< draft-psarkar-rtgwg-rlfa-node-protection-03.txt		draft-psarkar-rtgwg-rlfa-node-protection-04.txt >
	Routing Area Working Group P. Sarkar, Ed.		Routing Area Working Group P. Sarkar, Ed.
	Internet-Draft H. Gredler		Internet-Draft H. Gredler
	Intended status: Standards Track S. Hegde		Intended status: Standards Track S. Hegde
	Expires: June 23, 2014 H. Raghuveer		Expires: October 10, 2014 H. Raghuveer
	C. Bowers		C. Bowers
	Juniper Networks, Inc.		Juniper Networks, Inc.
	S. Litkowski		S. Litkowski
	Orange		Orange
	December 20, 2013		April 08, 2014
	Remote-LFA Node Protection and Manageability		Remote-LFA Node Protection and Manageability
	draft-psarkar-rtgwg-rlfa-node-protection-03		draft-psarkar-rtgwg-rlfa-node-protection-04
	Abstract		Abstract
	The loop-free alternates computed following the current Remote-LFA		The loop-free alternates computed following the current Remote-LFA
	[I-D.ietf-rtgwg-remote-lfa] specification gaurantees only link-		[I-D.ietf-rtgwg-remote-lfa] specification gaurantees only link-
	protection. The resulting Remote-LFA nexthops (also called PQ-		protection. The resulting Remote-LFA nexthops (also called PQ-
	nodes), may not gaurantee node-protection for all destinations being		nodes), may not gaurantee node-protection for all destinations being
	protected by it.		protected by it.
	This document describes procedures for determining if a given PQ-node		This document describes procedures for determining if a given PQ-node
	skipping to change at page 2, line 7 ¶		skipping to change at page 2, line 7 ¶
	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 http://datatracker.ietf.org/drafts/current/.		Drafts is at http://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 June 23, 2014.		This Internet-Draft will expire on October 10, 2014.
	Copyright Notice		Copyright Notice
	Copyright (c) 2013 IETF Trust and the persons identified as the		Copyright (c) 2014 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
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://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
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	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
	skipping to change at page 4, line 35 ¶		skipping to change at page 4, line 35 ¶
	| R3 | S->E->R3 | R2 | S=>N=>R1=>R2->R3 |		| R3 | S->E->R3 | R2 | S=>N=>R1=>R2->R3 |
	| E | S->E | R2 | S=>N=>R1=>R2->R3->E |		| E | S->E | R2 | S=>N=>R1=>R2->R3->E |
	| D1 | S->E->D1 | R2 | S=>N=>R1=>R2->R3->E->D1 |		| D1 | S->E->D1 | R2 | S=>N=>R1=>R2->R3->E->D1 |
	| D2 | S->E->R3->D2 | R2 | S=>N=>R1=>R2->R3->D2 |		| D2 | S->E->R3->D2 | R2 | S=>N=>R1=>R2->R3->D2 |
	+-------------+--------------+---------+-------------------------+		+-------------+--------------+---------+-------------------------+
	Table 1: Remote-LFA backup paths via PQ-node R2		Table 1: Remote-LFA backup paths via PQ-node R2
	A closer look at Table 1 shows that, while the PQ-node R2 provides		A closer look at Table 1 shows that, while the PQ-node R2 provides
	link-protection for all the destinations, it does not provide node-		link-protection for all the destinations, it does not provide node-
	protection for destinations E and F. In the event of the node-failure		protection for destinations E and D1. In the event of the node-
	on primary nexthop E, the alternate path from Remote-LFA nexthop R2		failure on primary nexthop E, the alternate path from Remote-LFA
	to E and D1 also becomes unavailable. So for a Remote-LFA nexthop to		nexthop R2 to E and D1 also becomes unavailable. So for a Remote-LFA
	provide node-protection for a given destination, it is mandatory		nexthop to provide node-protection for a given destination, it is
	that, the shortest path from the given PQ-node to the given		mandatory that, the shortest path from the given PQ-node to the given
	destination MUST not traverse the primary nexthop.		destination MUST not traverse the primary nexthop.
	In another extension of the topology in Figure 1 let us consider an		In another extension of the topology in Figure 1 let us consider an
	additional link between N and E.		additional link between N and E.
	D1		D1
	/		/
	S-x-E		S-x-E
	/ / \		/ / \
	N---+ R3--D2		N---+ R3--D2
	skipping to change at page 5, line 35 ¶		skipping to change at page 5, line 35 ¶
	| R3 | S->E->R3 | R3 | S=>N=>E=>R3 |		| R3 | S->E->R3 | R3 | S=>N=>E=>R3 |
	| E | S->E | R3 | S=>N=>E=>R3->E |		| E | S->E | R3 | S=>N=>E=>R3->E |
	| D1 | S->E->D1 | R3 | S=>N=>E=>R3->E->D1 |		| D1 | S->E->D1 | R3 | S=>N=>E=>R3->E->D1 |
	| D2 | S->E->D1 | R3 | S=>N=>E=>R3->D2 |		| D2 | S->E->D1 | R3 | S=>N=>E=>R3->D2 |
	+-------------+--------------+---------+------------------------+		+-------------+--------------+---------+------------------------+
	Table 2: Remote-LFA backup paths via PQ-node R3		Table 2: Remote-LFA backup paths via PQ-node R3
	Again a closer look at Table 2 shows that, unlike Table 1, where the		Again a closer look at Table 2 shows that, unlike Table 1, where the
	single PQ-node R2 provided node-protection, for destinations R3 and		single PQ-node R2 provided node-protection, for destinations R3 and
	G, if we choose R3 as the R-LFA nexthop, it does not provide node-		D1, if we choose R3 as the R-LFA nexthop, it does not provide node-
	protection for R3 and D1 anymore. If S chooses R3 as the R-LFA		protection for R3 and D1 anymore. If S chooses R3 as the R-LFA
	nexthop, in the event of the node-failure on primary nexthop E, the		nexthop, in the event of the node-failure on primary nexthop E, the
	alternate path from S to R-LFA nexthop R3 also becomes unavailable.		alternate path from S to R-LFA nexthop R3 also becomes unavailable.
	So for a Remote-LFA nexthop to provide node-protection for a given		So for a Remote-LFA nexthop to provide node-protection for a given
	destination, it is also mandatory that, the shortest path from S to		destination, it is also mandatory that, the shortest path from S to
	the chosen PQ-node MUST not traverse the primary nexthop node.		the chosen PQ-node MUST not traverse the primary nexthop node.
	2.2. Few Additional Definitions		2.2. Few Additional Definitions
	This document adds and enhances the following definitions extending		This document adds and enhances the following definitions extending
	skipping to change at page 6, line 15 ¶		skipping to change at page 6, line 15 ¶
	S-E link on any of the shortest path from the direct neighbor to the		S-E link on any of the shortest path from the direct neighbor to the
	router. This MUST exclude any direct neighbor for which there is		router. This MUST exclude any direct neighbor for which there is
	atleast one ECMP path from the direct neighbor traversing the		atleast one ECMP path from the direct neighbor traversing the
	link(S-E) being protected.		link(S-E) being protected.
	A node Y is in link-protecting extended P-space w.r.t to the link		A node Y is in link-protecting extended P-space w.r.t to the link
	(S-E) being protected, if and only if, there exists atleast one		(S-E) being protected, if and only if, there exists atleast one
	direct neighbor of S, Ni, other than primary nexthop E, that		direct neighbor of S, Ni, other than primary nexthop E, that
	satisfies the following condition.		satisfies the following condition.
	D_opt(Ni,Y) < D_opt(Ni,S) + D_opt(S,E) + D_opt(E,Y)		D_opt(Ni,Y) < D_opt(Ni,S) + D_opt(S,Y)
	Where,		Where,
	D_opt(A,B) : Distance on most optimum path from A to B.		D_opt(A,B) : Distance on most optimum path from A to B.
	E : The primary nexthop on shortest path from S
	to destination.
	Ni : A direct neighbor of S other than primary		Ni : A direct neighbor of S other than primary
	nexthop E.		nexthop E.
	Y : The node being evaluated for link-protecting		Y : The node being evaluated for link-protecting
	extended P-Space.		extended P-Space.
	Figure 3: Link-Protecting Ext-P-Space Condition		Figure 3: Link-Protecting Ext-P-Space Condition
	2.2.2. Node-Protecting Extended P-Space		2.2.2. Node-Protecting Extended P-Space
	The node-protecting extended P-space for a primary nexthop node E		The node-protecting extended P-space for a primary nexthop node E
	skipping to change at page 7, line 20 ¶		skipping to change at page 7, line 20 ¶
	to destination.		to destination.
	Ni : A direct neighbor of S other than primary		Ni : A direct neighbor of S other than primary
	nexthop E.		nexthop E.
	Y : The node being evaluated for node-protecting		Y : The node being evaluated for node-protecting
	extended P-Space.		extended P-Space.
	Figure 4: Node-Protecting Ext-P-Space Condition		Figure 4: Node-Protecting Ext-P-Space Condition
	It must be noted that a node Y satisfying the condition in Figure 4		It must be noted that a node Y satisfying the condition in Figure 4
	above only guarantees that the R-LFA alternate path segment from S		above only guarantees that the R-LFA alternate path segment from S
	via direct neighbor Ni to the PQ-node Y is not affected in the event		via direct neighbor Ni to the node Y is not affected in the event of
	of a node failure of E. It does not yet guarantee that the path		a node failure of E. It does not yet guarantee that the path segment
	segment from PQ-node Y to the destination is also unaffected by the		from node Y to the destination is also unaffected by the same failure
	same failure event.		event.
	2.2.3. Q-Space		2.2.3. Q-Space
	The Remote-LFA [I-D.ietf-rtgwg-remote-lfa] draft already defines		The Remote-LFA [I-D.ietf-rtgwg-remote-lfa] draft already defines
	this. The Q-space for a link S-E being protected is the set of		this. The Q-space for a link S-E being protected is the set of
	routers that can reach primary node E, without traversing the S-E		routers that can reach primary node E, without traversing the S-E
	link on any of the shortest path from the node Y to primary nexthop		link on any of the shortest path from the node Y to primary nexthop
	E. This MUST exclude any destination for which there is atleast one		E. This MUST exclude any destination for which there is atleast one
	ECMP path from the node Y to the primary nexthop E traversing the		ECMP path from the node Y to the primary nexthop E traversing the
	link(S-E) being protected.		link(S-E) being protected.
	skipping to change at page 9, line 7 ¶		skipping to change at page 9, line 7 ¶
	To choose a node-protecting R-LFA nexthop for a destination R3,		To choose a node-protecting R-LFA nexthop for a destination R3,
	router S needs to consider a PQ-node from the candidate node-		router S needs to consider a PQ-node from the candidate node-
	protecting PQ-space for the primary nexthop E on shortest path from S		protecting PQ-space for the primary nexthop E on shortest path from S
	to R3. As mentioned in Section 2.2.2, to consider a PQ-node as		to R3. As mentioned in Section 2.2.2, to consider a PQ-node as
	candidate node-protecting PQ-node, there must be atleast one direct		candidate node-protecting PQ-node, there must be atleast one direct
	neighbor Ni of S, such that all shortest paths from Ni to the PQ-node		neighbor Ni of S, such that all shortest paths from Ni to the PQ-node
	does not traverse primary nexthop node E.		does not traverse primary nexthop node E.
	Implementations should run the inequality in Section 2.2.2 Figure 4		Implementations should run the inequality in Section 2.2.2 Figure 4
	for all direct neighbor, other than primary nexthop node E, to		for all direct neighbor, other than primary nexthop node E, to
	determine whether a PQ-node Y is also a candidate node-protecting PQ-		determine whether a node Y is a candidate node-protecting PQ-node.
	node. All of the metrics needed by this inequality would have been		All of the metrics needed by this inequality would have been already
	already collected from the forward SPFs rooted at each of direct		collected from the forward SPFs rooted at each of direct neighbor S,
	neighbor S, computed as part of standard LFA [RFC5286]		computed as part of standard LFA [RFC5286] implementation. With
	implementation. With reference to the topology in Figure 2, Table 3		reference to the topology in Figure 2, Table 3 below shows how the
	below shows how the above condition can be used to determine the		above condition can be used to determine the candidate node-
	candidate node-protecting PQ-space for S-E link (primary nexthop E)		protecting PQ-space for S-E link (primary nexthop E)
	+----------+----------+----------+-----------+----------+-----------+		+------------+----------+----------+----------+---------+-----------+
	| PQ-node | Direct | D_opt | D_opt | D_opt | Condition |		| Candidate | Direct | D_opt | D_opt | D_opt | Condition |
	| (Y) | Nbr (Ni) | (Ni,Y) | (Ni,E) | (E,Y) | Met |		| PQ-node | Nbr (Ni) | (Ni,Y) | (Ni,E) | (E,Y) | Met |
	+----------+----------+----------+-----------+----------+-----------+		| (Y) | | | | | |
	| R2 | N | 2 (N,R2) | 1 (N,E) | 2 (E,R2) | Yes |		+------------+----------+----------+----------+---------+-----------+
	| R3 | N | 2 (N,R3) | 1 (N,E) | 1 (E,R3) | No |		| R2 | N | 2 (N,R2) | 1 (N,E) | 2 | Yes |
	+----------+----------+----------+-----------+----------+-----------+		| | | | | (E,R2) | |
			| R3 | N | 2 (N,R3) | 1 (N,E) | 1 | No |
			| | | | | (E,R3) | |
			+------------+----------+----------+----------+---------+-----------+
	Table 3: Node-protection evaluation for R-LFA repair tunnel to PQ-		Table 3: Node-protection evaluation for R-LFA repair tunnel to PQ-
	node		node
	As seen in the above Table 3 , R3 does not meet the node-protecting		As seen in the above Table 3 , R3 does not meet the node-protecting
	extended-p-space inequality And so, while R2 is in candidate node-		extended-p-space inequality And so, while R2 is in candidate node-
	protecting PQ space, R3 is not.		protecting PQ space, R3 is not.
	Some SPF implementations may also produce a list of links and nodes		Some SPF implementations may also produce a list of links and nodes
	traversed on the shortest path(s) from a given root to others. In		traversed on the shortest path(s) from a given root to others. In
	such implementations, router S may have executed a forward SPF with		such implementations, router S may have executed a forward SPF with
	each of it's direct neighbors as the SPF root, executed as part of		each of it's direct neighbors as the SPF root, executed as part of
	the standard LFA [RFC5286] computations. So S may re-use the list of		the standard LFA [RFC5286] computations. So S may re-use the list of
	links and nodes collected from the same SPF computations, to decide		links and nodes collected from the same SPF computations, to decide
	whether a PQ-node Y is a candidate node-protecting PQ-node or not. A		whether a node Y is a candidate node-protecting PQ-node or not. A
	PQ-node Y shall be considered as a node-protecting, if and only if,		node Y shall be considered as a node-protecting PQ-node, if and only
	there is atleast one direct neighbor of S, other than the primary		if, there is atleast one direct neighbor of S, other than the primary
	nexthop E, for which, the primary nexthop node E does not exist on		nexthop E, for which, the primary nexthop node E does not exist on
	the list of nodes traversed on any of the shortest path(s) from the		the list of nodes traversed on any of the shortest path(s) from the
	direct neighbor to the PQ-node. Table 4 below is an illustration of		direct neighbor to the PQ-node. Table 4 below is an illustration of
	the mechanism with the topology in Figure 2.		the mechanism with the topology in Figure 2.
	+---------+---------------------+-----------------+-----------------+		+-----------+-------------------+-----------------+-----------------+
	| PQ-node | Repair Tunnel | Link-Protection | Node-Protection |		| Candidate | Repair Tunnel | Link-Protection | Node-Protection |
	| | Path(Repairing | | |		| PQ-node | Path(Repairing | | |
	| | router to PQ-node) | | |		| | router to PQ- | | |
	+---------+---------------------+-----------------+-----------------+		| | node) | | |
	| R2 | S->N->R1->R2 | Yes | Yes |		+-----------+-------------------+-----------------+-----------------+
	| R2 | S->E->R3->R2 | No | No |		| R2 | S->N->R1->R2 | Yes | Yes |
	| R3 | S->N->E->R3 | Yes | No |		| R2 | S->E->R3->R2 | No | No |
	+---------+---------------------+-----------------+-----------------+		| R3 | S->N->E->R3 | Yes | No |
			+-----------+-------------------+-----------------+-----------------+
	Table 4: Protection of Remote-LFA tunnel to the PQ-node		Table 4: Protection of Remote-LFA tunnel to the PQ-node
	As seen in the above Table 4 while R2 is candidate node-protecting		As seen in the above Table 4 while R2 is candidate node-protecting
	Remote-LFA nexthop for R3 and G, it is not so for E and F, since the		Remote-LFA nexthop for R3 and D2, it is not so for E and D1, since
	primary nexthop E is in the shortest path from R2 to E and F.		the primary nexthop E is in the shortest path from R2 to E and F.
	2.3.2. Computing node-protecting paths from PQ-nodes to destinations		2.3.2. Computing node-protecting paths from PQ-nodes to destinations
	Once a computing router finds all the candidate node-protecting PQ-		Once a computing router finds all the candidate node-protecting PQ-
	nodes for a given directly attached primary link, it shall follow the		nodes for a given directly attached primary link, it shall follow the
	procedure in proposed in this section, to choose one or more node-		procedure in proposed in this section, to choose one or more node-
	protecting R-LFA paths, for destinations reachable through the same		protecting R-LFA paths, for destinations reachable through the same
	primary link in the primary SPF graph.		primary link in the primary SPF graph.
	To find a node-protecting R-LFA path for a given destination, the		To find a node-protecting R-LFA path for a given destination, the
	skipping to change at page 10, line 43 ¶		skipping to change at page 10, line 44 ¶
	destination remain unaffected in the event of a node failure of		destination remain unaffected in the event of a node failure of
	primary nexthop node. To ensure this, the computing router will need		primary nexthop node. To ensure this, the computing router will need
	to ensure that, the primary nexthop node should not be on any of the		to ensure that, the primary nexthop node should not be on any of the
	shortest paths from the PQ-node to the given destination.		shortest paths from the PQ-node to the given destination.
	This document proposes an additional forward SPF computation for each		This document proposes an additional forward SPF computation for each
	of the PQ-nodes, to discover all shortest paths from the PQ-nodes to		of the PQ-nodes, to discover all shortest paths from the PQ-nodes to
	the destination. The additional forward SPF computation for each PQ-		the destination. The additional forward SPF computation for each PQ-
	node, shall help determine, if a given primary nexthop node is on the		node, shall help determine, if a given primary nexthop node is on the
	shortest paths from the PQ-node to the given destination or not. To		shortest paths from the PQ-node to the given destination or not. To
	determine if a given PQ-node provides node-protecting alternate for a		determine if a given candidate node-protecting PQ-node provides node-
	given destination, the primary nexthop node should not be on any of		protecting alternate for a given destination, the primary nexthop
	the shortest paths from the PQ-node to the given destination. After		node should not be on any of the shortest paths from the PQ-node to
	running the forward SPF on a PQ-node (from the node-protecting PQ-		the given destination. On running the forward SPF on a candidate
	space) the computing router shall run the inequality in Figure 6		node-protecting PQ-node the computing router shall run the inequality
	below. PQ-nodes that does not qualify the condition for a given		in Figure 6 below. PQ-nodes that does not qualify the condition for
	destination, does not gaurantee node-protection for the path segment		a given destination, does not gaurantee node-protection for the path
	from the PQ-node to the given destination.		segment from the PQ-node to the given destination.
	D_opt(Y,D) < D_opt(Y,E) + Distance_opt(E,D)		D_opt(Y,D) < D_opt(Y,E) + Distance_opt(E,D)
	Where,		Where,
	D_opt(A,B) : Distance on most optimum path from A to B.		D_opt(A,B) : Distance on most optimum path from A to B.
	D : The destination node.		D : The destination node.
	E : The primary nexthop on shortest path from S		E : The primary nexthop on shortest path from S
	to destination.		to destination.
	Y : The node-protecting PQ-node being evaluated		Y : The node-protecting PQ-node being evaluated
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