Mike Weber:
> I'm running ethereal 0.10.6 with winpcap 3.1 beta 3 under winXP with all
> the patches windows update wanted to install except service pack 2. I'm
> running an Athlon64 3400+ on an NVidia nForce3 250Gb - based motherboard.
>
> While going through an analysis I noticed that probably ~90% of the
> segments generated from my machine are reported as having bad TCP
> checksums. There doesn't seem to be a problem transferring data; I've
> transferred gigabytes of data over this link over the last few days and
> haven't had trouble on a scale that correlates with the number of bad
> checksums I'm seeing. (I have had a problem where certain email message
> bodies never get ACK'd, but I don't know if that's a checksum problem or
> something else. It is the reason I broke out ethereal, though.)
>
> Is this something to worry about? Is it a bug in winpcap or ethereal? Or is
> the checksumming code in my NVidia NForce3 chipset (does tcp/ip offloading)
> broken?
>
> Thanks for any information pointers or advice!
>
Don't worry ...
It is most likely due to tcp checksum calculation offloading
http://www.ethereal.com/faq.html#q5.14
The packets with correct checksum is probably packets that are shorter than a certain length.