< draft-francois-spring-segment-routing-ti-lfa-00.txt		draft-francois-spring-segment-routing-ti-lfa-01.txt >
	Network Working Group Pierre Francois		Network Working Group Pierre Francois
	Internet-Draft IMDEA Networks Institute		Internet-Draft IMDEA Networks Institute
	Intended status: Standards Track Clarence Filsfils		Intended status: Standards Track Clarence Filsfils
	Expires: November 21, 2014 Ahmed Bashandy		Expires: April 26, 2015 Ahmed Bashandy
	Cisco Systems, Inc.		Cisco Systems, Inc.
	Bruno Decraene		Bruno Decraene
	Stephane Litkowski		Stephane Litkowski
	Orange		Orange
	May 20, 2014		Oct 23, 2014
	Topology Independent Fast Reroute using Segment Routing		Topology Independent Fast Reroute using Segment Routing
	draft-francois-spring-segment-routing-ti-lfa-00		draft-francois-spring-segment-routing-ti-lfa-01
	Abstract		Abstract
	This document presents a Fast Reroute (FRR) approach aimed at		This document presents Topology Independent Loop-free Alternate Fast
	providing link and node protection of node and adjacency segments		Re-route (TI-LFA), aimed at providing link and node protection of
	within the Segment Routing (SR) framework. This FRR behavior builds		node and adjacency segments within the Segment Routing (SR)
	on proven IP-FRR concepts being LFAs, remote LFAs (RLFA), and remote		framework. This Fast Re-route (FRR) behavior builds on proven IP-FRR
	LFAs with directed forwarding (DLFA). It extends these concepts to		concepts being LFAs, remote LFAs (RLFA), and remote LFAs with
	provide guaranteed coverage in any IGP network. We accommodate the		directed forwarding (DLFA). It extends these concepts to provide
	FRR discovery and selection approaches in order to establish		guaranteed coverage in any IGP network. We accommodate the FRR
	protection over post-convergence paths from the point of local		discovery and selection approaches in order to establish protection
	repair, dramatically reducing the operator's need to control the tie-		over post-convergence paths from the point of local repair,
	breaks among various FRR options.		dramatically reducing the operational need to control the tie-breaks
			among various FRR options.
	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 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 November 21, 2014.		This Internet-Draft will expire on April 26, 2015.
	Copyright Notice		Copyright Notice
	Copyright (c) 2014 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
	skipping to change at page 2, line 26 ¶		skipping to change at page 2, line 27 ¶
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3. Intersecting P-Space and Q-Space with post-convergence		3. Intersecting P-Space and Q-Space with post-convergence
	paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5		paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	3.1. P-Space property computation for a resource X . . . . . . . 5		3.1. P-Space property computation for a resource X . . . . . . . 5
	3.2. Q-Space property computation for a link S-F, over		3.2. Q-Space property computation for a link S-F, over
	post-convergence paths . . . . . . . . . . . . . . . . . . 5		post-convergence paths . . . . . . . . . . . . . . . . . . 5
	3.3. Q-Space property computation for a node F, over		3.3. Q-Space property computation for a node F, over
	post-convergence paths . . . . . . . . . . . . . . . . . . 6		post-convergence paths . . . . . . . . . . . . . . . . . . 6
	4. EPC Repair Tunnel . . . . . . . . . . . . . . . . . . . . . . . 6		4. TI-LFA Repair Tunnel . . . . . . . . . . . . . . . . . . . . . 6
	4.1. The repair node is a direct neighbor . . . . . . . . . . . 6		4.1. The repair node is a direct neighbor . . . . . . . . . . . 6
	4.2. The repair node is a PQ node . . . . . . . . . . . . . . . 6		4.2. The repair node is a PQ node . . . . . . . . . . . . . . . 6
	4.3. The repair is a Q node, neighbor of the last P node . . . . 7		4.3. The repair is a Q node, neighbor of the last P node . . . . 7
	4.4. Connecting distant P and Q nodes along		4.4. Connecting distant P and Q nodes along
	post-convergence paths . . . . . . . . . . . . . . . . . . 7		post-convergence paths . . . . . . . . . . . . . . . . . . 7
	5. Protecting segments . . . . . . . . . . . . . . . . . . . . . . 7		5. Protecting segments . . . . . . . . . . . . . . . . . . . . . . 7
	5.1. The active segment is a node segment . . . . . . . . . . . 7		5.1. The active segment is a node segment . . . . . . . . . . . 7
	5.2. The active segment is an adjacency segment . . . . . . . . 7		5.2. The active segment is an adjacency segment . . . . . . . . 7
	5.2.1. Protecting [Adjacency, Adjacency] segment lists . . . . 8		5.2.1. Protecting [Adjacency, Adjacency] segment lists . . . . 8
	5.2.2. Protecting [Adjacency, Node] segment lists . . . . . . 8		5.2.2. Protecting [Adjacency, Node] segment lists . . . . . . 8
	skipping to change at page 3, line 36 ¶		skipping to change at page 3, line 36 ¶
	As the capacity of the post-convergence path is typically planned by		As the capacity of the post-convergence path is typically planned by
	the operator to support the post-convergence routing of the traffic		the operator to support the post-convergence routing of the traffic
	for any expected failure, there is much less need for the operator to		for any expected failure, there is much less need for the operator to
	tune the decision among which protection path to choose. The		tune the decision among which protection path to choose. The
	protection path will automatically follow the natural backup path		protection path will automatically follow the natural backup path
	that would be used after local convergence. This also helps to		that would be used after local convergence. This also helps to
	reduce the amount of path changes and hence service transients: one		reduce the amount of path changes and hence service transients: one
	transition (pre-convergence to post-convergence) instead of two (pre-		transition (pre-convergence to post-convergence) instead of two (pre-
	convergence to FRR and then post-convergence).		convergence to FRR and then post-convergence).
	We provide an EPC-FRR approach that achieves guaranteed coverage		We provide the TI-LFA approach that achieves guaranteed coverage
	against link or node failure, in any IGP network, relying on the		against link or node failure, in any IGP network, relying on the
	flexibility of SR.		flexibility of SR.
	L ____		L ____
	S----------F--{____}--D		S----------F--{____}--D
	_|_ ___________ /		_|_ ___________ /
	{___}--Q--{___________}		{___}--Q--{___________}
	Figure 1: EPC Protection		Figure 1: TI-LFA Protection
	We use Figure 1 to illustrate the EPC-FRR approach.		We use Figure 1 to illustrate the TI-LFA approach.
	The Point of Local Repair (PLR), S, needs to find a node Q (a repair		The Point of Local Repair (PLR), S, needs to find a node Q (a repair
	node) that is capable of safely forwarding the traffic to a		node) that is capable of safely forwarding the traffic to a
	destination D affected by the failure of the protected link L, or		destination D affected by the failure of the protected link L, or
	node F. The PLR also needs to find a way to reach Q without being		node F. The PLR also needs to find a way to reach Q without being
	affected by the convergence state of the nodes over the paths it		affected by the convergence state of the nodes over the paths it
	wants to use to reach Q.		wants to use to reach Q.
	In Section 2 we define the main notations used in the document. They		In Section 2 we define the main notations used in the document. They
	are in line with [2].		are in line with [2].
	skipping to change at page 4, line 49 ¶		skipping to change at page 4, line 49 ¶
	state of the network.		state of the network.
	SPT_new(R, X) is the Shortest Path Tree rooted at node R in the state		SPT_new(R, X) is the Shortest Path Tree rooted at node R in the state
	of the network after the resource X has failed.		of the network after the resource X has failed.
	Dist_old(A,B) is the distance from node A to node B in SPT_old(A).		Dist_old(A,B) is the distance from node A to node B in SPT_old(A).
	Dist_new(A,B, X) is the distance from node A to node B in SPT_new(A,		Dist_new(A,B, X) is the distance from node A to node B in SPT_new(A,
	X).		X).
			Similarly to [4], we rely on the concept of P-Space and Q-Space for
			TI-LFA.
	The P-Space P(R,X) of a node R w.r.t. a resource X (e.g. a link S-F,		The P-Space P(R,X) of a node R w.r.t. a resource X (e.g. a link S-F,
	or a node F) is the set of nodes that are reachable from R without		or a node F) is the set of nodes that are reachable from R without
	passing through X. It is the set of nodes that are not downstream of		passing through X. It is the set of nodes that are not downstream of
	X in SPT_old(R).		X in SPT_old(R).
	The Extended P-Space P'(R,X) of a node R w.r.t. a resource X is the		The Extended P-Space P'(R,X) of a node R w.r.t. a resource X is the
	set of nodes that are reachable from R or a neighbor of R, without		set of nodes that are reachable from R or a neighbor of R, without
	passing through X.		passing through X.
	The Q-Space Q(D,X) of a destination node D w.r.t. a resource X is the		The Q-Space Q(D,X) of a destination node D w.r.t. a resource X is the
	skipping to change at page 5, line 24 ¶		skipping to change at page 5, line 28 ¶
	A symmetric network is a network such that the IGP metric of each		A symmetric network is a network such that the IGP metric of each
	link is the same in both directions of the link.		link is the same in both directions of the link.
	3. Intersecting P-Space and Q-Space with post-convergence paths		3. Intersecting P-Space and Q-Space with post-convergence paths
	In this section, we suggest to determine the P-Space and Q-Space		In this section, we suggest to determine the P-Space and Q-Space
	properties of the nodes along on the post-convergence paths from the		properties of the nodes along on the post-convergence paths from the
	PLR to the protected destination and compute an SR-based explicit		PLR to the protected destination and compute an SR-based explicit
	path from P to Q when they are not adjacent. Such properties will be		path from P to Q when they are not adjacent. Such properties will be
	used in Section 4 to compute the EPC-FRR repair list.		used in Section 4 to compute the TI-LFA repair list.
	3.1. P-Space property computation for a resource X		3.1. P-Space property computation for a resource X
	A node N is in P(R, X) if it is not downstream of X in SPT_old(R).		A node N is in P(R, X) if it is not downstream of X in SPT_old(R).
	A node N is in P'(R,X) if it is not downstream of X in SPT_old(N),		A node N is in P'(R,X) if it is not downstream of X in SPT_old(N),
	for at least one neighbor N of R.		for at least one neighbor N of R.
	3.2. Q-Space property computation for a link S-F, over post-convergence		3.2. Q-Space property computation for a link S-F, over post-convergence
	paths		paths
	skipping to change at page 6, line 19 ¶		skipping to change at page 6, line 19 ¶
	to the destination D are in the Q-Space of destination D w.r.t. node		to the destination D are in the Q-Space of destination D w.r.t. node
	F.		F.
	This can be found by intersecting the post-convergence path to D,		This can be found by intersecting the post-convergence path to D,
	assuming the failure of F with Q(D, F).		assuming the failure of F with Q(D, F).
	The post-convergence path to D requires to compute SPT_new(S, F).		The post-convergence path to D requires to compute SPT_new(S, F).
	A node N is in Q(D,F) if it is not downstream of F in rSPT_old(D).		A node N is in Q(D,F) if it is not downstream of F in rSPT_old(D).
	4. EPC Repair Tunnel		4. TI-LFA Repair Tunnel
	The EPC repair tunnel consists of an outgoing interface and a list of		The TI-LFA repair tunnel consists of an outgoing interface and a list
	segments (repair list) to insert on the SR header. The repair list		of segments (repair list) to insert on the SR header. The repair
	encodes the explicit post-convergence path to the destination, which		list encodes the explicit post-convergence path to the destination,
	avoids the protected resource X.		which avoids the protected resource X.
	The EPC repair tunnel is found by intersecting P(S,X) and Q(D,X) with		The TI-LFA repair tunnel is found by intersecting P(S,X) and Q(D,X)
	the post-convergence path to D and computing the explicit SR-based		with the post-convergence path to D and computing the explicit SR-
	path EP(P, Q) from P to Q when these nodes are not adjacent along the		based path EP(P, Q) from P to Q when these nodes are not adjacent
	post convergence path. The EPC repair list is expressed generally as		along the post convergence path. The TI-LFA repair list is expressed
	(Node_SID(P), EP(P, Q)).		generally as (Node_SID(P), EP(P, Q)).
	Most often, the EPC repair list has a simpler form, as described in		Most often, the TI-LFA repair list has a simpler form, as described
	the following sections.		in the following sections.
	4.1. The repair node is a direct neighbor		4.1. The repair node is a direct neighbor
	When the repair node is a direct neighbor, the outgoing interface is		When the repair node is a direct neighbor, the outgoing interface is
	set to that neighbor and the repair segment list is empty.		set to that neighbor and the repair segment list is empty.
	This is comparable to an LFA FRR repair.		This is comparable to an LFA FRR repair.
	4.2. The repair node is a PQ node		4.2. The repair node is a PQ node
	skipping to change at page 8, line 50 ¶		skipping to change at page 8, line 50 ¶
	Upon failure of S-F, packets reaching S with a segment list matching		Upon failure of S-F, packets reaching S with a segment list matching
	[adj(L), node(T), ...], would leave S with a segment list matching		[adj(L), node(T), ...], would leave S with a segment list matching
	[RT(Q),node(T), ...].		[RT(Q),node(T), ...].
	6. References		6. References
	[1] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,		[1] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
	Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Ytti,		Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Ytti,
	S., Henderickx, W., Tantsura, J., and E. Crabbe, "Segment		S., Henderickx, W., Tantsura, J., and E. Crabbe, "Segment
	Routing Architecture", draft-filsfils-spring-segment-routing-01		Routing Architecture", draft-filsfils-spring-segment-routing-04
	(work in progress), May 2014.		(work in progress), July 2014.
	[2] Shand, M. and S. Bryant, "IP Fast Reroute Framework", RFC 5714,		[2] Shand, M. and S. Bryant, "IP Fast Reroute Framework", RFC 5714,
	January 2010.		January 2010.
	[3] Filsfils, C., Francois, P., Shand, M., Decraene, B., Uttaro, J.,		[3] Filsfils, C., Francois, P., Shand, M., Decraene, B., Uttaro, J.,
	Leymann, N., and M. Horneffer, "Loop-Free Alternate (LFA)		Leymann, N., and M. Horneffer, "Loop-Free Alternate (LFA)
	Applicability in Service Provider (SP) Networks", RFC 6571,		Applicability in Service Provider (SP) Networks", RFC 6571,
	June 2012.		June 2012.
	[4] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and S. Ning,		[4] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N. So,
	"Remote LFA FRR", draft-ietf-rtgwg-remote-lfa-02 (work in		"Remote LFA FRR", draft-ietf-rtgwg-remote-lfa-08 (work in
	progress), May 2013.		progress), September 2014.
	[5] Bryant, S., Filsfils, C., Previdi, S., and M. Shand, "IP Fast
	Reroute using tunnels", draft-bryant-ipfrr-tunnels-03 (work in
	progress), November 2007.
	Authors' Addresses		Authors' Addresses
	Pierre Francois		Pierre Francois
	IMDEA Networks Institute		IMDEA Networks Institute
	Leganes		Leganes
	ES		ES
	Email: pierre.francois@imdea.org		Email: pierre.francois@imdea.org
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