPDAO: No-Path DAO. A DAO message which has target with lifetime 0.		NPDAO: No-Path DAO. A DAO message which has target with lifetime 0.
	DCO: Destination Cleanup Object, A new RPL control message type		DCO: Destination Cleanup Object, A new RPL control message type
	defined by this draft.		defined by this draft.
	Regular DAO: A DAO message with non-zero lifetime.		Regular DAO: A DAO message with non-zero lifetime.
			LLN: Low Power and Lossy Networks.
			Target Node: The node switching its parent whose routing adjacencies
			are updated (created/removed).
	This document also uses terminology described in [RFC6550].		This document also uses terminology described in [RFC6550].
	1.2. Current No-Path DAO messaging		1.2. Current NPDAO messaging
	RPL introduced No-Path DAO messaging in the storing mode so that the		RPL uses NPDAO messaging in the storing mode so that the node
	node switching its current parent can inform its parents and		changing it routing adjacencies can invalidate the previous route.
	ancestors to invalidate the existing route. Subsequently parents or		This is needed so that nodes along previous path can release any
	ancestors would release any resources (such as the routing entry) it		resources (such as the routing entry) it maintains on behalf of
	maintains on behalf of target node. The NPDAO message always		target node.
	traverses the RPL tree in upward direction, originating at the target
	node itself.
	For the rest of this document consider the following topology:		For the rest of this document consider the following topology:
	(6LBR)		(6LBR)
	|		|
	|		|
	|		|
	(A)		(A)
	/ \		/ \
	/ \		/ \
	skipping to change at page 4, line 44 ¶		skipping to change at page 4, line 34 ¶
	/ \		/ \
	/ \		/ \
	/ \		/ \
	(E) (F)		(E) (F)
	Figure 1: Sample topology		Figure 1: Sample topology
	Node (D) is connected via preferred parent (B). (D) has an alternate		Node (D) is connected via preferred parent (B). (D) has an alternate
	path via (C) towards the BR. Node (A) is the common ancestor for (D)		path via (C) towards the BR. Node (A) is the common ancestor for (D)
	for paths through (B)-(G) and (C)-(H). When (D) switches from (B) to		for paths through (B)-(G) and (C)-(H). When (D) switches from (B) to
	(C), [RFC6550] suggests sending No-Path DAO to (B) and regular DAO to		(C), RPL allows sending NPDAO to (B) and regular DAO to (C).
	(C).
	1.3. Cases when No-Path DAO may be used
	There are following cases in which a node switches its parent and may
	employ No-Path DAO messaging:
	Case I: Current parent becomes unavailable because of transient or
	permanent link or parent node failure.
	Case II: The node finds a better parent node i.e. the metrics of
	another parent is better than its current parent.
	Case III: The node switches to a new parent whom it "thinks" has a
	better metric but does not in reality.
	The usual steps of operation when the node switches the parent is
	that the node sends a No-Path DAO message via its current parent to
	invalidate its current route and subsequently it tries to establish a
	new routing path by sending a new DAO via its new parent.
	1.4. Why No-Path DAO is important?		1.3. Why NPDAO is important?
	Nodes in LLNs may be resource constrained. There is limited memory		Nodes in LLNs may be resource constrained. There is limited memory
	available and routing entry records are the one of the primary		available and routing entry records are one of the primary elements
	elements occupying dynamic memory in the nodes. Route invalidation		occupying dynamic memory in the nodes. Route invalidation helps 6LR
	helps 6LR nodes to decide which entries could be discarded to better		nodes to decide which entries could be discarded to better achieve
	achieve resource utilization in case of contention. Thus it becomes		resource utilization. Thus it becomes necessary to have efficient
	necessary to have efficient route invalidation mechanism. Also note		route invalidation mechanism. Also note that a single parent switch
	that a single parent switch may result in a "sub-tree" switching from		may result in a "sub-tree" switching from one parent to another.
	one parent to another. Thus the route invalidation needs to be done		Thus the route invalidation needs to be done on behalf of the sub-
	on behalf of the sub-tree and not the switching node alone. In the		tree and not the switching node alone. In the above example, when
	above example, when Node (D) switches parent, the route invalidation		Node (D) switches parent, the route invalidation needs to be done for
	needs to be done for (D), (E) and (F). Thus without efficient route		(D), (E) and (F). Thus without efficient route invalidation, a 6LR
	invalidation, a 6LR may have to hold a lot of unwanted route entries.		may have to hold a lot of stale route entries.
	2. Problems with current No-Path DAO messaging		2. Problems with current NPDAO messaging
	2.1. Lost NPDAO due to link break to the previous parent		2.1. Lost NPDAO due to link break to the previous parent
	When a node switches its parent, the NPDAO is to be sent via its		When a node switches its parent, the NPDAO is to be sent to its
	previous parent and a regular DAO via its new parent. In cases where		previous parent and a regular DAO to its new parent. In cases where
	the node switches its parent because of transient or permanent parent		the node switches its parent because of transient or permanent parent
	link/node failure then the NPDAO message is bound to fail. RPL		link/node failure then the NPDAO message is bound to fail.
	assumes communication link with the previous parent for No-Path DAO
	messaging.
	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.
	2.2. Invalidate routes to dependent nodes of the switching node		2.2. Invalidate routes to dependent nodes
	No-path DAO is sent by the node who has switched the parent but it		RPL does not specify how route invalidation will work for dependent
	does not work for the dependent child nodes below it. The		nodes rooted at switching node, resulting in stale routing entries of
	specification does not specify how route invalidation will work for		the dependent nodes. The only way for 6LR to invalidate the route
	sub-childs, resulting in stale routing entries on behalf of the sub-		entries for dependent nodes would be to use route lifetime expiry
	childs on the previous route. The only way for 6LR to invalidate the		which could be substantially high for LLNs.
	route entries for dependent nodes would be to use route lifetime
	expiry which could be substantially high for LLNs.
	In the example topology, when Node (D) switches its parent, Node (D)		In the example topology, when Node (D) switches its parent, Node (D)
	generates an NPDAO on its behalf. Post switching, Node (D) transmits		generates an NPDAO on its behalf. There is no NPDAO generated by
	a DIO with incremented DTSN so that child nodes, node (E) and (F),		these child nodes through the previous path resulting in stale
	generate DAOs to trigger route update on the new path for themselves.		entries on nodes (B) and (G) for nodes (E) and (F).
	There is no NPDAO generated by these child nodes through the previous
	path resulting in stale entries on nodes (B) and (G) for nodes (E)
	and (F).
	2.3. Route downtime caused by asynchronous operation of NPDAO and DAO		2.3. Possible route downtime caused by async operation of NPDAO and DAO
	A switching node may generate both an NPDAO and DAO via two different		A switching node may generate both an NPDAO and DAO via two different
	paths at almost the same time. There is a possibility that an NPDAO		paths at almost the same time. There is a possibility that an NPDAO
	generated may invalidate the previous route and the regular DAO sent		generated may invalidate the previous route and the regular DAO sent
	via the new path gets lost on the way. This may result in route		via the new path gets lost on the way. This may result in route
	downtime thus impacting downward traffic for the switching node. In		downtime impacting downward traffic for the switching node.
	the example topology, consider Node (D) switches from parent (B) to
	(C) because the metrics of the path via (C) are better. Note that
	the previous path via (B) may still be available (albeit at
	relatively bad metrics). An NPDAO sent from previous route may
	invalidate the existing route whereas there is no way to determine
	whether the new DAO has successfully updated the route entries on the
	new path.
	3. Requirements for the No-Path DAO Optimization		In the example topology, consider Node (D) switches from parent (B)
			to (C). An NPDAO sent from previous route may invalidate the
			existing route whereas there is no way to determine whether the new
			DAO has successfully updated the route entries on the new path.
			3. Requirements for the NPDAO Optimization
	3.1. Req#1: Tolerant to link failures to the previous parents		3.1. Req#1: Tolerant to link failures to the previous parents
	When the switching node sends the NPDAO message to the previous		When the switching node sends the NPDAO message to the previous
	parent, it is normal that the link to the previous parent is prone to		parent, it is normal that the link to the previous parent is prone to
	failure. Therefore, it is required that the NPDAO message MUST be		failure. Therefore, it is required that the NPDAO message must be
	tolerant to the link failure during the switching. The link referred		tolerant to the link failure. The link referred here represents the
	here represents the link between the node and its previous parent		link between the node and its previous parent (from whom the node is
	(from whom the node is now disassociating).		now disassociating).
	3.2. Req#2: Dependent nodes route invalidation on parent switching		3.2. Req#2: Dependent nodes route invalidation on parent switching
	While switching the parent node and sending NPDAO message, it is		It should be possible to do route invalidation for dependent nodes
	required that the routing entries to the dependent nodes of the		rooted at the switching node.
	switching node will be updated accordingly on the previous parents
	and other relevant upstream nodes.
	3.3. Req#3: No impact on traffic while NPDAO operation in progress		3.3. Req#3: Route invalidation should not impact data traffic
	While sending the NPDAO and DAO messages, it is possible that the		While sending the NPDAO and DAO messages, it is possible that the
	NPDAO successfully invalidates the previous path, while the newly		NPDAO successfully invalidates the previous path, while the newly
	sent DAO gets lost (new path not set up successfully). This will		sent DAO gets lost (new path not set up successfully). This will
	result into downstream unreachability to the current switching node.		result in downstream unreachability to the node switching paths.
	Therefore, it is desirable that the NPDAO is synchronized with the		Therefore, it is desirable that the route invalidation is
	DAO to avoid the risk of route downtime.		synchronized with the DAO to avoid the risk of route downtime.
	4. Proposed changes to RPL signaling		4. Proposed changes to RPL signaling
	4.1. Change in RPL route invalidation semantics		4.1. Change in RPL route invalidation semantics
	As described in Section 1.2, the NPDAO originates at the node		As described in Section 1.2, the NPDAO originates at the node
	switching the parent and traverses upstream towards the root. In		switching the parent and traverses upstream towards the root. In
	order to solve the problems as mentioned in Section 2, the draft adds		order to solve the problems as mentioned in Section 2, the draft adds
	new pro-active route invalidation message called as "Destination		new pro-active route invalidation message called as "Destination
	Cleanup Object" (DCO) that originates at a common ancestor node		Cleanup Object" (DCO) that originates at a common ancestor node
	skipping to change at page 8, line 5 ¶		skipping to change at page 7, line 5 ¶
	node A receives the regular DAO, it finds that it already has a		node A receives the regular DAO, it finds that it already has a
	routing table entry on behalf of the target address of node D. It		routing table entry on behalf of the target address of node D. It
	finds however that the next hop information for reaching node D has		finds however that the next hop information for reaching node D has
	changed i.e. the node D has decided to change the paths. In this		changed i.e. the node D has decided to change the paths. In this
	case, Node A which is the common ancestor node for node D along the		case, Node A which is the common ancestor node for node D along the
	two paths (previous and new), may generate a DCO which traverses		two paths (previous and new), may generate a DCO which traverses
	downwards in the network. The document in the subsequent section		downwards in the network. The document in the subsequent section
	will explain the message format changes to handle this downward flow		will explain the message format changes to handle this downward flow
	of NPDAO.		of NPDAO.
	4.2. Transit Information Option format change		4.2. Transit Information Option changes
	Every RPL message is divided into base message fields and additional		Every RPL message is divided into base message fields and additional
	Options. The base fields apply to the message as a whole and options		Options. The base fields apply to the message as a whole and options
	are appended to add message/use-case specific attributes. As an		are appended to add message/use-case specific attributes. As an
	example, a DAO message may be attributed by one or more "RPL Target"		example, a DAO message may be attributed by one or more "RPL Target"
	options which specifies the reachability information for the given		options which specifies the reachability information for the given
	targets. Similarly, a Transit Information option may be associated		targets. Similarly, a Transit Information option may be associated
	with a set of RPL Target options.		with a set of RPL Target options.
	The draft proposes a change in Transit Information option to contain		The draft proposes a change in Transit Information option to contain
	skipping to change at page 9, line 42 ¶		skipping to change at page 8, line 42 ¶
	RPLInstanceID: 8-bit field indicating the topology instance		RPLInstanceID: 8-bit field indicating the topology instance
	associated with the DODAG, as learned from the DIO.		associated with the DODAG, as learned from the DIO.
	K: The 'K' flag indicates that the recipient is expected to send a		K: The 'K' flag indicates that the recipient is expected to send a
	DCO-ACK back.		DCO-ACK back.
	D: The 'D' flag indicates that the DODAGID field is present. This		D: The 'D' flag indicates that the DODAGID field is present. This
	flag MUST be set when a local RPLInstanceID is used.		flag MUST be set when a local RPLInstanceID is used.
	Flags: The 6 bits remaining unused in the Flags field are reserved		Flags: The 6 bits remaining unused in the Flags field are reserved
	for flags. The field MUST be initialized to zero by the sender and		for future use. These bits MUST be initialized to zero by the sender
	MUST be ignored by the receiver.		and MUST be ignored by the receiver.
	Reserved: 8-bit unused field. The field MUST be initialized to zero		Reserved: 8-bit unused field. The field MUST be initialized to zero
	by the sender and MUST be ignored by the receiver.		by the sender and MUST be ignored by the receiver.
	DCOSequence: Incremented at each unique DCO message from a node and		DCOSequence: Incremented at each unique DCO message from a node and
	echoed in the DCO-ACK message.		echoed in the DCO-ACK message.
	DODAGID (optional): 128-bit unsigned integer set by a DODAG root that		DODAGID (optional): 128-bit unsigned integer set by a DODAG root that
	uniquely identifies a DODAG. This field is only present when the 'D'		uniquely identifies a DODAG. This field is only present when the 'D'
	flag is set. This field is typically only present when a local		flag is set. This field is typically only present when a local
	skipping to change at page 12, line 30 ¶		skipping to change at page 11, line 30 ¶
	Even with the changed semantics, the current NPDAO mechanism in		Even with the changed semantics, the current NPDAO mechanism in
	[RFC6550] can still be used. There are certain scenarios where		[RFC6550] can still be used. There are certain scenarios where
	current NPDAO signalling may still be used, for example, when the		current NPDAO signalling may still be used, for example, when the
	route lifetime expiry of the target happens or when the node simply		route lifetime expiry of the target happens or when the node simply
	decides to gracefully terminate the RPL session on graceful node		decides to gracefully terminate the RPL session on graceful node
	shutdown. Moreover a deployment can have a mix of nodes supporting		shutdown. Moreover a deployment can have a mix of nodes supporting
	the proposed DCO and the existing NPDAO mechanism.		the proposed DCO and the existing NPDAO mechanism.
	5. Acknowledgements		5. Acknowledgements
	Many thanks to Cenk Gundogan, Simon Duquennoy, and Georgios		Many thanks to Cenk Gundogan, Simon Duquennoy, Georgios
	Papadopoulous for their review and comments.		Papadopoulous, Peter Van Der Stok for their review and comments.
	6. IANA Considerations		6. IANA Considerations
	IANA is requested to allocate new ICMPv6 RPL control codes in RPL		IANA is requested to allocate new ICMPv6 RPL control codes in RPL
	[RFC6550] for DCO and DCO-ACK messages.		[RFC6550] for DCO and DCO-ACK messages.
	+------+---------------------------------------------+--------------+		+------+---------------------------------------------+--------------+
	| Code | Description | Reference |		| Code | Description | Reference |
	+------+---------------------------------------------+--------------+		+------+---------------------------------------------+--------------+
	| 0x04 | Destination Cleanup Object | This |		| 0x04 | Destination Cleanup Object | This |
	skipping to change at page 15, line 16 ¶		skipping to change at page 14, line 16 ¶
	Kundalahalli Village, Whitefield,		Kundalahalli Village, Whitefield,
	Bangalore, Karnataka 560037		Bangalore, Karnataka 560037
	India		India
	Phone: +91-080-49160700		Phone: +91-080-49160700
	Email: rabinarayans@huawei.com		Email: rabinarayans@huawei.com
	Zhen Cao		Zhen Cao
	Huawei		Huawei
	W Chang'an Ave		W Chang'an Ave
	Beijing 560037		Beijing
	China		China
	Email: zhencao.ietf@gmail.com		Email: zhencao.ietf@gmail.com
End of changes. 36 change blocks.
	153 lines changed or deleted		111 lines changed or added
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