Its header identifies source and destination ports and includes length and checksum fields. UDP does not establish a connection before sending, maintain a byte stream, or confirm that a datagram reached its destination.
This minimal service suits applications that can tolerate loss, need timely delivery, or provide their own recovery and congestion behavior. Domain Name System queries, real-time media, service discovery, and newer transports such as QUIC can use UDP, but each application defines what happens when datagrams are lost, duplicated, delayed, or reordered.
Key points
Core behaviorPreserve message boundaries and multiplex application traffic through port numbers without TCP-style connection setup or delivery state.
Application responsibilityAdd retransmission, ordering, duplicate handling, rate adaptation, and congestion control when the application requires them.
Security considerationAuthenticate peers when origin matters, validate message format and size, limit response amplification, and rate-limit exposed services; source addresses can be spoofed, and small requests can otherwise trigger larger replies to a victim.
Important limitationUDP provides neither delivery assurance nor confidentiality, peer authentication, or protection against replay. When used and validated, the UDP checksum detects some accidental corruption but is not a cryptographic integrity check.