The Great Port Forwarding Escape: Beating CGNAT

Ever get frustrated trying to host a game or share a project with a friend? It's a common problem, and it usually comes down to your router.

Think of your router as a security guard for your home network. By default, that guard blocks all outside traffic. This is a good thing; it keeps you safe. But sometimes, you need to let a specific type of traffic in, like for a Minecraft server.

That's where port forwarding comes in. It's like giving the guard a specific instruction: "When someone knocks for Minecraft on port 25565, let them through to my gaming PC."

Port Forwarding 101

Setting up port forwarding on a normal router is pretty simple:

1. Log in to your router's settings page (usually at an address like 192.168.1.1).

2. Find the "Port Forwarding" section.

3. Create a new rule. You'll need to tell it which port to open and which device on your network to send the traffic to.

This works great for most people. But what if it doesn't work for you?

The CGNAT Problem

Many internet providers, especially for mobile and newer connections, use something called CGNAT (Carrier-Grade Network Address Translation).

With CGNAT, you don't get your unique internet address. Instead, you share one with a bunch of other people. It's like living in an apartment building where everyone has the same mailbox number. No one can send you a letter directly because they don't know which apartment you're in.

This means you can't use regular port forwarding. Your router can't open a port if the traffic is blocked before it even gets to your home.

The Easy Fix: Reverse Tunneling

So, how do you get around CGNAT? With a method called reverse tunneling.

Instead of trying to get outside traffic in, you send traffic out. You run a command that creates a secure connection from your computer to a third-party service like Pinggy. This service then gives you a public link.

When someone visits that link, the service sends the traffic back through the connection you already made, right to your computer. It’s a clever way to get your local server online without needing to open any ports on your router.

For example, if you want to share a website running on port 8080, you just type this in your terminal:

ssh -p 443 -R0:localhost:8080 free.pinggy.io

This command makes a secure tunnel and gives you a public URL to share.

Some people suggest disabling your firewall or using something called a "DMZ" to fix these issues. Don't do this. It's like leaving all your doors and windows unlocked. It exposes your entire network and is a major security risk.

Port forwarding and reverse tunneling are much safer because they only open a specific door for a specific purpose, keeping the rest of your home network secure.

References:

1. How to Set Up Port Forwarding - Even Behind CGNAT

2. Multiple Port Forwarding