Correctness of Routing Vector Protocols as a Property of Network Cycles

Most analyses of routing vector protocols, such as the Border Gateway Protocol (BGP), are conducted in the context of a single destination in a given network. In that context, for arbitrary routing policies, it is computationally intractable to determine whether or not a routing vector protocol behaves correctly. In this paper, we consider the common scenario where routing policies are specified independently of the destination. In this scenario, we demonstrate that the correctness of a routing vector protocol for all destinations in a given network equates to a property of routing policies around its cycles, designated strict absorbency, similarly to the way that the correctness of a distance vector protocol equates to cycles of positive length. A number of pragmatic conclusions can be derived from this theoretical result. For example, we show that all next-hop routing policies, which are popular in inter-domain routing and in the interconnection of routing instances, cannot fully exploit the physical redundancy of a network. As another example, we show how sibling autonomous systems of the Internet can share all routes between them without introducing oscillations into BGP.