3Com 8807 Configuration Manual page 377

Configuring MED for AS
Comparing the MED
Routing Metrics from
the Peers in Different
ASs
Table 379 Configure the local preference
Operation
Configure the local preference
Restore the default local preference
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.
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.
Table 380 Configure an MED metric for the system
Operation
Configure an MED metric for the system
Restore the default MED metric of the system undo default med
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.
It is used to select the best route. The route with smaller MED value will be
selected.
Perform the following configuration in BGP view.
Table 381 Compare the MED routing metrics from the peers in different ASs
Operation
Compare the MED routing metrics from peers in
different ASs
Disable comparison of the MED routing metrics from
peers in different ASs
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.
Configuring BGP
Command
default local-preference value
undo default local-preference
Command
default med med-value
Command
compare-different-as-med
undo compare-different-as-med
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