Registry fix for Windows 10 L2TP VPN

If someone is getting the following error in Windows when trying to establish a L2TP/IPSec connection they likely need to edit their registry:

There are several ways to accomplish this. You can use a GUI to create the required entry, or there is a command you can enter in an elevated CMD prompt.

Using the Registry Editor GUI

1. Launch Registry Editor with admin rights.
2. Go to:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\PolicyAgent
3. Open the Edit menu > New submenu and click DWORD (32-bit) Value.
4. Paste AssumeUDPEncapsulationContextOnSendRule as the value name.
5. Right-click AssumeUDPEncapsulationContextOnSendRule and choose Modify.
6. At Value data, type 2.
7. Set Base to Hexadecimal.
8. Click OK.
9. Go to:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan
10. Open the Edit menu > New submenu and click DWORD (32-bit) Value.
11. Paste ProhibitIpSec as the value name.
12. Right-click ProhibitIpSec and choose Modify.
13. At Value data, type 0.
14. Set Base to Hexadecimal.
15. Click OK.
16. Restart the PC.

 

Using CMD

1. Launch Command Prompt as admin.
2. Paste the following (these are all single lines!):
   REG ADD HKLM\SYSTEM\CurrentControlSet\Services\PolicyAgent /v AssumeUDPEncapsulationContextOnSendRule /t REG_DWORD /d 0x2 /f
3. Once the operation completes successfully, also paste:
   REG ADD HKLM\SYSTEM\CurrentControlSet\Services\RasMan\Parameters /v ProhibitIpSec /t REG_DWORD /d 0x0 /f
4. Restart the PC.