The Ultimate Port Scanning Guide: Part 3 - UDP Port Scans
The relationship between UDP port scanning and ICMP Unlike TCP, UDP is a stateless protocol. It was designed for speed in an era where reliability couldn’t always be guaranteed. Effectively, UDP is mostly designed to be used for applications that care more whether or not a packet is sent than whether or not it is received. This presents a problem. If a host continuously sends UDP datagrams to a system that isn’t even listening, it could saturate a link.