Practical BGP

Communities in Practice—RFC 1998 and Other Routing Policies

You can think of communities as a way to tag a route with almost any policy or other information which might be useful in some way. For instance, communities are used, in various applications, to

• Tag routes coming from customers that you plan to advertise to peers

• Tag backbone routes that you plan to advertise to peers

• Tag peer routes or backbone (more-specific) routes that you don't intend to advertise to peers

• Indicate which routes belong to a particular virtual private network

• Tag routes coming from a given POP (point of presence) or geographic region in a network

• Convey the monetary cost of a link to an outside network.

• Carry the metrics of other protocols transparently through a virtual ...