I am trying to create a half life server by port forwarding through my router. It didn't work, I checked it out, and my public IP and my WAN IP were different. Then I realized I was in a carrier-grade network. I called the ISP and asked them if there was a way to do this without having to route to my router, and they said the guy is doing my router as a DMZ host. That was what I needed, requests to my public IP on any port were forwarded and forwarded to my router, and then my router only forwarded the port I was interested in, port 27015, UDP port of the half- Life server standards.
But it didn't work, I made sure that my localhost had a static IP and configured the DHCP to reserve one for me, created firewall rules to allow traffic on the 27015 port, and that I had all the correct ones I used IP addresses for my localhost, my default gateway, my pale address and my public address.
Me and the ISP guy chatted again and we decided the port was somehow closed. I quickly set up a Filezilla server (I forwarded 27015 as a listening port and a range of 11000-12000 to transfer files, both in the router and firewall rule) and asked if he wanted my home- List of my public IP and my port 27015. It worked, so everything was fine, checked with Wireshark.
Now I'm in a situation where I want this to work, but I'm not sure what's going on. The ISP type doesn't help much, and I think either the DMZ it set up doesn't allow UDP packets because filezilla uses TCP and Half-Life server uses UDP, or there is a firewall on the ISP router that UDP packets blocked or fetching this port 27015. This is not a general service.
I'm new to networking, I try to set this up as a challenge, I've learned a lot and read how to do things. Please do not hesitate to point out errors and suggest solutions. If I can't make it, I'll probably try to use ngrok to make the game server work.