Filtering BGP Routes Using AS-PATH InformationTo filter routes based on AS-PATH information, use these commands.1. Create a AS-PATH ACL and assign it a name.CONFIGURATION modeip as-path access-list as-path-name2. Create a AS-PATH ACL filter with a deny or permit action.AS-PATH ACL mode{deny | permit} as-regular-expression3. Return to CONFIGURATION mode.AS-PATH ACLexit4. Enter ROUTER BGP mode.CONFIGURATION moderouter bgp as-number5. Filter routes based on the criteria in the configured route map.CONFIG-ROUTER-BGP modeneighbor {ip-address | peer-group-name} filter-list as-path-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.• as-path-name: enter the name of a configured AS-PATH ACL.• in: apply the AS-PATH ACL map to inbound routes.• out: apply the AS-PATH ACL to outbound routes.To view which commands are configured, use the show config command in CONFIGURATION ROUTER BGP mode and theshow ip as-path-access-list command in EXEC Privilege mode.To forward all routes not meeting the AS-PATH ACL criteria, include the permit .* filter in your AS-PATH ACL.Configuring BGP Route ReflectorsBGP route reflectors are intended for ASs with a large mesh; they reduce the amount of BGP control traffic.NOTE: Dell Networking recommendsnot using multipath and add path simultaneously in a route reflector.With route reflection configured properly, IBGP routers are not fully meshed within a cluster but all receive routing information.Configure clusters of routers where one router is a concentration router and the others are clients who receive their updates fromthe concentration router.To configure a route reflector, use the following commands.• Assign an ID to a router reflector cluster.CONFIG-ROUTER-BGP modebgp cluster-id cluster-idYou can have multiple clusters in an AS.• Configure the local router as a route reflector and the neighbor or peer group identified is the route reflector client.Border Gateway Protocol IPv4 (BGPv4) 209
