TCP ping 4evR
while :; nc - z 10.10.10.10 21; sleep 10; done
Another good use – I use nc - z flag for scanning whenever transport is limited somehow and nmap isn’t reliable. I used this on another active box recently.
For scanning via nc I always add -w 1 so I don’t have to wait for longer timeouts and -vn to get results and omit dns resolution, eg. scan for the first 100 ports:
nc - zvn - w 1 22.214.171.124 1-100