US Patent 7697439 Method of determining transit costs across autonomous systems

A method for determining a cumulative network layer reachability cost of traversing one or more autonomous network routing systems comprises receiving first network route information from an originating customer edge router, wherein the first network route information identifies a route in a customer network; determining a transit cost from the provider edge router to an endpoint associated with the originating customer edge router based upon a metric value received in a cost community attribute; repeating the determining step for each of one or more autonomous systems that lie in a path from the originating customer edge router to a destination customer edge router, to result in determining an accumulated transit costs across one or more autonomous systems; and determining, based at least in part upon the accumulated transit cost, a best path from the provider edge router to the endpoint associated with the originating customer edge router.