★ L2TP VPN connection fails on Win10 system

L2TP VPN in Client-Initiated mode

Using Client-Initiated mode to create an L2TP tunnel, and using windows 10 to create a virtual private L2TP network connection, the Remote Host is unable to connect after entering the PPP username and password, displaying the error as: The L2TP connection attempt failed because the security layer could not negotiate compatible parameters with the remote computer.

1. View the establishment of l2tp sessions and tunnels to check whether L2TP is working

[LNS]display l2tp session

[LNS]display l2tp tunnel

Sessions and tunnels were established successfully.

2. The user is using windows 10 and L2TP stands for Layer 2 Tunneling Protocol, some of the reasons behind this error could be that the PPP (Point-to-Point Protocol) settings are misconfigured or the Microsoft CHAP v2 protocol is not enabled.

3. After PC installs the necessary windows update, the problem is solved.

Solution 1：Install the necessary Windows update

Microsoft has issued a software update to fix the VPN problem. Download the version from the Microsoft official website and update it to fix the problem.

https://answers.microsoft.com/en-us/windows/forum/all/the-l2tp-connection-attempt-failed-because-the/664649c8-cd05-49fb-b405-55d1e79e1ea3

Part 1: Uninstall the faulty update

Step 1: Navigate to Settings > Windows Update > View update history.

Step 2: Click Uninstall updates.

Step 3. Find the update and click Uninstall.

Part 2: Disable automatic updates

Disable the automatic updates to prevent Windows download and install the fault update again.

Step 1: Press Win + R, enter “gpedit.msc”, and click OK.

Step 2: Navigate to Computer Configuration > Administrative Templates > Windows Components > Windows Update > Manage end user experience, and click Configure Automatic Updates.

Step 3. Tick Enabled, choose to Notify for download and auto install and click OK.

Then Windows will notify you before downloading and installing updates.

Part 3: Install the necessary update

Step 1: Go to Windows Update and click View optional updates.

Step 2: Download and install the available update.

Windows 11, version 21H1 (original release): KB5010795

Windows Server 2022: KB5010796

Windows 10, version 21H2: KB5010793

Windows 10, version 21H1: KB5010793

Windows 10, version 20H2, Windows Server, version 20H2: KB5010793

Windows 10, version 20H1, Windows Server, version 20H1: KB5010793

Windows 10, version 1909, Windows Server, version 1909: KB5010792

Windows 10, version 1607, Windows Server 2016: KB5010790

Windows 10, version 1507: KB5010789

Windows 7 SP1: KB5010798

Windows Server 2008 SP2: KB5010799

Solution 2: Turn on the Microsoft CHAP Version 2 protocol and the LCP extensions.

When using VPN, Microsoft CHAP Version 2 protocol and LCP protocol extensions help configure and establish the Internet connection. You need to enable these protocols to fix the error.

Step 1: Open Control Panel, click View network status and tasks, and click Change adapter settings.

Step 2: Right-click the VPN connection and select Properties.

Step 3: Go to the Security tab, enable Allow these protocols, and check Microsoft CHAP version 2. Finally, click OK to save the changes.

Step 4: Go to the Options tab, click PPP Settings, check Enable LCP Extensions and click OK > OK.

Step 5: Restart the computer