Repair: The L2TP Connection Attempt Failed Because the Security Layer Encountered a Processing Error



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The error message: “The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer” is commonly referred to as VPN error 789. This is one of the most common VPN errors that occurs when a user tries to connect to L2TP. Here, the L2TP connection attempt failed because the security layer encountered a processing error during the first negotiation with the remote computer.

The error message: “The L2TP connection attempt failed because the security layer encountered a processing error during the first negotiation with the remote computer” is a common error to determine when the IPSec negotiation fails for L2TP/IPSec connections. It is only caused by a misconfiguration of the user’s operating system.

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

  • The L2TP-based VPN client (or VPN server) is behind NAT.
  • A fake certificate or pre-shared key is placed on the VPN server or client.
  • The trusted machine certificate or root machine certificate is not present on the VPN server.
  • The machine certificate on the VPN server does not have ‘server authentication’ as EKU.

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

Restart your VPN network adapter.

  1. Right-click on’Start’ and click on’Device Manager’.
  2. Locate’Network Adapters’ and click on the drop-down menu to expand the list.
  3. Find your’Network Adapter’.
  4. Right-click on it and select Uninstall.
  5. Now click on’OK’.
  6. Reboot your system.


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Changing IPSEC parameters

  • Open the Administration Tools from the Control Panel.
  • Double-click on Services.
  • Search for IPSEC services. (ike and AuthIP IPsec Keying Modules,IPsec policy agent) Confirm that the start type is automatic and that the status is set to Start. If necessary, double-click on IPsec Services to change these settings.
  • If it is not “started”, right click to start it.
  • Right-click and select Properties. For “Start type”, select “Automatic” and save.
  • Test the VPN connection.
  • Restart the VPN connection and test it.

Activation of MS-CHAP v2

  1. Make sure that the VPN connection is correctly configured to match the identification information of the VPN server to which you are trying to connect and add the connection.
  2. Once the connection is added, it will appear in the list of network adapters.
  3. Press Windows + R to open the Run command prompt.
  4. Type “ncpa.cpl” and press “Enter” to open the network adapter settings.
  5. Right-click on the added “VPN” connection and select “Properties”.
  6. Click on the “Security” tab and activate the “Allow these protocols” option.
  7. Activate the “Microsoft-CHAP Version 2” option and click on “OK”.
  8. Try to connect to the VPN and check that the problem persists.

https://blogs.technet.microhttps://blogs.technet.microsoft.com/rrasblog/2009/08/12/troubleshooting-common-vpn-related-errors/soft.com/rrasblog/2009/08/12/troubleshooting-common-vpn-related-errors/



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