175 lines
5.8 KiB
Plaintext
175 lines
5.8 KiB
Plaintext
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RFC 768 J. Postel
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ISI
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28 August 1980
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User Datagram Protocol
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----------------------
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Introduction
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------------
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This User Datagram Protocol (UDP) is defined to make available a
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datagram mode of packet-switched computer communication in the
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environment of an interconnected set of computer networks. This
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protocol assumes that the Internet Protocol (IP) [1] is used as the
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underlying protocol.
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This protocol provides a procedure for application programs to send
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messages to other programs with a minimum of protocol mechanism. The
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protocol is transaction oriented, and delivery and duplicate protection
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are not guaranteed. Applications requiring ordered reliable delivery of
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streams of data should use the Transmission Control Protocol (TCP) [2].
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Format
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------
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0 7 8 15 16 23 24 31
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+--------+--------+--------+--------+
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| Source | Destination |
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| Port | Port |
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+--------+--------+--------+--------+
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| | |
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| Length | Checksum |
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+--------+--------+--------+--------+
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| data octets ...
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+---------------- ...
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User Datagram Header Format
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Fields
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------
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Source Port is an optional field, when meaningful, it indicates the port
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of the sending process, and may be assumed to be the port to which a
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reply should be addressed in the absence of any other information. If
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not used, a value of zero is inserted.
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Postel [page 1]
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28 Aug 1980
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User Datagram Protocol RFC 768
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Fields
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Destination Port has a meaning within the context of a particular
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internet destination address.
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Length is the length in octets of this user datagram including this
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header and the data. (This means the minimum value of the length is
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eight.)
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Checksum is the 16-bit one's complement of the one's complement sum of a
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pseudo header of information from the IP header, the UDP header, and the
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data, padded with zero octets at the end (if necessary) to make a
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multiple of two octets.
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The pseudo header conceptually prefixed to the UDP header contains the
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source address, the destination address, the protocol, and the UDP
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length. This information gives protection against misrouted datagrams.
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This checksum procedure is the same as is used in TCP.
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0 7 8 15 16 23 24 31
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+--------+--------+--------+--------+
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| source address |
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+--------+--------+--------+--------+
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| destination address |
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+--------+--------+--------+--------+
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| zero |protocol| UDP length |
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+--------+--------+--------+--------+
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If the computed checksum is zero, it is transmitted as all ones (the
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equivalent in one's complement arithmetic). An all zero transmitted
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checksum value means that the transmitter generated no checksum (for
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debugging or for higher level protocols that don't care).
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User Interface
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--------------
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A user interface should allow
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the creation of new receive ports,
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receive operations on the receive ports that return the data octets
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and an indication of source port and source address,
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and an operation that allows a datagram to be sent, specifying the
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data, source and destination ports and addresses to be sent.
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[page 2] Postel
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28 Aug 1980
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RFC 768 User Datagram Protocol
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IP Interface
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IP Interface
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-------------
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The UDP module must be able to determine the source and destination
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internet addresses and the protocol field from the internet header. One
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possible UDP/IP interface would return the whole internet datagram
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including all of the internet header in response to a receive operation.
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Such an interface would also allow the UDP to pass a full internet
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datagram complete with header to the IP to send. The IP would verify
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certain fields for consistency and compute the internet header checksum.
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Protocol Application
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--------------------
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The major uses of this protocol is the Internet Name Server [3], and the
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Trivial File Transfer [4].
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Protocol Number
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---------------
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This is protocol 17 (21 octal) when used in the Internet Protocol.
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Other protocol numbers are listed in [5].
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References
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----------
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[1] Postel, J., "Internet Protocol," RFC 760, USC/Information
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Sciences Institute, January 1980.
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[2] Postel, J., "Transmission Control Protocol," RFC 761,
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USC/Information Sciences Institute, January 1980.
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[3] Postel, J., "Internet Name Server," USC/Information Sciences
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Institute, IEN 116, August 1979.
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[4] Sollins, K., "The TFTP Protocol," Massachusetts Institute of
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Technology, IEN 133, January 1980.
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[5] Postel, J., "Assigned Numbers," USC/Information Sciences
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Institute, RFC 762, January 1980.
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Postel [page 3]
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