Windows 10: L2TP VPN will not authenticate/communicate

I have a client using a VPN we established through a Unifi Security Gateway. This client is no longer able to connect to our VPN. I have checked that all the settings are correct as far as log in creds and the PSK. I have tried enabling MS CHAP v2 and it was already enabled. I have tried uninstalling and reinstalling network adapters in Device Manager. I have tried to manually recreate the VPN in Windows. I have tried about every suggestion I can find online for the last 4 hours.


The most valuable point of data I got from my troubleshooting is that when I manually change the VPN configuration to not include the username and password, and uncheck "remember me", and then try to connect, I can't even get the authentication window to pop up. After enough time, I get the error "l2tp connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer."


Is there something I'm missing here?

:)

 

Error: 788, when connecting to L2TP VPN

Hi there, recently I got this error when connecting to "L2TP/IPSec with certificate" VPN. I'm not sure what cause this.

I have already follow some of this steps with no luck :

• Adding AssumeUDPEncapsulationContextOnSendRule
• Restarting both IKE and IPSec services
• Allowing both CHAP and MS-CHAP v2
• Reset network connection
• Connect to different provider
• Re-adding VPN settings

There also little bit information can be found in the event viewer :

CoId={AEE0E2A8-34DF-41BB-B5F0-0458EFD41751}: The user xxx\xxx has started dialing a VPN connection using a per-user connection profile named yes. The connection settings are:

Dial-in User = *\

VpnStrategy = L2TP

DataEncryption = Requested

PrerequisiteEntry =

AutoLogon = No

UseRasCredentials = Yes

Authentication Type = PAP

Ipv4DefaultGateway = Yes

Ipv4AddressAssignment = By Server

Ipv4DNSServerAssignment = By Server

Ipv6DefaultGateway = Yes

Ipv6AddressAssignment = By Server

Ipv6DNSServerAssignment = By Server

IpDnsFlags =

IpNBTEnabled = Yes

UseFlags = Private Connection

ConnectOnWinlogon = No

IPsec authentication for L2TP = Machine certificate.

CoId={AEE0E2A8-34DF-41BB-B5F0-0458EFD41751}: The user xxx\xxx is trying to establish a link to the Remote Access Server for the connection named yes using the following device:

Server address/Phone Number = xxx.xxx.xxx.xxx

Device = WAN Miniport (L2TP)

Port = VPN3-1

MediaType = VPN.

CoId={AEE0E2A8-34DF-41BB-B5F0-0458EFD41751}: The user xxx\xxx dialed a connection named yes which has failed. The error code returned on failure is 788.

***Original title: VPN Error 788***

 

L2TP Protocol/Authentication

Please help as I am going mad!

I have a user who had a L2TP VPN, with a preshared key, confirgured on their machine which was working fine. It started throwing up a security error and failing to connect. When I checked the settings the protocol settings had been removed so I switched
it back to encrypted connection only, PAP protocol and clicked save. I then went to the VPN settings and noticed that the authentication had changed from Username and password to general. Now if I go in to the VPN advanced settings and click edit and change
the authentication back to username and password it then removes the protocol settings in VPN adapter settings. If I leave the authentication it fails to connect.

I have tried with a windows 7 machine using all of the same credentials and it connects to the VPN no problem?

Win10 Pro

V: 1703

Build: 15063.608

 

Error: 788, when connecting to L2TP VPN

Hi Syafii,



Thank you for writing to Microsoft Community Forums.



I understand that you are facing issues with connecting to L2TP VPN on your PC, and I certainly appreciate your efforts in trying to resolve the issue by following certain troubleshooting steps.



However, we do have a dedicated forum where you should be able to find support for the issue that you are facing. Let me help you in pointing towards the right direction, I would suggest you to post your query on

TechNet forums, where we have expertise and support professionals who are well equipped with the knowledge on L2TP VPN to assist you with your query.



Regards,

Prakhar Khare

Microsoft Community – Moderator