What is CGNAT and Why Should You Care?
Carrier Grade NAT explained and how it affects gaming and hosting.
The Internet ran out of addresses
The original addressing system for the internet (IPv4) allowed for about 4.3 billion unique addresses. In the 1980s, that seemed like infinity. Today, with billions of smartphones, laptops, and smart lightbulbs, we have completely run out.
Ideally, every home router would have its own unique Public IP address. But because they are scarce and expensive to buy, many newer ISPs use a technology called CGNAT (Carrier Grade Network Address Translation).
How CGNAT Works
Imagine an apartment building. Instead of every apartment having its own street door (Public IP), there is one main reception desk (The ISP’s CGNAT Gateway). All the mail for hundreds of apartments comes to that one desk, and the receptionist sorts it out and delivers it to the internal rooms.
Your router gets a “Private” IP address from the ISP, not a Public one. You share your Public IP with hundreds of other customers.
Why it (Usually) Doesn’t Matter
For outgoing traffic—you requesting a webpage, you streaming a movie—this works perfectly. The receptionist knows you asked for the movie and sends the data to you. You will not notice any difference in speed or browsing quality.
When it DOES Matter
CGNAT breaks Incoming Traffic. If someone on the internet tries to connect to you, they hit the reception desk, and the receptionist doesn’t know which apartment to send the traffic to. This causes issues for:
- Online Gaming: Consoles often report “Strict NAT” or “Double NAT.” You might struggle to host lobbies, join voice chat, or play peer-to-peer games.
- Port Forwarding: You simply cannot open ports. Security cameras, home servers, and smart home hubs that rely on direct access will fail.
- IP Bans: If one person in your “apartment block” (sharing your IP) gets banned from a website or game for cheating, you might get banned too because you have the same address.
The Solution
If you are a gamer or tech enthusiast, look for a CityFibre ISP that offers a true Public IPv4 address (either dynamic or static) or fully supports IPv6 (the new internet standard with infinite addresses). Most “Gaming” branded ISPs guarantee no CGNAT.