Restart Signaling for IS-IS
RFC 5306
| Document | Type |
RFC - Proposed Standard
(October 2008; No errata)
Obsoletes RFC 3847
|
|
|---|---|---|---|
| Last updated | 2015-10-14 | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 5306 (Proposed Standard) | |
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Ross Callon | ||
| Send notices to | (None) | ||
Network Working Group M. Shand
Request for Comments: 5306 L. Ginsberg
Obsoletes: 3847 Cisco Systems
Category: Standards Track October 2008
Restart Signaling for IS-IS
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.
Abstract
This document describes a mechanism for a restarting router to signal
to its neighbors that it is restarting, allowing them to reestablish
their adjacencies without cycling through the down state, while still
correctly initiating database synchronization.
This document additionally describes a mechanism for a restarting
router to determine when it has achieved Link State Protocol Data
Unit (LSP) database synchronization with its neighbors and a
mechanism to optimize LSP database synchronization, while minimizing
transient routing disruption when a router starts. This document
obsoletes RFC 3847.
Shand & Ginsberg Standards Track [Page 1]
RFC 5306 Restart Signaling for IS-IS October 2008
Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Timers . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Restart TLV . . . . . . . . . . . . . . . . . . . . . . . 5
3.2.1. Use of RR and RA Bits . . . . . . . . . . . . . . . . 6
3.2.2. Use of the SA Bit . . . . . . . . . . . . . . . . . . 8
3.3. Adjacency (Re)Acquisition . . . . . . . . . . . . . . . . 8
3.3.1. Adjacency Reacquisition during Restart . . . . . . . . 9
3.3.2. Adjacency Acquisition during Start . . . . . . . . . . 11
3.3.3. Multiple Levels . . . . . . . . . . . . . . . . . . . 12
3.4. Database Synchronization . . . . . . . . . . . . . . . . . 13
3.4.1. LSP Generation and Flooding and SPF Computation . . . 14
3.4.1.1. Restarting . . . . . . . . . . . . . . . . . . . . 14
3.4.1.2. Starting . . . . . . . . . . . . . . . . . . . . . 16
4. State Tables . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1. Running Router . . . . . . . . . . . . . . . . . . . . . . 17
4.2. Restarting Router . . . . . . . . . . . . . . . . . . . . 18
4.3. Starting Router . . . . . . . . . . . . . . . . . . . . . 19
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
7. Manageability Considerations . . . . . . . . . . . . . . . . . 20
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
9. Normative References . . . . . . . . . . . . . . . . . . . . . 21
Shand & Ginsberg Standards Track [Page 2]
RFC 5306 Restart Signaling for IS-IS October 2008
1. Overview
The Intermediate System to Intermediate System (IS-IS) routing
protocol [RFC1195] [ISO10589] is a link state intra-domain routing
protocol. Normally, when an IS-IS router is restarted, temporary
disruption of routing occurs due to events in both the restarting
router and the neighbors of the restarting router.
The router that has been restarted computes its own routes before
achieving database synchronization with its neighbors. The results
of this computation are likely to be non-convergent with the routes
computed by other routers in the area/domain.
Neighbors of the restarting router detect the restart event and cycle
their adjacencies with the restarting router through the down state.
The cycling of the adjacency state causes the neighbors to regenerate
their LSPs describing the adjacency concerned. This in turn causes a
temporary disruption of routes passing through the restarting router.
In certain scenarios, the temporary disruption of the routes is
highly undesirable. This document describes mechanisms to avoid or
minimize the disruption due to both of these causes.
When an adjacency is reinitialized as a result of a neighbor
restarting, a router does three things:
1. It causes its own LSP(s) to be regenerated, thus triggering SPF
runs throughout the area (or in the case of Level 2, throughout
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