A Distributed Method for Dynamic Resolution of BGP Oscillations

Autonomous Systems (AS) in the Internet use dif-ferent protocols for internal and external routing. BGP is the only external protocol. It allows ASes to define their own routing policy independently. Many papers cited in reference deal with a divergence behavior due to this flexibility. In fact, when routing policies are not conflicting, BGP is self-stabilising, which means that whatever the network configuration, BGP converges to a stable solution. Unfortunately, as experienced on the Internet, AS routing policies may be uncoherent, thus generating oscillations. In this paper we propose a dis-tributed dynamic method for detecting and solving os-cillations of BGP. It respects private policy choices and requires only a few low level constraints in order to con-verge to a stable solution. Essentially, a router has to maintain only local path stateful information to detect instabilities. In this case, it generates and launches a token linked to a route. Each router makes the decision to forward or not the token according to local data and local policy. If the originating router receives back the token, then it marks the route as barred. Nevertheless, routes may furtherly be unmarked. Finally, we express and define what coherence be-tween routing policies means. 1