Graceful Restart Mechanism for BGP with MPLS
RFC 4781

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Network Working Group                                         Y. Rekhter
Request for Comments: 4781                                   R. Aggarwal
Category: Standards Track                               Juniper Networks
                                                            January 2007

              Graceful Restart Mechanism for BGP with MPLS

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 Internet Society (2007).

Abstract

   A mechanism for BGP that helps minimize the negative effects on
   routing caused by BGP restart has already been developed and is
   described in a separate document ("Graceful Restart Mechanism for
   BGP").  This document extends this mechanism to minimize the negative
   effects on MPLS forwarding caused by the Label Switching Router's
   (LSR's) control plane restart, and specifically by the restart of its
   BGP component when BGP is used to carry MPLS labels and the LSR is
   capable of preserving the MPLS forwarding state across the restart.

   The mechanism described in this document is agnostic with respect to
   the types of the addresses carried in the BGP Network Layer
   Reachability Information (NLRI) field.  As such, it works in
   conjunction with any of the address families that could be carried in
   BGP (e.g., IPv4, IPv6, etc.).

Rekhter & Aggarwal          Standards Track                     [Page 1]
RFC 4781           Graceful Restart Mechanism for BGP       January 2007

Table of Contents

   1. Introduction ....................................................2
      1.1. Specification of Requirements ..............................3
   2. General Requirements ............................................3
   3. Capability Advertisement ........................................4
   4. Procedures for the Restarting LSR ...............................4
      4.1. Case 1 .....................................................4
      4.2. Case 2 .....................................................5
      4.3. Case 3 .....................................................5
   5. Alternative Procedures for the Restarting LSR ...................6
   6. Procedures for a Neighbor of a Restarting LSR ...................6
   7. Comparison between Alternative Procedures for the
      Restarting LSR ..................................................7
   8. Security Considerations .........................................8
   9. Acknowledgments .................................................9
   10. References .....................................................9
      10.1. Normative References ......................................9
      10.2. Informative References ....................................9

1.  Introduction

   In the case where a Label Switching Router (LSR) could preserve its
   MPLS forwarding state across restart of its control plane, and
   specifically its BGP component, and BGP is used to carry MPLS labels
   (e.g., as specified in [RFC3107]), it may be desirable not to perturb
   the LSPs going through that LSR (and specifically, the LSPs
   established by BGP) after failure or restart of the BGP component of
   the control plane.  In this document, we describe a mechanism that
   allows this goal to be accomplished.  The mechanism described in this
   document works in conjunction with the mechanism specified in
   [RFC4724].  The mechanism described in this document places no
   restrictions on the types of addresses (address families) that it can
   support.

   The mechanism described in this document is applicable to all LSRs,
   both those with the ability to preserve forwarding state during BGP
   restart and those without it (although the latter need to implement
   only a subset of this mechanism).  Supporting a subset of the
   mechanism described here by the LSRs that cannot preserve their MPLS
   forwarding state across the restart would not reduce the negative
   impact on MPLS traffic caused by their control plane restart.
   However, the impact would be minimized if their neighbor(s) are
   capable of preserving the forwarding state across the restart of
   their control plane, and if they implement the mechanism described
   here.  The subset includes all the procedures described in this
   document, except the procedures in Sections 4.1, 4.2, 4.3, and 5.

Rekhter & Aggarwal          Standards Track                     [Page 2]
RFC 4781           Graceful Restart Mechanism for BGP       January 2007

   For the sake of brevity, by "MPLS forwarding state" we mean one of
   the following mappings:
      <incoming label -> (outgoing label, next hop)>