Someone on this thread previously said something to the effect of MTU settings not working on Windows. I didn't believe it, but now I do, having just encountered the same problem. The weird part was, the MTU setting was working on ICS client machines, but not on the ICS system where the modem was attached. Windows just kept ignoring the MTU setting I entered into the registry.
After wasting several hours, I eventually found this info & fix (seems Windows also ignores MTU negotiation ICMP packets sent by the network itself!): http://www.netmax.com/fom/cache/467.html (Under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters, create a DWORD value with the name "EnablePMTUDiscovery", and the value of "1".)
It had been working before so I don't know why it suddenly decided to stop working. In any case, it works now with the above fix, I hope that discovery only happens once per session though.
After wasting several hours, I eventually found this info & fix (seems Windows also ignores MTU negotiation ICMP packets sent by the network itself!): http://www.netmax.com/fom/cache/467.html (Under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters, create a DWORD value with the name "EnablePMTUDiscovery", and the value of "1".)
It had been working before so I don't know why it suddenly decided to stop working. In any case, it works now with the above fix, I hope that discovery only happens once per session though.