< draft-ietf-roll-efficient-npdao-12.txt		draft-ietf-roll-efficient-npdao-13.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: December 5, 2019 Cisco		Expires: January 1, 2020 Cisco
	R. Sahoo		R. Sahoo
	Z. Cao		Z. Cao
	Huawei		Huawei
	June 3, 2019		June 30, 2019
	Efficient Route Invalidation		Efficient Route Invalidation
	draft-ietf-roll-efficient-npdao-12		draft-ietf-roll-efficient-npdao-13
	Abstract		Abstract
	This document describes the problems associated with No-Path		This document explains the problems associated with the current use
	Destination Advertisement Object (NPDAO) messaging used in Routing		of NPDAO messaging and also discusses the requirements for an
	Protocol for Low power and lossy networks (RPL) for route		optimized route invalidation messaging scheme. Further a new
	invalidation and signaling changes to improve route invalidation		proactive route invalidation message called as "Destination Cleanup
	efficiency.		Object" (DCO) is specified which fulfills requirements of an
			optimized route invalidation messaging.
	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 December 5, 2019.		This Internet-Draft will expire on January 1, 2020.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 14 ¶		skipping to change at page 2, line 15 ¶
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	1.1. Requirements Language and Terminology . . . . . . . . . . 3		1.1. Requirements Language and Terminology . . . . . . . . . . 3
	1.2. Current NPDAO messaging . . . . . . . . . . . . . . . . . 4		1.2. Current NPDAO messaging . . . . . . . . . . . . . . . . . 4
	1.3. Why NPDAO is important? . . . . . . . . . . . . . . . . . 5		1.3. Why Is NPDAO Important? . . . . . . . . . . . . . . . . . 5
	2. Problems with current NPDAO messaging . . . . . . . . . . . . 6		2. Problems with current NPDAO messaging . . . . . . . . . . . . 6
	2.1. Lost NPDAO due to link break to the previous parent . . . 6		2.1. Lost NPDAO due to link break to the previous parent . . . 6
	2.2. Invalidate routes of dependent nodes . . . . . . . . . . 6		2.2. Invalidate Routes of Dependent Nodes . . . . . . . . . . 6
	2.3. Possible route downtime caused by async operation of		2.3. Possible route downtime caused by asynchronous operation
	NPDAO and DAO . . . . . . . . . . . . . . . . . . . . . . 6		of NPDAO and DAO . . . . . . . . . . . . . . 6
	3. Requirements for the NPDAO Optimization . . . . . . . . . . . 6		3. Requirements for the NPDAO Optimization . . . . . . . . . . . 6
	3.1. Req#1: Remove messaging dependency on link to the		3.1. Req#1: Remove messaging dependency on link to the
	previous parent . . . . . . . . . . . . . . . . . . . . . 6		previous parent . . . . . . . . . . . . . . . . . . . . . 6
	3.2. Req#2: Dependent nodes route invalidation on parent		3.2. Req#2: Dependent nodes route invalidation on parent
	switching . . . . . . . . . . . . . . . . . . . . . . . . 7		switching . . . . . . . . . . . . . . . . . . . . . . . . 7
	3.3. Req#3: Route invalidation should not impact data traffic 7		3.3. Req#3: Route invalidation should not impact data traffic 7
	4. Changes to RPL signaling . . . . . . . . . . . . . . . . . . 7		4. Changes to RPL signaling . . . . . . . . . . . . . . . . . . 7
	4.1. Change in RPL route invalidation semantics . . . . . . . 7		4.1. Change in RPL route invalidation semantics . . . . . . . 7
	4.2. Transit Information Option changes . . . . . . . . . . . 8		4.2. Transit Information Option changes . . . . . . . . . . . 8
	4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 9		4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 9
	4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 10		4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 10
	4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 10		4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 10
	4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 10		4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 10
	4.3.4. Destination Cleanup Option Acknowledgment (DCO-ACK) . 10		4.3.4. Destination Cleanup Option Acknowledgment (DCO-ACK) . 11
	4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 11		4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 12
	4.4. DCO Base Rules . . . . . . . . . . . . . . . . . . . . . 12		4.4. DCO Base Rules . . . . . . . . . . . . . . . . . . . . . 12
	4.5. Unsolicited DCO . . . . . . . . . . . . . . . . . . . . . 12		4.5. Unsolicited DCO . . . . . . . . . . . . . . . . . . . . . 12
	4.6. Other considerations . . . . . . . . . . . . . . . . . . 13		4.6. Other considerations . . . . . . . . . . . . . . . . . . 13
	4.6.1. Dependent Nodes invalidation . . . . . . . . . . . . 13		4.6.1. Dependent Nodes invalidation . . . . . . . . . . . . 13
	4.6.2. NPDAO and DCO in the same network . . . . . . . . . . 13		4.6.2. NPDAO and DCO in the same network . . . . . . . . . . 13
	4.6.3. DCO with multiple preferred parents . . . . . . . . . 14		4.6.3. DCO with multiple preferred parents . . . . . . . . . 14
	5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14		5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
	6.1. New Registry for the Destination Cleanup Object (DCO)		6.1. New Registry for the Destination Cleanup Object (DCO)
	Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 15		Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 15
	6.2. New Registry for the Destination Cleanup Object		6.2. New Registry for the Destination Cleanup Object
	Acknowledgment (DCO-ACK) Status field . . . . . . . . . . 16		Acknowledgment (DCO-ACK) Status field . . . . . . . . . . 16
	6.3. New Registry for the Destination Cleanup Object (DCO)		6.3. New Registry for the Destination Cleanup Object (DCO)
	Acknowledgment Flags . . . . . . . . . . . . . . . . . . 16		Acknowledgment Flags . . . . . . . . . . . . . . . . . . 16
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 17		7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
	8. Normative References . . . . . . . . . . . . . . . . . . . . 18		8. Normative References . . . . . . . . . . . . . . . . . . . . 18
	Appendix A. Example Messaging . . . . . . . . . . . . . . . . . 18		Appendix A. Example Messaging . . . . . . . . . . . . . . . . . 18
	A.1. Example DCO Messaging . . . . . . . . . . . . . . . . . . 18		A.1. Example DCO Messaging . . . . . . . . . . . . . . . . . . 19
	A.2. Example DCO Messaging with multiple preferred parents . . 19		A.2. Example DCO Messaging with multiple preferred parents . . 20
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
	1. Introduction		1. Introduction
	RPL [RFC6550] (Routing Protocol for Low power and lossy networks)		RPL [RFC6550] (Routing Protocol for Low power and lossy networks)
	specifies a proactive distance-vector based routing scheme. RPL has		specifies a proactive distance-vector based routing scheme. RPL has
	an optional messaging in the form of DAO (Destination Advertisement		optional messaging in the form of DAO (Destination Advertisement
	Object) messages, which the 6LBR (6Lo Border Router) and 6LR (6Lo		Object) messages, which the 6LBR (6Lo Border Router) and 6LR (6Lo
	Router) can use to learn a route towards the downstream nodes. In		Router) can use to learn a route towards the downstream nodes. In
	storing mode, DAO messages would result in routing entries being		storing mode, DAO messages would result in routing entries being
	created on all intermediate 6LRs from the node's parent all the way		created on all intermediate 6LRs from the node's parent all the way
	towards the 6LBR.		towards the 6LBR.
	RPL allows the use of No-Path DAO (NPDAO) messaging to invalidate a		RPL allows the use of No-Path DAO (NPDAO) messaging to invalidate a
	routing path corresponding to the given target, thus releasing		routing path corresponding to the given target, thus releasing
	resources utilized on that path. A NPDAO is a DAO message with route		resources utilized on that path. A NPDAO is a DAO message with route
	lifetime of zero, originates at the target node and always flows		lifetime of zero, originates at the target node and always flows
	upstream towards the 6LBR. This document explains the problems		upstream towards the 6LBR. This document explains the problems
	associated with the current use of NPDAO messaging and also discusses		associated with the current use of NPDAO messaging and also discusses
	the requirements for an optimized route invalidation messaging		the requirements for an optimized route invalidation messaging
	scheme. Further a new pro-active route invalidation message called		scheme. Further a new proactive route invalidation message called as
	as "Destination Cleanup Object" (DCO) is specified which fulfills		"Destination Cleanup Object" (DCO) is specified which fulfills
	requirements of an optimized route invalidation messaging.		requirements of an optimized route invalidation messaging.
	The document only caters to the RPL's storing mode of operation		The document only caters to the RPL's storing mode of operation
	(MOP). The non-storing MOP does not require use of NPDAO for route		(MOP). The non-storing MOP does not require use of NPDAO for route
	invalidation since routing entries are not maintained on 6LRs.		invalidation since routing entries are not maintained on 6LRs.
	1.1. Requirements Language and Terminology		1.1. Requirements Language and Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	This specification requires readers to be familiar with all the terms		This specification requires readers to be familiar with all the terms
	and concepts that are discussed in "RPL: IPv6 Routing Protocol for		and concepts that are discussed in "RPL: IPv6 Routing Protocol for
	Low-Power and Lossy Networks" [RFC6550].		Low-Power and Lossy Networks" [RFC6550].
			Low Power and Lossy Networks (LLN):
			Network in which both the routers and their interconnect are
			constrained. LLN routers typically operate with constraints on
			processing power, memory, and energy (batter power). Their
			interconnects are characterized by high loss rates, low data
			rates, and instability.
	6LoWPAN Router (6LR):		6LoWPAN Router (6LR):
	An intermediate router that is able to send and receive Router		An intermediate router that is able to send and receive Router
	Advertisements (RAs) and Router Solicitations (RSs) as well as		Advertisements (RAs) and Router Solicitations (RSs) as well as
	forward and route IPv6 packets.		forward and route IPv6 packets.
	Directed Acyclic Graph (DAG):		Directed Acyclic Graph (DAG):
	A directed graph having the property that all edges are oriented		A directed graph having the property that all edges are oriented
	in such a way that no cycles exist.		in such a way that no cycles exist.
	Destination-Oriented DAG (DODAG):		Destination-Oriented DAG (DODAG):
	A DAG rooted at a single destination, i.e., at a single DAG root		A DAG rooted at a single destination, i.e., at a single DAG root
	with no outgoing edges.		with no outgoing edges.
	6LoWPAN Border Router (6LBR):		6LoWPAN Border Router (6LBR):
	A border router which is a DODAG root and is the edge node for		A border router which is a DODAG root and is the edge node for
	traffic flowing in and out of the 6LoWPAN network.		traffic flowing in and out of the 6LoWPAN network.
	Destination Advertisement Object (DAO):		Destination Advertisement Object (DAO):
	DAO messaging allows downstream routes to the nodes to be		DAO messaging allows downstream routes to the nodes to be
	skipping to change at page 4, line 26 ¶		skipping to change at page 4, line 32 ¶
	DODAG Information Object (DIO):		DODAG Information Object (DIO):
	DIO messaging allows upstream routes to the 6LBR to be		DIO messaging allows upstream routes to the 6LBR to be
	established. DIO messaging is initiated at the DAO root.		established. DIO messaging is initiated at the DAO root.
	Common Ancestor node		Common Ancestor node
	6LR/6LBR node which is the first common node between two paths of		6LR/6LBR node which is the first common node between two paths of
	a target node.		a target node.
	No-Path DAO (NPDAO):		No-Path DAO (NPDAO):
	A DAO message which has target with lifetime 0 used for the		A DAO message which has target with lifetime 0 used for the
	purpose of route invalidation.		purpose of route invalidation.
	Destination Cleanup Object (DCO):		Destination Cleanup Object (DCO):
	A new RPL control message type defined by this document. DCO		A new RPL control message code defined by this document. DCO
	messaging improves proactive route invalidation in RPL.		messaging improves proactive route invalidation in RPL.
	Regular DAO:		Regular DAO:
	A DAO message with non-zero lifetime. Routing adjacencies are		A DAO message with non-zero lifetime. Routing adjacencies are
	created or updated based on this message.		created or updated based on this message.
	Target node:		Target node:
	The node switching its parent whose routing adjacencies are		The node switching its parent whose routing adjacencies are
	updated (created/removed).		updated (created/removed).
	1.2. Current NPDAO messaging		1.2. Current NPDAO messaging
	RPL uses NPDAO messaging in the storing mode so that the node		RPL uses NPDAO messaging in the storing mode so that the node
	changing it routing adjacencies can invalidate the previous route.		changing its routing adjacencies can invalidate the previous route.
	This is needed so that nodes along the previous path can release any		This is needed so that nodes along the previous path can release any
	resources (such as the routing entry) it maintains on behalf of		resources (such as the routing entry) they maintain on behalf of
	target node.		target node.
	For the rest of this document consider the following topology:		For the rest of this document consider the following topology:
	(6LBR)		(6LBR)
	|		|
	|		|
	|		|
	(A)		(A)
	/ \		/ \
	skipping to change at page 5, line 34 ¶		skipping to change at page 5, 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 6LBR. Node (A) is the common ancestor for		path via (C) towards the 6LBR. Node (A) is the common ancestor for
	(D) for paths through (B)-(G) and (C)-(H). When (D) switches from		(D) for paths through (B)-(G) and (C)-(H). When (D) switches from
	(B) to (C), RPL allows sending NPDAO to (B) and regular DAO to (C).		(B) to (C), RPL allows sending NPDAO to (B) and regular DAO to (C).
	1.3. Why NPDAO is important?		1.3. Why Is NPDAO Important?
	Nodes in LLNs may be resource constrained. There is limited memory		Nodes in LLNs may be resource constrained. There is limited memory
	available and routing entry records are one of the primary elements		available and routing entry records are one of the primary elements
	occupying dynamic memory in the nodes. Route invalidation helps 6LR		occupying dynamic memory in the nodes. Route invalidation helps 6LR
	nodes to decide which entries could be discarded to better achieve		nodes to decide which entries could be discarded to better optimize
	resource utilization. Thus it becomes necessary to have an efficient		resource utilization. Thus it becomes necessary to have an efficient
	route invalidation mechanism. Also note that a single parent switch		route invalidation mechanism. Also note that a single parent switch
	may result in a "sub-tree" switching from one parent to another.		may result in a "sub-tree" switching from one parent to another.
	Thus the route invalidation needs to be done on behalf of the sub-		Thus the route invalidation needs to be done on behalf of the sub-
	tree and not the switching node alone. In the above example, when		tree and not the switching node alone. In the above example, when
	Node (D) switches parent, the route updates needs to be done for the		Node (D) switches parent, the route updates needs to be done for the
	routing tables entries of (C),(H),(A),(G), and (B) with destination		routing tables entries of (C),(H),(A),(G), and (B) with destination
	(D),(E) and (F). Without efficient route invalidation, a 6LR may		(D),(E) and (F). Without efficient route invalidation, a 6LR may
	have to hold a lot of stale route entries.		have to hold a lot of stale route entries.
	2. Problems with current NPDAO messaging		2. Problems with current NPDAO messaging
	2.1. Lost NPDAO due to link break to the previous parent		2.1. Lost NPDAO due to link break to the previous parent
	When a node switches its parent, the NPDAO is to be sent to its		When a node switches its parent, the NPDAO is to be sent to its
	previous parent and a regular DAO to its new parent. In cases where		previous parent and a regular DAO to its new parent. In cases where
	the node switches its parent because of transient or permanent parent		the node switches its parent because of transient or permanent parent
	link/node failure then the NPDAO message is bound to fail.		link/node failure then the NPDAO message is bound to fail.
	2.2. Invalidate routes of dependent nodes		2.2. Invalidate Routes of Dependent Nodes
	RPL does not specify how route invalidation will work for dependent		RPL does not specify how route invalidation will work for dependent
	nodes rooted at the switching node, resulting in stale routing		nodes rooted at the switching node, resulting in stale routing
	entries of the dependent nodes. The only way for 6LR to invalidate		entries of the dependent nodes. The only way for 6LR to invalidate
	the route entries for dependent nodes would be to use route lifetime		the route entries for dependent nodes would be to use route lifetime
	expiry which could be substantially high for LLNs.		expiry which could be substantially high for LLNs.
	In the example topology, when Node (D) switches its parent, Node (D)		In the example topology, when Node (D) switches its parent, Node (D)
	generates an NPDAO on its behalf. There is no NPDAO generated by the		generates an NPDAO on its behalf. There is no NPDAO generated by the
	dependent child nodes (E) and (F), through the previous path via (D)		dependent child nodes (E) and (F), through the previous path via (D)
	to (B) and (G), resulting in stale entries on nodes (B) and (G) for		to (B) and (G), resulting in stale entries on nodes (B) and (G) for
	nodes (E) and (F).		nodes (E) and (F).
	2.3. Possible route downtime caused by async operation of NPDAO and DAO		2.3. Possible route downtime caused by asynchronous operation of NPDAO
			and DAO
	A switching node may generate both an NPDAO and DAO via two different		A switching node may generate both an NPDAO and DAO via two different
	paths at almost the same time. There is a possibility that an NPDAO		paths at almost the same time. There is a possibility that an NPDAO
	generated may invalidate the previous route and the regular DAO sent		generated may invalidate the previous route and the regular DAO sent
	via the new path gets lost on the way. This may result in route		via the new path gets lost on the way. This may result in route
	downtime impacting downward traffic for the switching node.		downtime impacting downward traffic for the switching node.
	In the example topology, consider Node (D) switches from parent (B)		In the example topology, consider Node (D) switches from parent (B)
	to (C). An NPDAO sent via the previous route may invalidate the		to (C). An NPDAO sent via the previous route may invalidate the
	previous route whereas there is no way to determine whether the new		previous route whereas there is no way to determine whether the new
	skipping to change at page 7, line 26 ¶		skipping to change at page 7, line 26 ¶
	Therefore, it is desirable that the route invalidation is		Therefore, it is desirable that the route invalidation is
	synchronized with the DAO to avoid the risk of route downtime.		synchronized with the DAO to avoid the risk of route downtime.
	4. Changes to RPL signaling		4. Changes to RPL signaling
	4.1. Change in RPL route invalidation semantics		4.1. Change in RPL route invalidation semantics
	As described in Section 1.2, the NPDAO originates at the node		As described in Section 1.2, the NPDAO originates at the node
	changing to a new parent and traverses upstream towards the root. In		changing to a new parent and traverses upstream towards the root. In
	order to solve the problems as mentioned in Section 2, the document		order to solve the problems as mentioned in Section 2, the document
	adds a new pro-active route invalidation message called "Destination		adds a new proactive route invalidation message called "Destination
	Cleanup Object" (DCO) that originates at a common ancestor node and		Cleanup Object" (DCO) that originates at a common ancestor node and
	flows downstream between the new and old path. The common ancestor		flows downstream between the new and old path. The common ancestor
	node generates a DCO in response to the change in the next-hop on		node generates a DCO in response to the change in the next-hop on
	receiving a regular DAO with updated Path Sequence for the target.		receiving a regular DAO with updated Path Sequence for the target.
	The 6LRs in the path for DCO take action such as route invalidation		The 6LRs in the path for DCO take action such as route invalidation
	based on the DCO information and subsequently send another DCO with		based on the DCO information and subsequently send another DCO with
	the same information downstream to the next hop. This operation is		the same information downstream to the next hop. This operation is
	similar to how the DAOs are handled on intermediate 6LRs in storing		similar to how the DAOs are handled on intermediate 6LRs in storing
	MOP in [RFC6550]. Just like DAO in storing MOP, the DCO is sent		MOP in [RFC6550]. Just like DAO in storing MOP, the DCO is sent
	using link-local unicast source and destination IPv6 address. Unlike		using link-local unicast source and destination IPv6 address. Unlike
	DAO, which always travels upstream, the DCO always travels		DAO, which always travels upstream, the DCO always travels
	downstream.		downstream.
	In Figure 1, when node D decides to switch the path from B to C, it		In Figure 1, when node D decides to switch the path from B to C, it
	sends a regular DAO to node C with reachability information		sends a regular DAO to node C with reachability information
	containing target as address of D and an incremented Path Sequence.		containing the address of D as the target and an incremented Path
	Node C will update the routing table based on the reachability		Sequence. Node C will update the routing table based on the
	information in the DAO and in turn generate another DAO with the same		reachability information in the DAO and in turn generate another DAO
	reachability information and forward it to H. Node H also follows		with the same reachability information and forward it to H. Node H
	the same procedure as Node C and forwards it to node A. When node A		also follows the same procedure as Node C and forwards it to node A.
	receives the regular DAO, it finds that it already has a routing		When node A receives the regular DAO, it finds that it already has a
	table entry on behalf of the target address of node D. It finds		routing table entry on behalf of the target address of node D. It
	however that the next hop information for reaching node D has changed		finds however that the next hop information for reaching node D has
	i.e., node D has decided to change the paths. In this case, Node A		changed i.e., node D has decided to change the paths. In this case,
	which is the common ancestor node for node D along the two paths		Node A which is the common ancestor node for node D along the two
	(previous and new), should generate a DCO which traverses downwards		paths (previous and new), should generate a DCO which traverses
	in the network.		downwards in the network. Node A handles normal DAO forwarding to
			6LBR as required by [RFC6550].
	4.2. Transit Information Option changes		4.2. Transit Information Option changes
	Every RPL message is divided into base message fields and additional		Every RPL message is divided into base message fields and additional
	Options as described in Section 6 of [RFC6550]. The base fields		Options as described in Section 6 of [RFC6550]. The base fields
	apply to the message as a whole and options are appended to add		apply to the message as a whole and options are appended to add
	message/use-case specific attributes. As an example, a DAO message		message/use-case specific attributes. As an example, a DAO message
	may be attributed by one or more "RPL Target" options which specify		may be attributed by one or more "RPL Target" options which specify
	the reachability information for the given targets. Similarly, a		the reachability information for the given targets. Similarly, a
	Transit Information option may be associated with a set of RPL Target		Transit Information option may be associated with a set of RPL Target
	options.		options.
	This document specifies a change in the Transit Information Option to		This document specifies a change in the Transit Information Option to
	contain the "Invalidate previous route" (I) flag. This I-flag		contain the "Invalidate previous route" (I) flag. This I-flag
	signals the common ancestor node to generate a DCO on behalf of the		signals the common ancestor node to generate a DCO on behalf of the
	target node. The I-flag is carried in the Transit Information Option		target node. The I-flag is carried in the Transit Information Option
	which augments the reachability information for a given set of RPL		which augments the reachability information for a given set of RPL
	Target(s). Transit Information Option should be carried in the DAO		Target(s). Transit Information Option with I-flag set should be
	message with I-flag set in case route invalidation is sought for the		carried in the DAO message when route invalidation is sought for the
	corresponding target(s).		corresponding target(s).
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type = 0x06 | Option Length |E|I| Flags | Path Control |		| Type = 0x06 | Option Length |E|I| Flags | Path Control |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Path Sequence | Path Lifetime |		| Path Sequence | Path Lifetime |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Figure 2: Updated Transit Information Option (New I flag added)		Figure 2: Updated Transit Information Option (New I flag added)
	I (Invalidate previous route) flag: The 'I' flag is set by the target		I (Invalidate previous route) flag: The 'I' flag is set by the target
	node to indicate to the common ancestor node that it wishes to		node to indicate to the common ancestor node that it wishes to
	invalidate any previous route between the two paths.		invalidate any previous route between the two paths.
	[RFC6550] allows parent address to be sent in the Transit Information		[RFC6550] allows the parent address to be sent in the Transit
	Option depending on the mode of operation. In case of storing mode		Information Option depending on the mode of operation. In case of
	of operation the field is usually not needed. In case of DCO, the		storing mode of operation the field is usually not needed. In case
	parent address field MUST NOT be included.		of DCO, the parent address field MUST NOT be included.
	The common ancestor node SHOULD generate a DCO message in response to		The common ancestor node SHOULD generate a DCO message in response to
	this I-flag when it sees that the routing adjacencies have changed		this I-flag when it sees that the routing adjacencies have changed
	for the target. I-flag governs the ownership of the DCO message in a		for the target. The I-flag is intended to give the target node
	way that the target node is still in control of its own route		control over its own route invalidation, serving as a signal to
	invalidation.		request DCO generation.
	4.3. Destination Cleanup Object (DCO)		4.3. Destination Cleanup Object (DCO)
	A new ICMPv6 RPL control message type is defined by this		A new ICMPv6 RPL control message code is defined by this
	specification called as "Destination Cleanup Object" (DCO), which is		specification and is referred to as "Destination Cleanup Object"
	used for proactive cleanup of state and routing information held on		(DCO), which is used for proactive cleanup of state and routing
	behalf of the target node by 6LRs. The DCO message always traverses		information held on behalf of the target node by 6LRs. The DCO
	downstream and cleans up route information and other state		message always traverses downstream and cleans up route information
	information associated with the given target.		and other state information associated with the given target.
	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 | Reserved | DCOSequence |		| RPLInstanceID |K|D| Flags | Reserved | DCOSequence |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |		| |
	+ +		+ +
	| |		| |
	+ DODAGID(optional) +		+ DODAGID(optional) +
	skipping to change at page 9, line 39 ¶		skipping to change at page 9, line 39 ¶
	Figure 3: DCO base object		Figure 3: DCO base object
	RPLInstanceID: 8-bit field indicating the topology instance		RPLInstanceID: 8-bit field indicating the topology instance
	associated with the DODAG, as learned from the DIO.		associated with the DODAG, as learned from the DIO.
	K: The 'K' flag indicates that the recipient of DCO message is		K: The 'K' flag indicates that the recipient of DCO message is
	expected to send a DCO-ACK back. If the DCO-ACK is not received even		expected to send a DCO-ACK back. If the DCO-ACK is not received even
	after setting the 'K' flag, an implementation may retry the DCO at a		after setting the 'K' flag, an implementation may retry the DCO at a
	later time. The number of retries are implementation and deployment		later time. The number of retries are implementation and deployment
	dependent. A node receiving a DCO message without the 'K' flag set		dependent and are expected to be kept similar with those used in DAO
	MAY respond with a DCO-ACK, especially to report an error condition.		retries in [RFC6550]. A node receiving a DCO message without the 'K'
	An example error condition could be that the node sending the DCO-ACK		flag set MAY respond with a DCO-ACK, especially to report an error
	does not find the routing entry for the indicated target.		condition. An example error condition could be that the node sending
			the DCO-ACK does not 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 expect a response, and the sender SHOULD NOT
			retry the DCO.
	D: The 'D' flag indicates that the DODAGID field is present. This		D: The 'D' flag indicates that the DODAGID field is present. This
	flag MUST be set when a local RPLInstanceID is used.		flag MUST be set when a local RPLInstanceID is used.
	Flags: The 6 bits remaining unused in the Flags field are reserved		Flags: The 6 bits remaining unused in the Flags field are reserved
	for future use. These bits MUST be initialized to zero by the sender		for future use. These bits MUST be initialized to zero by the sender
	and MUST be ignored by the receiver.		and MUST be ignored by the receiver.
	Reserved: 8-bit unused field. The field MUST be initialized to zero		Reserved: 8-bit unused field. The field MUST be initialized to zero
	by the sender and MUST be ignored by the receiver.		by the sender and MUST be ignored by the receiver.
	DCOSequence: Incremented at each unique DCO message from a node and		DCOSequence: 8-bit field incremented at each unique DCO message from
	echoed in the DCO-ACK message. The initial DCOSequence can be chosen		a node and echoed in the DCO-ACK message. The initial DCOSequence
	randomly by the node.		can be chosen randomly by the node. Section 4.4 explains the
			handling of the DCOSequence.
	DODAGID (optional): 128-bit unsigned integer set by a DODAG root that		DODAGID (optional): 128-bit unsigned integer set by a DODAG root that
	uniquely identifies a DODAG. This field MUST be present when the 'D'		uniquely identifies a DODAG. This field MUST be present when the 'D'
	flag is set. DODAGID is used when a local RPLInstanceID is in use,		flag is set and MUST NOT be present if 'D' flag is not set. DODAGID
	in order to identify the DODAGID that is associated with the		is used when a local RPLInstanceID is in use, in order to identify
	RPLInstanceID.		the DODAGID that is associated with the RPLInstanceID.
	4.3.1. Secure DCO		4.3.1. Secure DCO
	A Secure DCO message follows the format in [RFC6550] Figure 7, where		A Secure DCO message follows the format in [RFC6550] Figure 7, where
	the base message format is the DCO message shown in Figure 3.		the base message format is the DCO message shown in Figure 3.
	4.3.2. DCO Options		4.3.2. DCO Options
	The DCO message MUST carry at least one RPL Target and the Transit		The DCO message MUST carry at least one RPL Target and the Transit
	Information Option and MAY carry other valid options. This		Information Option and MAY carry other valid options. This
	specification allows for the DCO message to carry the following		specification allows for the DCO message to carry the following
	options:		options:
	0x00 Pad1		0x00 Pad1
	0x01 PadN		0x01 PadN
	0x05 RPL Target		0x05 RPL Target
	0x06 Transit Information		0x06 Transit Information
	0x09 RPL Target Descriptor		0x09 RPL Target Descriptor
			Section 6.7 of [RFC6550] defines all the above mentioned options.
	The DCO carries an RPL Target Option and an associated Transit		The DCO carries an RPL Target Option and an associated Transit
	Information Option with a lifetime of 0x00000000 to indicate a loss		Information Option with a lifetime of 0x00000000 to indicate a loss
	of reachability to that Target.		of reachability to that Target.
	4.3.3. Path Sequence number in the DCO		4.3.3. Path Sequence number in the DCO
	A DCO message may contain a Path Sequence in the Transit Information		A DCO message may contain a Path Sequence in the Transit Information
	Option to identify the freshness of the DCO message. The Path		Option to identify the freshness of the DCO message. The Path
	Sequence in the DCO MUST use the same Path Sequence number present in		Sequence in the DCO MUST use the same Path Sequence number present in
	the regular DAO message when the DCO is generated in response to a		the regular DAO message when the DCO is generated in response to a
	DAO message. Thus if a DCO is received by a 6LR and subsequently a		DAO message. Thus if a DCO is received by a 6LR and subsequently a
	DAO is received with an old seqeunce number, then the DAO MUST be		DAO is received with an old sequence number, then the DAO MUST be
	ignored.		ignored. When the DCO is generated in response to a DCO from
			upstream parent, the Path Sequence MUST be copied from the received
			DCO.
	4.3.4. Destination Cleanup Option Acknowledgment (DCO-ACK)		4.3.4. Destination Cleanup Option Acknowledgment (DCO-ACK)
	The DCO-ACK message SHOULD be sent as a unicast packet by a DCO		The DCO-ACK message SHOULD be sent as a unicast packet by a DCO
	recipient in response to a unicast DCO message with 'K' flag set. If		recipient in response to a unicast DCO message with 'K' flag set. If
	'K' flag is not set then the receiver of the DCO message MAY send a		'K' flag is not set then the receiver of the DCO message MAY send a
	DCO-ACK to signal an error condition.		DCO-ACK, especially to report an error condition.
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| RPLInstanceID |D| Reserved | DCOSequence | Status |		| RPLInstanceID |D| Flags | DCOSequence | Status |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |		| |
	+ +		+ +
	| |		| |
	+ DODAGID(optional) +		+ DODAGID(optional) +
	| |		| |
	+ +		+ +
	| |		| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Figure 4: DCO-ACK base object		Figure 4: DCO-ACK base object
	RPLInstanceID: 8-bit field indicating the topology instance		RPLInstanceID: 8-bit field indicating the topology instance
	associated with the DODAG, as learned from the DIO.		associated with the DODAG, as learned from the DIO.
	D: The 'D' flag indicates that the DODAGID field is present. This		D: The 'D' flag indicates that the DODAGID field is present. This
	flag MUST be set when a local RPLInstanceID is used.		flag MUST be set when a local RPLInstanceID is used.
	Reserved: 7-bit unused field. The field MUST be initialized to zero		Flags: 7-bit unused field. The field MUST be initialized to zero by
	by the sender and MUST be ignored by the receiver.		the sender and MUST be ignored by the receiver.
	DCOSequence: The DCOSequence in DCO-ACK is copied from the		DCOSequence: 8-bit field. The DCOSequence in DCO-ACK is copied from
	DCOSequence received in the DCO message.		the DCOSequence received in the DCO message.
	Status: Indicates the completion. Status 0 is defined as unqualified		Status: Indicates the completion. Status 0 is defined as unqualified
	acceptance in this specification. Status 1 is defined as "No		acceptance in this specification. Status 1 is defined as "No
	routing-entry for the Target found". The remaining status values are		routing-entry for the Target found". The remaining status values are
	reserved as rejection codes.		reserved as rejection codes.
	DODAGID (optional): 128-bit unsigned integer set by a DODAG root that		DODAGID (optional): 128-bit unsigned integer set by a DODAG root that
	uniquely identifies a DODAG. This field MUST be present when the 'D'		uniquely identifies a DODAG. This field MUST be present when the 'D'
	flag is set. DODAGID is used when a local RPLInstanceID is in use,		flag is set and MUST NOT be present when 'D' flag is not set.
	in order to identify the DODAGID that is associated with the
	RPLInstanceID.		DODAGID is used when a local RPLInstanceID is in use, in order to
			identify the DODAGID that is associated with the RPLInstanceID.
	4.3.5. Secure DCO-ACK		4.3.5. Secure DCO-ACK
	A Secure DCO-ACK message follows the format in [RFC6550] Figure 7,		A Secure DCO-ACK message follows the format in [RFC6550] Figure 7,
	where the base message format is the DCO-ACK message shown in		where the base message format is the DCO-ACK message shown in
	Figure 4.		Figure 4.
	4.4. DCO Base Rules		4.4. DCO Base Rules
	1. If a node sends a DCO message with newer or different information		1. If a node sends a DCO message with newer or different information
	than the prior DCO message transmission, it MUST increment the		than the prior DCO message transmission, it MUST increment the
	DCOSequence field by at least one. A DCO message transmission		DCOSequence field by at least one. A DCO message transmission
	that is identical to the prior DCO message transmission MAY		that is identical to the prior DCO message transmission MAY
	increment the DCOSequence field.		increment the DCOSequence field. The DCOSequence counter follows
			the sequence counter operation as defined in Section 7.2 of
			[RFC6550].
	2. The RPLInstanceID and DODAGID fields of a DCO message MUST be the		2. The RPLInstanceID and DODAGID fields of a DCO message MUST be the
	same value as that of the DAO message in response to which the		same value as that of the DAO message in response to which the
	DCO is generated on the common ancestor node.		DCO is generated on the common ancestor node.
	3. A node MAY set the 'K' flag in a unicast DCO message to solicit a		3. A node MAY set the 'K' flag in a unicast DCO message to solicit a
	unicast DCO-ACK in response in order to confirm the attempt.		unicast DCO-ACK in response in order to confirm the attempt.
	4. A node receiving a unicast DCO message with the 'K' flag set		4. A node receiving a unicast DCO message with the 'K' flag set
	SHOULD respond with a DCO-ACK. A node receiving a DCO message		SHOULD respond with a DCO-ACK. A node receiving a DCO message
	without the 'K' flag set MAY respond with a DCO-ACK, especially		without the 'K' flag set MAY respond with a DCO-ACK, especially
	to report an error condition.		to report an error condition.
	5. A node receiving a unicast DCO message MUST verify the stored		5. A node receiving a unicast DCO message MUST verify the stored
	Path Sequence in context to the given target. If the stored Path		Path Sequence in context to the given target. If the stored Path
	Sequence is more fresh i.e., newer than the Path Sequence		Sequence is more fresh, newer than the Path Sequence received in
	received in the DCO, then the DCO MUST be dropped.		the DCO, then the DCO MUST be dropped.
	6. A node that sets the 'K' flag in a unicast DCO message but does		6. A node that sets the 'K' flag in a unicast DCO message but does
	not receive DCO-ACK in response MAY reschedule the DCO message		not receive DCO-ACK in response MAY reschedule the DCO message
	transmission for another attempt, up until an implementation		transmission for another attempt, up until an implementation
	specific number of retries.		specific number of retries.
	7. A node receiving a unicast DCO message with its own address in		7. A node receiving a unicast DCO message with its own address in
	the RPL Target Option MUST strip-off that Target Option. If this		the RPL Target Option MUST strip-off that Target Option. If this
	Target Option is the only one in the DCO message then the DCO		Target Option is the only one in the DCO message then the DCO
	message MUST be dropped.		message MUST be dropped.
	The scope of DCOSequence values is unique to each node.		The scope of DCOSequence values is unique to the node which generates
			it.
	4.5. Unsolicited DCO		4.5. Unsolicited DCO
	A 6LR may generate an unsolicited DCO to unilaterally cleanup the		A 6LR may generate an unsolicited DCO to unilaterally cleanup the
	path on behalf of the target entry. The 6LR has all the state		path on behalf of the target entry. The 6LR has all the state
	information namely, the Target address and the Path Sequence,		information, namely, the Target address and the Path Sequence,
	required for generating DCO in its routing table. The conditions why		required for generating DCO in its routing table. The conditions why
	6LR may generate an unsolicited DCO are beyond the scope of this		6LR may generate an unsolicited DCO are beyond the scope of this
	document but some possible reasons could be:		document but some possible reasons could be:
	1. On route expiry of an entry, a 6LR may decide to graciously		1. On route expiry of an entry, a 6LR may decide to graciously
	cleanup the entry by initiating DCO.		cleanup the entry by initiating DCO.
	2. 6LR needs to entertain higher priority entries in case the		2. 6LR needs to entertain higher priority entries in case the
	routing table is full thus resulting in an eviction of existing		routing table is full, thus resulting in eviction of an existing
	routing entry. In this case the eviction can be handled		routing entry. In this case the eviction can be handled
	graciously using DCO.		graciously using DCO.
	Note that if the 6LR initiates a unilateral path cleanup using DCO		Note that if the 6LR initiates a unilateral path cleanup using DCO
	and if it has the latest state for the target then the DCO would		and if it has the latest state for the target then the DCO would
	finally reach the target node. Thus the target node would be		finally reach the target node. Thus the target node would be
	informed of its invalidation.		informed of its invalidation.
	4.6. Other considerations		4.6. Other considerations
	skipping to change at page 13, line 23 ¶		skipping to change at page 13, line 33 ¶
	Current RPL [RFC6550] does not provide a mechanism for route		Current RPL [RFC6550] does not provide a mechanism for route
	invalidation for dependent nodes. This document allows the dependent		invalidation for dependent nodes. This document allows the dependent
	nodes invalidation. Dependent nodes will generate their respective		nodes invalidation. Dependent nodes will generate their respective
	DAOs to update their paths, and the previous route invalidation for		DAOs to update their paths, and the previous route invalidation for
	those nodes should work in the similar manner described for switching		those nodes should work in the similar manner described for switching
	node. The dependent node may set the I-flag in the Transit		node. The dependent node may set the I-flag in the Transit
	Information Option as part of regular DAO so as to request		Information Option as part of regular DAO so as to request
	invalidation of previous route from the common ancestor node.		invalidation of previous route from the common ancestor node.
	Dependent nodes do not have any indication regarding if any of its		Dependent nodes do not have any indication regarding if any of their
	parent nodes in turn have decided to switch their parent. Thus for		parents in turn have decided to switch their parent. Thus for route
	route invalidation the dependent nodes may choose to always set the		invalidation the dependent nodes may choose to always set the 'I'
	'I' flag in all its DAO message's Transit Information Option. Note		flag in all its DAO message's Transit Information Option. Note that
	that setting the I-flag is not counter productive even if there is no		setting the I-flag is not counterproductive even if there is no
	previous route to be invalidated.		previous route to be invalidated.
	4.6.2. NPDAO and DCO in the same network		4.6.2. NPDAO and DCO in the same network
	Even with the changed semantics, the current NPDAO mechanism in		The current NPDAO mechanism in [RFC6550] can still be used in the
	[RFC6550] can still be used, for example, when the route lifetime		same network where DCO is used. The NPDAO messaging can be used, for
	expiry of the target happens or when the node simply decides to		example, on route lifetime expiry of the target or when the node
	gracefully terminate the RPL session on graceful node shutdown.		simply decides to gracefully terminate the RPL session on graceful
	Moreover a deployment can have a mix of nodes supporting the DCO and		node shutdown. Moreover, a deployment can have a mix of nodes
	the existing NPDAO mechanism. It is also possible that the same node		supporting the DCO and the existing NPDAO mechanism. It is also
	supports both the NPDAO and DCO signaling.		possible that the same node supports both the NPDAO and DCO signaling
			for route invalidation.
	Section 9.8 of [RFC6550] states, "When a node removes a node from its		Section 9.8 of [RFC6550] states, "When a node removes a node from its
	DAO parent set, it SHOULD send a No-Path DAO message to that removed		DAO parent set, it SHOULD send a No-Path DAO message to that removed
	DAO parent to invalidate the existing router". This document		DAO parent to invalidate the existing router". This document
	introduces an alternate and more optimized way of route invalidation		introduces an alternative and more optimized way of route
	but it also allows existing NPDAO messaging to work. Thus an		invalidation but it also allows existing NPDAO messaging to work.
	implementation has two choices to make when a route invalidation is		Thus an implementation has two choices to make when a route
	to be initiated:		invalidation is to be initiated:
	1. Use NPDAO to invalidate the previous route and send regular DAO		1. Use NPDAO to invalidate the previous route and send regular DAO
	on the new path.		on the new path.
	2. Send regular DAO on the new path with the 'I' flag set in the		2. Send regular DAO on the new path with the 'I' flag set in the
	Transit Information Option such that the common ancestor node		Transit Information Option such that the common ancestor node
	initiates the DCO message downstream to invalidate the previous		initiates the DCO message downstream to invalidate the previous
	route.		route.
	This document recommends using option 2 for reasons specified in		This document recommends using option 2 for reasons specified in
	Section 3 in this document.		Section 3 in this document.
	skipping to change at page 14, line 33 ¶		skipping to change at page 14, line 46 ¶
	it initiates a DCO. With multiple preferred parents, this handling		it initiates a DCO. With multiple preferred parents, this handling
	does not change. But in this case it is recommended that an		does not change. But in this case it is recommended that an
	implementation initiates a DCO after a time period (DelayDCO) such		implementation initiates a DCO after a time period (DelayDCO) such
	that the common ancestor node may receive updated DAOs from all		that the common ancestor node may receive updated DAOs from all
	possible next-hops. This will help to reduce DCO control overhead		possible next-hops. This will help to reduce DCO control overhead
	i.e., the common ancestor can wait for updated DAOs from all possible		i.e., the common ancestor can wait for updated DAOs from all possible
	directions before initiating a DCO for route invalidation. After		directions before initiating a DCO for route invalidation. After
	timeout, the DCO needs to be generated for all the next-hops for whom		timeout, the DCO needs to be generated for all the next-hops for whom
	the route invalidation needs to be done.		the route invalidation needs to be done.
	This documents recommends using a DelayDCO timer value of 1sec. This		This document recommends using a DelayDCO timer value of 1sec. This
	value is inspired by the default DelayDAO value of 1sec in [RFC6550].		value is inspired by the default DelayDAO value of 1sec in [RFC6550].
	Here the hypothesis is that the DAOs from all possible parent set		Here the hypothesis is that the DAOs from all possible parent sets
	would be received on the common ancestor within this time period.		would be received on the common ancestor within this time period.
	Note that there is no requirement of synchronization between DCO and		Note that there is no requirement for synchronization between DCO and
	DAOs. The DelayDCO timer simply ensures that the DCO control		DAOs. The DelayDCO timer simply ensures that the DCO control
	overhead can be reduced and is only needed when the network contains		overhead can be reduced and is only needed when the network contains
	nodes using multiple preferred parent.		nodes using multiple preferred parent.
	5. Acknowledgments		5. Acknowledgments
	Many thanks to Alvaro Retana, Cenk Gundogan, Simon Duquennoy,		Many thanks to Alvaro Retana, Cenk Gundogan, Simon Duquennoy,
	Georgios Papadopoulous, Peter Van Der Stok for their review and		Georgios Papadopoulous, Peter Van Der Stok for their review and
	comments. Alvaro Retana helped shape this document's final version		comments. Alvaro Retana helped shape this document's final version
	with critical review comments.		with critical review comments.
	skipping to change at page 16, line 20 ¶		skipping to change at page 16, line 29 ¶
	should be located in existing category of "Routing Protocol for Low		should be located in existing category of "Routing Protocol for Low
	Power and Lossy Networks (RPL)".		Power and Lossy Networks (RPL)".
	New Status values may be allocated only by an IETF Review. Each		New Status values may be allocated only by an IETF Review. Each
	value is tracked with the following qualities:		value is tracked with the following qualities:
	o Status Code		o Status Code
	o Description		o Description
	o Defining RFC		o Defining RFC
	The following bits are currently defined:		The following values are currently defined:
	+------------+----------------------------------------+-------------+		+------------+----------------------------------------+-------------+
	| Status | Description | Reference |		| Status | Description | Reference |
	| Code | | |		| Code | | |
	+------------+----------------------------------------+-------------+		+------------+----------------------------------------+-------------+
	| 0 | Unqualified acceptance | This |		| 0 | Unqualified acceptance | This |
	| | | document |		| | | document |
	| 1 | No routing-entry for the indicated | This |		| 1 | No routing-entry for the indicated | This |
	| | Target found | document |		| | Target found | document |
	+------------+----------------------------------------+-------------+		+------------+----------------------------------------+-------------+
	skipping to change at page 17, line 17 ¶		skipping to change at page 17, line 23 ¶
	+------------+------------------------------+---------------+		+------------+------------------------------+---------------+
	| 0 | DODAGID field is present (D) | This document |		| 0 | DODAGID field is present (D) | This document |
	+------------+------------------------------+---------------+		+------------+------------------------------+---------------+
	DCO-ACK Base Flags		DCO-ACK Base Flags
	7. Security Considerations		7. Security Considerations
	This document introduces the ability for a common ancestor node to		This document introduces the ability for a common ancestor node to
	invalidate a route on behalf of the target node. The common ancestor		invalidate a route on behalf of the target node. The common ancestor
	node is directed to do so by the target node using the 'I' flag in		node could be directed to do so by the target node using the I-flag
	DCO's Transit Information Option. However, the common ancestor node		in DCO's Transit Information Option. However, the common ancestor
	is in a position to unilaterally initiate the route invalidation		node is in a position to unilaterally initiate the route invalidation
	since it possesses all the required state information, namely, the		since it possesses all the required state information, namely, the
	Target address and the corresponding Path Sequence. Thus a rogue		Target address and the corresponding Path Sequence. Thus a rogue
	common ancestor node could initiate such an invalidation and impact		common ancestor node could initiate such an invalidation and impact
	the traffic to the target node.		the traffic to the target node.
	This document also introduces an I-flag which is set by the target		This document also introduces an I-flag which is set by the target
	node and used by the ancestor node to initiate a DCO if the ancestor		node and used by the ancestor node to initiate a DCO if the ancestor
	nodes sees an update in the route adjacency. However, this flag		sees an update in the route adjacency. However, this flag could be
	could be spoofed by a malicious 6LR in the path and can cause		spoofed by a malicious 6LR in the path and can cause invalidation of
	invalidation of an existing active path. Note that invalidation will		an existing active path. Note that invalidation will happen only if
	happen only if the other conditions such as Path Sequence condition		the other conditions such as Path Sequence condition is also met.
	is also met. Having said that a malicious 6LR may spoof a DAO on		Having said that, such a malicious 6LR may spoof a DAO on behalf of
	behalf of the (sub) child with the I-flag set and can cause route		the (sub) child with the I-flag set and can cause route invalidation
	invalidation on behalf of the (sub) child node.		on behalf of the (sub) child node. Note that, using existing
			mechanisms offered by [RFC6550], a malicious 6LR might also spoof a
			DAO with lifetime of zero or otherwise cause denial of service by
			dropping traffic entirely, so the new mechanism described in this
			document does not present a substantially increased risk of
			disruption.
	This document assumes that the security mechanisms as defined in		This document assumes that the security mechanisms as defined in
	[RFC6550] are followed, which means that the common ancestor node and		[RFC6550] are followed, which means that the common ancestor node and
	all the 6LRs are part of the RPL network because they have the		all the 6LRs are part of the RPL network because they have the
	required credentials. A non-secure RPL network needs to take into		required credentials. A non-secure RPL network needs to take into
	consideration the risks highlighted in this section.		consideration the risks highlighted in this section as well as those
			highlighted in [RFC6550].
	All RPL messages support a secure version of messages which allows		All RPL messages support a secure version of messages which allows
	integrity protection using either a MAC or a signature. Optionally,		integrity protection using either a MAC or a signature. Optionally,
	secured RPL messages also have encryption protection for		secured RPL messages also have encryption protection for
	confidentiality.		confidentiality.
	The document adds new messages (DCO, DCO-ACK) which are syntactically		The document adds new messages (DCO, DCO-ACK) which are syntactically
	similar to existing RPL messages such as DAO, DAO-ACK. Secure		similar to existing RPL messages such as DAO, DAO-ACK. Secure
	versions of DCO and DCO-ACK are added similar to other RPL messages		versions of DCO and DCO-ACK are added similar to other RPL messages
	(such as DAO, DAO-ACK).		(such as DAO, DAO-ACK).
	skipping to change at page 19, line 4 ¶		skipping to change at page 19, line 20 ¶
	explain the example namely, the parameter 'tgt', which stands for		explain the example namely, the parameter 'tgt', which stands for
	Target Option and value of this parameter specifies the address of		Target Option and value of this parameter specifies the address of
	the target node. The parameter 'pathseq', which specifies the Path		the target node. The parameter 'pathseq', which specifies the Path
	Sequence value carried in the Transit Information Option. The		Sequence value carried in the Transit Information Option. The
	parameter 'I_flag' specifies the 'I' flag in the Transit Information		parameter 'I_flag' specifies the 'I' flag in the Transit Information
	Option. sequence of actions is as follows:		Option. sequence of actions is as follows:
	1. Node D switches its parent from node B to node C		1. Node D switches its parent from node B to node C
	2. D sends a regular DAO(tgt=D,pathseq=x+1,I_flag=1) in the updated		2. D sends a regular DAO(tgt=D,pathseq=x+1,I_flag=1) in the updated
	path to C		path to C
	3. C checks for a routing entry on behalf of D, since it cannot find		3. C checks for a routing entry on behalf of D, since it cannot find
	an entry on behalf of D it creates a new routing entry and		an entry on behalf of D it creates a new routing entry and
	forwards the reachability information of the target D to H in a		forwards the reachability information of the target D to H in a
	DAO(tgt=D,pathseq=x+1,I_flag=1).		DAO(tgt=D,pathseq=x+1,I_flag=1).
	4. Similar to C, node H checks for a routing entry on behalf of D,		4. Similar to C, node H checks for a routing entry on behalf of D,
	cannot find an entry and hence creates a new routing entry and		cannot find an entry and hence creates a new routing entry and
	forwards the reachability information of the target D to A in a		forwards the reachability information of the target D to A in a
	DAO(tgt=D,pathseq=x+1,I_flag=1).		DAO(tgt=D,pathseq=x+1,I_flag=1).
	5. Node A receives the DAO(tgt=D,pathseq=x+1,I_flag=1), and checks		5. Node A receives the DAO(tgt=D,pathseq=x+1,I_flag=1), and checks
	for a routing entry on behalf of D. It finds a routing entry but		for a routing entry on behalf of D. It finds a routing entry but
	checks that the next hop for target D is different (i.e., Node		checks that the next hop for target D is different (i.e., Node
	G). Node A checks the I_flag and generates		G). Node A checks the I_flag and generates
	DCO(tgt=D,pathseq=x+1) to previous next hop for target D which is		DCO(tgt=D,pathseq=x+1) to previous next hop for target D which is
	G. Subsequently, Node A updates the routing entry and forwards		G. Subsequently, Node A updates the routing entry and forwards
	the reachability information of target D upstream		the reachability information of target D upstream
	DAO(tgt=D,pathseq=x+1,I_flag=1).		DAO(tgt=D,pathseq=x+1,I_flag=1).
	6. Node G receives the DCO(tgt=D,pathseq=x+1). It checks if the		6. Node G receives the DCO(tgt=D,pathseq=x+1). It checks if the
	received path sequence is latest as compared to the stored path		received path sequence is later than the stored path sequence.
	sequence. If it is latest, Node G invalidates routing entry of		If it is later, Node G invalidates the routing entry of target D
	target D and forwards the (un)reachability information downstream		and forwards the (un)reachability information downstream to B in
	to B in DCO(tgt=D,pathseq=x+1).		DCO(tgt=D,pathseq=x+1).
	7. Similarly, B processes the DCO(tgt=D,pathseq=x+1) by invalidating		7. Similarly, B processes the DCO(tgt=D,pathseq=x+1) by invalidating
	the routing entry of target D and forwards the (un)reachability		the routing entry of target D and forwards the (un)reachability
	information downstream to D.		information downstream to D.
	8. D ignores the DCO(tgt=D,pathseq=x+1) since the target is itself.		8. D ignores the DCO(tgt=D,pathseq=x+1) since the target is itself.
	9. The propagation of the DCO will stop at any node where the node		9. The propagation of the DCO will stop at any node where the node
	does not have an routing information associated with the target.		does not have an routing information associated with the target.
	If the routing information is present and its Path Sequence is		If cached routing information is present and the cached Path
	higher, then still the DCO is dropped.		Sequence is higher than the value in the DCO, then the DCO is
			dropped.
	A.2. Example DCO Messaging with multiple preferred parents		A.2. Example DCO Messaging with multiple preferred parents
	(6LBR)		(6LBR)
	|		|
	|		|
	|		|
	(N11)		(N11)
	/ \		/ \
	/ \		/ \
	/ \		/ \
	(N21) (N22)		(N21) (N22)
	/ / \		/ / \
End of changes. 56 change blocks.
	122 lines changed or deleted		150 lines changed or added
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