Some time ago I published article about BGP local preference attribute. Today I’d like to show you how to configure BGP MED attribute.
What is it for?
The multi-exit discriminator MED determines an optimal route for incoming traffic of an AS. When a BGP device obtains multiple routes to the same destination but with different next hops from EBGP peers, the BGP device selects the route with the smallest MED value as the optimal route. Simply saying, configuring MED attribute, we would like to show the next hop for traffic coming from EBGP peer. The MED attribute is exchanged only between two neighboring ASs. The AS that receives the MED attribute does not advertise it to any other ASs.
Let’s look at typical scenario for MED attribute configuration: