Streamlining traceroute by estimating path lengths

Abstract

Traditional traceroute determines the path through a network by sending probe packets with progressively increasing TTL/hop count values so that routers that are progressively further from the inquirer send ICMP time exceeded messages and so reveal their identity. This process can be slow (because traceroute must wait for a timeout or response to one probe before sending the next) and inefficient (through repeated probing of routers near the inquirer that lie on the intersection of paths leading to multiple targets). This paper shows how this process can be streamlined by the inquirer sending a scout packet to the (reachable) target before sending route tracing probes. The inquirer uses the TTL of the response to this scout packet to estimate the length of the path to the target (with tolerance for path asymmetry), and can then either expedite the route tracing process (by sending probes to each of the estimated number of routers on the path in quick succession) or reduce the number of probes needed (by inverting the direction of traditional traceroute, tracing the path from the target towards the inquirer, and terminating the process when it reaches a router on a known path from the inquirer).