A router NAT CGNAT setup can make your home internet work perfectly for browsing, streaming, video calls, and most online games, while quietly preventing anything on your network from accepting connections from the internet. The usual clue is frustrating: you configure port forwarding correctly, test the port from outside your network, and it still appears closed.<\/p>\n
The reason is often that your router does not actually control the public IPv4 address. Your internet service provider does. When that happens, port forwarding rules on your router cannot reach your gaming server, security camera, NAS, remote desktop host, or other device from the public internet.<\/p>\n
Network Address Translation, usually called NAT, lets several devices on a local network share one public IPv4 address<\/a>. Your router assigns private addresses to devices inside your home, commonly addresses such as `192.168.1.25` or `10.0.0.14`. These private addresses work only within a local network and are not directly routable across the public internet.<\/p>\n Think of the public IP address as the street address for your house and private IP addresses as room numbers inside it. Your router receives traffic sent to the street address and uses NAT rules to deliver replies to the correct device. For outgoing traffic, this happens automatically. When your laptop opens a website, the router records the connection and knows where to send the website’s response.<\/p>\n Incoming traffic is different. If someone on the internet tries to reach your network first, the router needs instructions. Port forwarding provides those instructions. A rule can tell the router that traffic arriving on a specific port, such as TCP port 25565 for a game server, should go to a particular device on your network.<\/p>\n Carrier-Grade NAT, or CGNAT, adds another NAT layer at the ISP. Instead of assigning a unique public IPv4 address to every customer, the ISP assigns customers shared address space and translates their traffic through a pool of public IPv4 addresses. This helps providers conserve scarce IPv4 addresses, but it changes who controls inbound traffic.<\/p>\n With CGNAT, your router has a WAN address, but that address may not be publicly reachable. Your ISP’s CGNAT equipment sits between your router and the public internet. A port forwarding rule can pass traffic through your local router, but it cannot create a matching rule on the ISP’s equipment.<\/p>\nHow to tell whether your router NAT uses CGNAT<\/h2>\n