type this command in your terminal/console (whatever you call it)

$ hping2 host -p portnumber -S --tcp-timestamp

where host is the ip/hostname of a machine you want to check and portnumber is the open port on remote machine.

oh, you be root in order to use that command.

here's some example how it gonna work, scanning my college wireless gateway uptime.

novatech@bagiro:~$ sudo hping2 10.10.15.250 -p 443 -S --tcp-timestamp

HPING 10.10.15.250 (eth1 10.10.15.250): S set, 40 headers + 0 data bytes

len=56 ip=10.10.15.250 ttl=64 id=1 sport=443 flags=SA seq=0 win=8192 rtt=161.5 ms

  TCP timestamp: tcpts=986124

len=56 ip=10.10.15.250 ttl=64 id=1 sport=443 flags=SA seq=1 win=8192 rtt=196.2 ms

  TCP timestamp: tcpts=986126

  HZ seems hz=2

  System uptime seems: 5 days, 16 hours, 57 minutes, 43 seconds

shit, uptime are 5days ++ but i can only use internet in the morning.

note : i use port 443 since it's the only port opened on the gateway. that's all for today's lesson. see ya

get windows version of hping2 at http://wiki.hping.org/86