1. UDP Scan (-sU)

This technique is used to scan the open UDP ports of the target IP/host. Here, UDP scan sends UDP Packets to every ports of the target and waits till it get response. If, it receives error message stating that the ICMP is unreachable, this means that the port is closed. But, if gets any approachable response, then it means the port is open.

Command: nmap -sU <target>