IPv4 vs IPv6

Acutis · plain-English network help · updated June 2026

IPv4 vs IPv6, in plain English

IPv4 and IPv6 are two versions of the addressing system that gives every device on the internet a unique number. IPv4 is the original, familiar format that ran the internet for decades. IPv6 is the newer, much larger format built to fix one big problem: the world ran out of IPv4 addresses. They do the same job — labeling devices so data reaches the right place — but they look different and work side by side.

For most people, the practical answer is simple: you don't have to choose, and you usually won't notice which one you're using. But knowing the difference clears up a lot of confusion when you see an address that doesn't look the way you expect.

Why IPv6 had to exist: address exhaustion

IPv4 addresses are 32-bit numbers, which allows roughly 4.3 billion unique addresses. In the 1980s that seemed limitless. But with billions of phones, laptops, smart TVs, thermostats, and doorbells all coming online, the supply ran dry. The regional registries that hand out address blocks effectively exhausted their free IPv4 pools years ago.

IPv6 was designed as the long-term fix. It uses 128-bit addresses, which produces a pool so enormous — about 340 undecillion addresses — that running out is not a practical concern. There are enough IPv6 addresses to give every grain of sand on Earth its own, many times over.

The two formats side by side

The most visible difference is how the addresses are written.

• IPv4 uses dotted decimal. Four numbers from 0 to 255, separated by dots, like 203.0.113.5. Short, readable, and the format almost everyone pictures when they hear "IP address."
• IPv6 uses hexadecimal with colons. Eight groups of hex digits separated by colons, like 2001:0db8:85a3:0000:0000:8a2e:0370:7334. To keep them manageable, long runs of zeros can be collapsed with a double colon, shortening that example to 2001:db8:85a3::8a2e:370:7334.

IPv6 addresses look intimidating, but you rarely type them by hand. Your devices and DNS handle them for you, exactly as they do with IPv4.

NAT vs native addressing

Because IPv4 addresses are scarce, the internet leaned heavily on a workaround called NAT (Network Address Translation). NAT lets a whole household of devices share a single public IPv4 address — your router stands at the door and translates between your private addresses and the one public address the world sees. It works, but it adds a layer of indirection.

IPv6 was designed with so many addresses that this workaround isn't needed. With native IPv6, devices can have their own globally unique address rather than hiding behind a shared one. That can make some things simpler — like direct connections between devices — though routers still apply firewall rules to keep unsolicited traffic out.

Dual-stack: running both at once

The internet didn't switch from IPv4 to IPv6 overnight, and it never will in a single jump. Instead, most networks run dual-stack: they support both protocols at the same time. Your device gets an IPv4 address and an IPv6 address, and for each connection it quietly picks whichever works best for the site it's reaching.

This is why your home network can show both kinds of addresses, and why everything keeps working even though the two systems aren't directly compatible. Dual-stack is the bridge that lets the slow migration happen without breaking anything.

Do you actually need to care?

For everyday browsing, no. Your provider, router, and devices negotiate all of this automatically, and you'll likely never notice which protocol carried a given page. The main reasons to know the difference are practical recognition ones:

• When you check your address and see a long hex string, that's IPv6 — not an error.
• Some older apps, games, or services still expect IPv4, so seeing both addresses helps you troubleshoot.
• If you self-host or use remote access, knowing which protocol your provider gives you affects how you set things up.

The takeaway: IPv4 is the familiar, shrinking system; IPv6 is the vast, future-proof one; and dual-stack quietly runs both so you don't have to think about it.