Layer four traceroute

Layer Four Traceroute (LFT) is a fast traceroute engine, that also implements numerous other features including AS number lookups through several reliable sources, loose source routing, netblock name lookups, etc. and goes through many configurations of packet-filter based firewalls. LFT sends various TCP SYN and FIN probes (differing from Van Jacobson's UDP-based method) or UDP probes 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, UDP, 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.

Origins

The lft command first appeared in 1998 as 'fft'. Renamed as a result of confusion with fast fourier transforms, lft stands for 'layer four traceroute.' Results are often referred to as a 'layer four trace.'

External links

* [http://pwhois.org/lft/index.who Layer Four Traceroute Project]
* [http://www.pathanalyzer.com/ Path Analyzer Pro] Graphical version of Layer Four Traceroute based on LFT library which includes geolocation and other advanced features