By default, Windows NT Server and Windows NT Workstation both place a default route (0.0.0.0) on each network adapter in a computer. This causes the server to send packets of unknown IP addresses to the network adapter configured with the default route. This is the normal and desired action of a router.
However, you must change this default setting if a server is connected to a private network (intranet) and the Internet. You must disable the automatic addition of a default route on the network adapter for the private network. You do this on the PPTP server by adding the DontAddDefaultGateway Registry entry with a value of REG_DWORD 0x1 in the following Registry location:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services \network adapter\Parameters\Tcpip\DontAddDefaultGateway
This entry prevents the default route from being added to PPTP server’s network adapter. Use a Registry editor to add this entry, and then shut down and restart the computer.
After the DontAddDefaultGateway entry is created you must add static routes for the network adapter. These static routes must configure the PPTP server to route incoming data from the Internet to the correct server on the private network. This procedure is explained below.