Characterization of OSPF Convergence with Correlated Failures

As a popular link state protocol, Open Shortest Path First (OSPF) has been studied for years. A network running OSPF usually takes several tens of seconds to recover from a failure because the protocol timers delay the convergence. In this paper we characterize OSPF convergence behaviors in presence of correlated failures, where the reactive protocol dynamics could be enlarged. Our analysis demonstrates that the interactions between failure detection and routing calculation scheduling could lead to complicated protocol response to correlated failures. We also perform experimental study and the results conform to the analysis. Based on the understanding of OSPF convergence, we present some recommendations for configuring protocol timers in principle.