Internet Routing and Non-monotonic Reasoning

Abstract

Internet routing is the process of selecting paths across the Internet to connect the communicating hosts, it is unique in that path selection is jointly determined by a network of independently operated networks, known as domains or Autonomous Systems (ASes), that interconnect to form the Internet. In fact, the present routing infrastructure takes such an extreme position that it favors local autonomy—an AS can use arbitrary path preference to override the default shortest path policy, at the expense of potential global oscillation—a collection of AS preferences (policies) can fail to converge on a stable path, a path that is also the most preferred possible for every AS along the path. In this paper, we examine the route oscillation problem with non-monotonic reasoning. We observe that, in the absence of any AS specific policies, Internet routing degenerates into the monotonic computation of shortest path—a preferred (shorter) (super)path always extends another preferred (sub)path; But fully autonomous AS policies are non-monotonic—a path favored by one AS can be an extension of a less preferred path of a neighbor, to which an “upgrade” to a better path can cause this AS to downgrade to a less preferred path previously discarded. Based on this insight, we present an Answer Set Programming (ASP) formulation that allows for automatic oscillation detection. Our evaluation using the clingo ASP solver is promising: on realistic Internet topology and representative policies, clingo can detect anomalies within 35 s.