Summary

This chapter focuses on the configuration of the IS-IS routing protocol on Cisco routers. The early sections of this chapter look at enabling IS-IS routing on different network transport media types, specifically point-to-point, broadcast, and nonbroadcast multiaccess media. Specific media-dependent configurations are provided, covering point-to-point serial, ATM point-to-point, ATM multipoint subinterfaces, Frame Relay point-to-point, Frame Relay multipoint, and ISDN multipoint (BRI interface).

The chapter also explains the IS-IS configuration procedure. This involves a two-step process: configuring the IS-IS routing process and enabling IS-IS routing of the appropriate interfaces. This chapter also discusses how to enable IS-IS capabilities. Redistribution, summarization, and origination of a default route into the IS-IS environment are discussed and configuration examples are provided. Some time is spent discussing configuration of IS-IS over IP unnumbered interfaces, IP tunnels, and the use of secondary addresses.

IS-IS was originally designed to support a two-layer hierarchy with an addressing scheme that puts a whole router in one area. In the two-level hierarchy scheme, multiple stub Level 1 areas interconnect over a backbone. The stub Level 1 areas are interconnected by the Level 2 backbone. In this scheme, Level 1-only routers point default routes to Level 1-2 routers to route to other areas. This could potentially result in suboptimal routing. However, recent protocol enhancements allow leaking of interarea routes into Level 1, thus optimizing path selection for interarea destinations. This chapter also shows you how to configure the Level 2 to Level 1 route leaking capability.

Another recently added capability allows for multi-area support on a single router. The section on IS-IS multi-area support addresses the configuration requirements for this functionality.

The later sections of this chapter review a typical configuration of an IS-IS router in a service provider network and look at the various commands typically employed to optimize operation of the IS-IS process. In these sections, it is noted that the IOS command-line interface supports numerous commands that can be used to achieve network design objectives, such as scalability, fast convergence, and network stability.

This chapter is dedicated to getting the reader familiar with Cisco IOS configuration of the IS-IS protocol and discusses some "best practices" configuration options.