IP Fast Reroute Framework
RFC 5714

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Internet Engineering Task Force (IETF)                          M. Shand
Request for Comments: 5714                                     S. Bryant
Category: Informational                                    Cisco Systems
ISSN: 2070-1721                                             January 2010

                       IP Fast Reroute Framework

Abstract

   This document provides a framework for the development of IP fast-
   reroute mechanisms that provide protection against link or router
   failure by invoking locally determined repair paths.  Unlike MPLS
   fast-reroute, the mechanisms are applicable to a network employing
   conventional IP routing and forwarding.

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/rfc5714.

Copyright Notice

   Copyright (c) 2010 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.

Shand & Bryant                Informational                     [Page 1]
RFC 5714                IP Fast Reroute Framework           January 2010

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Scope and Applicability  . . . . . . . . . . . . . . . . . . .  5
   4.  Problem Analysis . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Mechanisms for IP Fast-Reroute . . . . . . . . . . . . . . . .  7
     5.1.  Mechanisms for Fast Failure Detection  . . . . . . . . . .  7
     5.2.  Mechanisms for Repair Paths  . . . . . . . . . . . . . . .  8
       5.2.1.  Scope of Repair Paths  . . . . . . . . . . . . . . . .  9
       5.2.2.  Analysis of Repair Coverage  . . . . . . . . . . . . .  9
       5.2.3.  Link or Node Repair  . . . . . . . . . . . . . . . . . 10
       5.2.4.  Maintenance of Repair Paths  . . . . . . . . . . . . . 10
       5.2.5.  Local Area Networks  . . . . . . . . . . . . . . . . . 11
       5.2.6.  Multiple Failures and Shared Risk Link Groups  . . . . 11
     5.3.  Mechanisms for Micro-Loop Prevention . . . . . . . . . . . 12
   6.  Management Considerations  . . . . . . . . . . . . . . . . . . 12
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  Informative References . . . . . . . . . . . . . . . . . . . . 14

1.  Introduction

   When a link or node failure occurs in a routed network, there is
   inevitably a period of disruption to the delivery of traffic until
   the network re-converges on the new topology.  Packets for
   destinations that were previously reached by traversing the failed
   component may be dropped or may suffer looping.  Traditionally, such
   disruptions have lasted for periods of at least several seconds, and
   most applications have been constructed to tolerate such a quality of
   service.

   Recent advances in routers have reduced this interval to under a
   second for carefully configured networks using link state IGPs.
   However, new Internet services are emerging that may be sensitive to
   periods of traffic loss that are orders of magnitude shorter than
   this.

   Addressing these issues is difficult because the distributed nature
   of the network imposes an intrinsic limit on the minimum convergence
   time that can be achieved.

   However, there is an alternative approach, which is to compute backup
   routes that allow the failure to be repaired locally by the router(s)
   detecting the failure without the immediate need to inform other
   routers of the failure.  In this case, the disruption time can be
   limited to the small time taken to detect the adjacent failure and
   invoke the backup routes.  This is analogous to the technique

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