CGNAT is the One Thing Worse Than Double NAT: What You Can Do About It

As a home lab enthusiast, you're likely no stranger to the frustration of dealing with Carrier Grade Network Address Translation, or CGNAT. This common problem can make even basic connectivity and browsing a challenge, especially when it comes to video calls, messaging apps, and peer-to-peer matchmaking in multiplayer games. In this article, we'll delve into the world of CGNAT, explore its effects on your network, and discuss the solutions available to you.

So, what is CGNAT? Simply put, it's a solution to the depletion of public-facing IPv4 addresses that puts your computer behind a double NAT situation. This means that your router has to handle Network Address Translation (NAT) not once, but twice – once for your private network and again for the ISP's virtual LAN. The result is a hardware nightmare as the routers won't communicate with each other, causing packets of data to get lost in transit.

The Effects of CGNAT

CGNAT may not seem like a major issue when it comes to basic web browsing or streaming media from your subscribed services. However, this is where the problems start to arise. Video calls, messaging apps, and peer-to-peer matchmaking in multiplayer games require both sides of the connection to be able to "see" each other at either end of the route. This means that CGNAT breaks these connections, making it impossible for you to host an email server or even get a direct public IP address.

But what about self-hosting? With CGNAT, there's no direct route back to the server when outside your network. This means that your apps can't use individual public IPs, port forwarding is not possible due to the carrier's routers not knowing where to send things, and an impossible barrier to hosting an email server.

CGNAT was initially designed as a temporary fix to fill in the gap between IPv4 and the adoption of IPv6. However, decades of network engineers, ISPs, and other business stakeholders insisting that CGNAT is the way to future-proof the internet has made it incredibly difficult to separate from the physical transport layer used to connect everything together.

The Solution: IPv6

So, what's the solution? The answer lies in IPv6 – a new version of the Internet Protocol that offers an enormous address space. With IPv6, you don't need NAT in any way, shape, or form, because the available IP address space is huge. And let's not forget that CGNAT still uses ports when addressing the shared IP space, which is not an infinite resource.

But worldwide adoption of IPv6 is slowing down, and you can't reach large chunks of the internet without IPv4. This means that we're stuck with solutions that make it workable for the end user, even if they don't address the wider problem. So, what are your options?

Solutions to CGNAT

There are several solutions available to help you overcome the effects of CGNAT:

  • VPNs: Many VPN providers enable port forwarding capabilities, which can fix the issue assuming your provider allows it.
  • Self-hosting tools like NetBird, Pangolin, and Tailscale: These tools use TURN (Relay) and STUN (Discovery) to pass packets across the internet, but this can be significantly slower and with higher latency than a direct connection.

The only way to truly fix things is to speed up the adoption of IPv6 worldwide, so that every network, server, domain, and website uses it exclusively. This means no NAT being implemented, no translation layers between IPv4 and IPv6, just IPv6 from client all the way through to the internet resource and back again.

But at this rate, it's unlikely that we'll see widespread adoption of IPv6 in our lifetime.

Conclusion

In conclusion, CGNAT is a major problem for home lab enthusiasts who self-host services. While there are solutions available to help you overcome its effects, the root cause of the issue lies in the depletion of public-facing IPv4 addresses and the slow adoption of IPv6 worldwide.

As we move forward, it's essential that we prioritize the adoption of IPv6 and work towards a future where NAT is no longer necessary. Until then, be prepared to get creative with your network setup and explore all available solutions to overcome the challenges posed by CGNAT.