listen tcp :
netcat -l 1234
listen udp :
netcat -u -l 1234
connect to another server tcp :
netcat 192.168.1.1 1234
connect to another server udp :
netcat -u 192.168.1.1 1234
port scanning :
netcat -z -n -v 198.168.1.1 1-1000 2>&1 | grep succeeded