NC Scan

TCP CONNECT Scan

Try's to complete the 3 way handshake. If complete the port is listed as Open. #nc -nvv -w 1 -z 10.0.0.19 3388-3390

UDP Scan

Send a UDP packet and if the port is closed we get back a ICMP packet. If no ICMP packet comes back then we assume the port is open or a FW/Win10 box is filtering the ICMP packet #nc -unvv -w 1 -z <ip> <port-range>

There are many more things you can do with NC but Nmap will almost always be the easer/better option for external scans.