Network Working Group P. Pillay-Esnault
Internet-Draft Cisco Systems
Intended status: Standards Track October 18, 2007
Expires: April 20, 2008
OSPFv3 Graceful Restart
draft-ietf-ospf-ospfv3-graceful-restart-06.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 . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 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. 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. Grace-LSA TLVs and
sub-TLVs will share the same IANA registry as the TLVs and sub-TLVs
used by the OSPFv2 grace-LSA.
6. Acknowledgments
Many thanks to Kireeti Kompella, Les Ginsberg, and David Ward with
whom much of this was discussed. The author also wishes to thank
Kunihiro Ishiguro, Vivek Dubey, and Acee Lindem 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.
[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:
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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.
Author's Address
Padma Pillay-Esnault
Cisco Systems
3750 Cisco Way
San Jose, CA 95134
USA
Email: ppe@cisco.com
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