Xprobe2 allows you to determine what operating system is running on a remote host. It sends several packets to a host and analyses the returned answers.

Xprobe2's functionality is comparable to the OS fingerprinting feature in nmap (written by a different Fyodor): - Outputs its level of confidence about the OS on the remote host. - Remains usable even if intermediate systems (routers, firewalls) make slight modifications to the packets. - Can list the type of intermediate device (e.g. "Linux IP masquerading"). - Modular architecture allows new fingerprinting tests and new OS signatures to be added.