BGP Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

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BGP Link-State

Updated: February 28, 2026

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Overview

Explains the protocol extension that distributes IGP link-state information via BGP, improves network topology visibility, and uses a dedicated AFI/SAFI to encode link-state attributes.

BGP Link-State (BGP-LS) is a protocol extension that

  • distributes IGP link-state information via BGP

  • improves network topology visibility for applications like SR-PCE, and

  • uses a dedicated AFI/SAFI (RFC7752) to encode link-state attributes.

Table 1. Feature History Table

Feature Name

Release Information

Feature Description

BGP Link-State

Release 25.4.1

Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only*)

*This feature is supported on:

  • 8011-32Y8L2H2FH

  • 8011-12G12X4Y-A

  • 8011-12G12X4Y-D

BGP Link-State

 Release 25.1.1

Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only*)

*This feature is supported on Cisco 8011-4G24Y4H-I routers.

BGP Link-State

Release 24.4.1

Introduced in this release on: Fixed Systems (8200 [ASIC: P100], 8700 [ASIC: P100, K100])(select variants only); Modular Systems (8800 [LC ASIC: P100])(select variants only*)

With BGP Link-State (BGP-LS), you can efficiently share IGP link-state information across your network, allowing applications such as Segment Routing Path Computation Element (SR-PCE) to gain greater topology awareness and optimize path computations using Segment Routing Traffic Engineering (SR-TE). This feature uses Address Family Identifier (AFI) and Sub-address Family Identifier (SAFI) to encode link-state data in the BGP-LS attribute as defined by RFC7752.

*This feature is supported on:

  • 8212-48FH-M

  • 8711-32FH-M

  • 8712-MOD-M

  • 88-LC1-36EH

  • 88-LC1-12TH24FH-E

  • 88-LC1-52Y8H-EM

BGP-LS extends BGP to carry Interior Gateway Protocol (IGP) link-state information using a specific Address Family Identifier (AFI) and Sub-address Family Identifier (SAFI). As defined in RFC7752, BGP-LS encodes each link-state object, such as a node, a link, or a prefix, in the BGP Network Layer Reachability Information (NLRI) format, while the properties of each object are conveyed using the BGP-LS path attribute. This approach enables controllers and applications to build a comprehensive topology view across multiple domains.

Example

A Segment Routing Path Computation Element (SR-PCE) can use BGP-LS data to discover node capabilities, learn mappings for SR segments, and compute optimal paths using Segment Routing Traffic Engineering (SR-TE). This enables SR-PCE to steer traffic on paths different from the underlying IGP-based distributed best-path computation.

Deployment scenarios for BGP Link-State

This figure illustrates a typical BGP-LS deployment.

Figure 1. Deployment scenario for BGP-LS

The deployment involves:

  • Configuring one or more BGP speakers (nodes) with BGP-LS in each IGP area.

  • Establishing an iBGP mesh between BGP speakers and route-reflectors.

  • Allowing route-reflectors to aggregate and share link-state information from all IGP areas and from eBGP peers in other autonomous systems (AS).

Functional limitations

IGPs do not use BGP-LS data from remote BGP peers, and BGP does not download the received BGP-LS information into other router components.

Instance-id usage

The identifier field in BGP Link-State, called the instance-id, specifies the IGP routing domain to which the NLRI is associated.

Some best practices for instance-id configuration are:

  • Assign a consistent instance-id value to all BGP-LS producers within a single IGP domain.

  • When only one protocol instance is present, configure the instance-id value to 0.

  • Use unique instance-id values for different routing protocol instances operating in separate IGP domains.

NLRIs with different instance-id values represent different IGP routing instances. If consistent instance-ids are not used, BGP-LS consumers may see duplicate objects or incorrect topology.

Enable the exchange of BGP Link-State information with a BGP neighbor.

Use this task to distribute IGP link-state data (OSPF or IS-IS) to a BGP neighbor for use by controllers or applications such as SR-PCE.

Before you begin

  • Ensure you have access to the router CLI.

  • Confirm that the neighbor uses a private IP address.

Procedure

1.

Run the configure comamnd to enter configuration mode.

Example:

Router# configure
2.

Specify the BGP AS number and enter BGP configuration mode.

Example:

Router(config)# router bgp 100
3.

Configure the neighbor using its IP address.

Example:

Router(config-bgp)# neighbor 10.0.0.2
4.

Set the remote AS number for the neighbor and enter the link-state address family.

Example:

Router(config-bgp-nbr)# remote-as 1
Router(config-bgp-nbr)# address-family link-state link-state
Router(config-bgp-nbr)# commit

The router exchanges BGP Link-State data with the specified neighbor.

Configure a unique domain distinguisher (four-octet ASN)

Assign a unique identifier (domain distinguisher) for BGP Link-State using a four-octet ASN.

The domain distinguisher helps differentiate routing domains when distributing link-state information.

Follow these steps to configure the domain distinguisher.

Procedure

1.

In configuration mode, specify the BGP AS number and enter BGP configuration mode.

Example:

Router# configure
Router(config)# router bgp 100
2.

Enter the link-state address family configuration mode.

Example:

Router(config-bgp)# address-family link-state link-state
3.

Assign a unique domain distinguisher.

Example:

Router(config-bgp-af)# domain-distinguisher 1234
Router(config-bgp-af)# commit

Possible range of domain-distinguisher: 1 to 4294967295

The router uses the specified four-octet ASN as the domain distinguisher for BGP-LS.

BGP Link-State (BGP-LS) enables the distribution of IGP link-state databases, including OSPF and IS-IS link-state data, across multiple, independent routing domains. This distribution allows controllers or applications to build end-to-end paths that span several domains.

To distribute OSPFv2 link-state data using BGP-LS:

  • Enter router configuration mode.

  • Configure the OSPF process.

  • Use the distribute link-state command with the appropriate instance-id.

Example configuration: 
Router# configure
Router(config)# router ospf 100
Router(config-ospf)# distribute link-state instance-id 32