Simple Concept behind port forward in NAT network

I think most of the household internet uses the NAT network. That is within the household, every device is having a unique private IPv4. Then many households are sharing one public IPv4. Suppose I set up a web server on local port 80 and then set the port forward from the public IPv4 port 80 to my local device. That means my web server is occupying the public IPv4's port 80 and other households cannot port-forward the public IPv4 port 80 to their local device? Is my understanding correct?

Thanks!

Solution 1:

Then many households are sharing one public IPv4.

This is called "Carrier Grade NAT" (CGNAT) and is different from normal NAT. In normal NAT, each household gets 1 public IP. In CGNAT, multiple households will be behind 1 public IP.

In a normal NAT situation, you can setup port forwarding rules on your router, and your router will follow them - it can do this because there's no further NAT between you and the carrier.

In a CGNAT situation, your ISP has to setup port forwarding rules on their carrier-grade router to get what you want to do to work (and they probably won't--they may sell you a static IP though). You can setup port forwarding on your own router but nothing's going to happen because the ISPs NAT is in front of you.