On the Services Router, Intermediate System-to-Intermediate System (IS-IS) protocol is an interior gateway routing protocol (IGP) that uses link-state information for routing network traffic. IS-IS uses the shortest path first (SPF) algorithm to determine routes. Using SPF, IS-IS evaluates network topology changes and determines if a full or partial route calculation is required. The protocol was originally developed for routing International Organization for Standards (ISO) connectionless network protocol (CLNP) packets.
This overview contains the following topics: