Why Does Windows L2TP Dial-Up Fail When the IPSec Function Is Not Configured?
By default, the L2TP VPN transmission policy of the Windows operating system requires IPSec. The system uses IPSec by default, and the client is disconnected during L2TP dial-up by default. Therefore, you must modify the registry of the Window operating system to disable the default setting.
To modify L2TP VPN settings, perform the following operations:
1. Choose Start > Run, enter regedit, and open the registry editor to locate the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Rasman\Parameters primary key.
2. Add the DWORD value to the primary key: The key name is ProhibitIpSec, data type is REG_DWORD, and value is 1.
3. Save the configuration and restart the PC to make the configuration take effect.
4. Complete the dial-up after the PC restarts. You can modify the registry by running the .bat file.