Microsoft Windows Registry Guide, Second Edition

Network Connections

This section contains two network customizations for Windows Server 2003. The section “Enabling IP Forwarding” shows you how to turn on IP forwarding in Windows Server 2003. The section “Changing MTU Settings” describes how you can optimize PPP and VPN connections by changing the MTU sizes in the registry.

Enabling IP Forwarding

By default, TCP/IP forwarding is disabled in Windows Server 2003. To enable IP forwarding, add the REG_DWORD value IPEnableRouter to the key HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters. Set this value to 0x01. This enables IP forwarding on all network adapters installed on the server.

Changing MTU Settings

This section describes how to change the default maximum transfer unit (MTU) size settings for Point-to-Point Protocol (PPP) connections or for virtual private network (VPN) connections. Windows uses a fixed MTU size of 1500 bytes for all PPP connections and a fixed MTU size of 1400 bytes for all VPN connections. These are the default settings for PPP clients, for VPN clients, for PPP servers, and for VPN servers that are running Routing and Remote Access.

PPP connections are connections such as modem connections and Integrated Services Digital Network (ISDN) connections, or direct cable connections over null serial cable or parallel cable. VPN connections are Point-to-Point Tunneling Protocol (PPTP) connections or Layer 2 Tunneling Protocol (L2TP) connections.

NOTE

Use the methods discussed here to edit the registry to modify the MTU size settings. If you experience any problems or any performance-related issues after you modify the MTU size settings, remove the registry keys that you added.

To change the MTU settings for PPP and VPN connections, add the REG_DWORD values ProtocolType, PPPProtocolType, and ProtocolMTU, as well as TunnelMTU, to HKLM\SYSTEM\CurrentControlSet\Services\Ndiswan\Parameters\Protocols\0. (Create this subkey if it doesn't already exist.) Table 6-4 describes what settings to put in each value. ProtocolType and PPPProtocolType are required values. You can add either ProtocolMTU, TunnelMTU, or both.