IS-IS overview

The Intermediate System to Intermediate System (IS-IS) protocol is a link-state Interior Gateway Protocol (IGP) that is based on the International Standard for Organization/ International Electrotechnical Commission (ISO/IEC) Open Systems Internet Networking model (OSI). In IS-IS, an intermediate system (router) is designated as either a Level 1 or Level 2 device. A Level 1 router routes traffic only within the area in which the router resides. A Level 2 router routes traffic between areas within a routing domain.

The implementation of IS-IS is based on the following specifications and draft specifications:

• ISO/IEC 10589 - "Information Technology - Telecommunication and information exchange between systems - Intermediate system to Intermediate system intra-domain routing information exchange protocol for use in conjunction with the protocol for providing the connection less-mode Network Service (ISO 8473)", 1992
• ISO/IEC 8473 - "Information processing systems - Data Communications - Protocols for providing the connectionless-mode network service", 1988
• ISO/IEC 9542 - "Information Technology - Telecommunication and information exchange between systems - End system to Intermediate system intra-domain routing information exchange protocol for use in conjunction with the protocol for providing the connection less-mode Network Service (ISO 8473)", 1988
• RFC 1195 - "Use of OSI IS-IS for Routing in TCP/IP and Dual Environments", 1990.
• RFC 2763 - "Dynamic Host Name Exchange Mechanism for IS-IS", 2000.
• RFC 2966 - "Domain-wide Prefix Distribution with Two-Level IS-IS", 2000
• RFC 3373 - "Three-Way Handshake for Intermediate System to Intermediate System (IS-IS) Point-to-Point Adjacencies", 2002
• Portions of the Internet Draft "IS-IS extensions for Traffic Engineering" draft-ieff-isis-traffic-02.txt (dated 2000). that describe the Extended IP reachability type-length-value (TLV type 135) and the extended Intermediate System (IS) reachability TLV (TLV type 22). These portions provide support for the wide metric version of IS-IS. No other portion is supported on Extreme‘s implementation of IS-IS.

Note

The Extreme device does not support routing of Connectionless-Mode Network Protocol (CLNP) packets. The Extreme device uses IS-IS for TCP/IP only.