Maintaining Safety in Interdomain Routing with Hierarchical Path-Categories

Abstract

The stable-paths problem is an abstraction of the basic functionality of the Internet’s BGP routing protocol. It has received considerable attention due to instabilities observed in BGP. In this abstraction, each node informs its neighboring nodes of its current path to the destination node. From the paths received from its neighbors, each node chooses the best path according to some local routing policy. However, since routing policies are chosen locally, conflicts may occur between nodes, resulting in unstable behavior. Deciding if a set of routing policies is stable is NP-hard. Thus, current solutions involve restricting routing policies to avoid instabilities, while maintaining enough flexibility for the routing policies to be useful. Recently, path-categories have been introduced. E.g., a simple system consists of a category of regular paths, and a category of backup paths. By combining path-categories into a total order (regular paths have higher priority than backup paths), it has been shown that the resulting system is stable if each category by itself is stable. In this paper, we relax the total-order of categories into a partial-order, and thus provide greater flexibility of routing choices at each node. We extend the definition of the stable-paths problem to allow such flexibility, and show that if each category is stable in itself, then the whole system is stable. In addition, we show an upper bound on the convergence time of the whole system provided each category in itself has a bounded convergence time.