Improving internet-wide routing protocols convergence with MRPC timers

Abstract

The behavior of routing protocols during convergence is critical as it impacts end-to-end performance. Network convergence is particularly important in BGP, the current interdomain routing protocol. In order to decrease the amount of exchanged routing messages and transient routes, BGP routers rely on MRAI timers and route flap damping. These timers are intended to limit the exchange of transient routing messages. In practice, these timers have been shown to be partly ineffective at improving convergence, making it even slower in some situations.In this paper, we propose to add a timer mechanism to routing protocols, that enforces an ordering of the routing messages such that path exploration is drastically reduced while controlling convergence time. Our approach is based on known results in generalized path algorithms and endomorphism semi-rings. Our timers, called MRPC (metrics and routing policies compliant), are set independently by each router and depend only on the metrics of the routes received by the router as well as the routing policies of the router. No sharing of information about routing policies between neighboring ASs is required by our solution. Similarly to the case of routing policies that may lead to BGP convergence problems, arbitrary routing policies can also make it impossible to enforce an ordering of the messages that will prevent path exploration to occur. We explain under which conditions path exploration can be avoided with our timers, and provide simulations to understand how they compare to MRAI.