Hard to come up with a subject for this that encapsulates the problem…
We are running an L2TP server on our router. It is used to access the management VLAN of our network. Our Mac and Windows devices connect to it just fine. Once connected, those clients can access all devices in our management VLAN with no issues and they can also access the Internet through that L2TP connection. Works perfectly.
Now, you connect an Android device with the built in VPN client to the router. It connects. I can access any http device on our management VLAN but when I try to access an HTTPS client, it fails. All our devices use self signed SSL certs. Once I click on the “proceed anyway” link in the browser on the Android device, the following page never loads. We can never get the log-in page for our devices to load on Android when connected via L2TP. If we take that same Android device and connect it to a WiFi AP that serves IPs from the management VLAN, everything functions fine.
So, it is something with the L2TP server connection on the Mikrotik that allows Mac and Windows clients to connect and work just fine but Android devices can not access HTTPS pages on our network (at least with self signed certs - we don’t have any commercially signed certs).
I’m not even sure where to start looking to solve this… We have the same behavior on 3 Mikrotik routers so it is clearly a configuration issue of some kind but I’m very confused why some platforms work and others do not.