LFT, short for Layer Four Traceroute, is a ‘traceroute’ application that works much faster than traditional Linux (traceroute) and Windows (tracert) options and can bypass restrictive packet-filters (firewalls). More importantly, LFT implements numerous other features including AS number lookups, loose source routing and netblock name lookups.
What makes LFT unique? LFT is the all-in-one traceroute tool because it can launch a variety of different probes using ICMP, UDP, and TCP protocols, or the RFC1393 trace method. For example, rather than only launching UDP probes in an attempt to elicit ICMP “TTL exceeded” from hosts in the path, LFT can send TCP SYN or FIN probes to target arbitrary services. Then, LFT listens for “TTL exceeded” messages, TCP RST (reset), and various other interesting heuristics from firewalls or other gateways in the path. LFT also distinguishes between TCP-based protocols (source and destination), which make its statistics slightly more realistic, and gives a savvy user the ability to trace protocol routes, not just layer-3 (IP) hops. With LFT’s verbose output, much can be discovered about a target network.
Here’s example output from LFT:
[[email protected] src]# lft -e -A -N -s 2222 -d 80 -m 2 -M 2 -a 5 -c 20 -t 800 -H 30 www.google.com
TTL LFT trace to hkg01s01-in-f103.1e100.net (126.96.36.199):80/tcp
1 [2XXX] [MY-AS] core-rtr1.myserver.net (188.8.131.52) 0.7/0.8ms
2  [csloxinfo-th] wan-mywan.net (184.108.40.206) 13.0/13.1ms
3  [csloxinfo-th] ge-1-1-CT45.csloxinfo.net (220.127.116.11) 13.4/13.4ms Continue reading "Layer Four Traceroute (LFT) and WhoB"