Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

 
 

BGP Link-Bandwidth Community

Overview

Within a BGP implementation, a link-bandwidth extended community encodes the bandwidth of a given next hop. BGP assists in load-balancing traffic by communicating the speeds of BGP links to remote peers. When you (the network administrator) combine a link-bandwidth community with multipath, the load-balancing algorithm of your choice distributes traffic flows across the set of next hops proportional to their relative bandwidths.

When the BGP link-bandwidth extended community is a transitive attribute across autonomous systems (ASs), the BGP group advertises the link-bandwidth extended community to neighboring ASs. You can choose to use the BGP link-bandwidth community as a nontransitive attribute so routers drop the link-bandwidth community at the AS boundary. The BGP group does not advertise nontransitive link-bandwidth communities to external BGP (EBGP) neighbors.

You can also configure BGP to automatically sense the bandwidth and import the community at a group or neighbor level. Using this link-bandwidth autosense feature, your network can automatically set the link-bandwidth value to the speed of the interface over which the device received the BGP route.

Only per-packet load balancing supports the BGP link-bandwidth community.

Benefits

  • With multipath enabled, link-bandwidth provides weighted equal-cost multipath (WECMP) for unequal load balancing.

  • Ensures high-bandwidth links carry more flows than low-bandwidth links.

  • Reduces the likelihood of traffic congestion.

Configuration

Bandwidth

By default, the link-bandwidth community is transitive. You can use either of these statements to configure the link-bandwidth community as transitive:

To make it nontransitive, use the following configuration:

Nontransitive Override

You can override a nontransitive configuration so that a BGP group sends the link-bandwidth extended community over an EBGP session even when link-bandwidth is nontransitive. To send the nontransitive link-bandwidth community across an EBGP neighbor, include the following configuration:

The send-non-transitive-link-bandwidth statement does not differentiate between the originated link-bandwidth community and one that has been received and readvertised. When you enable this option, BGP advertises all nontransitive link-bandwidth communities to the EBGP neighbor.

Aggregate Bandwidth

By default, the aggregate link-bandwidth community is transitive. You can use either of these statements to configure the link-bandwidth community as transitive:

To make it nontransitive, use the following configuration:

To divide the total link-bandwidth by the number of peers in the advertising group, enable the divide-equal statement:

Autosense

You can only enable autosense for single-hop EBGP sessions.

  1. Configure autosense for the BGP group.

    Configure the auto-sense statement at the neighbor hierarchy to detect and store the bandwidth toward that BGP neighbor. Configure it at the group hierarchy to detect and store the bandwidth for all neighbors under that BGP group:

  2. Configure the import policy with auto-link-bandwidth set to transitive or non-transitive. If you do not specify, by default auto-link-bandwidth is transitive:

  3. (Optional) To suppress frequent changes in the link-bandwidth value when bandwidth increases, you can configure the autosense hold-down timer. The hold-down timer is only triggered when the bandwidth increases. By default, the timer is set to 60 seconds:

Verification

Verify the configuration was successful using the following commands:

  • show route receive-protocol bgp peer-ip-address extensive

  • show route advertising-protocol bgp peer-ip-address extensive

  • show route address extensive

  • show bgp neighbor address

Platform Support

See Feature Explorer for platform and release support.