Network Working Group Acee Lindem
Internet Draft Anand Oswal
Expiration Date: November 2002 Redback Networks
June 2002
Extended Hitless OSPF Restart
draft-lindem-ospf-hitless-extended-restart-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
This memo documents an enhancement to OSPF "hitless restart" whereby
an OSPF router can request that its forwarding state be maintained
longer that the router dead interval on one or more router
interfaces. This is useful when the OSPF software is being
updated and the router dead interval on one or more interfaces is
configured to a small value.
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Internet Draft Extended Hitless OSPF Restart June 2002
Table of Contents
1 Overview ............................................... 2
2 Changes to restarting router operation ................. 2
3 Changes to helper neighbor operation ................... 2
4 Backward compatibility ................................. 3
5 Security Considerations ................................ 3
6 References ............................................. 3
7 Acknowledgments ........................................ 3
8 Authors' Addresses ..................................... 3
1. Overview
"Hitless OSPF Restart" [Ref2] describes an enhancement to the
OSPF protocol [Ref1] which allows an OSPF router to continue
forwarding after the OSPF routing software has been restarted.
This memo documents an extension which allows the restart time
to exceed the router dead interval on one or more interfaces. This
useful when the routing software is being updated and the router
dead interval on one or more interfaces is configured to a very
small value.
2. Changes to restarting router operation
When the restarting router is to be brought down for a period which
may exceed the router dead interval on one or more router
interfaces, a unique value will be used for the Hitless restart
reason (Type=2, length=1) TLV. Currently, a value of 4 (extended
maintenance) is used for this purpose. Once the grace-LSA has been
originated on an interface, the restarting router must assure that
it does not send any hello packets until it actually restarts. This
is required to prevent helper neighbors from resetting their router
dead interval timer corresponding to the restarting router to the
configured value.
Routers that support both planned and unplanned restart should save
the restart reason in non-volatile storage. When the OSPF restarts
restarts, the saved restart reason is examined to determine whether
or not grace-LSAs need to be originated. The restart reason will be
0 (unknown) for unplanned restarts. This indicates the restarting
router must originate grace-LSAs prior to sending any hellos
(as specified in section 5 of "Hitless OSPF restart" [Ref2]).
3. Changes to helper neighbor operation
When a router Y receives a grace-LSA from router X and all
criteria for entering helper are satisfied (as specified in section
3.1 of "Hitless OSPF restart" [Ref2]), it will enter helper mode. If
Hitless restart reason TLV in the grace-LSA indicates "extended
maintenance" and the router dead interval will expire sooner
than the grace period expiration, the router dead interval
timer for the restarting router will be reset to expire at the
same time as the grace period expiration.
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Internet Draft Extended Hitless OSPF Restart June 2002
Additionally, local policy may be implemented to disallow
router dead interval extension when entering helper mode.
4. Backward compatibility
This extension to "Hitless OSPF Restart" [Ref2] does not introduce
any new backward compatibility issues. If an OSPF router supports
hitless OSPF restart but does not support this extension and the
router dead timer for a restarting OSPF router expires, it will
simply exit helper mode and the resume normal OSPF operation.
5. Security Considerations
The described technique does not introduce any new security issues
into OSPF protocol.
6. References
[1] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[2] Moy, J., "OSPF Hitless Restart", work in progress.
7. Acknowledgments
The authors wish to thank Naiming Shen and Tony Przygienda for their
helpful comments.
8. Authors' Addresses
Acee Lindem Anand Oswal
Redback Networks Redback Networks
102 Carric Bend Court 350 Holger Way
Cary, NC 27519 San Jose, CA 95134
e-mail: acee@redback.com e-mail: aoswal@redback.com
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