9.2 Route Filtering and Manipulation Process (Policies)
9.2.9 Configuration example: peer groups
The network shown in the figure demonstrates the use of BGP peer groups. RTC has internal peering sessions with RTD, RTE, and RTH and has similar policies towards each. Instead of formulating and applying similar policies for each neighbor individually, RTC could define a peer group that contains the policies, and then places its internal neighbors in the peer group.

Note: Click on topology to view command outputs.

The configuration defines a peer group called INTERNALMAP that contains the following policies:

  • A route map named INTERNAL
  • A filter list for outgoing updates (filter list 1)
  • A filter list for incoming updates (filter list 2)

The configuration applies the peer group to all internal neighbors -- RTD, RTE, and RTH. While members of a peer group inherit all the configuration options of the peer group, they can also be configured to override configuration options. That is, peer group members can be configured to override policies inherited from the peer group. The configuration of RTC, for example, also defines a filter-list 3 for incoming updates from the neighbor at IP address 172.16.12.1 (RTH). Filter-list 3 will override any incoming policies set by the peer group INTERNALMAP for neighbor RTH. The commands configure a BGP peer group named EXTERNALMAP on RTC and apply it to the exterior neighbors in AS3 and AS2:

In this configuration, the neighbor remote-as router configuration commands are placed outside the neighbor peer-group router configuration commands because different external ASs have to be defined. Also note that this configuration defines filter-list 3, which can be used to override configuration options for incoming updates from the neighbor at IP address 172.16.20.3 (RTF).
Lab Activity
  In this lab, you will learn how to configure a peer group to assign policies to a group of BGP neighbors that share the same update policies.