Hi ,
Route filtering based on NLRI can be done using the distribute list, the prefix list or route maps. The prefix list is easier to configure and modify compared to the distribute list.
To filter BGP routes using the distribute list, the prefix list or route maps, proceed with these options:
To filter BGP routes using distribute lists, configure a simple or extended Access Control List (ACL) and bind it to a neighbor. This filters the routing updates exchanged with the neighbor. To define an IP ACL, issue the access-list command in global configuration mode. To filter updates exchanged with a neighbor based on this ACL, issue the neighbor distribute-list command in router configuration mode.
To filter BGP routes using prefix lists, configure the prefix lists and bind them to a neighbor. This filters the routing updates exchanged with the neighbor. To configure a prefix list, issue the ip prefix-list command in router configuration mode. To filter updates exchanged with a neighbor based on this prefix list, issue the neighbor prefix-list command in router configuration mode.
To filter BGP routes using route maps, configure an ACL or prefix list, use it in a route map and bind the route map to a neighbor. This filters the routing updates exchanged with the neighbor. To define an IP ACL, issue the access-list command in global configuration mode. To configure a prefix list, issue the ip prefix-list command in global configuration mode. To create a route map, issue the route-map command in global configuration mode and bind the ACL or prefix list by issuing the match ip address command in route map configuration mode. While matching a prefix list, use the prefix-list keyword. To filter updates exchanged with a neighbor based on this route map, issue the neighbor route-map command in router configuration mode.
Check the below links.
http://www.cisco.com/en/US/customer/tech/tk365/technologies_configuration_example09186a008009456d.shtml#defaultroutes
http://www.cisco.com/en/US/customer/tech/tk365/technologies_tech_note09186a00801310cb.shtml
Hope it helps you.
Thanks,
satish
