Every device on the internet needs an IP address — a number that says "this is me, send the data here." For decades that number looked like 192.0.2.1. But the internet grew far bigger than its designers ever imagined, and we literally ran out of addresses. Enter IPv6.
If you've seen a weird long address full of colons and hex and wondered what it was, this is the explainer. No deep networking required.
What an IP address is for
When data travels the internet, it needs a destination — like a postal address for packets. That's the IP address. DNS turns a name like example.com into one of these addresses (via A and AAAA records), and the packets find their way there.
There are two versions of these addresses in use today: the old IPv4 and the newer IPv6.
IPv4: the original (and we ran out)
IPv4 addresses are 32-bit, written as four numbers: 192.0.2.1. That's the format you've seen your whole life.
The problem: 32 bits allows about 4.3 billion unique addresses. That sounded like plenty in the 1980s. Then came smartphones, laptops, smart TVs, doorbells, fridges… and 4.3 billion stopped being nearly enough. The world has been out of fresh IPv4 addresses for years, propped up by clever workarounds (like NAT, where many devices share one public address).
IPv6: effectively endless
IPv6 addresses are 128-bit, written as groups of hex separated by colons: 2001:db8::1. The longer format unlocks a number so large it's hard to grasp — about 340 undecillion (that's 3.4 × 10³⁸) addresses. Enough to give every grain of sand on Earth billions of its own.
It's not just more room; IPv6 also brings some efficiency and security improvements baked in. But the headline is simple: we'll never run out.
Side by side
| IPv4 | IPv6 | |
|---|---|---|
| Size | 32-bit | 128-bit |
| Looks like | 192.0.2.1 | 2001:db8::1 |
| Total addresses | ~4.3 billion | ~340 undecillion |
| Status | Exhausted (workarounds in use) | The long-term future |
| Separator | Dots | Colons |
How the transition works
You can't flip the whole internet overnight, so most of the world runs dual-stack: devices and services speak both IPv4 and IPv6 at once. A visitor connects over whichever they support, and adoption of IPv6 keeps climbing year over year. The two will coexist for a long time yet.
Do you actually need to care?
For most people building websites and apps: not urgently, but increasingly yes.
- Your hosting and CDN likely handle IPv6 for you already.
- Some users — especially on mobile networks — connect over IPv6, so supporting it (an AAAA record alongside your A record) means you're reachable for everyone.
- If you run infrastructure, IPv6 is steadily moving from "nice to have" to "expected."
Practical takeaway: make sure your domain has both an A (IPv4) and AAAA (IPv6) record if your host supports it, so no visitor is left out.
A monitoring note
Because both versions are in play, which one you check matters. A service can be perfectly reachable over IPv4 but misconfigured on IPv6 (or vice-versa) — so checks default to IPv4, with the option to test IPv6 explicitly where it's supported. If you've added an AAAA record, it's worth confirming it actually works.
The bottom line
| In one line | |
|---|---|
| IPv4 | The original 32-bit addresses — and we ran out. |
| IPv6 | 128-bit addresses — effectively unlimited. |
| Now | Both run side by side (dual-stack). |
| You | Support both (A + AAAA) so everyone can reach you. |
IPv6 isn't exotic — it's just the internet making room to keep growing. You rarely have to think about it directly, but a quick check that your domain works over both versions means you're future-proof and reachable for every visitor.
Inspect a domain's A/AAAA records with the free DNS lookup, and learn the records in DNS record types explained.