Thanks Sundar.

Let me clarify my question a bit further. Let's say Router_A in AS_100 advertises to Router_X in AS_200 that the MED for its AS is 10. Further, let's say that Router_B from AS_100 advertises to Router_Y in AS_200. However, it says that its MED is 5. My question is do Router_A and Router_B (which are both from AS_100) advertise to each other what MED they are going to use to advertise to AS_200?

Futher, how do they calculate the MED? Or is it something that the admin configures on Router_A and Router_B in order to influence which router will be used by AS_200 to ingress into AS_100?

You would normally set the MED using a outbound route-map to the router in the neighboring AS. Router A and B each send their MED separately. Routers in AS 200 select the best MED (i.e. the best exit point towards AS100).

The other way to set the MED is to automatically convert the IGP metric into a MED that will be advertised to the neighboring AS.

Hope this helps,

Paras,

As hritter pointed out MED is set using a outbound route-map on the router in the neighboring AS. In your case, both routerA & routerB would be sending the prefix with their own configured metric(s) to AS200. The routers in AS200 would choose the path with the lower metric to get to AS100 if the path selection gets to the MED level.

Here's a nice little example that should you a basic idea of how MED works.

http://cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094934.shtml

HTH

Sundar