I am experiencing a problem that has me very confused and I wonder if anybody 
has seen this or could suggest an idea.

My embedded device runs lwip and has been working great with IPv4.  It uses a 
WiFi module to handle raw Ethernet packets that I send it and I get raw 
Ethernet from it. I updated to latest lwip to add IPv6 support.  I was able to 
add it and it seemed to work great.  That is, with my windows XP machine (IP6 
enabled) I could communicate fine with the IP6 embedded device.  But someone 
else in my company then tried it with their Windows 7 machine and couldn't 
connect.  Since then we have tried many different machines - XP, Vista, Win7.  
Only the Windows 7 machines have problems.

A strange thing is that they can ping the embedded device fine but can't open a 
TCP connection.  I have done many Wireshark captures and can see that the Win7 
PC sends a SYN and the embedded device responds with a SYN,ACK. But then the PC 
acts as though it never received the SYN,ACK because it just times out and 
sends the SYN again.  I have compared Wireshark captures from PCs that are able 
to connect and PCs that are not able to connect and those SYN and SYN,ACK 
packets look identical except for IP and MAC addresses.

I thought maybe it's the WiFi routers but they are just bridged to pass 
everything through and it does seem that they are routing the packets OK as the 
PC wireshark logs show - the SYN,ACK from the embedded device gets to the PC 
but the PC never responds with the ACK.

Is there some special thing to configure windows 7 to work with IP6 or 
something I am missing? Any Ideas??
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