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Versions: 00 01 02 03 04 05 06 07 08 RFC 5187

Network Working Group                                  P. Pillay-Esnault
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                               A. Lindem
Expires: October 30, 2008                               Redback Networks
                                                          April 28, 2008


                        OSPFv3 Graceful Restart
             draft-ietf-ospf-ospfv3-graceful-restart-08.txt

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Abstract

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










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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Grace Link State Advertisement  . . . . . . . . . . . . . . . . 3
     2.1.  Grace LSA - LS Type . . . . . . . . . . . . . . . . . . . . 3
     2.2.  Grace LSA Format  . . . . . . . . . . . . . . . . . . . . . 4
   3.  Additional Considerations for OSPFv3 Graceful Restart . . . . . 5
     3.1.  Preservation of LSA ID to Prefix Correspondence . . . . . . 5
     3.2.  Preservation of Interface IDs for Link-LSAs,
           Network-LSAs, and Router-LSAs . . . . . . . . . . . . . . . 5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8

































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1.  Introduction

   Graceful OSPF restart [GRACE] describes a mechanism to restart the
   control plane of an OSPFv2 [OSPFv2] router which 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 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, 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 link-local scope LSA with the LS type equal
   to 0x000b.

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

                     Grace-LSA Type and Function code



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   The U-bit is set to 0 since this is a link-local scoped LSA and the
   flooding scope is not impacted by whether or not the LSA is known.
   The S2-bit and S1-bit are also set to 0 to indicate 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             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Link State ID                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    Advertising Router                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    LS sequence number                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |        LS checksum            |            Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +-                            TLVs                             -+
       |                             ...                               |


                             Grace-LSA Format

   The Link State ID of a grace-LSA in OSPFv3 is the interface ID of the
   interface originating the LSA.

   The format of each TLV 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Type             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Value...                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                TLV Format

   Grace-LSA TLVs are formatted according to section 2.3.2 of [OSPF-TE].

   The following is the list of TLVs that can appear in the body of a
   grace-LSA.



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      Grace Period (Type=1, length=4).  The number of seconds that the
      router's neighbors should continue to advertise the router as
      fully adjacent, regardless of the state of database
      synchronization between the router and its neighbors.  This TLV
      MUST always appear in a grace-LSA.

      Graceful restart reason (Type=2, length=1).  Encodes the reason
      for the router restart, as one of the following: 0 (unknown), 1
      (software restart), 2 (software reload/upgrade) or 3 (switch to
      redundant control processor).  This TLV MUST always appear in a
      grace-LSA.


3.  Additional Considerations for OSPFv3 Graceful Restart

   This section describes OSPFv3 unique considerations in addition to
   those described in [GRACE].

3.1.  Preservation of LSA ID to Prefix Correspondence

   In OSPFv2, there is a direct correspondence between summary and
   external LSA IDs and the prefixes being advertised.  However, in
   OSPFv3, the LSA ID for inter-area prefix LSAs and external LSAs is
   simply an unsigned 32-bit integer.  Hence, to avoid network churn
   during graceful restart, the restarting router MUST preserve the LSA
   ID to prefix correspondence across graceful restarts.

3.2.  Preservation of Interface IDs for Link-LSAs, Network-LSAs, and
      Router-LSAs

   In OSPFv3, the LSA ID for link-local-LSAs and network-LSAs and link
   descriptions in router-LSAs map to their corresponding Interface ID.
   Changes in the Interface ID during graceful restart will result in a
   mismatch between the restarting router's pre-restart LSAs and its
   neighbor adjacency state.  These disparities will cause the graceful
   restart to terminate prematurely.

   Synchronizing interface ID changes between neighbors is possible.
   However, placing the burden on the restarting router to preserve
   interface IDs across restarts provides for a more robust, more
   deterministic, and simpler mechanism.  Therefore, the OSPFv3
   interface ID, as described in section 3.1.2 of [OSPFv3], MUST be
   preserved by the restarting router across restarts.

   Many implementations currently use the interface's MIB-II IfIndex
   [MIB-INTF] for Interface ID.  The persistence of Interface ID across
   reboots is described in section 3.1.5 of [MIB-PERS].




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4.  Security Considerations

   [OSPFv3-AUTH] relies on manual key distribution which precludes the
   use of replay protection utilizing sequence numbers.  The replay of
   an OSPF Link-Update containing a grace-LSA would allow an attacker to
   deceive neighboring routers into believing that a router that has
   been taken out of service (either intentionally or via a malicious
   action by the same attacker) is still active and is in the process of
   graceful restart.  However, this attack is much more difficult than
   the obvious replay of standard OSPFv3 hello packets to accomplish the
   same thing by keeping the adjacency up.  Since hello packets are sent
   more predictably and knowledge of the key is not required, the risk
   added by OSPFv3 graceful restart is insignificant.  Hence, this
   document does not raise any new security concerns other than those
   covered in [OSPFv3], [OSPFv3-AUTH], and [GRACE].


5.  IANA Considerations

   A new LSA function code will be required for the OSPFv3 grace-LSA.
   Assignment of 0x000b has been suggested herein in the "OSPFv3 LSA
   Function Codes" sub-registry of the "Open Shortest Path First v3
   (OSPFv3) Parameters" registry.  OSPFv3 grace-LSA TLVs and sub-TLVs
   use the "OSPFv2 Grace LSA Top Level TLV" IANA sub-registry of the
   "Open Shortest Path First v2 (OSPFv2) Parameters" registry.


6.  Acknowledgments

   Many thanks to Kireeti Kompella, Les Ginsberg, and David Ward with
   whom much of this was discussed.  The authors also wish to thank
   Kunihiro Ishiguro and Vivek Dubey for their comments.

   This document was produced using Marshall Rose's xml2rfc tool.


7.  References

7.1.  Normative References

   [GRACE]    Moy, J., Pillay-Esnault, P., and A. Lindem, "Graceful OSPF
              Restart", RFC 3623, November 2003.

   [OSPF-TE]  Katz, D., Yeung, D., and K. Kompella, "Traffic Engineering
              Extensions to OSPF", RFC 3630, September 2003.

   [OSPFv2]   Moy, J., "OSPF Version 2", RFC 2328, April 1998.




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   [OSPFv3]   Moy, J., Ferguson, D., and R. Coltun, "OSPF for IPv6",
              RFC 2740, March 1997.

   [RFC2119]  Bradner, S., "Key words for use in RFC's to Indicate
              Requirement Levels", RFC 2119, March 1997.

7.2.  Informative References

   [MIB-INTF]
              McCloghrie, K. and M. Rose, "Management Information  Base
              for network management of TCP/IP-based internets:
              MIB-II", RFC 1213, March 1991.

   [MIB-PERS]
              McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, June 2000.

   [OSPFv3-AUTH]
              Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, June 2006.


Authors' Addresses

   Padma Pillay-Esnault
   Cisco Systems
   3750 Cisco Way
   San Jose, CA  95134
   USA

   Email: ppe@cisco.com


   Acee Lindem
   Redback Networks
   102 Carric Bend Court
   Cary, NC  27519
   USA

   Email: acee@redback.com











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