Touring the internet in a TCP sidecar

An accurate router-level topology of the Internet would benefit many research areas, including network diagnosis, inter-domain traffic engineering, and overlay construction. We present TCP Sidecar and Passenger, two elements of a system for router-level Internet topology discovery. Sidecar transparently injects measurement probes into non-measurement TCP streams, while Passenger combines TTL-limited probes with the often-ignored IP record route option. The combined approach mitigates problems associated with traceroute-based topology discovery, including abuse reports, spurious edge inference from multi-path routing, unresolved IP aliases, long network timeouts, and link discovery behind NATs and firewalls. We believe that we are the first mapping project to measure MPLS use with ICMP extensions and record route behavior when the TTL is not decremented. We are able to discover NATs when monitoring TCP connections that tunnel through them. In this paper, we present preliminary results for TCP Sidecar and Passenger on PlanetLab. Our experiments inject measurement probes into traffic generated both from the CoDeeN Web proxy project and from a custom web crawler to 166,745 web sites.