3Com Switch 8800 Configuration Guide
Chapter 21 BGP Configuration
21-20
By default, the local preference is 100.
21.2.13 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.
Table 21-33
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
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.
21.2.14 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.
Table 21-34
Compare the MED routing metrics from the peers in different ASs
Operation
Command
Compare the MED routing metrics from the
peers in different ASs
compare-different-as-med
Configure not to compare the MED routing
metrics from the peers in different ASs
undo compare-different-as-med
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.
