http://www.rfc-editor.org/rfc/rfc5302.txt
RFC 5302: Domain-Wide Prefix Distribution with Two-Level IS-IS, T. Li, H. Smit, T. Przygienda2008-10-01T23:00:00-00:00This document extends the semantics presented in RFC 1195 so that a routing domain running with both level 1 and level 2 Intermediate Systems (IS) (routers) can distribute IP prefixes between level 1 and level 2, and vice versa. This distribution requires certain restrictions to ensure that persistent forwarding loops do not form. The goal of this domain-wide prefix distribution is to increase the granularity of the routing information within the domain. [STANDARDS-TRACK]