Dell S4820T Configuration Manual page 228

For inbound and outbound updates the order of preference is:
• prefix lists (using the neighbor distribute-list command)
• AS-PATH ACLs (using the neighbor filter-list command)
• route maps (using the neighbor route-map command)
Prior to filtering BGP routes, create the prefix list, AS-PATH ACL, or route map.
For configuration information about prefix lists, AS-PATH ACLs, and route maps, refer to
Lists (ACLs).
NOTE: When you configure a new set of BGP policies, to ensure the changes are made, always
reset the neighbor or peer group by using the clear ip bgp command in EXEC Privilege mode.
To filter routes using prefix lists, use the following commands.
1. Create a prefix list and assign it a name.
CONFIGURATION mode
ip prefix-list prefix-name
2. Create multiple prefix list filters with a deny or permit action.
CONFIG-PREFIX LIST mode
seq sequence-number {deny | permit} {any | ip-prefix [ge | le] }
• ge: minimum prefix length to be matched.
• le: maximum prefix length to me matched.
For information about configuring prefix lists, refer to
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 configured prefix list.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | peer-group-name} distribute-list prefix-list-name {in
| out}
Configure the following parameters:
• ip-address or peer-group-name: enter the neighbor's IP address or the peer group's name.
• prefix-list-name: enter the name of a configured prefix list.
• in: apply the prefix list to inbound routes.
• out: apply the prefix list to outbound routes.
As a reminder, the following are rules concerning prefix lists:
228
Access Control Lists (ACLs).
Border Gateway Protocol IPv4 (BGPv4)
Access Control