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

Set priority for adding prefixes to RIB

Updated: September 8, 2026

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Provides instructions for configuring IS-IS to prioritize prefix addition to the RIB using access lists, prefix lists, or tag values, optimizing routing convergence and enabling policy-based route selection.

Ensure that certain prefixes are added to the RIB before others, helping to optimize network convergence and meet specific routing policies.

Use this task when you need IS-IS to prioritize which prefixes are added to the RIB based on an access list, prefix list, or tag value.

Before you begin

  • Verify if IS-IS routing is enabled on your device.

  • Prepare the access list, prefix list, or tag values you want to use for prioritization.

Procedure

  1. Enter IS-IS router configuration mode for the desired routing instance.

    Example:

    Router(config)# router isis isp

  2. Specify the address family (IPv4 or IPv6) and enter address family configuration mode.

    Example:

    Router(config-isis)# address-family ipv4 unicast

  3. Configure the router to generate and accept only wide-link metrics for the specified level.

    Example:

    Router(config-isis-af)# metric-style wide level 1

  4. Set the prefix priority for SPF processing using an access list, prefix list, or tag value.

    Example:

    Router(config-isis-af)# spf prefix-priority high tag 3