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Graceful Restart Mechanism for BGP
RFC 4724

Document type: RFC - Proposed Standard (January 2007)
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 4724 (Proposed Standard)
Responsible AD: Bill Fenner
Send notices to: idr-chairs@tools.ietf.org

Network Working Group                                          S. Sangli
Request for Comments: 4724                                       E. Chen
Category: Standards Track                                  Cisco Systems
                                                             R. Fernando
                                                              J. Scudder
                                                              Y. Rekhter
                                                        Juniper Networks
                                                            January 2007

                   Graceful Restart Mechanism for BGP

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document describes a mechanism for BGP that would help minimize
   the negative effects on routing caused by BGP restart.  An End-of-RIB
   marker is specified and can be used to convey routing convergence
   information.  A new BGP capability, termed "Graceful Restart
   Capability", is defined that would allow a BGP speaker to express its
   ability to preserve forwarding state during BGP restart.  Finally,
   procedures are outlined for temporarily retaining routing information
   across a TCP session termination/re-establishment.

   The mechanisms described in this document are applicable to all
   routers, both those with the ability to preserve forwarding state
   during BGP restart and those without (although the latter need to
   implement only a subset of the mechanisms described in this
   document).

Sangli, et al.              Standards Track                     [Page 1]
RFC 4724           Graceful Restart Mechanism for BGP       January 2007

Table of Contents

   1. Introduction ....................................................2
      1.1. Specification of Requirements ..............................2
   2. Marker for End-of-RIB ...........................................3
   3. Graceful Restart Capability .....................................3
   4. Operation .......................................................6
      4.1. Procedures for the Restarting Speaker ......................6
      4.2. Procedures for the Receiving Speaker .......................7
   5. Changes to BGP Finite State Machine .............................9
   6. Deployment Considerations ......................................11
   7. Security Considerations ........................................12
   8. Acknowledgments ................................................13
   9. IANA Considerations ............................................13
   10. References ....................................................13
      10.1. Normative References .....................................13
      10.2. Informative References ...................................13

1.  Introduction

   Usually, when BGP on a router restarts, all the BGP peers detect that
   the session went down and then came up.  This "down/up" transition
   results in a "routing flap" and causes BGP route re-computation,
   generation of BGP routing updates, and unnecessary churn to the
   forwarding tables.  It could spread across multiple routing domains.
   Such routing flaps may create transient forwarding blackholes and/or
   transient forwarding loops.  They also consume resources on the
   control plane of the routers affected by the flap.  As such, they are
   detrimental to the overall network performance.

   This document describes a mechanism for BGP that would help minimize
   the negative effects on routing caused by BGP restart.  An End-of-RIB
   marker is specified and can be used to convey routing convergence
   information.  A new BGP capability, termed "Graceful Restart
   Capability", is defined that would allow a BGP speaker to express its
   ability to preserve forwarding state during BGP restart.  Finally,
   procedures are outlined for temporarily retaining routing information
   across a TCP session termination/re-establishment.

1.1  Specification of Requirements

   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 RFC 2119 [RFC2119].

Sangli, et al.              Standards Track                     [Page 2]

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