[NEBULA] How to make a VPN connection from my Android phone to the NSG?

Hi All,

On VPN I'm a newbie (dev background). The NSG is behind coax cable internet (as the NSG has no coax I can't directly give it internet. I suspect I need to open up some ports, and configure the VLAN it can access, and probably create a user account to access it.

I tried various settings using the L2TP protocol, but checking all combinations is taking for ever. Which ports do I need to open for this (500, 4500, ??)?

And on my Android 9/pie phone (S9+) there are also settings related to the config of the protocol I can't match with the custom L2TP settings in the NSG. On Android I see: IPSec PSK, IPSec RSA, IPSec Hybrid, Xauth, …)

I'm probably overlooking some obvious checkbox or so, can someone help?