Windows Built In VPN


New Member
Hi Forum,

I have setup a L2TP/IPSec VPN using a synology NAS and Widows 11 client.

I have successfully setup 1 laptop and it connects without an issue. My seconed laptop tho is having issues

event view has error 789
"the user system dialed a connection named VPN name which failed. the error code returned on failure is 789"

I have tried reinstalling all network devices Wi-Fi and Mini port
I have tried adding registry key AssumeUDPEncapsulationContextOnSendRule value 2 + ProhibitIpSec value 0
I have ensured all settings are fine LCP Extensions on, MS-CHAP v2 on,
I have tried reinstalling Windows OS
I have opened ports 500,1701,4500 in firewall for UDP
I have ensured IPSec Policy Agent service is running
I have ensured IKE and AuthIP IPSec service is running

Anyone any advice.
Last edited:

Error code 789 typically indicates a problem with the L2TP/IPSec connection. Here are a few troubleshooting steps you can try to resolve the issue:

1. Verify the VPN server settings: Double-check the L2TP/IPSec VPN server settings on your Synology NAS. Make sure the server address, authentication methods, and shared secret match the settings on your Windows 11 client.

2. Check firewall settings: Ensure that the necessary ports and protocols are allowed through both the Windows Firewall and any other firewall software or hardware that might be blocking the VPN connection. The required ports for L2TP/IPSec are UDP 500, UDP 4500, and ESP (IP protocol 50).

3. Disable antivirus and security software temporarily: Some antivirus or security software might interfere with VPN connections. Try disabling them temporarily and see if the issue persists. If the VPN connection works after disabling the software, you may need to add an exception or configure the software to allow VPN traffic.

4. Update network drivers on the problematic laptop: Outdated or incorrect network drivers can cause connectivity issues. Update the network drivers on the laptop experiencing the problem by visiting the manufacturer's website or using a driver update tool.

5. Restart networking devices: Power cycle your router, modem, and NAS. Sometimes, a simple restart can resolve connectivity problems.

6. Enable logging on the VPN server: Enable logging on your Synology NAS VPN server to get more detailed error information. Check the VPN server logs or event logs for any possible clues about the connection failure.

7. Test from a different network: If possible, try connecting to the VPN from a different network, such as a mobile hotspot or a friend's Wi-Fi. This will help determine if the problem is specific to your network or if it persists across different networks.

These are some general troubleshooting steps to help identify and resolve the issue with your L2TP/IPSec VPN setup. If none of these solutions work, you may need to consult the documentation or support resources provided by Synology or seek assistance from their forums or customer support.

I hope this helps! Let me know if you have any further questions.