UDP
the User Datagram ProtocolUDP is the fire-and-forget transport. It wraps data in a tiny header and sends it, with no handshake and no acknowledgements — and no promise it will arrive. What it trades away in safety it wins back in speed.
UDP sends datagrams with no setup and no guarantees — fast, thin, and best-effort.
Open the UDP lab →
No handshake, no guarantees. Four datagrams on a clean wire, then one that vanishes—and nobody reports it.
How it works
Four small fields, then the data. There’s nothing to set up and nothing to remember — which is exactly why UDP is so fast and so cheap.
What UDP does, step by step
There’s no connection to open — the first packet is the data, sent immediately.
Just source and destination ports, a length and a checksum — eight bytes in all.
The datagram goes out with no acknowledgement; a lost one is simply gone.
If order or reliability matter, the application (or a layer like QUIC) adds them on top.
In cybersecurity
Having no handshake makes UDP fast — and makes it trivial to spoof and a favourite tool for amplification attacks.
A small spoofed request draws a huge reply to the victim — DNS and NTP are classic amplifiers.
With no handshake to complete, the source address is never verified.
UDP is plaintext — secure it with DTLS or ride it under QUIC.
Stateless floods are cheap to send and hard to filter without rate limits.
With no connection to track, stateful firewalls treat UDP with cruder rules.
Closed ports may not reply at all, so UDP scans are slow but stealthy.