Verifying Policy-based Routing at Internet Scale

Routing policy configuration plays a crucial role in determining the path that network traffic takes to reach a destination. Network administrators/operators typically decide the routing policy for their networks/routers independently. The paths/routes resulted from these independently configured routing policies might not necessarily meet the intent of the network administrators/operators. Even the very basic networkwide properties of the routing policies such as reachability between a pair of nodes need to be verified.In this paper, we propose a scheme that characterizes routingpolicy verification problems into a Satisfiability Modulo Theories (SMT) problems. The key idea is to formulate the SMT model in a policy-aware manner so as to reduce/eliminate the mutual dependencies between variables as much as possible. Further, we reduce the size of the generated SMT model through pruning. We implement and evaluate the policy-aware model through an outof-box SMT solver. The experimental results show that the policyaware model can reduce the time it takes to perform verification by as much as 100x even under a modest topology size. It takes only a few minutes to answer a query for a topology containing tens of thousands of nodes.