Hello,
I have been running OPNsense on a dedicated machine for some time, and all my devices and services are behind it. I'm still quite new to networking, so I have mostly configured the default settings and followed a few online guides for specific tasks, but nothing particularly advanced.
Recently, I wanted to play a game with some friends and host a server using my existing infrastructure. The problem is that my OPNsense firewall is behind my ISP's router, which means I have a double NAT setup.
I did not perform any special configuration when I installed OPNsense. I simply connected the OPNsense WAN interface to one of the ISP router's Ethernet ports, and that was it. All my experiments and services run within the OPNsense network, and until now I never needed anything different. However, as soon as I needed external access to something inside my network, I started running into problems.
Specifically, I need help configuring port forwarding. I need to forward port 50505 (UDP) to a specific IP address within my OPNsense network (something like 192.168.1.x).
I understand that I also need to configure port forwarding on the ISP router, and I have no problem doing that. In fact, I tested the same service directly behind the ISP router without OPNsense, and it worked correctly.
However, for some reason, none of the guides I found online, nor the instructions provided by AI tools (Google Search and Microsoft Copilot), have worked in my case. Their explanations seem logical, but no matter what I try, I cannot get it working. That is why I am here looking for a solution specific to my setup.
This is my network infrastructure from the Internet to the service, to provide a complete overview:
Internet → ISP Router → OPNsense WAN* → OPNsense LAN → Server (local IP) running a service on UDP port 50505
* I am currently in the process of implementing High Availability (HA) for my OPNsense setup. Right now, I have two IP addresses assigned by the ISP router, both static: one physical IP and one virtual IP. The HA configuration is not complete yet because I do not have the second device ready. A third IP address has also been reserved for the future setup.
I am not sure whether this unfinished HA configuration could be causing the problem or not, which is one of the reasons I am asking for help.
My current port-forwarding configuration for the double NAT setup is the following:
ISP Router → Forward UDP 50505 to → Virtual IP used by the OPNsense WAN HA configuration → Forward UDP 50505 to → Server with a static IP running the service on UDP 50505
I will attach an screenshot of the relevant configurations that may help explain my setup and show what has already been configured (my layout is in Spanish :P).
If you need any additional information or context, please let me know and I will be happy to provide it.
Thank you.