As the Internet grows and routing complexity increases, network-level instabilities are becoming more and more common. End-to-end communications are especially susceptible to service disruptions, while diagnosing and mitigating these disruptions are extremely challenging. In this dissertation, we design and build systems for diagnosing routing anomalies and improving robustness of end-to-end communications. The rst piece of this work describes PlanetSeer, a novel distributed system for diagnosing routing anomalies. PlanetSeer passively monitors traf c in wide-area services, such as Content Distribution Networks (CDNs) or Peer-to-Peer (P2P) systems, to detect anomalous behavior. It then coordinates active probes from multiple vantage points to con rm the anomaly, characterize it, and determine its scope. There are.
