Windows 11 VPN Connection - The L2TP connection attempt failed because the security layer

Question

Hi,

I am trying to connect VPN

I got this error: Windows 11 VPN Connection Error: The L2TP connection attempt failed because the security layer encountered a processing error during inital negotiations with the remote computer.

Specifications are

Edition Windows 11 Home Single Language

Version 22H2

Tried possible solutions mentioned in https://github.com/hwdsl2/setup-ipsec-vpn/blob/master/docs/clients.md#ikev1-troubleshooting
But not working. Any help would be appreciable.

Thank you!

Answer 1

Steps to Fix L2TP VPN Connection Issue on Windows 11

1. Open Command Prompt as Administrator:
   • Press Win + X and select Windows Terminal (Admin) or Command Prompt (Admin).
2. Add Registry Entries:
   • Copy and paste the following commands into the Command Prompt and press Enter after each command:

          REG ADD HKLM\SYSTEM\CurrentControlSet\Services\PolicyAgent /v AssumeUDPEncapsulationContextOnSendRule /t REG_DWORD /d 0x2 /f
          REG ADD HKLM\SYSTEM\CurrentControlSet\Services\RasMan\Parameters /v ProhibitIpSec /t REG_DWORD /d 0x0 /f
     

3. Restart Your Computer:
   • After executing the commands, restart your computer to apply the changes.

Explanation

1. AssumeUDPEncapsulationContextOnSendRule:
   • This registry entry allows IPSec to work in a NAT (Network Address Translation) environment. Setting it to 0x2 enables IPSec to traverse NAT, which is essential for many home and small office networks.
2. ProhibitIpSec:
   • This registry entry ensures that IPSec is not prohibited, allowing L2TP/IPSec VPN to function correctly.

By following these steps, you should be able to resolve the L2TP VPN connection issue on your Windows 11 system. If the problem persists, further troubleshooting may be required, such as checking network configurations or uninstalling recent updates.

Answer 2

Issue is resolved by using correct IP address and followed steps mentioned in https://github.com/hwdsl2/setup-ipsec-vpn/blob/master/docs/clients.md#windows-error-809

After correct configuration was getting error 809

Error 809: The network connection between your computer and the VPN server could not be established because the remote server is not responding. This could be because one of the network devices (e.g, firewalls, NAT, routers, etc) between your computer and the remote server is not configured to allow VPN connections. Please contact your Administrator or your service provider to determine which device may be causing the problem.

Solved by using following command

REG ADD HKLM\SYSTEM\CurrentControlSet\Services\PolicyAgent /v AssumeUDPEncapsulationContextOnSendRule /t REG_DWORD /d 0x2 /f

REG ADD HKLM\SYSTEM\CurrentControlSet\Services\RasMan\Parameters /v ProhibitIpSec /t REG_DWORD /d 0x0 /f

Answer 3

Try these steps, see if this helps:

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, select L2TP/IPSec as the type of VPN, and click Advanced Settings.

Step 4. Tick Use preshared key for authentication and click OK.