Dell Force10 S4820T S4820T Configuration Guide - Page 227

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. Note: FTOS supports up to 255 characters in a set community statement inside a route map. 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. 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. 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. Use these commands in the following sequence, starting in the CONFIGURATION mode to filter routes using prefix lists. Step Command Syntax 1 ip prefix-list prefix-name 2 seq sequence-number {deny | permit} {any | ip-prefix [ge | le] } 3 exit 4 router bgp as-number Command Mode CONFIGURATION CONFIG-PREFIX LIST CONFIG-PREFIX LIST CONFIGURATION Purpose Create a prefix list and assign it a name. 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. Return to the CONFIGURATION mode. Enter ROUTER BGP mode. Border Gateway Protocol IPv4 (BGPv4) | 227