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.

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