IS-IS Overview

The Intermediate System-to-Intermediate System (IS-IS) protocol is an interior gateway protocol (IGP) that uses link-state information to make routing decisions.

IS-IS is a link-state IGP that uses the shortest path first (SPF) algorithm to determine routes. IS-IS evaluates the topology changes and determines whether to perform a full SPF recalculation or a partial route calculation (PRC). This protocol originally was developed for routing International Organization for Standardization (ISO) Connectionless Network Protocol (CLNP) packets.

Note: Because IS-IS uses ISO addresses, the configuration of the Internet Protocol version 6 (IPv6) and Internet Protocol version 4 (IPv4) implementations of IS-IS is identical.

This chapter discusses the following topics that provide background information about IS-IS:

• IS-IS Standards
• IS-IS Terminology
• ISO Network Addresses
• IS-IS Packets
• Persistent Route Reachability
• IS-IS Extensions to Support Traffic Engineering
• IS-IS Extensions to Support Route Tagging

Copyright © 2008, Juniper Networks, Inc. All rights reserved. Trademark Notice.