Flowroute: inferring forwarding table updates using passive flow-level measurements

The reconvergence of routing protocols in response to changes in network topology can impact application performance. While improvements in protocol specification and implementation have significantly reduced reconvergence times, increasingly performance-sensitive applications continue to raise the bar for these protocols. As such, monitoring the performance of routing protocols remains a critical activity for network operators. We design tool{}, a tool based on passive data plane measurements that we use in conjunction with control plane monitors for offline debugging and analysis of forwarding table dynamics. We discuss practical constraints that affect tool{}, and show how they can be addressed in real deployment scenarios. As an application of tool{}, we study forwarding table updates by backbone routers at a tier-1 ISP. We detect interesting behavior such as delayed forwarding table updates and routing loops due to buggy routers -- confirmed by network operators -- that are not detectable using traditional control plane monitors.