The IS-IS Routing Protocol may be used as an IGP to support IP as well as OSI. This allows a single routing protocol to be used to support pure IP environments, pure OSI environments, and dual environments. Integrated IS-IS is deployed extensively in an IP-only environment in the top-tier Internet service provider (ISP) networks. The IS-IS working group of the Internet Engineering Task Force (IETF) developed the specification for Integrated IS-IS (RFC 1195).
Two primary methods are available for routing protocols to support dual OSI and IP routers. One method, known as "Ships in the Night," makes use of completely independent routing protocols for each of the two protocol suites. This specification presents an alternative approach, which makes use of a single integrated protocol for interior routing (that is, for calculating routes within a routing domain) for both protocol suites.
By supporting both IP and OSI traffic, this integrated protocol design supports traffic to IP hosts, OSI end systems, and dual end systems. The IS-IS Protocol can be used to support pure-IP environments, pure-OSI environments, and dual environments. IS-IS allows the interconnection of dual (IP and OSI) routing domains with other dual domains, with IP-only domains, and with OSI-only domains.
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