Graceful OSPF Restart
RFC 3623
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RFC - Proposed Standard
(November 2003; No errata)
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Last updated |
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2015-10-14
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IETF
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No shepherd assigned
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IESG state |
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RFC 3623 (Proposed Standard)
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Unknown
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Responsible AD |
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Alex Zinin
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In authors' 48 hours (I guess the state change to RFC Ed Queue is overdue)
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Send notices to |
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<rohit@utstar.com>, <john.moy@sycamorenet.com>
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Network Working Group J. Moy
Request for Comments: 3623 Sycamore Networks
Category: Standards Track P. Pillay-Esnault
Juniper Networks
A. Lindem
Redback Networks
November 2003
Graceful OSPF 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.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This memo documents an enhancement to the OSPF routing protocol,
whereby an OSPF router can stay on the forwarding path even as its
OSPF software is restarted. This is called "graceful restart" or
"non-stop forwarding". A restarting router may not be capable of
adjusting its forwarding in a timely manner when the network topology
changes. In order to avoid the possible resulting routing loops, the
procedure in this memo automatically reverts to a normal OSPF restart
when such a topology change is detected, or when one or more of the
restarting router's neighbors do not support the enhancements in this
memo. Proper network operation during a graceful restart makes
assumptions upon the operating environment of the restarting router;
these assumptions are also documented.
Moy, et al. Standards Track [Page 1]
RFC 3623 Graceful OSPF Restart November 2003
Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Operation of Restarting Router . . . . . . . . . . . . . . . . 3
2.1. Entering Graceful Restart. . . . . . . . . . . . . . . . 4
2.2. When to Exit Graceful Restart. . . . . . . . . . . . . . 5
2.3. Actions on Exiting Graceful Restart. . . . . . . . . . . 6
3. Operation of Helper Neighbor . . . . . . . . . . . . . . . . . 7
3.1. Entering Helper Mode . . . . . . . . . . . . . . . . . . 7
3.2. Exiting Helper Mode. . . . . . . . . . . . . . . . . . . 8
4. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 9
5. Unplanned Outages. . . . . . . . . . . . . . . . . . . . . . . 10
6. Interaction with Traffic Engineering . . . . . . . . . . . . . 11
7. Possible Future Work . . . . . . . . . . . . . . . . . . . . . 11
8. Intellectual Property Rights Notice. . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 11
A. Grace-LSA Format . . . . . . . . . . . . . . . . . . . . . . . 13
B. Configurable Parameters. . . . . . . . . . . . . . . . . . . . 15
Security Considerations. . . . . . . . . . . . . . . . . . . . . . 16
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 18
1. Overview
Today many Internet routers implement a separation of control and
forwarding functions. Certain processors are dedicated to control
and management tasks such as OSPF routing, while other processors
perform the data forwarding tasks. This separation creates the
possibility of maintaining a router's data forwarding capability
while the router's control software is restarted/reloaded. We call
such a possibility "graceful restart" or "non-stop forwarding".
The OSPF protocol presents a problem to graceful restart whereby,
under normal operation, OSPF intentionally routes around a restarting
router while it rebuilds its link-state database. OSPF avoids the
restarting router to minimize the possibility of routing loops and/or
black holes caused by lack of database synchronization. Avoidance is
accomplished by having the router's neighbors reissue their LSAs,
omitting links to the restarting router.
However, if (a) the network topology remains stable and (b) the
restarting router is able to keep its forwarding table(s) across the
restart, it would be safe to keep the restarting router on the
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