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SESK: Stuff Everyone Should Know · sesk.info/tech-udp-best-effort-datagrams

Which protection does UDP itself not guarantee?

UDP does not guarantee delivery or duplicate protection.

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  1. A destination port field
  2. Delivery and duplicate protection ✔
  3. A datagram length field

Why: UDP sends self-contained datagrams with little transport overhead. It does not promise that a datagram arrives or that a repeated datagram is suppressed, so an application must add those behaviors if needed.

Huh, didn't know that: UDP preserves message boundaries, unlike TCP's byte-stream interface.

The dad joke
UDP sent a message but skipped the delivery receipt.
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References

Answer: Delivery and duplicate protection. UDP sends self-contained datagrams with little transport overhead. It does not promise that a datagram arrives or that a repeated datagram is suppressed, so an application must add those behaviors if needed.

  1. RFC 768: User Datagram Protocol www.rfc-editor.org/rfc/rfc768.html
    delivery and duplicate protection are not guaranteed.
    Checked 2026-10-10.

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