< draft-ietf-rtgwg-multihomed-prefix-lfa-07.txt		draft-ietf-rtgwg-multihomed-prefix-lfa-08.txt >
	Routing Area Working Group P. Sarkar, Ed.		Routing Area Working Group P. Sarkar, Ed.
	Internet-Draft Arrcus, Inc.		Internet-Draft Arrcus, Inc.
	Updates: 5286 (if approved) U. Chunduri, Ed.		Updates: 5286 (if approved) U. Chunduri, Ed.
	Intended status: Standards Track Huawei USA		Intended status: Standards Track Huawei USA
	Expires: March 23, 2019 S. Hegde		Expires: April 19, 2019 S. Hegde
	Juniper Networks, Inc.		Juniper Networks, Inc.
	J. Tantsura		J. Tantsura
	Nuage Networks		Apstra, Inc.
	H. Gredler		H. Gredler
	RtBrick, Inc.		RtBrick, Inc.
	September 19, 2018		October 16, 2018
	LFA selection for Multi-Homed Prefixes		LFA selection for Multi-Homed Prefixes
	draft-ietf-rtgwg-multihomed-prefix-lfa-07		draft-ietf-rtgwg-multihomed-prefix-lfa-08
	Abstract		Abstract
	This document shares experience gained from implementing algorithms		This document shares experience gained from implementing algorithms
	to determine Loop-Free Alternates for multi-homed prefixes. In		to determine Loop-Free Alternates (LFAs) for multi-homed prefixes.
	particular, this document provides explicit inequalities that can be		In particular, this document provides explicit inequalities that can
	used to evaluate neighbors as a potential alternates for multi-homed		be used to evaluate neighbors as a potential alternates for multi-
	prefixes. It also provides detailed criteria for evaluating		homed prefixes. It also provides detailed criteria for evaluating
	potential alternates for external prefixes advertised by OSPF ASBRs.		potential alternates for external prefixes advertised by OSPF ASBRs.
	This documents updates and expands some of the "Routing Aspects" as		This documents updates and expands some of the "Routing Aspects" as
	specified in Section 6 of RFC 5286.		specified in Section 6 of RFC 5286.
	Requirements Language		Requirements Language
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	document are to be interpreted as described in RFC8174 [RFC8174].		"OPTIONAL" in this document are to be interpreted as described in BCP
			14 RFC8174 [RFC2119] RFC8174 [RFC8174] when, and only when, they
			appear in all capitals, as shown here.
	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 March 23, 2019.
			This Internet-Draft will expire on April 19, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 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 26 ¶		skipping to change at page 2, line 29 ¶
	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. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3		1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. LFA inequalities for MHPs . . . . . . . . . . . . . . . . . . 4		2. LFA inequalities for MHPs . . . . . . . . . . . . . . . . . . 4
	3. LFA selection for the multi-homed prefixes . . . . . . . . . 4		3. LFA selection for the multi-homed prefixes . . . . . . . . . 5
	3.1. Improved coverage with simplified approach to MHPs . . . 6		3.1. Improved coverage with simplified approach to MHPs . . . 6
	3.2. IS-IS ATT Bit considerations . . . . . . . . . . . . . . 7		3.2. IS-IS ATT Bit considerations . . . . . . . . . . . . . . 8
	4. LFA selection for the multi-homed external prefixes . . . . . 8		4. LFA selection for the multi-homed external prefixes . . . . . 8
	4.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . 8		4.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . 8
	4.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 8		4.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 8
	4.2.1. Rules to select alternate ASBR . . . . . . . . . . . 8		4.2.1. Rules to select alternate ASBR . . . . . . . . . . . 9
	4.2.1.1. Multiple ASBRs belonging different area . . . . . 9		4.2.1.1. Multiple ASBRs belonging different area . . . . . 11
	4.2.1.2. Type 1 and Type 2 costs . . . . . . . . . . . . . 10		4.2.1.2. Type 1 and Type 2 costs . . . . . . . . . . . . . 11
	4.2.1.3. RFC1583compatibility is set to enabled . . . . . 10		4.2.1.3. RFC1583compatibility is set to enabled . . . . . 11
	4.2.1.4. Type 7 routes . . . . . . . . . . . . . . . . . . 10		4.2.1.4. Type 7 routes . . . . . . . . . . . . . . . . . . 11
	4.2.2. Inequalities to be applied for alternate ASBR		4.2.2. Inequalities to be applied for alternate ASBR
	selection . . . . . . . . . . . . . . . . . . . . . . 11		selection . . . . . . . . . . . . . . . . . . . . . . 12
	4.2.2.1. Forwarding address set to non-zero value . . . . 11		4.2.2.1. Forwarding address set to non-zero value . . . . 12
	4.2.2.2. ASBRs advertising type1 and type2 cost . . . . . 11		4.2.2.2. ASBRs advertising type1 and type2 cost . . . . . 12
	5. LFA Extended Procedures . . . . . . . . . . . . . . . . . . . 12		5. LFA Extended Procedures . . . . . . . . . . . . . . . . . . . 13
	5.1. Links with IGP MAX_METRIC . . . . . . . . . . . . . . . . 12		5.1. Links with IGP MAX_METRIC . . . . . . . . . . . . . . . . 13
	5.2. Multi Topology Considerations . . . . . . . . . . . . . . 13		5.2. Multi Topology Considerations . . . . . . . . . . . . . . 14
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
	7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
	8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 14		8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 15		9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
	10.1. Normative References . . . . . . . . . . . . . . . . . . 15		10.1. Normative References . . . . . . . . . . . . . . . . . . 16
	10.2. Informative References . . . . . . . . . . . . . . . . . 15		10.2. Informative References . . . . . . . . . . . . . . . . . 16
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
	1. Introduction		1. Introduction
	A framework for the development of IP fast- reroute mechanisms is		A framework for the development of IP fast-reroute mechanisms is
	detailed in [RFC5714]. The use of Loop-Free Alternates (LFA) for IP		detailed in [RFC5714]. The use of LFAs for IP Fast Reroute is
	Fast Reroute is specified in [RFC5286]. Section 6.1 of [RFC5286]		specified in [RFC5286]. Section 6.1 of [RFC5286] describes a method
	describes a method to determine loop-free alternates for multi-homed		to determine LFAs for multi-homed prefixes (MHPs). This document
	prefixes (MHPs). This document describes a procedure using explicit		describes a procedure using explicit inequalities that can be used by
	inequalities that can be used by a computing router to evaluate a		a computing router to evaluate a neighbor as a potential alternate
	neighbor as a potential alternate for a multi-homed prefix. The		for a multi-homed prefix. The results obtained are equivalent to
	results obtained are equivalent to those obtained using the method		those obtained using the method described in Section 6.1 of
	described in Section 6.1 of [RFC5286]. However, some may find this		[RFC5286]. However, some may find this formulation useful.
	formulation useful.
	Section 6.3 of [RFC5286] discusses complications associated with		Section 6.3 of [RFC5286] discusses complications associated with
	computing LFAs for multi-homed prefixes in OSPF. This document		computing LFAs for multi-homed prefixes in OSPF. This document
	provides detailed criteria for evaluating potential alternates for		provides detailed criteria for evaluating potential alternates for
	external prefixes advertised by OSPF ASBRs, as well as explicit		external prefixes advertised by OSPF ASBRs, as well as explicit
	inequalities.		inequalities.
	This document also provides clarifications, additional considerations		This document also provides clarifications, additional considerations
	to [RFC5286], to address a few coverage and operational observations.		to [RFC5286], to address a few coverage and operational observations.
	These observations are in the area of handling IS-IS attach (ATT) bit		These observations are in the area of handling IS-IS attach (ATT) bit
	in Level-1 (L1) area, links provisioned with MAX_METRIC for traffic		in Level-1 (L1) area, links provisioned with MAX_METRIC for traffic
	engineering (TE) purposes and in the area of Multi Topology (MT) IGP		engineering (TE) purposes and in the area of Multi Topology (MT) IGP
	deployments. These are elaborated in detail in Section 3.2 and		deployments. These are elaborated in detail in Section 3.2 and
	Section 5.		Section 5.
			This specification uses the same terminology introduced in [RFC5714]
			to represent LFA and builds on the inequalities notation used in
			[RFC5286] to compute LFAs for MHPs.
	1.1. Acronyms		1.1. Acronyms
	AF - Address Family		AF - Address Family
	ATT - IS-IS Attach Bit		ATT - IS-IS Attach Bit
	ECMP - Equal Cost Multi Path		ECMP - Equal Cost Multi Path
	IGP - Interior Gateway Protocol		IGP - Interior Gateway Protocol
	IS-IS - Intermediate System to Intermediate System		IS-IS - Intermediate System to Intermediate System
			LFA - Loop-Free Alternate
	LSP - IS-IS Link State PDU		LSP - IS-IS Link State PDU
	OSPF - Open Shortest Path First		OSPF - Open Shortest Path First
	MHP - Multi-homed Prefix		MHP - Multi-homed Prefix
	MT - Multi Topology		MT - Multi Topology
	SPF - Shortest Path First PDU		SPF - Shortest Path First PDU
	2. LFA inequalities for MHPs		2. LFA inequalities for MHPs
	This document proposes the following set of LFA inequalities for		This document proposes the following set of LFA inequalities for
	selecting the most appropriate LFAs for multi-homed prefixes (MHPs).		selecting the most appropriate LFAs for multi-homed prefixes (MHPs).
	They can be derived from the inequalities in [RFC5286] combined with		They can be derived from the inequalities in [RFC5286] combined with
	the observation that D_opt(N,P) = Min (D_opt(N,PO_i) + cost(PO_i,P))		the observation that D_opt(N,P) = Min (D_opt(N,PO_i) + Cost(PO_i,P))
	over all PO_i		over all PO_i
	Link-Protection:		Link-Protection:
	D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) +		D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,S) +
	D_opt(S,PO_best) + cost(PO_best,P)		D_opt(S,PO_best) + Cost(PO_best,P)
	Link-Protection + Downstream-paths-only:		Link-Protection + Downstream-paths-only:
	D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(S,PO_best) + cost(PO_best,P)		D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(S,PO_best) + Cost(PO_best,P)
	Node-Protection:		Node-Protection:
	D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,E) +		D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,E) +
	D_opt(E,PO_best) + cost(PO_best,P)		D_opt(E,PO_best) + Cost(PO_best,P)
	Where,		Where,
	P - The multi-homed prefix being evaluated for		P - The multi-homed prefix being evaluated for
	computing alternates		computing alternates
	S - The computing router		S - The computing router
	N - The alternate router being evaluated		N - The alternate router being evaluated
	E - The primary next-hop on shortest path from S to		E - The primary next-hop on shortest path from S to
	prefix P.		prefix P.
	PO_i - The specific prefix-originating router being		PO_i - The specific prefix-originating router being
	evaluated.		evaluated.
	PO_best - The prefix-originating router on the shortest path		PO_best - The prefix-originating router on the shortest path
	from the computing router S to prefix P.		from the computing router S to prefix P.
	Cost (X,P) - Cost of reaching the prefix P from prefix		Cost(X,P) - Cost of reaching the prefix P from prefix
	originating node X.		originating node X.
	D_opt(X,Y) - Distance on the shortest path from node X to node		D_opt(X,Y) - Distance on the shortest path from node X to node
	Y.		Y.
	Figure 1: LFA inequalities for MHPs		Figure 1: LFA inequalities for MHPs
	3. LFA selection for the multi-homed prefixes		3. LFA selection for the multi-homed prefixes
	To compute a valid LFA for a given multi-homed prefix P, a computing		To compute a valid LFA for a given multi-homed prefix P, a computing
	router S MUST follow one of the appropriate procedures below, for		router S MUST follow one of the appropriate procedures below, for
	skipping to change at page 6, line 27 ¶		skipping to change at page 6, line 33 ¶
	failure optimal point of attachment, at the expense of potentially		failure optimal point of attachment, at the expense of potentially
	lower coverage. If an implementation chooses to simplify the multi-		lower coverage. If an implementation chooses to simplify the multi-
	homed prefix calculation by assuming that the MHP is solely attached		homed prefix calculation by assuming that the MHP is solely attached
	to the router that was its pre-failure optimal point of attachment,		to the router that was its pre-failure optimal point of attachment,
	the procedure described in this memo can potentially improve coverage		the procedure described in this memo can potentially improve coverage
	for equal cost multi path (ECMP) MHPs without incurring extra		for equal cost multi path (ECMP) MHPs without incurring extra
	computational cost.		computational cost.
	This document improves the above approach to provide loop-free		This document improves the above approach to provide loop-free
	alternatives without any additional cost for ECMP MHPs as described		alternatives without any additional cost for ECMP MHPs as described
	through the below example network. The approach specified here MAY		through the below example network presented in Figure 3. The
	also be applicable for handling default routes as explained in		approach specified here MAY also be applicable for handling default
	Section 3.2.		routes as explained in Section 3.2.
	5 +---+ 8 +---+ 5 +---+		5 +---+ 8 +---+ 5 +---+
	+-----| S |------| A |-----| B |		+-----| S |------| A |-----| B |
	| +---+ +---+ +---+		| +---+ +---+ +---+
	| | |		| | |
	| 5 | 5 |		| 5 | 5 |
	| | |		| | |
	+---+ 5 +---+ 4 +---+ 1 +---+		+---+ 5 +---+ 4 +---+ 1 +---+
	| C |---| E |-----| M |-------| F |		| C |---| E |-----| M |-------| F |
	+---+ +---+ +---+ +---+		+---+ +---+ +---+ +---+
	| 10 5 |		| 10 5 |
	+-----------P---------+		+-----------P---------+
	Figure 3: MHP with same ECMP Next-hop		Figure 3: MHP with same ECMP Next-hop
	In the above network a prefix p, is advertised from both Node E and		In the above network a prefix P, is advertised from both Node E and
	Node F. With simplified approach taken as specified in [RFC5286]		Node F. With simplified approach taken as specified in [RFC5286]
	Section 6.1, prefix P will get only link protection LFA through the		Section 6.1, prefix P will get only link protection LFA through the
	neighbor C while a node protection path is available through neighbor		neighbor C while a node protection path is available through neighbor
	A. In this scenario, E and F both are pre-failure optimal points of		A. In this scenario, E and F both are pre-failure optimal points of
	attachment and share the same primary next-hop. Hence, an		attachment and share the same primary next-hop. Hence, an
	implementation MAY compare the kind of protection A provides to F		implementation MAY compare the kind of protection A provides to F
	(link-and-node protection) with the kind of protection C provides to		(link-and-node protection) with the kind of protection C provides to
	E (link protection) and inherit the better alternative to prefix P		E (link protection) and inherit the better alternative to prefix P
	and here it is A.		and here it is A.
	However, in the below network prefix P has an ECMP through both node		However, in the below example network presented in Figure 4, prefix P
	E and node F with cost 20. Though it has 2 pre-failure optimal		has an ECMP through both node E and node F with cost 20. Though it
	points of attachment, the primary next-hop to each pre-failure		has 2 pre-failure optimal points of attachment, the primary next-hop
	optimal point of attachment is different. In this case, prefix P		to each pre-failure optimal point of attachment is different. In
	MUST inherit corresponding LFAs of each primary next-hop calculated		this case, prefix P MUST inherit corresponding LFAs of each primary
	for the router advertising the same respectively. In the below		next-hop calculated for the router advertising the same respectively.
	diagram that would be node E's and node F's LFA i.e., node N1 and		In the below diagram that would be node E's and node F's LFA i.e.,
	node N2 respectively.		node N1 and node N2 respectively.
	4 +----+		4 +----+
	+------------------| N2 |		+------------------| N2 |
	| +----+		| +----+
	| | 4		| | 4
	10 +---+ 3 +---+		10 +---+ 3 +---+
	+------| S |----------------| B |		+------| S |----------------| B |
	| +---+ +---+		| +---+ +---+
	| | |		| | |
	| 10 | 1 |		| 10 | 1 |
	skipping to change at page 9, line 7 ¶		skipping to change at page 10, line 7 ¶
	4.2.1. Rules to select alternate ASBR		4.2.1. Rules to select alternate ASBR
	The process to select an alternate ASBR is best explained using the		The process to select an alternate ASBR is best explained using the
	rules below. The below process is applied when primary ASBR for the		rules below. The below process is applied when primary ASBR for the
	concerned prefix is chosen and there is an alternate ASBR originating		concerned prefix is chosen and there is an alternate ASBR originating
	same prefix.		same prefix.
	1. If RFC1583Compatibility is disabled		1. If RFC1583Compatibility is disabled
	1a. if primary ASBR and alternate ASBR belong to intra area		1a. if primary ASBR and alternate ASBR belong to intra-area
	non-backbone go to step 2.		non-backbone go to step 2.
	1b. If primary ASBR and alternate ASBR belong to		1b. If primary ASBR and alternate ASBR belong to
	intra-area backbone and/or inter-area path go		intra-area backbone and/or inter-area path go
	to step 2.		to step 2.
	1c. for other paths, skip this alternate ASBR and		1c. for other paths, skip this alternate ASBR and
	consider next ASBR.		consider next ASBR.
	2. Compare cost types (type 1/type 2) advertised by alternate ASBR and		2. Compare cost types (type 1/type 2) advertised by alternate ASBR and
	by the primary ASBR		by the primary ASBR
	2a. If not the same type skip alternate ASBR and consider next ASBR.		2a. If not the same type skip alternate ASBR and
			consider next ASBR.
	2b. If same proceed to step 3.		2b. If same proceed to step 3.
	3.If cost types are type 1, compare costs advertised by alternate ASBR		3.If cost types are type 1, compare costs advertised by alternate ASBR
	and by the primary ASBR		and by the primary ASBR
	3a. If costs are the same then program ECMP FRR and return.		3a. If costs are the same then program ECMP FRR and return.
	3b. else go to step 5..		3b. else go to step 5..
	4 If cost types are type 2, compare costs advertised by alternate ASBR		4 If cost types are type 2, compare costs advertised by alternate ASBR
	and by the primary ASBR		and by the primary ASBR
	4a. If costs are different, skip alternate ASBR and		4a. If costs are different, skip alternate ASBR and
	consider next ASBR.		consider next ASBR.
	4b. If cost are the same, proceed to step 4c to compare		4b. If cost are the same, proceed to step 4c to compare
	cost to reach ASBR/forwarding address.		cost to reach ASBR/forwarding address.
	4c. If cost to reach ASBR/forwarding address are also same program ECMP FRR and return.		4c. If cost to reach ASBR/forwarding address are also same
	4d. If cost to reach ASBR/forwarding address are different go to step 5.		program ECMP FRR and return.
			4d. If cost to reach ASBR/forwarding address are different
			go to step 5.
	5. If route type (type 5/type 7)		5. If route type (type 5/type 7)
	5a. If route type is same, check route p-bit,		5a. If route type is same, check route p-bit,
	forwarding address field for routes from both		forwarding address field for routes from both
	ASBRs match. If p-bit and forwarding address matches proceed to step 6.		ASBRs match. If p-bit and forwarding address matches
			proceed to step 6.
	If not, skip this alternate ASBR and consider		If not, skip this alternate ASBR and consider
	next ASBR.		next ASBR.
	5b. If route type is not same, skip this alternate ASBR		5b. If route type is not same, skip this alternate ASBR
	and consider next alternate ASBR.		and consider next alternate ASBR.
	6. Apply inequality on the alternate ASBR.		6. Apply inequality on the alternate ASBR.
	Figure 5: Rules for selecting alternate ASBR in OSPF		Figure 5: Rules for selecting alternate ASBR in OSPF
	4.2.1.1. Multiple ASBRs belonging different area		4.2.1.1. Multiple ASBRs belonging different area
	When "RFC1583compatibility" is set to disabled, OSPF [RFC2328]		When "RFC1583compatibility" is set to disabled, OSPF [RFC2328]
	defines certain rules of preference to choose the ASBRs. While		defines certain rules of preference to choose the ASBRs. While
	selecting alternate ASBR for loop evaluation for LFA, these rules		selecting alternate ASBR for loop evaluation for LFA, these rules
	should be applied to ensure that the alternate neighbor does not		should be applied to ensure that the alternate neighbor does not
	cause loop.		cause looping.
	When there are multiple ASBRs belonging to different area advertising		When there are multiple ASBRs belonging to different area advertising
	the same prefix, pruning rules as defined in [RFC2328] section 16.4.1		the same prefix, pruning rules as defined in [RFC2328] section 16.4.1
	are applied. The alternate ASBRs pruned using above rules are not		are applied. The alternate ASBRs pruned using above rules are not
	considered for LFA evaluation.		considered for LFA evaluation.
	4.2.1.2. Type 1 and Type 2 costs		4.2.1.2. Type 1 and Type 2 costs
	If there are multiple ASBRs not pruned via rules defined in		If there are multiple ASBRs not pruned via rules defined in
	Section 4.2.1.1, the cost type advertised by the ASBRs is compared.		Section 4.2.1.1, the cost type advertised by the ASBRs is compared.
	skipping to change at page 11, line 14 ¶		skipping to change at page 12, line 16 ¶
	4.2.2. Inequalities to be applied for alternate ASBR selection		4.2.2. Inequalities to be applied for alternate ASBR selection
	The alternate ASBRs selected using above mechanism described in		The alternate ASBRs selected using above mechanism described in
	Section 4.2.1, are evaluated for Loop free criteria using below		Section 4.2.1, are evaluated for Loop free criteria using below
	inequalities.		inequalities.
	4.2.2.1. Forwarding address set to non-zero value		4.2.2.1. Forwarding address set to non-zero value
	Link-Protection:		Link-Protection:
	F_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) +		F_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,S) +
	F_opt(S,PO_best) + cost(PO_best,P)		F_opt(S,PO_best) + Cost(PO_best,P)
	Link-Protection + Downstream-paths-only:		Link-Protection + Downstream-paths-only:
	F_opt(N,PO_i)+ cost(PO_i,P) < F_opt(S,PO_best) + cost(PO_best,P)		F_opt(N,PO_i)+ Cost(PO_i,P) < F_opt(S,PO_best) + Cost(PO_best,P)
	Node-Protection:		Node-Protection:
	F_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,E) +		F_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,E) +
	F_opt(E,PO_best) + cost(PO_best,P)		F_opt(E,PO_best) + Cost(PO_best,P)
	Where,		Where,
	P - The multi-homed prefix being evaluated for		P - The multi-homed prefix being evaluated for
	computing alternates		computing alternates
	S - The computing router		S - The computing router
	N - The alternate router being evaluated		N - The alternate router being evaluated
	E - The primary next-hop on shortest path from S to		E - The primary next-hop on shortest path from S to
	prefix P.		prefix P.
	PO_i - The specific prefix-originating router being		PO_i - The specific prefix-originating router being
	evaluated.		evaluated.
	PO_best - The prefix-originating router on the shortest path		PO_best - The prefix-originating router on the shortest path
	from the computing router S to prefix P.		from the computing router S to prefix P.
	cost(X,Y) - External cost for Y as advertised by X		Cost(X,Y) - External cost for Y as advertised by X
	F_opt(X,Y) - Distance on the shortest path from node X to Forwarding		F_opt(X,Y) - Distance on the shortest path from node X to Forwarding
	address specified by ASBR Y.		address specified by ASBR Y.
	D_opt(X,Y) - Distance on the shortest path from node X to node Y.		D_opt(X,Y) - Distance on the shortest path from node X to node Y.
	Figure 6: LFA inequality definition when forwarding address is non-		Figure 6: LFA inequality definition when forwarding address is non-
	zero		zero
	4.2.2.2. ASBRs advertising type1 and type2 cost		4.2.2.2. ASBRs advertising type1 and type2 cost
	Link-Protection:		Link-Protection:
	D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) +		D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,S) +
	D_opt(S,PO_best) + cost(PO_best,P)		D_opt(S,PO_best) + Cost(PO_best,P)
	Link-Protection + Downstream-paths-only:		Link-Protection + Downstream-paths-only:
	D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(S,PO_best) + cost(PO_best,P)		D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(S,PO_best) + Cost(PO_best,P)
	Node-Protection:		Node-Protection:
	D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,E) +		D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,E) +
	D_opt(E,PO_best) + cost(PO_best,P)		D_opt(E,PO_best) + Cost(PO_best,P)
	Where,		Where,
	P - The multi-homed prefix being evaluated for		P - The multi-homed prefix being evaluated for
	computing alternates		computing alternates
	S - The computing router		S - The computing router
	N - The alternate router being evaluated		N - The alternate router being evaluated
	E - The primary next-hop on shortest path from S to		E - The primary next-hop on shortest path from S to
	prefix P.		prefix P.
	PO_i - The specific prefix-originating router being		PO_i - The specific prefix-originating router being
	evaluated.		evaluated.
	PO_best - The prefix-originating router on the shortest path		PO_best - The prefix-originating router on the shortest path
	from the computing router S to prefix P.		from the computing router S to prefix P.
	cost(X,Y) - External cost for Y as advertised by X.		Cost(X,Y) - External cost for Y as advertised by X.
	D_opt(X,Y) - Distance on the shortest path from node X to node Y.		D_opt(X,Y) - Distance on the shortest path from node X to node Y.
	Figure 7: LFA inequality definition for type1 and type 2 cost		Figure 7: LFA inequality definition for type1 and type 2 cost
	5. LFA Extended Procedures		5. LFA Extended Procedures
	This section explains the additional considerations in various		This section explains the additional considerations in various
	aspects as listed below to the base LFA specification [RFC5286].		aspects as listed below to the base LFA specification [RFC5286].
	5.1. Links with IGP MAX_METRIC		5.1. Links with IGP MAX_METRIC
	skipping to change at page 14, line 42 ¶		skipping to change at page 15, line 42 ¶
	8. Contributing Authors		8. Contributing Authors
	The following people contributed substantially to the content of this		The following people contributed substantially to the content of this
	document and should be considered co-authors.		document and should be considered co-authors.
	Chris Bowers		Chris Bowers
	Juniper Networks, Inc.		Juniper Networks, Inc.
	1194 N. Mathilda Ave,		1194 N. Mathilda Ave,
	Sunnyvale, CA 94089, USA		Sunnyvale, CA 94089, USA
	Email: cbowers@juniper.ne		Email: cbowers@juniper.net
	Bruno Decraene		Bruno Decraene
	Orange,		Orange,
	France		France
	Email: bruno.decraene@orange.com		Email: bruno.decraene@orange.com
	9. Security Considerations		9. Security Considerations
	Existing OSPF security considerations and stronger authentication and		Existing OSPF security considerations and stronger authentication and
	manual key management mechanisms are specified in [RFC7474] SHOULD be		manual key management mechanisms are specified in [RFC7474] SHOULD be
	considered for OSPF deployments. Security concerns for IS-IS are		considered for OSPF deployments. Security concerns for IS-IS are
	addressed in [RFC5304] and [RFC5310]. Further security analysis for		addressed in [RFC5304] and [RFC5310]. Further security analysis for
	IS-IS protocol is done in [RFC7645] SHOULD be considered for IS-IS		IS-IS protocol is done in [RFC7645] SHOULD be considered for IS-IS
	deployments. This document does not introduce any change in any of		deployments. This document does not change any of the discussed
	the protocol [RFC1195] [RFC5120] [RFC2328] [RFC5838] specifications		protocol specifications [RFC1195] [RFC5120] [RFC2328] [RFC5838], and
	discussed here and also this does not introduce any new security		the security considerations of the LFA base specification [RFC5286]
	issues other than as noted in the LFA base specification [RFC5286].		therefore continue to apply.
	10. References		10. References
	10.1. Normative References		10.1. Normative References
			[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
			Requirement Levels", BCP 14, RFC 2119,
			DOI 10.17487/RFC2119, March 1997,
			<https://www.rfc-editor.org/info/rfc2119>.
	[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for		[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
	IP Fast Reroute: Loop-Free Alternates", RFC 5286,		IP Fast Reroute: Loop-Free Alternates", RFC 5286,
	DOI 10.17487/RFC5286, September 2008,		DOI 10.17487/RFC5286, September 2008,
	<https://www.rfc-editor.org/info/rfc5286>.		<https://www.rfc-editor.org/info/rfc5286>.
	[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
	RFC 5714, DOI 10.17487/RFC5714, January 2010,
	<https://www.rfc-editor.org/info/rfc5714>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	10.2. Informative References		10.2. Informative References
	[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and		[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
	dual environments", RFC 1195, DOI 10.17487/RFC1195,		dual environments", RFC 1195, DOI 10.17487/RFC1195,
	December 1990, <https://www.rfc-editor.org/info/rfc1195>.		December 1990, <https://www.rfc-editor.org/info/rfc1195>.
	skipping to change at page 16, line 28 ¶		skipping to change at page 17, line 28 ¶
	[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,		[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
	DOI 10.17487/RFC5308, October 2008,		DOI 10.17487/RFC5308, October 2008,
	<https://www.rfc-editor.org/info/rfc5308>.		<https://www.rfc-editor.org/info/rfc5308>.
	[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,		[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
	and M. Fanto, "IS-IS Generic Cryptographic		and M. Fanto, "IS-IS Generic Cryptographic
	Authentication", RFC 5310, DOI 10.17487/RFC5310, February		Authentication", RFC 5310, DOI 10.17487/RFC5310, February
	2009, <https://www.rfc-editor.org/info/rfc5310>.		2009, <https://www.rfc-editor.org/info/rfc5310>.
			[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
			RFC 5714, DOI 10.17487/RFC5714, January 2010,
			<https://www.rfc-editor.org/info/rfc5714>.
	[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and		[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
	R. Aggarwal, "Support of Address Families in OSPFv3",		R. Aggarwal, "Support of Address Families in OSPFv3",
	RFC 5838, DOI 10.17487/RFC5838, April 2010,		RFC 5838, DOI 10.17487/RFC5838, April 2010,
	<https://www.rfc-editor.org/info/rfc5838>.		<https://www.rfc-editor.org/info/rfc5838>.
	[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.		[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
	McPherson, "OSPF Stub Router Advertisement", RFC 6987,		McPherson, "OSPF Stub Router Advertisement", RFC 6987,
	DOI 10.17487/RFC6987, September 2013,		DOI 10.17487/RFC6987, September 2013,
	<https://www.rfc-editor.org/info/rfc6987>.		<https://www.rfc-editor.org/info/rfc6987>.
	skipping to change at page 17, line 26 ¶		skipping to change at page 18, line 29 ¶
	Shraddha Hegde		Shraddha Hegde
	Juniper Networks, Inc.		Juniper Networks, Inc.
	Electra, Exora Business Park		Electra, Exora Business Park
	Bangalore, KA 560103		Bangalore, KA 560103
	India		India
	Email: shraddha@juniper.net		Email: shraddha@juniper.net
	Jeff Tantsura		Jeff Tantsura
	Nuage Networks		Apstra, Inc.
	755 Ravendale Drive
	Mountain View, CA 94043
	USA
	Email: jefftant.ietf@gmail.com		Email: jefftant.ietf@gmail.com
	Hannes Gredler		Hannes Gredler
	RtBrick, Inc.		RtBrick, Inc.
	Email: hannes@rtbrick.com		Email: hannes@rtbrick.com
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