Cisco Systems 78-11741-02 manual Configuring the BGP Version, Configuring the MED Metric, IPC-310

Configuring BGP

Configuring Basic BGP Features

The configuration of this feature in conjunction with the iBGP Multipath Load Sharing feature allows you to use an outbound route map to include BGP route reflectors in the forwarding path.

The BGP Next Hop Propagation feature allows you to perform the following tasks:

•Bring the route reflector into the forwarding path, which can be used with the iBGP Multipath Load Sharing feature to configure load balancing.

•Configure interprovider Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs) by not modifying the next hop attribute when advertising routes to an eBGP peer.

•Turn off the next hop calculation for an eBGP peer. This feature is useful for configuring the end-to-end connection of a label-switched path.

To configure an eBGP multihop peer to propagate the next hop unchanged, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# neighbor ip-address	Configures the router to send BGP updates to BGP peers
next-hop-unchanged	without modifying the next hop attribute.
	Caution This command should be configured only on
		route-reflector clients and not on a route reflector.

Configuring the BGP Version

By default, BGP sessions begin using BGP Version 4 and negotiating downward to earlier versions if necessary. To prevent negotiation and force the BGP version used to communicate with a neighbor, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# neighbor {ip-address	Specifies the BGP version to use when communicating with
peer-group-name}version number	a neighbor.

Configuring the MED Metric

BGP uses the MED metric as a hint to external neighbors about preferred paths. (The name of this metric for BGP Versions 2 and 3 is INTER_AS_METRIC.) To set the MED of the redistributed routes, Use the following command in router configuration mode. All the routes without a MED will also be set to this value.

Command	Purpose
Router(config-router)# default-metricnumber	Sets an MED.

Alternatively, you can set the MED using the route-maprouter configuration command. See the “BGP Route Map Examples” section at the end of this chapter for examples of using BGP route maps.

Cisco IOS IP Configuration Guide

IPC-310