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Port Forwarding Behind CGNAT

#webdev #pinggy #devops #tutorial

Ever tried hosting a game server or accessing your home computer remotely, only to realize nothing works, no matter how many YouTube tutorials you follow? You tweak router settings, open ports, maybe even reboot your modem a few times, still no luck.

Welcome to the world of CGNAT.
It's that invisible layer your ISP doesn’t mention but quietly blocks you from doing all the cool stuff-like sharing your Minecraft world, running a personal website, or debugging APIs from your local server.

But here’s the good news:
You don’t need to be a network engineer to fix this. You just need to understand what’s going on behind the scenes—and how to sneak past CGNAT with a trick called reverse tunneling.

Do You Even Need Port Forwarding?

Before diving into commands and router settings, ask yourself a simple question:
“Do I need my device or service to be accessible from the internet?”

If you’re doing things like:

  • Hosting multiplayer game servers (like Minecraft or CS2)
  • Running a local website that you want to share online
  • Using SSH to connect to your home computer remotely
  • Streaming media from a server at home
  • Managing IoT gadgets from a distance

…then yes, port forwarding is for you.

If not, if you're just browsing, streaming Netflix, or working locally, you can skip all of this.

So What Is Port Forwarding?

Imagine your home network is a gated community. The router is the gatekeeper. Normally, it doesn’t let anyone in unless they’re expected.
Port forwarding is like telling the guard, “Hey, if someone knocks on this gate, let them through to this house.”

More technically, it maps a specific port on your public IP to a local device inside your network. So when someone hits your public IP at port 8080, your router knows to forward that request to, say, your laptop running a web server on port 8080.

Setting Up Port Forwarding the Traditional Way

If you’re on a regular home broadband connection (without CGNAT), the steps are pretty standard:

  1. Log into your router
    Open a browser and go to 192.168.1.1 or 192.168.0.1. You'll need your admin credentials.

  2. Find the Port Forwarding section
    Look for terms like “Virtual Server”, “NAT”, or “Gaming.”

  3. Create a rule
    You'll enter:

  • A service name (for your reference)
  • The internal IP of your device (like 192.168.1.100)
  • The port you want to open (e.g., 22 for SSH or 8080 for web servers)
  • The protocol (usually TCP or UDP)
  1. Save and reboot (if needed)

Voilà! Now people can access that specific service, if your ISP hasn’t locked things down behind the scenes.

The CGNAT Problem

Here’s where it gets messy.

CGNAT (Carrier-Grade NAT) is something many ISPs now use to save on IPv4 addresses. It means you’re sharing a public IP address with a bunch of other customers. This makes regular port forwarding impossible—because your router isn't the one directly connected to the internet.

How to Know If You're Behind CGNAT:

  • Log into your router and check the WAN IP address.
  • If it starts with 10.x.x.x, 100.64.x.x, 172.16.x.x, or 192.168.x.x, it’s a private IP.
  • That means CGNAT is in play.

port

The impact?

  • No direct inbound connections
  • Port forwarding rules won’t do anything
  • UPnP won’t help
  • Game servers and remote services won’t be reachable

A Workaround That Actually Works: Tunneling with Pinggy

Instead of trying to fight CGNAT head-on, there's a different approach: reverse tunneling. That’s where tools like Pinggy come in.

The idea? Your device creates an outgoing connection (which CGNAT allows), and Pinggy routes the traffic back through that secure tunnel.

Quick Example for HTTP: 

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

  • Connects your local port 8080 (e.g., for a web server)
  • Sends it through Pinggy’s server
  • Gives you a public URL you can share or access from anywhere

Example for SSH (Remote Terminal Access): 

ssh -p 443 -o StrictHostKeyChecking=no -o ServerAliveInterval=30 -R0:localhost:22 tcp@a.pinggy.io
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Now you can SSH into your home computer using the public address provided by Pinggy.

It’s fast. It’s simple. And best of all, no router or ISP permission required.

Extra Features

Pinggy also lets you:

  • Link a custom domain to your tunnel
  • Add password protection or IP whitelists
  • Inspect traffic in real-time with a web debugger
  • Create multiple tunnels from a dashboard

These aren’t essential, but they’re handy if you want to get fancy.

Don’t Disable Your Firewall

Some folks, in frustration, consider turning off their firewall or enabling DMZ (which exposes an entire device to the internet).

Please don’t.

That’s like unlocking your front door, opening all the windows, and putting up a sign that says “Come on in.”

Port forwarding, done right, gives you precise control:

  • Only the ports you want are exposed
  • The rest of your devices stay protected
  • You can turn it off anytime

Conclusion

Port forwarding isn’t dead, it’s just changing. If you’re behind a traditional router, the old way still works fine. But if CGNAT has locked you out, tools like Pinggy offer a smart workaround that doesn’t require wrestling with your ISP or renting expensive cloud servers.

Whether you're building something cool, testing software, gaming with friends, or just trying to access your stuff remotely, it’s never been easier to make it happen.

References:

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

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