Network Working Group Padma Pillay-Esnault
Internet Draft Juniper Networks
January 2004
Category: Standards Track
Expires: June 2004
Grace LSA in OSPFv3
draft-pillay-esnault-ospf-v3-grace-lsa-03.txt
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This memo describes the OSPF version 3 specific Grace Link State
Advertisement used to perform a graceful restart.
Pillay-Esnault Standards Track [Page 1]
Internet Draft Grace LSA in OSPFv3 January 2004
1. Introduction
Graceful OSPF restart [GRACEFUL] describes a mechanism to restart the
control plane of an OSPFv2 router which still has its forwarding
plane intact with a minimum of disruption to the network.
The methods described in [GRACEFUL] work for point to point links
for OSPF version 3. In [GRACEFUL] broadcast and point to multipoint
links use the Interface Address TLV for OSPF version 2 which is
inapplicable in OSPF version 3. This memo describes the new Grace
LSA specific to OSPF version 3.
2. The Grace Link State Advertisement
The grace-LSA is used by a restarting router to signal its immediate
neighbors of its intent to undergo graceful restart and requests his
neighbors aid. The grace-LSA contain the restarting router
grace-period and information on the reason of initiating the restart
process. The neighbors helper role consists of continuing to
advertise the restarting router as FULL for the specified grace
period left regardless of the actual neighbor state.
In OSPF version 3, the Designated router is identified by its
router-id as opposed to its interface address in OSPF version 2 on a
broadcast segment. The grace-LSA for OSPF version 2 carries the
interface address of the restarting router for the helper to identify
the restarting neighbor per [GRACEFUL].
Broadcast and point-to-multi-point segments do not need to carry
a TLV is added to carry the router ID for a broadcast segment in
OSPF version 3 as the Designated Router can be identified for the
advertising router of the grace-LSA. In essence, there is no
equivalent router-address TLV for OSPF version 3 and it is not needed.
The grace-LSA body format will remain the same as described in
[GRACEFUL].
Pillay-Esnault Standards Track [Page 2]
Internet Draft Grace LSAs in OSPFv3 October 2002
2.1 Grace LSA version 3 - 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
The U-bit is set to 0 to indicate that this is a Link Local LSA
The S2-bit and S1-bit are also both set to 0 to indicate a
link-local scope.
2.2 Grace LSA Format
This grace LSA format is as follows
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 -+
| ... |
The Link State ID of a grace-LSA in OSPF version 3 is the
interface ID of the interface the LSA is originated on.
The format of the TLVs within the body of a grace-LSA is the same as
the TLV format used by the Traffic Engineering Extensions to OSPF
[OSPF-TE]. The TLV header consists of a 16-bit Type field and a
16-bit length field, and is followed by zero or more bytes of value.
The length field indicates the length of the value portion in bytes.
The value portion is padded to four-octet alignment, but the
padding is not included in the length field.
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Internet Draft Grace LSAs in OSPFv3 January 2004
The following is the list of TLVs that can appear in the body of a
grace-LSA.
o 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 the state of database
synchronization between the router and its neighbors. This TLV
is mandatory in a Grace LSA.
o 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 is mandatory in a
grace-LSA.
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Internet Draft Grace LSAs in OSPFv3 January 2004
Normative References
[OSPFv3] Coltun, R., D. Ferguson, and J. Moy, "OSPF for IPv6", RFC
2740, December 1999
[GRACEFUL] Moy J., Pillay-Esnault P., Lindem A., "Graceful OSPF
Restart", RFC 3623, November 2003.
[OSPF-TE] Katz, D., D. Yeung and K. Kompella, "Traffic Engineering
Extensions to OSPF", RFC 3630, September 2003
Security Considerations
The OSPF v3 security mechanisms to prevent tampering and spoofing of
LSAs suffice.
Acknowledgments
Many thanks to Kireeti Kompella with whom much of this was discussed.
The author also wish to thank Acee Lindem and Kunihiro Ishiguro for
their comments.
Authors' Addresses
Padma Pillay-Esnault
Juniper Networks, Inc.
1194 N. Mathilda Ave
Sunnyvale, CA 94089
Email: padma@juniper.net
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Internet Draft Grace LSA in OSPFv3 January 2004
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Internet Draft Grace LSA in OSPFv3 January 2004
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Pillay-Esnault Standards Track [Page 5]
