What is an ICMP port used for?

The Internet Control Message Protocol, or IMCP, handles errors and exchanges control messages. The term "port" is used in combination with ICMP when it refers to a "destination unreachable" error, which indicates that a frame was discarded because it was not able to reach its destination.

The ICMP port error is typically the result of a router in the communications path discarding a frame, but it is also sometimes caused by the destination computer lacking sufficient resources to handle the frame at that time. ICMP is commonly used by network devices, such as routers, to send error messages to designate that a host or a router could not be reached.