VPN Connection (Fritzbox) works for Android Client but not for Windows and Ubuntu

Question

I use a Fritzbox 7530 Router in my home network as a VPN server. The VPN is configured as "IPSec Xauth PSK" with following settings: server name, IPSecID, IPSec shared key, user name and password. The connection works just fine using an Android Device with a preinstalled VPN client but I cannot do the same using Windows 10 Pro or Ubuntu 20. In both configurations the connection cannot be established at all.

Android phone settings (VPN works just fine):

Windows 10 Pro settings:

Ubuntu 20 settings:

I guess if it works fine with Android it has to work with any system which fulfils the requirments. Do you have an experience with such problems?

Answer 1

XAUTH is not supported by all VPN clients, and this is by design.

The reason for this is found in the article VPN server for remote clients using IKEv1 XAUTH with PSK

Using XAUTH PSK is the least secure mode of running IKE/IPsec. The reason is that everyone in the "group" has to know the PreShared Key (called PSK or secret). Even if you require further authentication, such as a username and password, someone that knows the PSK can launch a man-in-the-middle attack pretending to be the VPN server, If the client connects to the rogue server, it will tell the attacker their username and password.

The article lists clients that do support this unsafe security protocol :

Supported clients:

• All Apple iphones, ipads
• Mac OSX
• Android
• Linux with NetworkManager or commandline
• Microsoft Windows using a third party client such as the Cisco client, or the free Shrew Soft client

You could use one of the above clients, or choose another VPN that doesn't use XAUTH PSK.

Answer 2

Unfortunately this is just not possible with Windows 10. I‘ve tried for ages but there is something with the protocols the Fritz!Box expects.

There is however a programme for windows made by AVM that allows you to generate a setup file for the VPN Client Fritz!Fernzugang. For further instructions see here (unfortunately in German).

Answer 3

Unfortunately it's really impossible to connect to the "IPSec Xauth PSK" from Windows how @harrymc noticed in his answer. I could solve the problem by creating a virtual machine with Android following this video How to Install Android on VirtualBox (2021).

As Android supports this kind of VPN connections I could do it the same way I did on my phone and it works like a charm. I know this is not the best way to solve the problem, but I'll stick to it for now.

Please fill free to post other ideas if you have some.

P.S.

A few words on what I learned from this experience: I did not know that "IPSec Xauth PSK" and "L2TP IPSec PSK" a different methods and are not compatible to each other.

Here you can see the VPN kinds supported by Android by default: