Enterasys Networks X-PeditionTM manual Next Hop, Local Preference

Overview

BGP considers the ORIGIN attribute in its decision-making process to set a preference ranking among multiple routes. Namely, BGP prefers the path with the lowest origin type, where IGP is lower than EGP, and EGP is lower than INCOMPLETE.

The attribute is configured with the set origin command.

Next Hop

The NEXT_HOP attribute is the next IP address used to reach a destination. Usually, BGP chooses the next hop automatically but in networks where BGP neighbors may not have direct access to all other neighbors on the same subnet, BGP's automatic next hop selection can result in broken routing.

Use the neighbor next-hop-selfcommand to disable automatic next-hop selection. It forces the BGP speaker to report itself as the next hop for an advertised route it advertised to a neighbor. Typically, this command prevents third-party next hops from being used on NBMA media such as Frame Relay.

Next-hop is set on an outbound route map using the set ip next-hopcommand or the neighbor next-hop-selfcommand depending on the granularity required.

Local Preference

The LOCAL_PREF attribute informs other peers within an AS of the originator's degree of preference for a particular route out of an AS (it influences egress traffic). The degree of preference given to a route is compared with that of other routes for the same destination with higher LOCAL_PREF values preferred, as shown in Figure 6-3. LOCAL_PREF is local to the AS, is traded between IBGP peers only; it is not advertised to EBGP peers.

Refer to “BGP Community with Route Maps Examples” on page 6-26for a configuration example.

XSR User’s Guide 6-5