layer-four traceroute

 lft sends various TCP SYN and FIN probes (differing from Van Jacobson's
 UDP-based method) utilizing the IP protocol "time to live" field and
 attempts to elicit an ICMP TIME_EXCEEDED response from each gateway along
 the path to some host.
 lft also listens for various TCP and ICMP messages along the way to assist
 network managers in ascertaining per-protocol heuristic routing information
 and can optionally retrieve various information about the networks it
 traverses.