RFC 3277 (rfc3277) - Page 1 of 6
Intermediate System to Intermediate System (IS-IS) Transient Blackhole Avoidance
Alternative Format: Original Text Document
Network Working Group D. McPherson
Request for Comments: 3277 TCB
Category: Informational April 2002
Intermediate System to Intermediate System (IS-IS)
Transient Blackhole Avoidance
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document describes a simple, interoperable mechanism that can be
employed in Intermediate System to Intermediate System (IS-IS)
networks in order to decrease the data loss associated with
deterministic blackholing of packets during transient network
conditions. The mechanism proposed here requires no IS-IS protocol
changes and is completely interoperable with the existing IS-IS
specification.
1. Introduction
When an IS-IS router that was previously a transit router becomes
unavailable as a result of some transient condition such as a reboot,
other routers within the routing domain must select an alternative
path to reach destinations which have previously transited the failed
router. Presumably, the newly selected router(s) comprising the path
have been available for some time and, as a result, have complete
forwarding information bases (FIBs) which contain a full set of
reachability information for both internal and external (e.g., BGP)
destination networks.
When the previously failed router becomes available again, it is only
seconds before the paths that had previously transited the router are
again selected as the optimal path by the IGP. As a result,
forwarding tables are updated and packets are once again forwarded
along the path. Unfortunately, external destination reachability
information (e.g., learned via BGP) is not yet available to the
router, and as a result, packets bound for destinations not learned
via the IGP are unnecessarily discarded.
McPherson Informational