Controlling traffic coming back into your network is more difficult. 
With geographically diverse networks, where one ISP connection is a 
lot closer to one part of the network than another, you may want to 
use the MED (multiexit discriminator) attribute, which specifies the 
path external traffic should use when destined for one of your 
internal networks. Although the MED attribute is a fairly simple way 
to control incoming traffic, it will work only if both Internet 
connections go to the same ISP because it won't be propagated outside 
that ISP's AS. Prepending is another way to control incoming traffic.



