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Versions: (draft-psarkar-rtgwg-multihomed-prefix-lfa) 00 01

Routing Area Working Group                                P. Sarkar, Ed.
Internet-Draft                                                Individual
Intended status: Informational                                  S. Hegde
Expires: July 20, 2017                                         C. Bowers
                                                  Juniper Networks, Inc.
                                                        U. Chunduri, Ed.
                                                     Huawei Technologies
                                                             J. Tantsura
                                                              Individual
                                                             B. Decraene
                                                                  Orange
                                                              H. Gredler
                                                           RtBrick, Inc.
                                                        January 16, 2017


                 LFA selection for Multi-Homed Prefixes
               draft-ietf-rtgwg-multihomed-prefix-lfa-01

Abstract

   This document shares experience gained from implementing algorithms
   to determine Loop-Free Alternates for multi-homed prefixes.  In
   particular, this document provides explicit inequalities that can be
   used to evaluate neighbors as a potential alternates for multi-homed
   prefixes.  It also provides detailed criteria for evaluating
   potential alternates for external prefixes advertised by OSPF ASBRs.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."



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   This Internet-Draft will expire on July 20, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  LFA inequalities for MHPs . . . . . . . . . . . . . . . . . .   4
   3.  LFA selection for the multi-homed prefixes  . . . . . . . . .   4
     3.1.  Improved coverage with simplified approach to MHPs  . . .   6
     3.2.  IS-IS ATT Bit considerations  . . . . . . . . . . . . . .   7
   4.  LFA selection for the multi-homed external prefixes . . . . .   8
     4.1.  IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  OSPF  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
       4.2.1.  Rules to select alternate ASBR  . . . . . . . . . . .   8
       4.2.2.  Multiple ASBRs belonging different area . . . . . . .   9
       4.2.3.  Type 1 and Type 2 costs . . . . . . . . . . . . . . .  10
       4.2.4.  RFC1583compatibility is set to enabled  . . . . . . .  10
       4.2.5.  Type 7 routes . . . . . . . . . . . . . . . . . . . .  10
       4.2.6.  Inequalities to be applied for alternate ASBR
               selection . . . . . . . . . . . . . . . . . . . . . .  10
         4.2.6.1.  Forwarding address set to non-zero value  . . . .  10
         4.2.6.2.  ASBRs advertising type1 and type2 cost  . . . . .  11
   5.  LFA Extended Procedures . . . . . . . . . . . . . . . . . . .  12
     5.1.  Links with IGP MAX_METRIC . . . . . . . . . . . . . . . .  12
     5.2.  Multi Topology Considerations . . . . . . . . . . . . . .  13
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15




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1.  Introduction

   The use of Loop-Free Alternates (LFA) for IP Fast Reroute is
   specified in [RFC5286].  Section 6.1 of [RFC5286] describes a method
   to determine loop-free alternates for a multi-homed prefixes (MHPs).
   This document describes a procedure using explicit inequalities that
   can be used by a computing router to evaluate a neighbor as a
   potential alternate for a multi-homed prefix.  The results obtained
   are equivalent to those obtained using the method described in
   Section 6.1 of [RFC5286].  However, some may find this formulation
   useful.

   Section 6.3 of [RFC5286] discusses complications associated with
   computing LFAs for multi-homed prefixes in OSPF.  This document
   provides detailed criteria for evaluating potential alternates for
   external prefixes advertised by OSPF ASBRs, as well as explicit
   inequalities.

   This document also provide clarifications, additional considerations
   to [RFC5286], to address a few coverage and operational observations.
   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
   engineering (TE) purposes and in the area of Multi Topology (MT) IGP
   deployments.  All these are elaborated in detail in Section 3.2 and
   Section 5.

1.1.  Acronyms

   AF      -  Address Family

   ATT     -  IS-IS Attach Bit

   ECMP    -  Equal Cost Multi Path

   IGP     -  Interior Gateway Protocol

   IS-IS   -  Intermediate System to Intermediate System

   OSPF    -  Open Shortest Path First

   MHP     -  Multi-homed Prefix

   MT      -  Multi Topology

   SPF     -  Shortest Path First PDU






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2.  LFA inequalities for MHPs

   This document proposes the following set of LFA inequalities for
   selecting the most appropriate LFAs for multi-homed prefixes (MHPs).
   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))
   over all PO_i

   Link-Protection:
   D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) +
                                 D_opt(S,PO_best) + cost(PO_best,P)

   Link-Protection + Downstream-paths-only:
   D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(S,PO_best) + cost(PO_best,P)

   Node-Protection:
   D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,E) +
                                 D_opt(E,PO_best) + cost(PO_best,P)

   Where,
      S            - The computing router
      N            - The alternate router being evaluated
      E            - The primary next-hop on shortest path from S to
                     prefix P.
      PO_i         - The specific prefix-originating router being
                     evaluated.
      PO_best      - The prefix-originating router on the shortest path
                     from the computing router S to prefix P.
      Cost (X,P)   - Cost of reaching the prefix P from prefix
                    originating node X.
      D_opt(X,Y)   - Distance on the shortest path from node X to node
                     Y.

                    Figure 1: LFA inequalities for MHPs

3.  LFA selection for the multi-homed prefixes

   To compute a valid LFA for a given multi-homed prefix P, through an
   alternate neighbor N a computing router S MUST follow one of the
   appropriate procedures below.











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        Link-Protection :
        =================
        1. If alternate neighbor N is also prefix-originator of P,
           1.a. Select N as a LFA for prefix P (irrespective of
                the metric advertised by N for the prefix P).
        2. Else, evaluate the link-protecting LFA inequality for P with
           the N as the alternate neighbor.
           2.a. If LFA inequality condition is met,
                select N as a LFA for prefix P.
           2.b. Else, N is not a LFA for prefix P.

        Link-Protection + Downstream-paths-only :
        =========================================
        1. Evaluate the link-protecting + downstream-only LFA inequality
           for P with the N as the alternate neighbor.
           1.a. If LFA inequality condition is met,
                select N as a LFA for prefix P.
           1.b. Else, N is not a LFA for prefix P.

        Node-Protection :
        =================
        1. If alternate neighbor N is also prefix-originator of P,
           1.a. Select N as a LFA for prefix P (irrespective of
                the metric advertised by N for the prefix P).
        2. Else, evaluate the appropriate node-protecting LFA inequality
           for P with the N as the alternate neighbor.
           2.a. If LFA inequality condition is met,
                select N as a LFA for prefix P.
           2.b. Else, N is not a LFA for prefix P.

                Figure 2: Rules for selecting LFA for MHPs

   In case an alternate neighbor N is also one of the prefix-originators
   of prefix P, N MAY be selected as a valid LFA for P.

   However if N is not a prefix-originator of P, the computing router
   SHOULD evaluate one of the corresponding LFA inequalities, as
   mentioned in Figure 1, once for each remote node that originated the
   prefix.  In case the inequality is satisfied by the neighbor N router
   S MUST choose neighbor N, as one of the valid LFAs for the prefix P.

   When computing a downstream-only LFA, in addition to being a prefix-
   originator of P, router N MUST also satisfy the downstream-only LFA
   inequality specified in Figure 1.

   For more specific rules please refer to the later sections of this
   document.




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3.1.  Improved coverage with simplified approach to MHPs

   LFA base specification [RFC5286] Section 6.1 recommends that a router
   compute the alternate next-hop for an IGP multi-homed prefix by
   considering alternate paths via all routers that have announced that
   prefix and the same has been elaborated with appropriate inequalities
   in the above section.  However, [RFC5286] Section 6.1 also allows for
   the router to simplify the multi-homed prefix calculation by assuming
   that the MHP is solely attached to the router that was its pre-
   failure optimal point of attachment, at the expense of potentially
   lower coverage.  If an implementation chooses to simplify the multi-
   homed prefix calculation by assuming that the MHP is solely attached
   to the router that was its pre-failure optimal point of attachment,
   the procedure described in this memo can potentially improve coverage
   for equal cost multi path (ECMP) MHPs without incurring extra
   computational cost.

   While the approach as specified in [RFC5286] Section 6.1 last
   paragraph, is to simplify the MHP as solely attached to the router
   that was its pre-failure optimal point of attachment; though it is a
   scalable approach and simplifies computation, [RFC5286] notes this
   may result in little less coverage.

   This memo improves the above approach to provide loop-free
   alternatives without any additional cost for equal cost multi path
   MHPs as described through the below example network.  The approach
   specified here MAY also be applicable for handling default routes as
   explained in Section 3.2.


                         5   +---+  8   +---+  5  +---+
                       +-----| S |------| A |-----| B |
                       |     +---+      +---+     +---+
                       |       |                    |
                       |     5 |                  5 |
                       |       |                    |
                     +---+ 5 +---+   4 +---+  1    +---+
                     | C |---| E |-----| M |-------| F |
                     +---+   +---+     +---+       +---+
                               |   10           5    |
                               +-----------p---------+

                   Figure 3: MHP with same ECMP Next-hop

   In the above network a prefix p, is advertised from both Node E and
   Node F.  With simplified approach taken as specified in [RFC5286]
   Section 6.1, prefix p will get only link protection LFA through the
   neighbor C while a node protection path is available through neighbor



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   A.  In this scenario, E and F both are pre-failure optimal points of
   attachment and share the same primary next-hop.  Hence, an
   implementation MAY compare the kind of protection A provides to F
   (link-and-node protection) with the kind of protection C provides to
   E (link protection) and inherit the better alternative to prefix p
   and here it is A.

   However, in the below network prefix p has an ECMP through both node
   E and node F with cost 20.  Though it has 2 pre-failure optimal
   points of attachment, the primary next-hop to each pre-failure
   optimal point of attachment is different.  In this case, prefix p
   shall inherit corresponding LFA to each primary next-hop calculated
   for the router advertising the same respectively (node E's and node
   F's LFA).


                             +---+         3      +---+
                             | S |----------------| B |
                             +---+                +---+
                               |                    |
                            10 |                  1 |
                               |                    |
                             +---+        6        +---+
                             | E |-----------------| F |
                             +---+                 +---+
                               |   10          16    |
                               +-----------p---------+

                Figure 4: MHP with different ECMP Next-hops

   In summary, if there are multiple pre-failure points of attachment
   for a MHP and primary next-hop of a MHP is same as that of the
   primary next-hop of the router that was pre-failure optimal point of
   attachment, an implementation MAY provide the better protection to
   MHP without incurring any additional computation cost.

3.2.  IS-IS ATT Bit considerations

   Per [RFC1195] a default route needs to be added in Level1 (L1) router
   to the closest reachable Level1/Level2 (L1/L2) router in the network
   advertising ATT (attach) bit in its LSP-0 fragment.  All L1 routers
   in the area would do this during the decision process with the next-
   hop of the default route set to the adjacent router through which the
   closest L1/L2 router is reachable.  The base LFA specification
   [RFC5286] does not specify any procedure for computing LFA for a
   default route in IS-IS L1 area.  Potentially one MAY consider a
   default route is being advertised from the border L1/L2 router where
   ATT bit is set and can do LFA computation for the default route.



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   But, when multiple ECMP L1/L2 routers are reachable in an L1 area
   corresponding best LFAs SHOULD be given for each primary next-hop
   associated with default route.  Considerations as specified in
   Section 3 and Section 3.1 are applicable for default routes, if the
   default route is considered as ECMP MHP.

4.  LFA selection for the multi-homed external prefixes

   Redistribution of external routes into IGP is required in case of two
   different networks getting merged into one or during protocol
   migrations.  External routes could be distributed into an IGP domain
   via multiple nodes to avoid a single point of failure.

   During LFA calculation, alternate LFA next-hops to reach the best
   ASBR could be used as LFA for the routes redistributed via that ASBR.
   When there is no LFA available to the best ASBR, it may be desirable
   to consider the other ASBRs (referred to as alternate ASBR hereafter)
   redistributing the external routes for LFA selection as defined in
   [RFC5286] and leverage the advantage of having multiple re-
   distributing nodes in the network.

4.1.  IS-IS

   LFA evaluation for multi-homed external prefixes in IS-IS is similar
   to the multi-homed internal prefixes.  Inequalities described in sec
   2 would also apply to multi-homed external prefixes as well.

4.2.  OSPF

   Loop free Alternates [RFC 5286] describes mechanisms to apply
   inequalities to find the loop free alternate neighbor.  For the
   selection of alternate ASBR for LFA consideration, additional rules
   have to be applied in selecting the alternate ASBR due to the
   external route calculation rules imposed by [RFC 2328].

   This document also defines the inequalities defined in RFC [5286]
   specifically for the alternate loop-free ASBR evaluation.

4.2.1.  Rules to select alternate ASBR

   The process to select an alternate ASBR is best explained using the
   rules below.  The below process is applied when primary ASBR for the
   concerned prefix is chosen and there is an alternate ASBR originating
   same prefix.







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   1. If RFC1583Compatibility is disabled

             1a. if primary ASBR and alternate ASBR are intra area
                     non-backbone path go to step 2.
             1b. If primary ASBR and alternate ASBR belong to
                     intra-area backbone and/or inter-area path go
                     to step 2.
             1c. for other paths, skip the alternate ASBR and
                     consider next ASBR.

   2. If cost type (type1/type2) advertised by alternate
      ASBR same as primary
           2a. If  not same skip alternate ASBR and consider next ASBR.

   3. If cost type is type1
             3a. If cost is same, program ECMP
             3b. else go to step 5.

   4  If cost type is type 2
             4a. If cost is different, skip alternate ASBR and
                     consider next ASBR
             4b. If type2 cost is same, compare type 1 cost.
             4c. If type1 cost is also same program ECMP.
             4d. If type 1 cost is different go to step 5.

   5. If route type (type 5/type 7)
              5a. If route type is same, check route p-bit,
                      forwarding address field for routes from both
                      ASBRs
                      match. If not skip alternate ASBR and consider
                      next ASBR.
              5b. If route type is not same, skip ASBR
                      and consider next ASBR.

    6. Apply inequality on the alternate ASBR.

           Figure 5: Rules for selecting alternate ASBR in OSPF

4.2.2.  Multiple ASBRs belonging different area

   When "RFC1583compatibility" is set to disabled, OSPF[RFC2328] defines
   certain rules of preference to choose the ASBRs.  While selecting
   alternate ASBR for loop evaluation for LFA, these rules should be
   applied and ensured that the alternate neighbor does not loop the
   traffic back.

   When there are multiple ASBRs belonging to different area advertising
   the same prefix, pruning rules as defined in RFC 2328 section 16.4.1



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   are applied.  The alternate ASBRs pruned using above rules are not
   considered for LFA evaluation.

4.2.3.  Type 1 and Type 2 costs

   If there are multiple ASBRs not pruned via rules defined in 3.2.2,
   the cost type advertised by the ASBRs is compared.  ASBRs advertising
   Type1 costs are preferred and the type2 costs are pruned.  If two
   ASBRs advertise same type2 cost, the alternate ASBRs are considered
   along with their type1 cost for evaluation.  If the two ASBRs with
   same type2 as well as type1 cost, ECMP FRR is programmed.  If there
   are two ASBRs with different type2 cost, the higher cost ASBR is
   pruned.  The inequalities for evaluating alternate ASBR for type 1
   and type 2 costs are same, as the alternate ASBRs with different
   type2 costs are pruned and the evaluation is based on equal type 2
   cost ASBRS.

4.2.4.  RFC1583compatibility is set to enabled

   When RFC1583Compatibility is set to enabled, multiple ASBRs belonging
   to different area advertising same prefix are chosen based on cost
   and hence are valid alternate ASBRs for the LFA evaluation.

4.2.5.  Type 7 routes

   Type 5 routes always get preference over Type 7 and the alternate
   ASBRs chosen for LFA calculation should belong to same type.  Among
   Type 7 routes, routes with p-bit and forwarding address set have
   higher preference than routes without these attributes.  Alternate
   ASBRs selected for LFA comparison should have same p-bit and
   forwarding address attributes.

4.2.6.  Inequalities to be applied for alternate ASBR selection

   The alternate ASBRs selected using above mechanism described in
   3.2.1, are evaluated for Loop free criteria using below inequalities.

4.2.6.1.  Forwarding address set to non-zero value













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  Link-Protection:
  F_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) +
                                F_opt(S,PO_best) + cost(PO_best,P)

  Link-Protection + Downstream-paths-only:
  F_opt(N,PO_i)+ cost(PO_i,P) < F_opt(S,PO_best) + cost(PO_best,P)

  Node-Protection:
  F_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,E) +
                                F_opt(E,PO_best) + cost(PO_best,P)

  Where,
  S            - The computing router
  N            - The alternate router being evaluated
  E            - The primary next-hop on shortest path from S to
                            prefix P.
  PO_i         - The specific prefix-originating router being
                            evaluated.
  PO_best      - The prefix-originating router on the shortest path
                            from the computing router S to prefix P.
  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
                 address specified by ASBR Y.
  D_opt(X,Y)   - Distance on the shortest path from node X to node Y.


    Figure 6: LFA inequality definition when forwarding address in non-
                                   zero

4.2.6.2.  ASBRs advertising type1 and type2 cost





















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   Link-Protection:
   D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) +
                                 D_opt(S,PO_best) + cost(PO_best,P)

   Link-Protection + Downstream-paths-only:
   D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(S,PO_best) + cost(PO_best,P)

   Node-Protection:
   D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,E) +
                                 D_opt(E,PO_best) + cost(PO_best,P)

   Where,
   S            - The computing router
   N            - The alternate router being evaluated
   E            - The primary next-hop on shortest path from S to
                             prefix P.
   PO_i         - The specific prefix-originating router being
                             evaluated.
   PO_best      - The prefix-originating router on the shortest path
                             from the computing router S to prefix P.
   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.


       Figure 7: LFA inequality definition for type1 and type 2 cost

5.  LFA Extended Procedures

   This section explains the additional considerations in various
   aspects as listed below to the base LFA specification [RFC5286].

5.1.  Links with IGP MAX_METRIC

   Section 3.5 and 3.6 of [RFC5286] describes procedures for excluding
   nodes and links from use in alternate paths based on the maximum link
   metric (as defined in for IS-IS in [RFC5305] or as defined in
   [RFC3137] for OSPF).  If these procedures are strictly followed,
   there are situations, as described below, where the only potential
   alternate available which satisfies the basic loop-free condition
   will not be considered as alternative.











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                             +---+  10  +---+  10 +---+
                             | S |------|N1 |-----|D1 |
                             +---+      +---+     +---+
                               |                    |
                            10 |                 10 |
                               |MAX_MET(N2 to S)    |
                               |                    |
                               |       +---+        |
                               +-------|N2 |--------+
                                       +---+
                                     10  |
                                       +---+
                                       |D2 |
                                       +---+


                    Figure 8: Link with IGP MAX_METRIC

   In the simple example network, all the link costs have a cost of 10
   in both directions, except for the link between S and N2.  The S-N2
   link has a cost of 10 in the direction from S to N2, and a cost of
   MAX_METRIC in the direction from N2 to S (0xffffff /2^24 - 1 for IS-
   IS and 0xffff for OSPF) for a specific end to end Traffic Engineering
   (TE) requirement of the operator.  At node S, D1 is reachable through
   N1 with cost 20, and D2 is reachable through N2 with cost 20.  Even
   though neighbor N2 satisfies basic loop-free condition (inequality 1
   of [RFC5286]) for D1 this could be excluded as potential alternative
   because of the current exclusions as specified in section 3.5 and 3.6
   procedure of [RFC5286].  But, as the primary traffic destined to D2
   continue to use the link and hence irrespective of the reverse metric
   in this case, the same link MAY be used as a potential LFA for D1.

   Alternatively, reverse metric of the link MAY be configured with
   MAX_METRIC-1, so that the link can be used as an alternative while
   meeting the TE requirements.

5.2.  Multi Topology Considerations

   Section 6.2 and 6.3.2 of [RFC5286] state that multi-topology OSPF and
   ISIS are out of scope for that specification.  This memo clarifies
   and describes the applicability.

   In Multi Topology (MT) IGP deployments, for each MT ID, a separate
   shortest path tree (SPT) is built with topology specific adjacencies,
   the LFA principles laid out in [RFC5286] are actually applicable for
   MT IS-IS [RFC5120] LFA SPF.  The primary difference in this case is,
   identifying the eligible-set of neighbors for each LFA computation
   which is done per MT ID.  The eligible-set for each MT ID is



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   determined by the presence of IGP adjacency from Source to the
   neighboring node on that MT-ID apart from the administrative
   restrictions and other checks laid out in [RFC5286].  The same is
   also applicable for OSPF [RFC4915] [MT-OSPF] or different AFs in
   multi instance OSPFv3 [RFC5838].

   However for MT IS-IS, if a default topology is used with MT-ID 0
   [RFC5286] and both IPv4 [RFC5305] and IPv6 routes/AFs [RFC5308]  are
   present, then the condition of network congruency is applicable for
   LFA computation as well.  Network congruency here refers to, having
   same address families provisioned on all the links and all the nodes
   of the network with MT-ID 0.  Here with single decision process both
   IPv4 and IPv6 next-hops are computed for all the prefixes in the
   network and similarly with one LFA computation from all eligible
   neighbors per [RFC5286], all potential alternatives can be computed.

6.  Acknowledgements

   Thanks to Alia Atlas and Salih K A for their useful feedback and
   inputs.

7.  IANA Considerations

   N/A. - No protocol changes are proposed in this document.

8.  Security Considerations

   This document does not introduce any change in any of the protocol
   specifications and also this does not introduce any new security
   issues other than as noted in the LFA base specification [RFC5286].

9.  References

9.1.  Normative References

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <http://www.rfc-editor.org/info/rfc1195>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.








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9.2.  Informative References

   [RFC3137]  Retana, A., Nguyen, L., White, R., Zinin, A., and D.
              McPherson, "OSPF Stub Router Advertisement", RFC 3137,
              DOI 10.17487/RFC3137, June 2001,
              <http://www.rfc-editor.org/info/rfc3137>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <http://www.rfc-editor.org/info/rfc4915>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <http://www.rfc-editor.org/info/rfc5120>.

   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,
              <http://www.rfc-editor.org/info/rfc5286>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <http://www.rfc-editor.org/info/rfc5305>.

   [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
              DOI 10.17487/RFC5308, October 2008,
              <http://www.rfc-editor.org/info/rfc5308>.

   [RFC5838]  Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
              R. Aggarwal, "Support of Address Families in OSPFv3",
              RFC 5838, DOI 10.17487/RFC5838, April 2010,
              <http://www.rfc-editor.org/info/rfc5838>.

   [RFC7916]  Litkowski, S., Ed., Decraene, B., Filsfils, C., Raza, K.,
              Horneffer, M., and P. Sarkar, "Operational Management of
              Loop-Free Alternates", RFC 7916, DOI 10.17487/RFC7916,
              July 2016, <http://www.rfc-editor.org/info/rfc7916>.

Authors' Addresses

   Pushpasis Sarkar (editor)
   Individual

   Email: pushpasis.ietf@gmail.com




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   Shraddha Hegde
   Juniper Networks, Inc.
   Electra, Exora Business Park
   Bangalore, KA  560103
   India

   Email: shraddha@juniper.net


   Chris Bowers
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089
   US

   Email: cbowers@juniper.net


   Uma Chunduri (editor)
   Huawei Technologies
   2330 Central Expressway
   Santa Clara, CA  95050
   USA

   Email: uma.chunduri@huawei.com


   Jeff Tantsura
   Individual

   Email: jefftant.ietf@gmail.com


   Bruno Decraene
   Orange

   Email: bruno.decraene@orange.com


   Hannes Gredler
   RtBrick, Inc.

   Email: hannes@rtbrick.com








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