How to create VPN L2TP on macOS?

To prepare a macOS device to make an L2TP VPN connection, you must configure the L2TP connection in the network settings.

1. In the Apple menu, select System Preferences.
2. Click the Network icon.
3. Click the "+" icon in the lower left corner to create a new network interface.
4. In the Interface drop-down list, select VPN.
5. From the VPN Type drop-down list, select L2TP over IPSec.
6. In the Service Name text box, type a name for this VPN connection, such as "L2TP Gainserver".

7. Click Create.
   The settings for the VPN connection appear.

You can use the default configuration or you can create your own configuration. These steps use the default configuration.

8. In the Server Address text box, type Gainserver IP address to connect to.
9. In the Account Name text box, type your Gainserver user name. 
10. Click Authentication Settings.
11. In the Password text box, type the password of the user.
12. Our Gain server is configured to use a pre-shared key as the IPSec credential method:
    • Select Shared Secret.
    • In the Shared Secret text box, type the pre-shared key ; gainservervpn

13. Click OK & Apply to save the configuration changes.

How to start L2TP connection?

The name of the VPN connection is the service name you used when you configured the L2TP connection on the client computer. 

To start the L2TP connection:

1. In the Apple menu, select System Preferences.
2. Click the Network icon.
3. Select the VPN connection you created in the Network dialog box.
4. Click Connect.