BGP Peer Group Example Edge Router at a Peering Point

AS 745

Edge router at a peering point

AS 745

Edge router at a peering point

Remove a peer group parameter for a single neighbor

AS 123

Remove a peer group parameter for a single neighbor router bgp 123

neighbor Peering peer-group neighbor Peering filter-list 10 in neighbor Peering route-map PeerMap out neighbor Peering maximum-prefix 50 neighbor Peering remove-private-AS

neighbor 1,2,3.4 remote-as 745 neighbor 1.2.3.4 peer-group Peering neighbor 2.3.4.5 remote-as 837 neighbor 2.3.4.5 peer-group Peering w no neighbor 2.3.4.5 maximum-prefix 50 no neighbor 2.3.4.5 filter-list 10 in

© 2004 Cisco Systems, li

In this example, the router in AS 123 is being configured with a peer group named "Peering." This peer group is used for all peer providers because they share an almost identical routing policy. The peer group is first created as a template, which is configured with an incoming AS-path filter-list (list 10) and an outgoing route-map named "PeerMap." The maximum number of received prefixes is also set in the peer group to 50. The peer group has also been configured to remove private AS numbers (AS numbers in the range 64512 to 65535 inclusive) from all AS paths before the routes are sent to the peer AS.

The neighbors in AS 745 and in AS 837 are then assigned to the peer group, meaning that the router in AS 123 will attempt to open BGP sessions with those routers. If the BGP sessions are successfully established, filter-list 10 and the route-map PeerMap, as configured in the peer group, will be applied to incoming and outgoing routes from both neighbors, respectively.

As defined in the router configuration, filter-list 10 filters out any incoming routes from peer group members unless otherwise specified. However, in the case of the neighbor in AS 837, the individual configuration of no filter-list 10 will override the peer group configuration, and thus, the filter-list will not be used for this neighbor. The limitation on the number of received routes from AS 837 is also removed from the neighbor in AS 837.

The peer group is a very powerful tool when you are dealing with a large number of neighbors with almost identical configurations. However, if any of the customers that are assigned to the peer group require routing information that is different from other members of the peer group, then that neighbor must be removed from the peer group and configured individually.

Copyright © 2004, Cisco Systems, Inc. Optimizing BGP Scalability 7-51

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