Stable Path(s) Assignment for Inter-domain Routing

The Border Gateway Protocol (BGP) is the inter-domain routing protocol in the Internet that allows each autonomous system (AS) to select routes to the destinations based on locally determined policies. It has been shown that the policy autonomy exercised by ASes may result in persistent oscillations in BGP. Current solutions either rely on globally consistent policy assignments (which are hard to achieve in a distributed fashion), or require significant deviations from locally assigned policies (which reduce flexibility). In this paper, we take a different approach. Namely, we propose multipath routing to resolve the conflict with policy autonomy and system stability. We design an algorithm STABLE PATH(S) ASSIGNMENT (SPA), that provably detects persistent oscillations and eliminates these oscillations by assigning multiple paths to some ASes in the network. We design a distributed protocol for SPA and present tight bounds on the number of paths assigned by the algorithm to the ASes. Using simulations on the AS graph, we show that SPA assigns at most two paths to any AS in the network (in 99.9% of the instances), while assigning a single path in absence of persistent oscillations. Our evaluation results suggest that SPA can effectively detect networks that have a stable state but can potentially face persistent oscillations, and assigns a single path to the ASes in such networks.