Reference Guide

Border Gateway Protocol IPv4 (BGPv4) | 213
• If the prefix list contains no filters, all routes are permitted.
• If none of the routes match any of the filters in the prefix list, the route is denied. This action is called
an implicit deny. (If you want to forward all routes that do not match the prefix list criteria, you must
configure a prefix list filter to permit all routes. For example, you could have the following filter as the
last filter in your prefix list
permit 0.0.0.0/0 le 32).
• Once a route matches a filter, the filter’s action is applied. No additional filters are applied to the route.
To view the BGP configuration, use the
show config command in the ROUTER BGP mode. To view a
prefix list configuration, use the
show ip prefix-list detail or show ip prefix-list summary commands in
EXEC Privilege mode.
Use these commands in the following sequence, starting in the CONFIGURATION mode to filter routes
using a route map.
Use the
show config command in CONFIGURATION ROUTER BGP mode to view the BGP
configuration. Use the
show route-map command in EXEC Privilege mode to view a route map
configuration.
Use these commands in the following sequence, beginning in the CONFIGURATION mode to filter routes
based on AS-PATH information.
Step Command Syntax Command Mode Purpose
1 route-map map-name [permit |
deny] [sequence-number]
CONFIGURATION Create a route map and assign it a name.
2
{match | set} CONFIG-ROUTE-MAP Create multiple route map filters with a
match or set action.
Refer to Access Control Lists (ACLs) for
information on configuring route maps.
3
exit
CONFIG-ROUTE-MAP Return to the CONFIGURATION mode.
4
router bgp as-number CONFIGURATION Enter ROUTER BGP mode.
neighbor {ip-address |
peer-group-name} route-map
map-name {in | out}
CONFIG-ROUTER-BGP Filter routes based on the criteria in the
configured route map. Configure the
following parameters:
• ip-address or peer-group-name: enter the
neighbor’s IP address or the peer group’s
name.
• map-name: enter the name of a
configured route map.
• in: apply the route map to inbound
routes.
• out: apply the route map to outbound
routes.
Step Command Syntax Command Mode Purpose
1
ip as-path access-list
as-path-name
CONFIGURATION Create a AS-PATH ACL and assign it a name.