The L2TP Connection Attempt Failed: Understanding and Fixing the Security Layer Processing Error

The Layer 2 Tunneling Protocol, commonly known as L2TP, is utilized to establish secure Virtual Private Network (VPN) connections. VPNs are a common method used to overcome certain security limitations and enable remote access to private networks, protecting confidential data transmissions from being intercepted. Despite its benefits, recent reports suggest that users face issues while trying to establish L2TP connections. A commonly observed error message received by users states “The L2TP connection attempt failed because the security layer encountered a processing error during the initial negotiations with the remote computer.” This article highlights the root causes of the “L2TP Connection Attempt Failed” error and suggests solutions to overcome it.

Reasons behind the “L2TP Connection Attempt Failed” Error

After conducting an analysis, it was identified that a key reason behind the “L2TP Connection Attempt Failed” error is the disabled Microsoft CHAP v2 protocol in the VPN connection’s properties. This protocol is required for most VPN connections to function correctly, and its absence could lead to errors and connection failures. Additionally, the Point-to-Point protocol (PPP) must be configured appropriately before attempting a VPN connection. The LCP protocol within PPP requires specific extensions to be enabled for a successful connection to occur.

Solutions to Fix the Error

The following solutions need to be implemented in the specified order to avoid potential conflicts, and should resolve the “L2TP Connection Attempt Failed” error for good:

Solution 1: Enable MS-CHAP v2

1. Ensure the VPN connection is configured correctly and has the appropriate credentials to match the VPN server you wish to connect to.
2. Open the “Run” prompt by pressing the “Windows” key and “R” simultaneously and type “ncpa.cpl” and press “Enter” to access the Network Adapter Settings.
3. Find the “VPN” connection that has been added, right-click on it, and select “Properties”.
4. Navigate to the “Security” tab, check the “Allow These Protocols” option and select “Microsoft-CHAP Version 2” option.
5. Click “OK” to enable the protocol.
6. Attempt connecting to the VPN to check if the error persists.

Solution 2: Enable LCP Protocol Extensions

1. Open the “Run” prompt by pressing the “Windows” key and “R” simultaneously and type “ncpa.cpl” and press “Enter” to access the Network Adapter Settings.
2. Select the “VPN” connection that has been added, right-click on it, and select “Properties”.
3. Click on the “Options” tab and select “PPP Settings”.
4. Check the “Enable LCP Extensions” option.
5. Select “OK” to save your settings.
6. Attempt connecting to the VPN to check if the error persists.

By following these steps, users should be able to establish reliable VPN connectivity and overcome the “L2TP Connection Attempt Failed” error.