Domain-wide Prefix Distribution with Two-Level IS-IS

摘要

This document describes extensions to the Intermediate System toIntermediate System (IS-IS) protocol to support optimal routingwithin a two-level domain. The IS-IS protocol is specified in ISO10589, with extensions for supporting IPv4 (Internet Protocol)specified in RFC 1195 [2].This document extends the semantics presented in RFC 1195 so that arouting domain running with both level 1 and level 2 IntermediateSystems (IS) [routers] can distribute IP prefixes between level 1 andlevel 2 and vice versa. This distribution requires certainrestrictions to insure that persistent forwarding loops do not form.The goal of this domain-wide prefix distribution is to increase thegranularity of the routing information within the domain.