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April 27, 2025

L2TP/IPSec Issues within Windows 10/11

I’ve been experiencing persistent issues establishing a functional L2TP/IPSec VPN connection at home. After thorough research, I discovered that modifying the Windows registry was necessary to enable proper operation.

  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:

PowerShell

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
  1. 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.