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Configuring Integrated IS-IS
IS-IS Configuration Task List
IPC-278
Cisco IOS IP Configuration Guide
Small IS-IS networks are built as a single area that includes all the routers in the network. As the network
grows larger, it is usually reorganized into a backbone area made up of the connected set of all Level 2
routers from all areas, which is in turn connected to local areas. Within a local area, routers know how
to reach all system IDs. Between areas, routers know how to reach the backbone, and the backbone
routers know how to reach other areas.
Routers establish Level 1 adjacencies to perform routing within a local area (intra-area routing). Routers
establish Level 2 adjacencies to perform routing between Level 1 areas (interarea routing).
Some networks use legacy equipment that supports only Level 1 routing. These devices are typically
organized into many small areas that cannot be aggregated due to performance limitations. Cisco routers
are used to interconnect each area to the Level 2 backbone.
A single Cisco router can participate in routing in up to 29 areas, and can perform Level 2 routing in the
backbone. In general, each routing process corresponds to an area. By default, the first instance of the
routing process configured performs both Level 1 and Level 2 routing. You can configure additional
router instances, which are automatically treated as Level 1 areas. You must configure the parameters
for each instance of the IS-IS routing process individually.
For IS-IS multiarea routing, you can configure only one process to perform Level 2 routing, although
you can define up to 29 Level 1 areas for each Cisco router. If Level 2 routing is configured on any
process, all additional processes are automatically configured as Level 1. You can configure this process
to perform Level 1 routing at the same time. If Level 2 routing is not desired for a router instance, remove
the Level 2 capability using the is-type router configuration command. Use the is-type router
configuration command also to configure a different router instance as a Level 2 router.
Network entity titles (NETs) define the area addresses for the IS-IS area and the system ID of the router.
Refer to the “Configuring ISO CLNS” chapter in the Cisco IOS Apollo Domain, Banyan VINES, ISO
CLNS, and XNS Configuration Guide for a more detailed discussion of NETs.
To enable IS-IS and specify the area for each instance of the IS-IS routing process, use the following
commands in global configuration mode:
See the “IS-IS Configuration Examples” section at the end of this chapter for examples of configuring
IS-IS as an IP routing protocol.
Command Purpose
Step 1
Router(config)# router isis [area tag]
Enables IS-IS routing for the specified routing process, and places
the router in router configuration mode.
Use the area tag arguments to identify the area to which this IS-IS
router instance is assigned. A value for tag is required if you are
configuring multiple IS-IS areas.
The first IS-IS instance configured is Level 1-2 by default. Later
instances are automatically Level 1. You can change the level of
routing to be performed by a particular routing process using the
is-type router configuration command.
Step 2
Router(config)# net network-entity-title
Configures NETs for the routing process. Specify a NET for each
routing process if you are configuring multiarea IS-IS. You can
specify a name for a NET and for an address.
Note Multiarea IS-IS is supported only for ISO CLNS.