BOOL __stdcall SetMTUDecrement ( DWORD dwMTUDecrement );

Return Value:
TRUE if call was successful, FALSE otherwise

System wide MTU decrement value to set.

Some network applications need to insert additional headers into the packet. The examples of these applications are IP in IP tunneling, IPSEC based VPNs and etc. This function sets the parameter in the registry key which helper driver reads during it’s initialization and subtracts it’s value from the real MTU when MSTCP requests it from the network, so this API call requires a system reboot to take effect.