Configuring ISIS for IP Routing

This section reviews the basic tasks involved in enabling IS-IS on Cisco routers. In addition to the basic configuration, numerous Cisco IOS Software commands exist for enabling various optimization and management capabilities, such as modifying hello timers, logging IS-IS adjacency changes, performing authentication, and so on. Chapter 11 covers some of these options in greater detail. For completeness, however, you should consult the "IOS Network Protocols Configuration Guide," available at

Enabling IS-IS on point-to-point and LAN broadcast? type links is simple and similar in both cases. Additionally, on LAN type links, you can use the interface-level command isis priority value to select a preferred router to be DIS. The default interface priority is 64. A higher value is preferred.

The following sections provide examples that elaborate on configuring IS-IS specifically:

• Configuring IS-IS on point-to-point serial links

• Configuring IS-IS on broadcast links (that is, LAN media)

• Configuring IS-IS on NBMA links, including the following:

- ATM point-to-point

- ATM multipoint

• IP default route advertisement

• Redistribution

• IP route summarization

Configuring IS-IS on Point-to-Point Serial Links

Figure 10-14 shows two routers, RT1 and RT2, connected back to back by a serial link. Both routers are placed in the same IS-IS area. Figure 10-15 shows a similar setup but with RT1 and RT2 in different areas. The AreaIDs of RT1 and RT2 are mismatched to put them in different areas.

Figure 10-14. IS-IS Configuration: Network Diagram for Example 10-2

Figure 10-14. IS-IS Configuration: Network Diagram for Example 10-2

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