I writing to this
list because the TCP workgroup was shutdown a while ago.
We have a
compatibility problem between two third party implementations of the TCP
checksum.
The problem concerns
the representation of zero, which has two 1-s complement representations
(0000 and ffff).
We don't have source
to either stack but I managed to deduce the problem from looking at a packet
trace. The receiver drops all datagrams containing a TCP with a TCP
checksum of ffff.
My view is that the
receiver is in error; it should be checking the special case of
0.
All the receiver
code I have seen doesn't work this way. The normal approach is to
calculate the1-s complement sum with checksum in place and check that this
is zero. The methods I konw always return just one
representation for zero, hence there is no special case.
Any
thoughts?
Thanks,
Chris
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