TIE Breaking: Tunable Interdomain Egress Selection

In a large backbone network, the routers often have multiple egress points they could use to direct traffic toward an external destination. Today's routers select the ldquoclosestrdquo egress point, based on the intradomain routing configuration, in a practice known as early-exit or hot-potato routing. In this paper, we argue that hot-potato routing is restrictive, disruptive, and convoluted and propose an alternative called TIE (Tunable Interdomain Egress selection). TIE is a flexible mechanism that allows routers to select the egress point for each destination prefix based on both the intradomain topology and the goals of the network administrators. In fact, TIE is designed from the start with optimization in mind, to satisfy diverse requirements for traffic engineering and network robustness. We present two example optimization problems that use integer-programming and multicommodity-flow techniques, respectively, to tune the TIE mechanism to satisfy networkwide objectives. Experiments with traffic, topology, and routing data from two backbone networks demonstrate that our solution is both simple (for the routers) and expressive (for the network administrators).