Reference Guide

Border Gateway Protocol IPv4 (BGPv4) | 225
Filter BGP routes
Filtering routes allows you to implement BGP policies. You can use either IP prefix lists, route maps,
AS-PATH ACLs or IP Community lists (via a route map) to control which routes are accepted and
advertised by the BGP neighbor or peer group. Prefix lists filter routes based on route and prefix length,
while AS-Path ACLs filter routes based on the Autonomous System number. Route maps can filter and set
conditions, change attributes, and assign update policies.
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 IP 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.
Note: Dell Networking OS supports up to 255 characters in a set community statement inside a
route map.
Note: With Dell Networking OS, you can create inbound and outbound policies. Each of the
commands used for filtering, has in and out parameters that must be applied. In Dell Networking
OS, 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.