Reference Guide

212 | Border Gateway Protocol IPv4 (BGPv4)
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For inbound and outbound updates the order of preference is:
• prefix lists (using
neighbor distribute-list command)
• AS-PATH ACLs (using
neighbor filter-list command)
• route maps (using
neighbor route-map command)
Prior to filtering BGP routes, you must create the prefix list, AS-PATH ACL, or route map to be used.
Refer to Access Control Lists (ACLs) in the Access Control Lists (ACLs) chapter for configuration
information on prefix lists, AS-PATH ACLs, and route maps.
Use these commands in the following sequence, starting in the CONFIGURATION mode to filter routes
using prefix lists.
As a reminder, below are some rules concerning prefix lists:
Note: With FTOS, you can create inbound and outbound policies. Each of the commands used for
filtering, has in and out parameters that must be applied. In FTOS, the order of preference varies
depending on whether the attributes are applied for inbound updates or outbound updates.
Note: When you configure a new set of BGP policies, always reset the neighbor or peer group by
entering the clear ip bgp command in EXEC Privilege mode.
Step Command Syntax Command Mode Purpose
1 ip prefix-list prefix-name CONFIGURATION Create a prefix list and assign it a name.
2
seq sequence-number {deny |
permit} {any | ip-prefix [ge | le] }
CONFIG-PREFIX
LIST
Create multiple prefix list filters with a deny
or permit action.
ge: Minimum prefix length to be matched
le: maximum prefix length to me matched
Refer to Access Control Lists (ACLs) for
information on configuring prefix lists.
3
exit
CONFIG-PREFIX
LIST
Return to the CONFIGURATION mode.
4
router bgp as-number CONFIGURATION Enter ROUTER BGP mode.
5
neighbor {ip-address |
peer-group-name} distribute-list
prefix-list-name {in | out}
CONFIG-ROUTER-
BGP
Filter routes based on the ccriteria in the
configured prefix list. 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.