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

[Dirk Koopman]

What *is* the correct alignment for a Linux test application running on
i686?

Dirk

On Mon, 2002-07-22 at 13:09, Jani Monoses wrote:
> Hi
> as Florian said it could be an alignment issue.
> I had bad checksums because the data in httpd was not 4byte aligned.
> In the file where those binary structs live (fsdata.c) make the structs 
> aligned with the gcc attribute feature.I used an ARM processor.
> Jani.
> 
> > 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
> > 
> > [This message was sent through the lwip discussion list.]
> [This message was sent through the lwip discussion list.]


[This message was sent through the lwip discussion list.]