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Loop-Free Alternate (LFA) Applicability in Service Provider (SP) Networks
RFC 6571

Internet Engineering Task Force (IETF)                  C. Filsfils, Ed.
Request for Comments: 6571                                 Cisco Systems
Category: Informational                                 P. Francois, Ed.
ISSN: 2070-1721                                 Institute IMDEA Networks
                                                                M. Shand

                                                             B. Decraene
                                                          France Telecom
                                                               J. Uttaro
                                                                    AT&T
                                                              N. Leymann
                                                            M. Horneffer
                                                        Deutsche Telekom
                                                               June 2012

                Loop-Free Alternate (LFA) Applicability
                   in Service Provider (SP) Networks

Abstract

   In this document, we analyze the applicability of the Loop-Free
   Alternate (LFA) method of providing IP fast reroute in both the core
   and access parts of Service Provider networks.  We consider both the
   link and node failure cases, and provide guidance on the
   applicability of LFAs to different network topologies, with special
   emphasis on the access parts of the network.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6571.

Filsfils, et al.              Informational                     [Page 1]
RFC 6571            LFA Applicability in SP Networks           June 2012

Copyright Notice

   Copyright (c) 2012 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
   2. Terminology .....................................................4
   3. Access Network ..................................................6
      3.1. Triangle ...................................................8
           3.1.1. E1C1 Failure ........................................8
           3.1.2. C1E1 Failure ........................................9
           3.1.3. uLoop ...............................................9
           3.1.4. Conclusion .........................................10
      3.2. Full Mesh .................................................10
           3.2.1. E1A1 Failure .......................................10
           3.2.2. A1E1 Failure .......................................11
           3.2.3. A1C1 Failure .......................................11
           3.2.4. C1A1 Failure .......................................12
           3.2.5. uLoop ..............................................12
           3.2.6. Conclusion .........................................12
      3.3. Square ....................................................13
           3.3.1. E1A1 Failure .......................................13
           3.3.2. A1E1 Failure .......................................14
           3.3.3. A1C1 Failure .......................................15
           3.3.4. C1A1 Failure .......................................15
           3.3.5. Conclusion .........................................17
           3.3.6. A Square Might Become a Full Mesh ..................17
           3.3.7. A Full Mesh Might Be More Economical Than a
                  Square .............................................17
      3.4. Extended U ................................................18
           3.4.1. E1A1 Failure .......................................19

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