IS-IS overview

Intermediate System-to-Intermediate System (IS-IS) is a dynamic routing protocol designed by the International Organization for Standardization (ISO) to operate on the connectionless network protocol (CLNP).

The IS-IS routing protocol was modified and extended in RFC 1195 by the International Engineer Task Force (IETF) for application in both TCP/IP and OSI reference models, and the new one is named "Integrated IS-IS" or "Dual IS-IS".

IS-IS is an Interior Gateway Protocol (IGP) used within an Autonomous System. It adopts the Shortest Path First (SPF) algorithm for route calculation.

The term "router" in this chapter refers to both routers and Layer 3 switches.