IS-IS Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

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IS-IS Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

Enable IS-IS and configure level 1 or level 2 routing

Updated: September 8, 2026

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Provides instructions for enabling IS-IS on network devices and configuring level 1 or level 2 routing, guiding users through the essential steps for IS-IS deployment in Cisco IOS XR.

Set up IS-IS protocol and define the router’s participation in intra-area, backbone, or both routing domains.

IS-IS is a dynamic routing protocol used to exchange routing information in large networks. You can configure IS-IS before assigning IP addresses, but actual routing will not occur until an IP address is configured on at least one interface. The routing level determines how the router forms adjacencies and participates within the network.

Before you begin

  • Ensure the router has at least one configured IP address.

  • Identify the network entity title (NET) and desired IS-IS routing level for your topology.

Procedure

  1. Enable IS-IS for the desired routing instance.

    Example:

    Router# configure
Router(config)# router isis isp

    By default, all IS-IS instances are automatically Level 1 and Level 2. You can change the level of routing to be performed by a particular routing instance by using the is-type router configuration command.

  2. Configure a network entity title (NET) for the IS-IS instance.

    Example:

    
Router(config-isis)# net 47.0004.004d.0001.0001.0c11.1110.00

    • Specify a NET for each routing instance if you are configuring multi-instance IS-IS.

    • This example configures a router with area ID 47.0004.004d.0001 and system ID 0001.0c11.1110.00.

    • To specify more than one area address, specify additional NETs. Although the area address portion of the NET differs, the systemID portion of the NET must match exactly for all of the configured items.

  3. (Optional) Choose the IS-IS routing level for this instance.

    Example:

    
Router(config-isis)# is-type level-2-only

    By default, every IS-IS instance acts as a level-1-2 router.

    Use these options as needed:

    • - level-1 : Only intra-area routing (Level 1 adjacencies).

    • - level-2-only : Only backbone routing (Level 2 adjacencies).

    • - level-1-2 : Default; both intra-area and backbone routing.

  4. (Optional) Verify the IS-IS configuration.

    Example:

    
Router# show isis protocol

    Displays summary information about the IS-IS instance.