Enterasys Networks Security Router X-PeditionTM - Manual (Page 153)

Overview
XSR User’s Guide 6-5
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-self command 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-hop command or the
neighbor next-hop-self command 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 6-26 for a configuration example.