# What is User Datagram Protocol (UDP)?

> User Datagram Protocol (UDP) is a transport protocol that carries independent messages, called datagrams, between application endpoints over Internet Protocol networks.

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## Content

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 behavior:** Preserve message boundaries and multiplex application traffic through port numbers without TCP-style connection setup or delivery state.
- **Application responsibility:** Add retransmission, ordering, duplicate handling, rate adaptation, and congestion control when the application requires them.
- **Security consideration:** Authenticate 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 limitation:** UDP 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.

### Related terms

[TCP/IP protocol suite](<https://yellowcube.eu/glossary/tcp-ip-protocol-suite/>) · [Domain Name System (DNS)](<https://yellowcube.eu/glossary/domain-name-system/>) · [Internet Control Message Protocol (ICMP)](<https://yellowcube.eu/glossary/internet-control-message-protocol/>) · [Packet loss](<https://yellowcube.eu/glossary/packet-loss/>) · [Network traffic](<https://yellowcube.eu/glossary/network-traffic/>)

### Sources

[RFC 768: User Datagram Protocol](https://www.rfc-editor.org/info/rfc768) · [RFC 8085: UDP Usage Guidelines](https://www.rfc-editor.org/info/rfc8085) · [RFC 9868: Transport Options for UDP](https://www.rfc-editor.org/info/rfc9868/)

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