We were trying to change something on WinMX and we got a message, 'You cannot switch to this setting because we did not find a UDP Port.' What is a UDP port?We were trying to change something on WinMX and we got a message, "You cannot switch to this setting because we did not find a UDP port." What is a UDP port?A User Datagram Protocol port is an internetworking software abstraction, not a physical thing like a USB port. In\u00a0 Internetworking with TCP\/IP , Douglas Comer explains, "We will imagine that each machine contains a set of abstract destination points called protocol ports. Each protocol port is identified by a positive integer."\u00a0The TCP\/IP protocol suite uses these imagined destination endpoints to distinguish among multiple destination processes in a single host computer. Think of an office phone number extension. Connection-oriented services such as e-mail use TCP to establish reliable communication streams between hosts while other applications and services might use UDP to transport messages between systems.In either case the Source Port and Destination Port are part of the network addressing used to establish the connection. IP receives datagrams and delivers them to the appropriate processing software based on the connection type and protocol port number. WinMX is just telling you that it is not being allowed to access a particular UDP port number for its connections.