P0f v2 is a versatile passive OS fingerprinting tool. P0f can identify the operating system on:

   - machines that connect to your box (SYN mode),
   - machines you connect to (SYN+ACK mode),
   - machine you cannot connect to (RST+ mode),
   - machines whose communications you can observe.

P0f can also do many other tricks, and can detect or measure the following:

   - firewall presence, NAT use (useful for policy enforcement),
   - existence of a load balancer setup,
   - the distance to the remote system and its uptime,
   - other guy's network hookup (DSL, OC3, avian carriers) and his ISP.

All this even when the device in question is behind an overzealous packet firewall, when our favourite" target="_blank">http://www.nmap.org/">favourite active scanner can't do much. P0f does not generate ANY additional network traffic, direct or indirect. No name lookups, no mysterious probes, no ARIN queries, nothing. How? It's simple: magic. Find out more here.