# Watch on the eth0 interface
root# p0f -i eth0 -v

p0f: passive os fingerprinting utility, version 1.8.2
(C) Michal Zalewski <lcamtuf@gis.net>, William Stearns wstearns@pobox.com
p0f: file: '/etc/p0f.fp', 150 fprints, iface: 'eth0', rule: 'all'.

172.16.217.179 [1 hops]: Linux 2.2.9 - 2.2.18
  + 172.16.217.179:1631 -> 192.168.164.74:22
192.168.164.74 [14 hops]: SunOS 5.8
  + 192.168.164.74:60786 -> 172.16.18.82:80
169.207.233.226 [18 hops]: Linux 2.4.2 - 2.4.14 (1)
  + 169.207.233.226:33328 -> 216.162.217.179:23
172.16.217.179 [1 hops]: Linux 2.2.9 - 2.2.18
  + 172.16.217.179:1633 -> 10.20.196.98:
10.20.196.98: UNKNOWN [5840:56:1460:1:162:1:1:60].
  + 10.20.196.98:2118 -> 172.16.217.179:25
10.20.196.98 [9 hops]: Linux 2.4.2 - 2.4.14 (1)
  + 10.20.196.98:2119 -> 172.16.217.179:110