[lwip-users] [lwip] lwIP 0.5.3 tcp Checksum issues?

[Michael Portmann]

Hi all.

  Are there any known issues with 0.5.3 with regards to checksum calculation?

  Specifically, I am testing my own httpd server (heavily modified from the 
original using the raw api) and pages don't get displayed. I am tracking this 
down to the fact that the responding packet of data is sent, but packet 
sniffing software says it has an invalid tcp checksum and my PC isn't ACKing. 
The data just keeps getting resent with the same incorrect checksum.

  The main index web page supplied in the lwIP archive works ok, others don't, 
so it seems to depend on the data content.

  What's strange is I had tested this code and it works under the win32 port 
(and still does work) - although due to different timings the exact sequence of 
events are different.

  What's even more annoying is that I have compared the ROM pbuf checksum total 
with the win32 port's ROM pbuf checksum total - they are equal. I have 
calculated manually the TCP pbuf checksum and added this all up with the pseudo 
header and get the same checksum as that which was sent with the packet !! 
Surely the packet sniffing software and windows 2000 checksum implementation is 
correct ? ! I can assume that can't I ? ! :-)

Regards,
Michael Portmann

HYDRA Electronic Design Solutions Pty Ltd
140 Ashley Street, Underdale, SA 5032.
Ph. +61 8 8234-0477
Fx. +61 8 8234-1840

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