The User Datagram Protocol (UDP), part of the TCP/IP suite, provides a simple datagram-based process-to-process communication mechanism. UDP extends the message address to include a port address in addition to the host Internet address. The port address identifies one of several distinct destinations within a single host. Thus UDP accepts messages addressed to a particular port on a particular host, and tries to deliver them, using IP to transport the messages between the hosts. Like IP, UDP makes no guarantees that messages are delivered correctly or even delivered at all.

However, it is this relatively low-overhead process-to-process delivery mechanism that makes UDP so useful to many other protocols and utilities, such as BOOTP, DHCP, DNS, RIP, SNMP, and NFS.