Selection of Loop-Free Alternates for Multi-Homed Prefixes
RFC 8518

Document Type RFC - Proposed Standard (March 2019; No errata)
Updates RFC 5286
Last updated 2019-03-11
Replaces draft-chunduri-rtgwg-lfa-extended-procedures, draft-psarkar-rtgwg-multihomed-prefix-lfa
Stream IETF
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Reviews
Stream WG state Submitted to IESG for Publication
Document shepherd Stewart Bryant
Shepherd write-up Show (last changed 2018-02-08)
IESG IESG state RFC 8518 (Proposed Standard)
Consensus Boilerplate Yes
Telechat date
Responsible AD Martin Vigoureux
Send notices to Stewart Bryant <stewart.bryant@gmail.com>
IANA IANA review state IANA OK - No Actions Needed
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Internet Engineering Task Force (IETF)                    P. Sarkar, Ed.
Request for Comments: 8518                                  Arrcus, Inc.
Updates: 5286                                           U. Chunduri, Ed.
Category: Standards Track                                     Huawei USA
ISSN: 2070-1721                                                 S. Hegde
                                                  Juniper Networks, Inc.
                                                             J. Tantsura
                                                            Apstra, Inc.
                                                              H. Gredler
                                                           RtBrick, Inc.
                                                              March 2019

       Selection of Loop-Free Alternates for Multi-Homed Prefixes

Abstract

   Deployment experience gained from implementing algorithms to
   determine Loop-Free Alternates (LFAs) for multi-homed prefixes (MHPs)
   has revealed some avenues for potential improvement.  This document
   provides explicit inequalities that can be used to evaluate neighbors
   as potential alternates for MHPs.  It also provides detailed criteria
   for evaluating potential alternates for external prefixes advertised
   by OSPF ASBRs.  This document updates Section 6 of RFC 5286 by
   expanding some of the routing aspects.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8518.

Sarkar, et al.               Standards Track                    [Page 1]
RFC 8518                 LFA Selection for MHPs               March 2019

Copyright Notice

   Copyright (c) 2019 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
   (https://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 ...................................................4
      1.2. Requirements Language ......................................4
   2. LFA Inequalities for MHPs .......................................4
   3. LFA Selection for MHPs ..........................................6
      3.1. Improved Coverage with Simplified Approach to MHPs .........7
      3.2. IS-IS ATT Bit Considerations ...............................9
   4. LFA Selection for Multi-Homed External Prefixes ................10
      4.1. IS-IS .....................................................10
      4.2. OSPF ......................................................10
           4.2.1. Rules to Select Alternate ASBRs ....................10
               4.2.1.1. Multiple ASBRs Belonging to Different Areas ..12
               4.2.1.2. Type 1 and Type 2 Costs ......................12
               4.2.1.3. RFC1583Compatibility is Set to "Enabled" .....12
               4.2.1.4. Type 7 Routes ................................13
           4.2.2. Inequalities to Be Applied for Alternate ASBR
                  Selection ..........................................13
               4.2.2.1. Forwarding Address Set to Non-zero Value .....13
               4.2.2.2. ASBRs Advertising Type 1 and Type 2 Costs ....14
   5. LFA Extended Procedures ........................................15
      5.1. Links with IGP MAX_METRIC .................................15
      5.2. MT Considerations .........................................16
   6. IANA Considerations ............................................16
   7. Security Considerations ........................................17
   8. References .....................................................17
      8.1. Normative References ......................................17
      8.2. Informative References ....................................17
   Acknowledgements ..................................................19
   Contributors ......................................................19
   Authors' Addresses ................................................20
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