Starting with SP4, you can get RPC and third-party Socket applications to use the Winsock Proxy.

The Winsock Proxy allows Windows Sockets applications on your LAN to think they are directly connected to the Internet, even though Microsoft Proxy Server is acting as the host/gateway.

Normally, RPC bypasses the Winsock32.dll and communicates directly with the device driver. To change this, use Regedt32 to navigate to:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc

On the Edit menu, Add Value name UseWinsockForIP as a type REG_DWORD and set the data value to 1 (0 is the default).

To enable third party applications to use the Winsock 2.1 LSP (Layered Service Provider):

1. Copy SystemRoot%\System32\Rpcltscm.dll to SystemRoot%\System32\RpcltJSI.dll.

2. For each protocol being implemented by the LSP, replace the Rpcltscm.dll string in the ServerProtocols sub-key with RpcltJSI.dll.

      Example: For the TCP/IP protocol, change:

      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ServerProtocols\ncacn_ip_tcp=rpcltscm.dll

                TO

      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ServerProtocols\ncacn_ip_tcp=rpcltJSI.dll

3. You must restart your computer.