OSPFv3 Graceful Restart
RFC 5187

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• 08

Network Working Group                                  P. Pillay-Esnault
Request for Comments: 5187                                 Cisco Systems
Category: Standards Track                                      A. Lindem
                                                        Redback Networks
                                                               June 2008

                        OSPFv3 Graceful Restart

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.

Abstract

   This document describes the OSPFv3 graceful restart.  The OSPFv3
   graceful restart is identical to that of OSPFv2 except for the
   differences described in this document.  These differences include
   the format of the grace Link State Advertisements (LSAs) and other
   considerations.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Grace Link State Advertisement  . . . . . . . . . . . . . . . . 2
     2.1.  Grace LSA - LS Type . . . . . . . . . . . . . . . . . . . . 2
     2.2.  Grace LSA Format  . . . . . . . . . . . . . . . . . . . . . 3
   3.  Additional Considerations for OSPFv3 Graceful Restart . . . . . 4
     3.1.  Preservation of LSA ID to Prefix Correspondence . . . . . . 4
     3.2.  Preservation of Interface IDs for Link-LSAs,
           Network-LSAs, and Router-LSAs . . . . . . . . . . . . . . . 4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 6

Pillay-Esnault & Lindem     Standards Track                     [Page 1]
RFC 5187                OSPFv3 Graceful Restart                June 2008

1.  Introduction

   Graceful OSPF restart [GRACE] describes a mechanism to restart the
   control plane of an OSPFv2 [OSPFv2] router that still has its
   forwarding plane intact with a minimum of disruption to the network.

   In general, the methods described in [GRACE] work for OSPFv3 [OSPFv3]
   as well.  However, OSPFv3 will use a grace-LSA with a different
   format to signal that a router is initiating (or is about to
   initiate) a graceful restart.  This document describes other OSPFv3
   differences as well.

   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 [RFC2119].

2.  Grace Link State Advertisement

   An OSPFv3 router initiating a graceful restart of its OSPFv3 software
   originates grace-LSAs.  A grace-LSA requests that the router's
   neighbors aid in its graceful restart by continuing to advertise the
   router as fully adjacent during the specified grace period.  The
   grace-LSA contains the restarting router grace-period and the reason
   code indicating the reason for the graceful restart.

   In OSPFv3 (refer to section 2.11 of [OSPFv3]), neighboring routers on
   any link are always identified by their router IDs.  This contrasts
   with the OSPFv2 behavior where neighbors on point-to-point networks
   and virtual links are identified by their Router IDs, while neighbors
   on broadcast, Non-Broadcast Multi-Access (NBMA), and point-to-
   multipoint links are identified by their IPv4 interface addresses.
   Consequently, there is no requirement for the router-address TLV
   [GRACE] for OSPFv3 graceful restart.

   The TLV formats of the grace-LSA described in [GRACE] remain
   unchanged.

2.1.  Grace LSA - LS Type

   A grace-LSA is defined as an LSA with the LS type equal to 0x000b.

              LSA function code  LS Type  Description
              ------------------------------------------
              11                 0x000b   GRACE-LSA

                     Grace-LSA Type and Function Code

Pillay-Esnault & Lindem     Standards Track                     [Page 2]
RFC 5187                OSPFv3 Graceful Restart                June 2008

   The S2-bit and S1-bit are set to 0 to indicate link-local flooding
   scope.  The U-bit is set to 0 since it isn't applicable to LSAs with
   link-local flooding scope.

2.2.  Grace LSA Format

   The format of a grace LSA is:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           LS age              |0|0|0|          11             |