🌐 The Question That Started It All
Ever wondered how your message reaches your friend, or how your search query reaches servers running in another country or even another continent?
It all happens through the Internet — but if you're a CS student or networking enthusiast, you’ve probably heard of IP addresses and routers.
- Where do IP addresses come from?
- How do ISPs manage to connect millions of people with a limited pool of addresses?
These were the exact questions I had while simulating my own ISP.
🛠️ The ISP Simulation Journey
In my project, I simulated how an ISP provides internet access using:
- DHCP for automatic IP assignment
- OSPF (Open Shortest Path First) as a routing protocol
- DORA (the DHCP handshake process)
- PPPoE for subscriber authentication
- CGNAT for address sharing
- BGP (Border Gateway Protocol) to represent ISP-to-ISP connections
One critical challenge I faced:
👉 How can so many routers and users operate on such a limited IPv4 address range without exhausting it completely?
That’s when I discovered Carrier-Grade NAT (CGNAT).
🔎 What is CGNAT?
CGNAT (Carrier-Grade NAT) is a special type of Network Address Translation used by ISPs.
- It allows thousands of users to share a single public IPv4 address.
- Internally, users get private IP addresses, but all their traffic is translated and sent through one shared public IP acquired by the ISP.
This helps ISPs deal with the IPv4 exhaustion crisis.
⚠️ The Downsides of CGNAT
While CGNAT solves IPv4 scarcity, it comes with significant trade-offs:
- ❌ Double NAT (your home router + ISP’s CGNAT)
- ❌ Port forwarding breaks → you can’t host servers from home
- ❌ DNS record issues → web servers need unique public IPs
- ❌ Inaccurate geolocation
- ❌ Networking limitations for advanced setups
So yes — CGNAT makes it harder for power users, developers, and gamers who need advanced network features.
🌍 IPv4 vs IPv6 — The Bigger Picture
- IPv4 = ~4.3 billion unique addresses (almost all exhausted)
- IPv6 = 340 undecillion addresses (basically infinite for our needs)
So why do we still use IPv4?
- Legacy systems, devices, and servers are hardcoded for IPv4.
- Transitioning the entire Internet infrastructure takes time and money.
- IPv4 addresses are even bought, sold, and traded — like digital real estate.
IPv6 adoption is growing, but IPv4 remains the Internet’s backbone — held together by solutions like CGNAT.
💡 Final Thoughts
Building my own ISP simulation taught me how much complexity hides behind something as “simple” as connecting to the Internet.
- ISPs rely on protocols like OSPF, BGP, DHCP, and PPPoE just to keep things running.
- CGNAT is a clever but messy workaround that keeps IPv4 alive.
- The future lies in IPv6, but the world still runs on IPv4 — and will, for years to come.
🤝 Over to You
Have you ever run into CGNAT issues — like broken port forwarding or server hosting problems?
Do you think ISPs should push harder for IPv6 adoption?
Let’s discuss in the comments 👇
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