Command Reference Guide

48 ● default med 3Com Router 5000 Family and Router 6000 Family
Command Reference
default med
Purpose Use the default med command to configure the system MED value.
Use the undo default med command to restore the default MED value.
Syntax default med med-value
undo default med
Parameters med-value
MED value to be specified. Valid values are 0 to
4294967295.
If no value is specified, the default med-value is 0.
Example Routers RTA and RTB belong to AS100, and router RTC belongs to AS200. RTC is the
peer of RTA and RTB. The network between RTA and RTC is X.25 network and the
network between RTB and RTC is Ethernet. So the MED of RTA can be configured as
25 to allow RTC to select the route transmitted by RTB first.
[3Com -bgp] default med 25
View This command can be used in the following views:
■ BGP Unicast view
■ BGP Multicast view
■ VPNv4 view
■ VPN Instance view
Description Multi-exit discriminator (MED) is an external metric for routes. Different from local
preference, MED is exchanged between ASs and will stay in the AS once it enters the
AS. The smaller an MED is, the better a route is. So the route with a lower MED is
preferred. When a router running BGP obtains several routes with identical
destination address and different next-hops from various external peers, it will select
the best route depending on the MED value. In the case that all other conditions are
the same, the system first selects the route with the smaller MED value as the external
route of the autonomous system.