Cisco Systems Cisco Systems Cisco Systems Cisco Systems Sun Microsystems This draft specifies the IS-IS extensions necessary to support multi- link IPv4 and IPv6 networks, as well as to provide true link state routing to any protocols running directly over layer 2. While supporting this concept involves several pieces, this document only describes extensions to IS-IS. We leave it to the systems using these IS-IS extensions to explain how the information carried in IS-IS is used.1. Overview There are a number of systems (for example, [RBRIDGES]) which have proposed using layer 2 addresses carried in a link state routing protocol, specifically IS-IS [IS-IS] [RFC1195], to provide true layer 2 routing in specific environments. This draft proposes a set of TLVs and sub-TLVs to be added to [IS-IS] level 1 PDUs, and three new PDU types, to support these proposed systems. This draft does not propose new forwarding mechanisms using this additional information carried within IS-IS. There is a short section included on two possible ways to build a shortest path first tree including this information, to illustrate how this information might be used.