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===== UDP Zero Checksum Conversion ===== The UDP protocol as specified in IETF RFC 768 introduces a special case that MUST be handled correctly when computing checksums. A checksum that sums up to zero MUST be stored in the checksum field as negative zero in ones’ complement arithmetic: 0xFFFF. A device MAY apply the same logic to all checksums in a protocol independent manner. Transport checksums are computed with ones’ complement arithmetic. In this arithmetic, a positive integer is converted to its negative complement by flipping all bits, and vice versa. Adding any number and its complement will produce all ones, or 0xFFFF. Every number thus has a complement. This includes zero: both 0x000 and 0xFFFF represent zero. RFC 768 adds explicit support for transmitting a datagram without checksum. This is signaled by setting the checksum field to 0x0000. To distinguish this lack of checksum from a computed checksum that sums up to zero, a sum that adds up to 0 MUST be written as 0xFFFF. <span id="receive-checksum"></span>
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