Chapter 5. IS-IS Network Design

The Intermediate System-to-Intermediate System (IS-IS) protocol is typically treated as something of a mystery in the IP networking world. Originally developed by the International Organization for Standardization (ISO) (now called the ITU), IS-IS was designed to route connection-oriented network services (CONS) and connectionless network services (CLNS) packets. Although IS-IS is similar to Open Shortest Path First (OSPF) in theory, it is operationally different enough to confuse network designers who are familiar with OSPF but have not studied IS-IS.

This chapter covers many of the same network designs covered in Chapter 4, "OSPF Network Design," but focuses on how to deploy IS-IS, illustrating some of the differences between the protocols. The chapter begins with deployment on a three-layer and two-layer hierarchy. The chapter then moves into specific topologies and some considerations in scaling IS-IS networks.

• ISO 10589, published by the ITU

• RFC 1195, "Use of OSI IS-IS for Routing in TCP/IP and Dual Environments"

• IS-IS Deployment in IP Networks, published by Addison-Wesley, by Russ White and Alvaro Retana

• Routing TCP/IP, Volume I, published by Cisco Press, by Jeff Doyle

Whereas flooding domains are called areas in the OSPF protocol, they are called routing domains within the IS-IS protocol, and routers are called intermediate systems (ISs) within IS-IS. These terms are used throughout this chapter.

In this chapter, the summarization of topology information is referred to as summarization, and the summarization of reachability information is referred to as aggregation. Although these terms are normally used interchangeably in real network design and maintenance, this chapter makes this distinction just for readability.