Layer Four Traceroute (LFT) and WhoB

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:

[root@server src]# lft -e -A -N -s 2222 -d 80 -m 2 -M 2 -a 5 -c 20 -t 800 -H 30
Tracing ............*****.........................T
TTL LFT trace to (
1 [2XXX] [MY-AS] ( 0.7/0.8ms
2 [4750] [csloxinfo-th] ( 13.0/13.1ms
3 [4750] [csloxinfo-th] ( 13.4/13.4ms Continue reading "Layer Four Traceroute (LFT) and WhoB"

MTR – The Network Diagnostic Swiss Army Knief

MTR, a Linux shell command, combines the functionality of the ‘traceroute’ and ‘ping’ programs in a single network diagnostic tool.

When MTR starts, it investigates the network connection between the host MTR runs on and HOSTNAME (e.g., by sending packets with purposly low TTLs. It continues to send packets with low TTL’s, noting the response time of the transit routers. This allows MTR to print the response percentage and response times of the internet route to the remote host. A sudden increase in packetloss or response time is often an indication of a problematic or saturated link.

Compared to mixing and matching ping and traceroute commands, MTR is a true network diagnostic swiss army knief. For those bound to Windows destkops, Microsofts command link “pathping” is similar to MTR but lacks the real time tracing and statistical data.

MTR Example:

[shell] Continue reading “MTR – The Network Diagnostic Swiss Army Knief”