Stable Policy Routing with Provider Independence

Thousands of competing autonomous systems (ASes) mustcooperate with each other to provide global Internet connectivity.These ASes encode various economic, business,and performance decisions in their routing policies. The currentinterdomain routing system enables ASes to express policyusing rankings that determine how each router in an ASorders the different routes to a destination, and filters thatdetermine which routes are hidden from each neighboringAS. Since the Internet is composed of many independent,competing networks, the interdomain routing system shouldallow providers to set their rankings independently, and tohave no constraints on allowed filters. This paper studiesrouting protocol stability under these constraints. We firstdemonstrate that certain rankings that are commonly usedin practice may not ensure routing stability. We then provethat, with ranking independence and unrestricted filtering,guaranteeing that the routing system will converge to a stablepath assignment essentially requires ASes to rank routesbased on AS-path lengths. Finally, we discuss the implicationsof these results for the future of interdomain routing.