Cisco Systems 78-11741-02 manual Configuring BGP Peer Groups, Creating the Peer Group, IPC-320

Configuring BGP

Configuring Advanced BGP Features

To disable client-to-client route reflection, use the no bgp client-to-client reflection command in router configuration mode:

Command	Purpose
Router(config-router)# no bgp client-to-client	Disables client-to-client route reflection.
reflection

As the iBGP learned routes are reflected, routing information may loop. The route reflector model has the following mechanisms to avoid routing loops:

•Originator ID is an optional, nontransitive BGP attribute. It is a 4-byte attributed created by a route reflector. The attribute carries the router ID of the originator of the route in the local autonomous system. Therefore, if a misconfiguration causes routing information to come back to the originator, the information is ignored.

•Cluster-list is an optional, nontransitive BGP attribute. It is a sequence of cluster IDs that the route has passed. When a route reflector reflects a route from its clients to nonclient peers, and vice versa, it appends the local cluster ID to the cluster-list. If the cluster-list is empty, a new cluster-list is created. Using this attribute, a route reflector can identify if routing information is looped back to the same cluster due to misconfiguration. If the local cluster ID is found in the cluster-list, the advertisement is ignored.

•Use set clauses in outbound route maps to modify attributes, possibly creating routing loops. To avoid this behavior, set clauses of outbound route maps are ignored for routes reflected to iBGP peers.

Configuring BGP Peer Groups

Often, in a BGP speaker, many neighbors are configured with the same update policies (that is, the same outbound route maps, distribute lists, filter lists, update source, and so on). Neighbors with the same update policies can be grouped into peer groups to simplify configuration and, more importantly, to make updating more efficient. When you have many peers, this approach is highly recommended.

The three steps to configure a BGP peer group, described in the following sections, are as follows:

1.Creating the Peer Group

2.Assigning Options to the Peer Group

3.Making Neighbors Members of the Peer Group

You can disable a BGP peer or peer group without removing all the configuration information using the neighbor shutdown router configuration command.

Creating the Peer Group

To create a BGP peer group, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# neighbor peer-group-name	Creates a BGP peer group.
peer-group

Cisco IOS IP Configuration Guide

IPC-320