December 2020

How to Fix The L2TP Connection Attempt Failed Error

If you are using a VPN and you will be prompted with error 789 Windows 10 VPN:

The L2TP connection attempt failed because the security layer encountered a processing error during the first negotiations with the remote computer.

This error occurs when your system is not properly configured to connect to the L2TP server Thus, the connection attempt failed even before connecting to the server.

It is also due to a misconfiguration of your operating system, such as Windows 10 in this case. This general error occurs when IPSec negotiation fails for L2TP / IPSec connections.

Other possible reasons:

  • The L2TP VPN client (or VPN server) is behind NAT.
  • Incorrect certificate or pre-installed key specified on VPN server or client.
  • The VPN server does not have a computer certificate or a trusted root computer certificate.
  • The computer certificate on the VPN server does not have server authentication like EKU

Here are the solutions to help you fix Windows 10 VPN error 789 on your PC.

Use the Services snap-in

  1. Press W8K + R and type services.msc in the Run dialog box. Press Enter to open the Services snap-in.
  2. In the Services snap-in, locate the IKE and AuthIP IPSec key modules, and the IPSec Policy Agent Services.
  3. Double-click these services, set them to startup type Automatic, and click the Start button to start them. When these services are started, there are no more problems.
  4. Close the service harness.

Enable LCP Extensions

As with the reason analyzed above, correct PPP settings are also important to enable LCP extensions. So let’s see how to enable LCP extensions in VPN properties.

The first two steps are the same as shown in the method above. After opening the properties of the VPN connection, follow these steps.

Step 1. In the Properties window, go to the Options tab and select PPP settings. Then select the Enable LCP Extensions checkbox and click OK.
Step 2. Then click OK to apply the change. After that, you can try to restore the VPN connection and see if the problem is resolved or not.

Activate MS-CHAP v2

Since it is important that Microsoft CHAP v2 is enabled before attempting to connect to a VPN on Windows 10, at this point we will enable the protocol. Hence:

  • Make sure the VPN connection is configured correctly and matches the credentials of the VPN server you want to connect to and add the connection.
  • After adding the connection, it will appear in the list of network adapters.
  • Press Windows + R to open the Run window.
  • Type “ncpa.cpl” and press Enter to open the network adapter settings.
  • Right-click the added VPN connection and select Properties.
  • Click the Security tab and select the Allow these protocols check box.
  • Activate the option “Microsoft-CHAP Version 2” and click “OK”.
  • Try connecting to a VPN and see if the problem persists.