A thorough examination of what an L2TP connection error is, what causes it, and how to resolve it.

L2TP is a popular VPN that uses the Layer 2 tunneling protocol to get around a specific area’s security restrictions. However, you may come across that Because the security control in Windows experienced a processing problem, the L2TP connectivity attempt failed.

The security tab function finds a problem while attempting to connect to a remote VPN server, resulting in VPN error 789.

The L2TP connectivity attempt fails when a user attempts to create a new client-side connection using a Windows 2000 terminals session because the security control detects a programming mistake. A problem with the machine or the VPN itself might cause the problem. 

Moreover, the Operating System settings to use the L2TP VPN may be incorrect, resulting in the connection ending locally well before it begins. In this article, we’ll go through a couple of game-changing methods for resolving this VPN issue.

Contents show

1 A list of methods

2 VPN Network Connections Interface must be reinstalled

3 In the PPP options, allow the LCP modifications

4 Enable the MS-CHAP v2 protocol from Microsoft

5 Fix the IPSEC variables by starting them

6 Check the certification on the VPN service

7 Build a separate key in the UDPE Encapsulation Registry

8 The reasons behind the connectivity request were denied

A list of methods


The problem “The L2TP Connection Attempt Failed Because the Security Layer Encountered a Processing Error” might be caused by one of two things. On the Desktop or Pc, either the MS-CHAP v2 protocol is deactivated or the PPP configurations are incorrectly set up.

 If correcting these issues doesn’t work, I’ve included alternative options for resolving the problem.

VPN Network Connections Interface must be reinstalled

Many situations show that the problem of VPN 789 arises in a remote computer due to network adapter unreliability. Consequently, the VPN service has a tough time getting the data for setup. Frequently, merely restarting the Network Adapter Settings program reduces the problem. 

Since the authentication process in Windows encountered a processing problem, the L2TP connectivity plan backfired. To use it, open Device Manager, and uninstall the old Driver Software before installing the new one downloaded from the internet. Here’s how to go about doing it:

Launch the Run dialog box by using the Win+R shortcut keys. In the Run search window, type devmgmt.msc. Click the OK button to open Device Manager in a new window. On the left side of the screen, double-click the Network Adapter. Make a right-click on the Network Adapter once the drivers have been split out. Select the Delete or Uninstall device from the drop-down menu. Click Uninstall once more, and then restart the Computer when the procedure is finished. Return to a previous session, open an internet browser, go to the manufacturer’s website for software, and get the compatible one. Install the file on your computer.

In the PPP options, allow the LCP modifications

There’s a chance that the LCP modifications are enabled in the Point to Point Protocol (PPP) settings. The L2TP connectivity may be hampered as a result of this. The LCP modifications can be enabled in the following way.

Open the Run dialogue box by pressing Win logo+ X, then typing ncpa.cpl and clicking OK. The Network Connectivity window will now appear. Go to Properties by right-clicking on your Vpn service. Just go to the Options tab in the Properties panel. Select the Allow LCP add-ons option from the PPP Settings… menu. After clicking OK to preserve the changes, press OK again.

After you enable the LCP extensions option, reconnect the VPN and see if you’re ready to use it now.

Enable the MS-CHAP v2 protocol from Microsoft

The L2TP connectivity plan backfired because the security feature detected a programming problem when the Microsoft CHAP v2 protocol was disabled. 

As a result, activate it and try to resolve the problem using the instructions below

Right-click on Start, choose Run, and input ncpa.cpl into the provided text box. Right-click the Vpn service once Network Adapter Options appear. Select Properties from the drop-down menu that appears. Go to the Security section when a fresh popup appears. Scroll to the bottom of the Permit All Protocols radio option and select it. Click over Microsoft-CHAP Version 2 and check the tiny box next to it. After clicking OK, try reconnecting the Vpn connection.

Fix the IPSEC variables by starting them

The security feature detected a processing issue, and the L2TP connectivity request was denied.

According to the vast majority of people who have come into this issue, After removing the IPsec services Key exchange Modules and IPsec Policy Agent tasks, the L2TP connectivity effort failed. 

As a result, allowing these protocols may address the issue with the Self-Hosted Vpn connection. This is how to make the services available –

Obtain access to the taskbar Using the press Win+Q hotkeys combined search. As in the empty box, type services and hit the Enter button.
Look for the IKE, and AuthIP IPsec Keying Module functions in the Service panel. Double-click it, then select Automatic from the Startup Type drop-down menu in the General panel. Click on Start after hovering over the Service status section. Finally, click the Apply option, then OK to preserve your changes. Return to the Services pane and search for the IPsec Policy Agent activity. Double-click it and choose Automatic as the Startup option. To begin, press the Start button, then perhaps the OK button. Reopen the VPN after applying the settings and try to connect again.

Check the certification on the VPN service

When an incorrect certification or shared information and a poorly configured key are used to access a VPN service, the security feature may encounter a processing problem, resulting in The L2TP connectivity effort failed so because the security feature found a programming issue. 

As a result, double-checking that the certification you’re using is correct and legitimate is crucial. At the very same time, a distinct and properly configured password must be set on the client’s or Secure VPN end.

By validating the identical information on the customer and VPN provider, you may certainly utilize a Pre-Shared Key (PSK). To prevent the L2TP connectivity attempt from failing because the security feature met a processing issue on Windows, be extra careful before installing them.

Build a separate key in the UDPE Encapsulation Registry

Users are frequently confronted when the security feature is still behind Network address translation, it encounters a programming fault, and the L2TP connectivity attempt fails (NAT).

The same thing can happen if the VPN connection is incorrectly set up to run behind the same NAT service, or if there are numerous connection problems. 

Users won’t be able to link to the VPN service effectively if this creates potential failures. In such a scenario, you’ll need to change some Registry Editor entries, and to do so, follow the steps below —

It’s crucial to duplicate the registry keys before continuing.

In the taskbar’s search field, enter Regedit and hit Enter. Navigate to the path HKEYLOCAL_MACHINE_SYSTEM/CurrentContro/lSetServices/PolicyAgent in the left panel once you’ve opened Registry Editor. When you go to Policy Agent, go to the right side panel. Select New => DWORD (32-bit) Value from the context menu that displays when you right-click an empty place. AssumeUDPEncapsulationContextOnSendRule is the creation of a new DWORD. Double-click the freshly generated DWORD and set the Value data to 2 before pressing OK. Restart your computer and rejoin your VPN connection when it comes up.

The reasons behind the connectivity request were denied

After reviewing various examples, we discovered that the following factors might have a role in causing the problem. Because the l2tp connection attempt failed because the security layer encountered a processing error.

Using a duplicate certification or a discussed key on the VPN connection. Network address translation is used by the L2TP VPN server (NAT). On the VPN client, there is no trusted device certification or root machine certificate. The VPN server’s machine certificates do not include server authentication,’ like EKU does (Extended Key Usage). Registry entries such as AssumeUDPEncapsulationContextOnSendRule may be missing, resulting in the VPN server’s connection failing repeatedly. Removing the IPsec Keying Components and Policy Agent services, both of which are necessary for any self-hosted VPN. PPP (Point to Point Protocol) parameters incorrectly set up harm the VPN connection. Stopping the Microsoft CHAP v2 protocol on the VPN properties window server’s peripheral.


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