RE: [lwip-users] TCP Checksum errors.

[FreeRTOS.org Info]

> Hi,
> 
> I know this isn't much to go on, but I think I am getting TCP 
> checksum errors.
> 
> I am using an ST7101 chip, running OS21.
> 
> I have got much of the LWIP stack running, DHCP works and DNS 
> resolution is fine (I think both of these use UDP).
> 
> But, the httpd example is giving wireshark some TCP Checksum 
> errors, and the PC based browsers doesn't get the response 
> from the HTTP GET request.
> 
> Now, because anything using the UDP half of the transport 
> layer seems fine, I am assuming that I have a problem 
> somewhere in the TCP half, specifically in the checksum calcs.
> 
> I have read elsewhere on these lists that there may be some 
> hardware level checksum calcs happening, I need to read my 
> docs to see if that is being enabled on my chip.
> 
> Do the above sound like reasonable assumptions?
> 
> 
> 
> Help/comments/advice appreciated.

Often the checksum is added by the hardware and Wireshark never sees it -
hence it flags errors.  There is an option in Wireshark to ignore these
errors.  In my experience it is very normal to see errors in Wireshark, only
to find that if you step through the code the checksums verify with no
problem.

Regards,
Richard.

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