On Mon, Jan 20, 2003 at 10:23:16AM +0100, devik wrote:
> Hi,
>
> anyone knows when TCP checksum is updated ?
Normally, TCP checksum is not supposed to be changed (or even read)
at all during transfer (see rfc793 or TCP/IP Illustrated Vol.1).
If NAT is in use then it needs to be accounted for, of course, because
TCP chksum involves a pseudoheader which contains both source and
destination addresses - but this is not the case, as you say.
> On other side if it simply passes packet thru (because nothing
> except TTL is changed and TTL is not part of TCP checksum) then
> the checksum should really ensure that nothing is changed
> between sender and reciever and if data are invalid then error
> would be on sender's or reciever's side.
Or imho even more probably, the problem could be the line. I've had a
couple of these during last 3 years. Namely, is there a serial line
(possibly wireless) involved?
pvl
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