Cisco Systems 78-11741-02 manual Disabling Next Hop Processing Using a Specific Address, IPC-309

Configuring BGP

Configuring Basic BGP Features

Disabling Next Hop Processing Using a Specific Address

To disable next hop processing and provide a specific address to be used instead of the next hop address, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# neighbor {ip-address	Disables next hop processing on BGP updates to a neighbor.
peer-group-name}next-hop-self

Configuring this command causes the current router to advertise its peering address as the next hop for the specified neighbor. Therefore, other BGP neighbors will forward to it packets for that address. This configuration is useful in a nonmeshed environment because you know that a path exists from the present router to that address. In a fully meshed environment, this configuration is not useful because it will result in unnecessary extra hops and because there might be a direct access through the fully meshed cloud with fewer hops.

Disabling Next Hop Processing Using a Route Map

To override the inbound next hop setting for BGP routes and specify that the next hop of the matching routes is to be the IP address of the remote peer, or to set the peering address of the local router to be the next hop of the matching routes, use the neighbor next-hop-selfrouter configuration command.

To configure the neighbor peering address to be used for the next hop address, use the following command in route map configuration mode:

Command	Purpose
Router(config-route-map)# set ip next-hopip-address	In an inbound route map of a BGP peer, sets the next hop of
[...ip-address][peer-address]	the matching routes to be the neighbor peering address,
	overriding any third-party next hops and allowing the same
	route map to be applied to multiple BGP peers to override
	third-party next hops.
	With an outbound route map of a BGP peer, sets the next hop
	of the received address to the peering address of the local
	router, disabling the next hop calculation.
	The next hop must be an adjacent router.

Configuring BGP Next Hop Propagation

The BGP Next Hop Propagation feature provides additional flexibility when designing and migrating networks. The BGP Next Hop Propagation feature allows a route reflector to modify the next hop attribute for a reflected route and allows BGP to send an update to an eBGP multihop peer with the next hop attribute unchanged.

Caution Incorrectly setting BGP attributes for a route reflector can cause inconsistent routing, routing loops, or a loss of connectivity. Setting BGP attributes for a route reflector should be attempted only by an experienced network operator.

Cisco IOS IP Configuration Guide

IPC-309