Framework for Loop-Free Convergence Using the Ordered Forwarding Information Base (oFIB) Approach
RFC 6976

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Internet Engineering Task Force (IETF)                          M. Shand
Request for Comments: 6976                        Individual Contributor
Category: Informational                                        S. Bryant
ISSN: 2070-1721                                               S. Previdi
                                                             C. Filsfils
                                                           Cisco Systems
                                                             P. Francois
                                                Institute IMDEA Networks
                                                          O. Bonaventure
                                        Universite catholique de Louvain
                                                               July 2013

                  Framework for Loop-Free Convergence
     Using the Ordered Forwarding Information Base (oFIB) Approach

Abstract

   This document describes an illustrative framework of a mechanism for
   use in conjunction with link-state routing protocols that prevents
   the transient loops that would otherwise occur during topology
   changes.  It does this by correctly sequencing the forwarding
   information base (FIB) updates on the routers.

   This mechanism can be used in the case of non-urgent (management
   action) link or node shutdowns and restarts or link metric changes.
   It can also be used in conjunction with a fast reroute mechanism that
   converts a sudden link or node failure into a non-urgent topology
   change.  This is possible where a complete repair path is provided
   for all affected destinations.

   After a non-urgent topology change, each router computes a rank that
   defines the time at which it can safely update its FIB.  A method for
   accelerating this loop-free convergence process by the use of
   completion messages is also described.

   The technology described in this document has been subject to
   extensive simulation using pathological convergence behavior and real
   network topologies and costs.  However, the mechanisms described in
   this document are purely illustrative of the general approach and do
   not constitute a protocol specification.  This document represents a
   snapshot of the work of the Routing Area Working Group at the time of
   publication and is published as a document of record.  Further work
   is needed before implementation or deployment.

Shand, et al.                 Informational                     [Page 1]
RFC 6976            Loop-Free Convergence Using oFIB           July 2013

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/rfc6976.

Copyright Notice

   Copyright (c) 2013 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, et al.                 Informational                     [Page 2]
RFC 6976            Loop-Free Convergence Using oFIB           July 2013

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  The Purpose of This Document  . . . . . . . . . . . . . .   4
     1.2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  The Required FIB Update Order . . . . . . . . . . . . . . . .   6
     2.1.  Single Link Events  . . . . . . . . . . . . . . . . . . .   6
       2.1.1.  Link Down / Metric Increase . . . . . . . . . . . . .   6
       2.1.2.  Link Up / Metric Decrease . . . . . . . . . . . . . .   7
     2.2.  Multi-Link Events . . . . . . . . . . . . . . . . . . . .   8
       2.2.1.  Router Down Events  . . . . . . . . . . . . . . . . .   8
       2.2.2.  Router Up Events  . . . . . . . . . . . . . . . . . .   8
       2.2.3.  Line-Card Failure/Restoration Events  . . . . . . . .   8
   3.  Applying Ordered FIB Updates  . . . . . . . . . . . . . . . .   9