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Cisco ASR 901 Aggregation Services Router Command Reference Guide
OL-26031-07
Chapter 1 CLI Command Reference
router isis
router isis
To enable the Intermediate System-to-Intermediate System (IS-IS) routing protocol and to specify an
IS-IS process, use the router isis command in global configuration mode. To disable IS-IS routing, use
the no form of this command.
router isis area-tag
no router isis area-tag
Syntax Description
Defaults This command is disabled by default.
Command Modes Global configuration
Command History
Usage Guidelines This command is used to enable routing for an area. An appropriate network entity title (NET) must be
configured to specify the area address of the area and system ID of the router. Routing must be enabled
on one or more interfaces before adjacencies may be established and dynamic routing is possible.
If you have IS-IS running and at least one International Standards Organization Interior Gateway
Routing Protocol (ISO-IGRP) process, the IS-IS process and the ISO-IGRP process cannot both be
configured without an area tag. The null tag can be used by only one process. If you run ISO-IGRP and
IS-IS, a null tag can be used for IS-IS, but not for ISO-IGRP at the same time. However, each area in an
IS-IS multiarea configuration should have a nonnull area tag to facilitate identification of the area.
You can configure only one IS-IS routing process to perform Level 2 (interarea) routing. You can
configure this process to perform Level 1 (intra-area) routing at the same time. You can configure up to
29 additional processes as Level 1-only processes. If Level 2 routing is configured on any process, all
additional processes are automatically configured as Level 1.
An interface cannot be part of more than one area, except in the case where the associated routing
process is performing both Level 1 and Level 2 routing. On media such as WAN media where
subinterfaces are supported, different subinterfaces could be configured for different areas.
If Level 2 routing is not desired for a given area, use the is-type command to remove Level 2. Level 2
routing can then be enabled on some other router instance.
area-tag Meaningful name for a routing process. If it is not specified, a null
tag is assumed and the process is referenced with a null tag. This
name must be unique among all IP or Connectionless Network
Service (CLNS) router processes for a given router.
Required for multiarea IS-IS configuration. Optional for
conventional IS-IS configuration.
Release Modification
15.1(2)SNG Support for this command was introduced on the Cisco ASR 901 router.
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