IS-IS Overview

IS-IS, or Intermediate System to Intermediate System, is an open standard routing protocol. ISO published the standard as a way to route datagrams as part of their OSI stack. IETF later republished the standard, and added IP route support.

It is a link-state routing protocol, similar to OSPF. It forms neighbor adjacencies, has areas, exchanges link-state packets, builds a link-state database and runs the Dijkstra SPF algorithm to find the best path to each destination, which is installed in the routing table.

IS-IS in RBFS supports segment routing based on RFC 8667. IS-IS Segment Routing enhances the IS-IS protocol by introducing new TLVs to carry segment routing information within IS-IS protocol packets. It introduces Segment IDs (SIDs) to represent different types of segments, such as node SIDs and adjacency SIDs.

RFC and draft compliance are partial except as specified.

Supported Platforms

Not all features are necessarily supported on each hardware platform. Refer to the Platform Guide for the features and the sub-features that are or are not supported by each platform.