For more information about how to back up and restore the registry, see How to back up and restore the registry in Windows. Then, you can restore the registry if a problem occurs. For added protection, back up the registry before you modify it. Therefore, make sure that you follow these steps carefully. However, serious problems might occur if you modify the registry incorrectly. This section, method, or task contains steps that tell you how to modify the registry. To change the MTU settings for VPN connections, add the ProtocolType DWORD value, the PPPProtocolType DWORD value, and the TunnelMTU DWORD value to the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Ndiswan\Parameters\Protocols\0 Under Base, click Decimal, type the MTU size that you want in the Value data box, and then click OK.Ĭhange the MTU settings for VPN connections In the Value data box, type 21, make sure Hexadecimal is selected under Base, and then click OK. Type PPPProtocolType, and then press ENTER. In the Value data box, type 800, make sure Hexadecimal is selected under Base, and then click OK.
In the Value data box, type ProtocolType, and then click OK. Using a standard Windows command prompt and ping using the -f flag is a quick and easy way to diagnose MTU and fragmentation issues across a VPN tunnel. On the Edit menu, point to New, and then click DWORD Value.