Re: [lwip-users] Works with Win7, not Windows XP?

[Niall Donovan]

Hi,

  There is evidence that Windows 7 and 8 ignore the MSS value if it is less 576. I have TCP links working between my embedded app and both Windows XP and Windows 7. In my case XP was always working (TCP_MSS  = 1518) but when I moved to windows 7 I had tried TCP_MSS   256 to start and it ignored it and defaulted to MSS=576 (windows sent me 576 byte chunks, overflowing my pbufs). I now have TCP_MSS = 576 in my embedded system and it works for both Win XP and Win 7. You also need to ensure that you have allocated pbufs of the necessary size for this MSS to work.

Check out this link for more info: http://ask.wireshark.org/questions/9573/windows-7-ignores-tcp-mss

Regards

Niall.

On 29 October 2013 19:30, ThomasJ <address@hidden> wrote:

Hi All

Maybe someone can help me.

We are using lwip in a new embedded device. The device communicate with our
server software with TCP connection.
The device works fine as long the server software runs on a Windows 7
machine, but not when the code runs a WindowsXP system.
The server software and the device software is the same in all cases.

It is in the situation, where the server sends a big chunk of data to the
device (1033 bytes). When the server runs on WinXP the device crahes. The
stack trace is some where in the receive input function. On Win7 every thing
works.

I have tried to change the MSS, TCP WND and memory size.
A MSS of 128, mem pool of 20 and memory size of 15*1024 works perfect with
Windows 7. But to get it to work with WinXP I have to increase the MSS to
536 or 1460 to make it work. Then it is slow in the case i send a big chunk
of data to the device and it sometimes still crashes.

So it guess it has something todo with the MSS parameter, but I can figure
out what. Maybe receive describtors used?

Im using FreeRTOS and a LPC1788. I keep the memory inside the PIRAM, so I
need a low memory usage.
Maybe it something with WinXP ignoring MSS lower then 536 bytes? And then
the stack cant handle the data?

May next move is to analyze with wirexhark on a Win7 and XP system.

Any help appricated.

Best regards Thomas



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