Chapter 10. Understanding Intermediate System-to-Intermediate System (IS-IS)

This chapter covers the following key topics:

• IS-IS protocol overview

• IS-IS protocol concepts

• IS-IS link-state database

• Configuring IS-IS for IP routing

This chapter presents the fundamental concepts behind the Intermediate System-to-Intermediate System (IS-IS) routing protocol. Specifically, the material covered is slanted toward Integrated IS-IS and its usability for routing in IP environments.

The IS-IS protocol is one of the popular Interior Gateway Protocols (IGP) used on the Internet. OSPF, which is also covered in this book, is another popular IGP. The IS-IS protocol architecture easily lends itself to adaptation for various applications. IS-IS is one of the key underlying protocols for Multiprotocol Label Switching (MPLS) ‚ based traffic engineering ⁴ . More recently, there has been activity in the Internet Engineering Task Force (IETF) to standardize IS-IS for routing in IPv6 environments ⁹ . However, the scope of this chapter is limited to the key concepts and architectural organization of the IS-IS protocol and its relevant capabilities for unicast IP routing. The material presented is useful for a quick review of the protocol fundamentals; you are encouraged to consult the listed references at the end of the chapter for further reading.