Editing UDP Protocol (section)

== 3. UDP Header Structure ==

The UDP header is fixed at 8 bytes and contains only four fields:

{| class="wikitable"
! Field !! Size (bits) !! Description
|-
| Source Port || 16 || Port number of the sending application. Can be zero if not needed.
|-
| Destination Port || 16 || Port number used by the receiving application or service.
|-
| Length || 16 || Total length of UDP header and data in bytes.
|-
| Checksum || 16 || Optional in IPv4 (0 means unused). Required in IPv6 for error detection.
|}

; Header layout (in order):
: Source Port → Destination Port → Length → Checksum

There are no sequence numbers, acknowledgments, retransmission logic, or flow control.  
UDP relies on the application layer to implement any needed reliability.