Troubleshooting guide

Additional BGP Configuration

Deleting communities from a route can be accomplished by first creating a community list that permits

the communities that are to be deleted (refer to

Configuring a Community List on page 13). Next,

create a route map (refer to Route Map on page 23) and use the set comm-list delete command to

specify a list of communities to delete:

(config-route-map)#set comm-list <name> delete

<name> Specifies the name of the community list that contains the communities to delete.

Apply the route map to the neighbor as an inbound policy (refer to Applying a Route Map Entry to a

BGP Neighbor on page 30).

If a network defines local communities, the administrator might need to remove these from the routes

before the local router advertises the routes to an external neighbor. This scenario requires the

administrator to configure a community list that permits the local communities. The community list is then

matched to a route map entry and the route map is applied to the BGP neighbor as an outbound policy.

Description

Use the description command to identify the specified interface connected to a BGP neighbor.

(config-bgp-neighbor)#description <text>

<text> Identifies the specified interface using up to 80 alphanumeric characters.

Distance

The administrative distance is a local variable that allows a router to choose the best route when there are

multiple paths to the same network. Use the distance bgp command to set the administrative distance for

BGP routes.

(config-bgp)#distance bgp <external> <internal> <local>

<external> Sets the administrative distance for BGP routes learned via eBGP sessions. Range is 1 to 255.

<internal> Sets the administrative distance for BGP routes learned via iBGP sessions. Range is 1 to 255.

<local> Sets the administrative distance for BGP routes learned via the network command and

redistribution. Range is 1 to 255.

If a route map is already in place to set policies or filter routes, this route map should also

be used to delete the specified communities. Each route map sequence number entry that

could potentially let in a route should be evaluated to determine if deleting communities

also applies. If so, the set comm-list <name> delete command should be added for each

applicable route map sequence number. This is because the router stops processing a route

map as soon as it finds a match. If a separate, earlier entry permits a route (as described in

the preceding paragraphs), the router will immediately add the route to the BGP database

without applying any policies that are set in later entries.

By default, external is set to 20, internal to 200, and local to 200. Normally, these default

settings should not be changed.