IPv4 vs IPv6: why the internet ran out of numbers

IPv4 has about 4.3 billion possible addresses. That sounded infinite in 1981, when the whole internet was a few hundred university computers. It stopped sounding infinite once every phone, doorbell, and thermostat wanted one. The last big blocks of IPv4 ran out in 2011.

The replacement, IPv6, has 340 undecillion addresses — that’s 340 followed by 36 zeros. Enough to give every grain of sand on Earth its own internet connection, several times over. It was finalized in 1998. And here we are, decades later, still running both. That gap between “fixed” and “deployed” is the interesting part of this story.

How the internet survived running out

The workaround is called NAT — network address translation — and you’re almost certainly using it right now. Your router gets one public IPv4 address, and every device in your house shares it. The router keeps a ledger of which conversation belongs to which device.

Carriers then did the same trick one level up: thousands of customers sharing a pool of public addresses. That’s called CGNAT, and it’s why your “public” IP is sometimes shared with strangers — and why you can get blocked from a site because someone else misbehaved on your shared address. NAT kept IPv4 alive, but it broke the internet’s original idea that any device could talk directly to any other. Ask anyone who’s fought port forwarding to host a game server.

What IPv6 actually changes for you

With IPv6, every device gets its own public address. No sharing, no NAT gymnastics, no buying recycled IPv4 blocks at auction — yes, that’s a real market, and prices ran north of $30 per address at the peak. Connections can be a touch faster too, since traffic skips the translation step.

The address looks different: IPv4 reads like 203.0.113.42, IPv6 like 2001:db8:85a3::8a2e:370:7334. If the tool on our homepage shows you an address with colons, you’re on IPv6 right now — roughly half of traffic to Google is these days.

Why the transition is taking forever

IPv6 isn’t backward compatible. An IPv6-only device can’t reach an IPv4-only site without a translation layer, so everyone has to run both systems — which means nobody feels urgency. NAT took the pressure off, and upgrading routers and provider gear costs money that doesn’t generate a single new sale.

My take: IPv6 will win by attrition, not by a switchover day. Mobile networks already lean on it heavily because managing NAT for millions of phones is misery. You don’t need to do anything — but if your provider offers IPv6 and your router has it disabled, turning it on is free and mildly future-proofs your setup. Just check for VPN leaks afterward, which our homepage tool will show you in one glance.