Optimal Algorithms for Computing Policy-Conforming Paths in the Internet

Abstract

Border Gateway Protocol (BGP) is an interdomain routing protocol that allows Autonomous Systems (ASes) to apply local policies for selecting routes and propagating routing information. These routing policies are typically constrained by the contractual commercial agreements between administrative domains. For example, an AS sets its routing policy so that it does not provide transit services between two of its providers. As a result, a route selected for a packet in the Internet may not be the shortest AS path. In this paper, we formulate two common routing policies in the Internet and the problem of computing routing policy conforming paths. We present optimal algorithms for computing the policy-conforming paths in the Internet and show the complexity of these algorithms. Understanding AS paths chosen in the Internet is critical to answer “what if” questions such as which ISPs an AS should peer with next in order to reduce the path length of the AS’ customers to a content provider, or which ISP an AS should select as a provider in order to be “closer” to a popular content provider. Deriving AS paths in the Internet is also important for understanding how the global AS level topology evolution impacts the actual AS paths taken by packets.