Administrator Guide

● 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).
● After a route matches a filter, the filter’s action is applied. No additional filters are applied to the route.
DellEMC# configure terminal
DellEMC(conf)# ip prefix-list route10
DellEMC(conf)# seq 10 permit 10.10.10.0/24 ge 32
DellEMC(conf)#exit
DellEMC(conf)# router bgp
DellEMC(conf-router_bgp)#neighbor 10.10.10.2 distribute-list route10 out
The commands show the configuration of an IP prefix list named route10, which permits routes to network 10.10.10.0/24. The
neighbor command configures to use IP prefix list route10 to determine, which routes to be distributed to the neighbor
10.10.10.2. So the routes from 10.10.10.1/24 network is distributed to neighbor 10.10.10.2 since the IP prefix list route10
explicitly permits the routes to be distributed to the neighbor.
To view the BGP configuration, use the show config command in 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.
Filtering BGP Routes Using Route Maps
To filter routes using a route map, use these commands.
1. Create a route map and assign it a name.
CONFIGURATION mode
route-map map-name [permit | deny] [sequence-number]
2. Create multiple route map filters with a match or set action.
CONFIG-ROUTE-MAP mode
{match | set}
For information about configuring route maps, see Access Control Lists (ACLs).
3. Return to CONFIGURATION mode.
CONFIG-ROUTE-MAP mode
exit
4. Enter ROUTER BGP mode.
CONFIGURATION mode
router bgp as-number
5. Filter routes based on the criteria in the configured route map.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | ipv6-address | peer-group-name} route-map map-name {in | out}
Configure the following parameters:
● ip-address or ipv6-address or peer-group-name: enter the neighbor’s IPv4 or IPv6 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.
DellEMC# configure terminal
DellEMC(conf)# route-map route1 permit
DellEMC(conf-route-map)# set as-path prepend 400
DellEMC(conf-route-map)#exit
DellEMC(conf)# router bgp 400
DellEMC(conf-router_bgp)# neighbor 10.10.10.1 route-map route1 out
DellEMC(conf-router_bgp)#
In the above example, a route-map named route1 is created with a permit clause. Within the route-map, a set clause is
configured to prepend an AS is configured. This configuration adds the configured AS number to the AS-Path for each route.
The configured route-map is applied to the outbound routes of the neighbor 10.10.10.1.
Border Gateway Protocol (BGP)
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