3Com Switch 8800 Family Configuration Guide

Configuring BGP 377
The local preference is transmitted only when the IBGP peers exchange the update
packets and it will not be transmitted beyond the local AS.
By default, the local preference is 100.
Configuring MED for AS Multi-Exit Discriminators (MED) attribute is the external metric for a route. AS uses
the local preference to select the route to the outside, and uses the MED to
determine the optimum route for entering the AS. When a router running BGP
gets routes with the same destination address but different next hops through
different external peers, it will select the route of the smallest MED as the
optimum route, provided that all the other conditions are the same.
Perform the following configuration in BGP view.
By default, MED metric is 0.
The router configured above only compares the route MED metrics of different
EBGP peers in the same AS. Using the compare-different-as-med command,
you can compare the route MED metrics of the peers in different ASs.
Comparing the MED
Routing Metrics from
the Peers in Different
ASs
It is used to select the best route. The route with smaller MED value will be
selected.
Perform the following configuration in BGP view.
By default, MED comparison is not allowed among the routes from the neighbors
in different ASs.
It is not recommended to use this configuration unless you can make sure that the
ASs adopt the same IGP and routing method.
Tab le 379 Configure the local preference
Operation Command
Configure the local preference default local-preference value
Restore the default local preference undo default local-preference
Tab le 380 Configure an MED metric for the system
Operation Command
Configure an MED metric for the system default med med-value
Restore the default MED metric of the system undo default med
Tab le 381 Compare the MED routing metrics from the peers in different ASs
Operation Command
Compare the MED routing metrics from peers in
different ASs
compare-different-as-med
Disable comparison of the MED routing metrics from
peers in different ASs
undo compare-different-as-med