Restart Signaling for IS-IS
RFC 5306
Document | Type |
RFC - Proposed Standard
(October 2008; No errata)
Obsoleted by RFC 8706
Obsoletes RFC 3847
|
|
---|---|---|---|
Authors | Mike Shand , Les Ginsberg | ||
Last updated | 2018-12-20 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized 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 the domain). 2. It sets SRMflags on its own LSP database on the adjacency concerned.Show full document text