Administrator Guide

Filtering BGP using IP prex lists
An IP prex lists contains a list of networks. When applying an IP prex list to a BGP neighbor, you can able to send or receive the routes
whose destination is in the IP prex list.
Filtering BGP routes based on IP prex lists involves the following steps:
• Create a prex list. The steps 1 to 3 in the following conguration commands shows how to create a prex list.
• Applying the created prex list to a BGP neighbor. The steps 4 and 5 show how the prex list is applied to a neighbor.
To congure an IP prex list, use the following commands.
1 Create a prex list and assign it a name.
CONFIGURATION mode
ip prefix-list prefix-name
2 Create multiple prex list lters with a deny or permit action.
CONFIG-PREFIX LIST mode
seq sequence-number {deny | permit} {any | ip-prefix [ge | le] }
•
ge: minimum prex length to be matched.
• le: maximum prex length to me matched.
For information about conguring prex lists, refer to Access Control Lists (ACLs).
3 Return to CONFIGURATION mode.
CONFIG-PREFIX LIST mode
exit
4 Enter ROUTER BGP mode.
CONFIGURATION mode
router bgp as-number
5 Filter routes based on the criteria in the congured prex list.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | ipv6-address | peer-group-name} distribute-list prefix-list-name {in |
out}
Congure 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.
• prefix-list-name: enter the name of a congured prex list.
• in: apply the prex list to inbound routes.
• out: apply the prex list to outbound routes.
As a reminder, the following are rules concerning prex lists:
• If the prex list contains no lters, all routes are permitted.
• If none of the routes match any of the lters in the prex list, the route is denied. This action is called an implicit deny. (If you want to
forward all routes that do not match the prex list criteria, you must congure a prex list lter to permit all routes. For example, you
could have the following lter as the last lter in your prex list permit 0.0.0.0/0 le 32).
• After a route matches a lter, the lter’s action is applied. No additional lters are applied to the route.
Example of conguring an IP prex list and applying it to a BGP neighbor
DellEMC# configure terminal
DellEMC(conf)# ip prefix-list route10
212
Border Gateway Protocol (BGP)