I have set-up a VPN server running OpenVPN on my Linux Server (Unbuntu 20.04) and would like to connect remotely with the VPN client from a GL-AXT1800. I could not find a clear description on how to do this on my documentation. Also since my public IP is public, I am looking to see how DynDNS helps. Anyone with that experience willing to share some wisdom?
The Linux Server needs to be accessible from the internet. Usually that means there will be a modem and router between it and the internet. That router needs to have the public IP, and you need to set it up to forward port 1194 traffic to the linux server’s internal IP. Now, the router’s public IP could be truly static, and never changing, in which case you are done. But if it might change from time to time to a different public IP, then you want a dynamic dns service so you can have your openvpn client connect to a name, not an IP number, and for that name to resolve to whatever the IP is then. DynDNS and other similar dynamic dns services do that by periodically seeing what their IP is, and then sending that out to all the dns servers that your name now resolves to whatever the IP is.
So your client is configured to reach your dynamic name ip on port 1194. That traffic is forwarded by the router to your Linux server, and your client makes the connection to the server.
The second part is your client configuration. Usually that can be exported from the OpenVPN server, with a certificate and user/password combo; you import that configuration to the VPN client on the AXT1800.
Setting up a server on linux is pretty intricate unless you are using Access Server or the pivpn.io scripts. In fact, I don’t know how, but if you have done the hard work to get a server set up you can probably find instructions on Youtube or something for the export.
To be honest, I’d buy another GL router for the server side, or switch out the router you have for one that supports OpenVPN/Wireguard connections.