Reverse traceroute

Traceroute is the most widely used Internet diagnostic tool today. Network operators use it to help identify routing failures, poor performance, and router misconfigurations. Researchers use it to map the Internet, predict performance, geolocate routers, and classify the performance of ISPs. However, traceroute has a fundamental limitation that affects all these applications: it does not provide reverse path information. Although various public traceroute servers across the Internet provide some visibility, no general method exists for determining a reverse path from an arbitrary destination. In this paper, we address this longstanding limitation by building a reverse traceroute system. Our system provides the same information as traceroute, but for the reverse path, and it works in the same case as traceroute, when the user may lack control of the destination. We use a variety of measurement techniques to incrementally piece together the path from the destination back to the source. We deploy our system on PlanetLab and compare reverse traceroute paths with traceroutes issued from the destinations. In the median case our tool finds 87% of the hops seen in a directly measured traceroute along the same path, versus only 38% if one simply assumes the path is symmetric, a common fallback given the lack of available tools. We then illustrate how we can use our reverse traceroute system to study previously unmeasurable aspects of the Internet: we present a case study of how a content provider could use our tool to troubleshoot poor path performance, we uncover more than a thousand peer-to-peer AS links invisible to current topology mapping efforts, and we measure the latency of individual backbone links with average error under a millisecond.