VPN error code - The L2TP connection attempt failed because the security layer encountered a processing error...

Question

Hi,

We've got some really flaky behavior with the native VPN software connecting to a Draytek Vigor series router (actually different models too). The error we get is 'The L2TP connection attempt failed because the security layer encountered a processing error during the initial negotiations with the remote computer'.

The thing is, it works perfectly on one Windows 11 computer, and fails on at least five other Windows 11 and 10 computers, some on the same LAN and on a different network altogether. I experienced this same flaky behavior at another client site, with one computer successfully connecting (coincidentally, it now can't at a separate site) and others not being able to connect with the same error. This is not an update issue, neither is it the uninstall and reinstall miniport solution. There's no rhyme or reason to it. Any ideas?

***moved from Windows / Windows 11 / Internet and connectivity***

Answer 1

Hello,

Based on the information you provided, I suggest you do the following to see if the problem can be solved:

1. Press win+r to open the run box, enter regedit to open the registry
2. Find HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Rasman\Parameters and change the value of AllowL2TPweakcryphto to 1.
3. Restart the computer

NOTE: It is recommended to back up the registry before modifying it.

How to back up and restore the registry in Windows - Microsoft Support

Best regards

Zunhui

Answer 2

Hi,

After searching on an error I was getting in the event in my application logs, Event 20227, RasClient - 'The user DOMAIN\username dialed a connection named <VPN connection name> which has failed. The error code returned on failure is 789', I found a forum post where the users had the same flaky behavior. A poster said that if you have a pre-shared key with a special character at the end, it can cause this behavior. We did have a special character on the end. As soon as I changed it, the VPNs all started working!

Answer 3

Hi Robert Harris8,

Thank you for your reply.

I'm glad you found a solution that works for you.

Thank you very much for your support of Microsoft products, and thank you very much for your selfless sharing.

Your sharing can expand the perspective of thinking for me and other users, and promote the continuous development of the community.

If you encounter problems in the subsequent use of Microsoft products, you are welcome to post in the community for consultation at any time.

Best regards

Zunhui