Ftp-WG: Updating the checksum

    Date:        Sun, 16 Feb 2003 02:28:26 -0500
    From:        "Mohammad Awad" <[email protected]>
    Message-ID:  <[email protected]>

You probably shouldn't be sending questions about IP checksums
to the FTP extensions working group mailing list (we also
probably shouldn't be answering them here).

  | Can anyone help please?

I suspect that 1071 is incorrect, or meant to be interpreted differently
(the C in the example may be meant to be the calculated sum, not the 1's
complement of that which is stored in the checksum field).

But in any case, it is obvious that if you add 1 to a word in the message
you must subtract 1 from the checksum (word, in the message) as the sum
of all words in the message must be 0 for the message to be considered
valid (that it is a 1's complement sum, and a 1's complement "0" is irrelevant
for this - though obviously important for the implementation).

kre