Windows

How to Fix ‘The L2TP Connection Attempt Failed Because the Security Layer Encountered a Processing Error’

An L2TP connection uses the Layer 2 Tunneling Protocol and is used mostly for supporting Virtual Private Networks. A Virtual Private Network(VPN) is used to mask the origin of connection by reflecting the connection over a server located in a different area than the origin of the connection. This can help many people to hide their locations from certain websites in order to bypass some security restrictions.

However, quite recently, a lot of reports have been coming in where users are unable to make a VPN connection and a “The L2TP connection attempt failed because the security layer encountered a processing error during the initial negotiations with the remote computer” Error is returned while trying to do so. In this article, we will discuss the reasons due to which it is triggered and also provide viable solutions to fix it completely.

The L2TP Connection Attempt Failed Because the Security Layer Encountered a Processing Error on Windows 10

What Causes the “L2TP Connection Attempt Failed” Error?

After receiving numerous reports from multiple users, we decided to investigate the issue and devised a set of solutions to fix it completely. Also, we looked into the reasons due to which it is triggered and listed them as follows.

  • Disabled Protocols: In some cases, the error is triggered if the Microsoft CHAP v2 protocol is disabled inside the VPN Connection’s properties. This protocol needs to be enabled in order for most VPN connections to work.
  • PPP Settings: The Point to Point protocol needs to be properly configured before users can attempt a VPN connection. This protocol contains an LCP protocol and the LCP Protocol has some further extensions that need to be enabled in order for the connection to work properly.

Now that you have a basic understanding of the nature of the problem, we will move on towards the solutions. Make sure to implement these in the specific order in which they are presented to avoid conflicts.

Solution 1: Enabling MS-CHAP v2

Since it is important that the Microsoft CHAP v2 protocol is enabled before trying to connect to a VPN in Windows 10, in this step, we will be enabling the protocol. For that:

  1. Make sure that the VPN connection has been properly configured to match the credentials of the VPN server that you are trying to connect to and add the connection.
  2. Once the connection has been added, it will appear in the network adapter list.
  3. Press “Windows” + “R” to open the “Run” prompt.
  4. Type in “ncpa.cpl” and press “Enter” to open the Network Adapter Settings.
    Typing in “ncpa.cpl” and pressing “Enter”
  5. Right-click on the “VPN” connection that has been added and select “Properties“.
    Right-clicking on the VPN and selecting “Properties”
  6. Click on the “Security” tab and check the “Allow These Protocols” option.
    Selecting the “Allow these Protocols” option
  7. Check the “Microsoft-CHAP Version 2” option and click on “OK”.
    Checking the “Microsoft-CHAP Version 2” option
  8. Try to connect to the VPN and check to see if the issue persists.

Solution 2: Enabling LCP Extensions

It is also important that the PPP Settings are configured to allow LCP Extensions, therefore, in this step, we will be changing the VPN properties and enabling the extensions. For that:

  1. Press “Windows” + “R” to open the “Run” prompt.
    Opening Run Prompt
  2. Type in “ncpa.cpl” and press “Enter” to open the Network Adapter Settings.
  3. Right-click on the “VPN” connection that has been added and select “Properties“.
    Right-clicking on the VPN and selecting “Properties”
  4. Click on the “Options” tab and select “PPP Settings“.
  5. Check the “Enable LCP Extensions” option and click on the “OK” button.
    Checking the “Enable LCP Extensions” button and selecting “OK”
  6. Again, select the “OK” option to save your settings.
  7. Try to connect to the VPN and check to see if the issue persists.

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How to Fix ‘The L2TP Connection Attempt Failed Because the Security Layer Encountered a Processing Error’

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