Port forwarding to ISP router

Hi I’m a beginner here so thanks in advance!

I bought a Flint (GL-AX1800) and Beryl to travel remotely.
I’ve connected my Flint to my ISP router so that when I travel, I’ll connect via ethernet to Beryl which will connect to my home Flint.
I’m having difficulty port forwarding and understanding to what router I need to port forward to…if that makes sense. I have my static IP address of my ISP router but do I need to buy a static one for my Flint router?
Any help/insight would be useful.
Thanks again!

Because You have only one IPv4 address, every system from the Internet can only reach your ISP router.
But you can define in your router ‘if someone knocks on port 51820/UDP, forward it to device’. All traffic to this port will go to the device.

51820/UDP is the default for wireguard. If you are using another service, you’ll need to change the port and maybe the protocol (UDP or TCP). is an example IP address of your Flint. You need to put your own.

Your described setup:
Flint - ISP - Internet - Beryl

It could make sense, but it really depends on what you want to archive. And where the other devices are connected.

Your ISP Router are not allowed to use Network.
I recommend to setup a static DHCP lease in your ISP router for your Flint
Your ISP Router cor two addresses:

  • Internal: (for example)
  • External: (Internet IPv4)

Your Flint will get two addresses:

  • Internal:
  • External: (for Example, either fixed or set by ISP Router DHCP)

The configuration in your ISP router is very different from device to device.

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Hi, thank you for taking the time to answer!
Let me see if I’m understanding correctly.

My intended set up was work computer - ethernet - Beryl (travel) ----- flint - ethernet - ISP - internet
Would this make sense? So I would have to port forward my Beryl to Flint but then I would also have to port forward Flint to my ISP…?

And to port forward let’s say wireguard (using mullvad), do I need to install openwrt on my routers?

Thanks again for your advice!!

I do think you already got it half the way.

work computer - beryl — some kind of connection (WAN, hotel WLAN, tethering, USB modem, …), here begins the internet, stop.

The Flint cant be before the ISP. This is a whole other side.

Than there is either the Flint as modem or the ISP modem, depends on your setup and what is provided by your ISP. Let’s assume you go online by your providers Router with modem.

Internet - Some outlet on the wall (fiber, DSL, ISDN, …) - ISPs router - Flint - (Multiple devices in your Home Network)

You should not need any portforwarding, because mullvad is the entry. Your clients will ask mullvad, if they are allowed to access. And as you have no access to their infrastructure, it is enough to trust them to handle their ports.

WireGuard and OpenVPN are two different solutions for the same goal. Either you are using WireGuard or you are using OpenVPN. But on all ends the same, they are not compatible. I don’t know what solution mullvad is providing, since I am not using an external endpoint.

The whole Picture:

“Work Comp.” LAN-ethernet-LAN “Beryl” (WAN/WLAN/Tethering)-internet-WAN “ISP router” LAN-ethernet-WAN “Flint” LAN/WLAN-(multiple clients)

Please make sure either the Beryl or the Flint will change the LAN IP. If both have as Network, the routing won’t work.


Wow, thank you for taking the time to break this down for me!
Let me try this set up now that I understand it a bit better and I’ll let you know how things go!!