Appendix C. Integrated IS-IS Basics of Operation

Intermediate System-to-Intermediate System (IS-IS) was standardized by the International Telecommunication Union (ITU) in the International Organization for Standardization (ISO) standard 10589 in 1990. IS-IS was originally designed for use with End System-to-Intermediate System (ES-IS) to provide routing information for Connectionless Network Service (CLNS) and other routed protocols that the ITU standardized.

The Internet Engineering Task Force (IETF) has, over the years, added extensions to IS-IS to support IP routing, Multiprotocol Label Switching (MPLS) traffic engineering (TE), and other capabilities, through a series of RFCs, including these:

• RFC 1195?/span> "Use of Open System Interconnection (OSI) IS-IS for Routing in TCP/IP and Dual Environments"

• RFC 2973?/span> "IS-IS Mesh Groups"

• RFC 3567?/span> "Intermediate System-to-Intermediate System (IS-IS) Cryptographic Authentication"

• RFC 3784?/span> "Intermediate System-to-Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)"

• RFC 3847?/span> "Restart Signaling for Intermediate System-to-Intermediate System (IS-IS)"

Until 2003, the IETF issued only informational RFCs for the IS-IS protocol, which means they are not authoritative for building interoperable implementations of the protocol. This has led to the reissuance of many of these modifications to the protocols by the ITU. The IETF has recently, however, decided to issue standards track RFCs for IS-IS. The ITU can refer to these as authoritative definitions of how the protocol works, directly, so the entire community can work together on specifying new extensions to the protocol.