RFC 768 · August 1980 · J. Postel
User Datagram Protocol
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Built by hand from RFC 768. Every arrow, step and field cites the RFC sentence it comes from, and an automated test checks each quote against the RFC text. Provisional: not yet reviewed by a second engineer. Help verify this visual
RFC 768 This protocol provides a procedure for application programs to send messages to other programs with a minimum of protocol mechanism.
Source Port · 16 bits
Optional. When used, it is the sending process's port, and a reply can be sent back to it. If not used, it is set to zero.
Source Port is an optional field, when meaningful, it indicates the port of the sending process, and may be assumed to be the port to which a reply should be addressed in the absence of any other information. If not used, a value of zero is inserted.
Not shown: The pseudo header layout (source address, destination address, zero, protocol, UDP length) used for the checksum; Sending a computed checksum of zero as all ones; The user interface and IP interface descriptions; Protocol number 17 in the IP Protocol field.
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