Configuring BGP
Configuring Advanced BGP Features
IPC-312
Cisco IOS IP Configuration Guide
To create an aggregate address in the routing table, use the following commands in router configuration
mode:
See the “BGP Aggregate Route Examples” section at the end of this chapter for examples of using BGP
aggregate routes.
Disabling Automatic Summarization of Network Numbers
In BGP Version 3, when a subnet is redistributed from an IGP into BGP, only the network route is
injected into the BGP table. By default, this automatic summarization is enabled. To disable automatic
network number summarization, use the following command in router configuration mode:
Configuring BGP Community Filtering
BGP supports transit policies via controlled distribution of routing information. The distribution of
routing information is based on one of the following three values:
•IP address (see the “Configuring BGP Route Filtering by Neighbor” section earlier in this chapter).
•The value of the autonomous system path attribute (see the “Configuring BGP Path Filtering by
Neighbor” section earlier in this chapter).
•The value of the communities attribute (as described in this section).
The communities attribute is a way to group destinations into communities and apply routing decisions
based on the communities. This method simplifies the configuration of a BGP speaker that controls
distribution of routing information.
A community is a group of destinations that share some common attribute. Each destination can belong
to multiple communities. Autonomous system administrators can define to which communities a
destination belongs. By default, all destinations belong to the general Internet community. The
community is carried as the communities attribute.
Command Purpose
Router(config-router)# aggregate-address address
mask
Creates an aggregate entry in the BGP routing table.
Router(config-router)# aggregate-address address
mask as-set
Generates autonomous system set path information.
Router(config-router)# aggregate-address
address-mask summary-only
Advertises summary addresses only.
Router(config-router)# aggregate-address address
mask suppress-map map-name
Suppresses selected, more specific routes.
Router(config-router)# aggregate-address address
mask advertise-map map-name
Generates an aggregate based on conditions specified by the
route map.
Router(config-router)# aggregate-address address
mask attribute-map map-name
Generates an aggregate with attributes specified in the route
map.
Command Purpose
Router(config-router)# no auto-summary Disables automatic network summarization.