How to Fix ‘The L2TP Connection Attempt Failed’ Processing Error

The "L2TP Connection Attempt Failed" error normally does not allow the VPN to connect and flashes a security-related error message. Because of this, L2TP was unable to establish a connection with the distant server. If you face this issue, it's because of the Windows 10 latest update that broke your VPN encrypted connection.

There was a processing error in the security layer of Windows 10. Due to this, the L2TP connection attempt failed.

Others could be the use of incorrect pre-shared keys or other VPN configuration issues and network issues preventing UDP ports required for VPN communication.

Now that you have an idea about what the problem is, we can move on to the solutions. To keep disagreements at bay, just do what's asked.

1. Open MS-CHAP v2 API.

Since it modernizes the login procedure of the VPN, it is essential that MS-CHAP v2 be upgraded to. Compared to its predecessor, MS-CHAP v2 is very much secure. It fortifies the relationship by allowing authentication on both the client and the server's end. That helps evade security breaches that may get the connection terminated.

Immediately after adding the VPN connection, make sure you put the correct credentials of the VPN server.

From this dialogue, once you have added the connection, it will be shown in the list of network adapters.

Open the Run dialog by pressing Windows + R.

You can open Network Adapter Settings by typing ncpa.cpl and pressing Enter. - Hit Enter after typing in: ncpa.cpl

While you are inside the VPN connection right-click on it and select Properties. - The VPN properties accessed through right click menu

Click the Security tab, check the box labeled Allow These Protocols. Check Allow these Protocols box

When you get a window asking for protocol selection, click the box in front of Microsoft-CHAP Version 2 and then click OK.Selecting Microsoft-CHAP Version 2

Try connecting to the VPN and see if the issue is resolved.

2. Enable LCP Extensions

To get rid of VPN connection problems, including that of L2TP error, one can use the adjustment of the parameters of Link Control Protocol. These can be done, especially, by enabling LCP extensions. Using such add-ons lets you make a more complex and versatile connection between your PC and a VPN server. They, for the sake of stability in VPN connectivity, offer advanced error detection and alternatives in order to establish the network. These extensions can be enabled to fix those connection problems which don't allow the L2TP tunnel to work correctly.

Press Windows + R to bring up the Run dialog. Run Initialization Prompt

Type in ncpa.cpl and press Enter to open up Network Adapter Settings.

While inside the VPN connection, right-click on it, and access its Properties through the right-click menu.

Access VPN properties through right click menu

From Options, select PPP Settings.

Check the box, Enable LCP Extensions, and click OK to set your preference.

Try reconnecting to the VPN to see if the issue still occurs.

We trust these steps will help facilitate better resolution of the processing error "The L2TP connection attempt failed". And with that said, good luck.