IPv4 vs IPv6: What's the Difference?
The internet is in the middle of a decades-long migration from IPv4 to IPv6. Both are versions of the Internet Protocol — the system of addresses that lets devices find each other online — but they differ in one critical way: how many addresses they can provide.
The short version
- IPv4 uses 32-bit addresses, allowing about 4.3 billion unique addresses. We have effectively run out.
- IPv6 uses 128-bit addresses, allowing roughly 340 undecillion addresses — enough for every grain of sand on Earth to have billions of its own.
How the formats compare
| IPv4 | IPv6 | |
|---|---|---|
| Example | 192.0.2.146 | 2001:db8:85a3::8a2e:370:7334 |
| Length | 32 bits | 128 bits |
| Notation | Decimal, dot-separated | Hexadecimal, colon-separated |
| Total addresses | ~4.3 billion | ~3.4 × 10³⁸ |
| Configuration | Often manual / DHCP | Auto-configuration built in |
Why IPv6 was created
When IPv4 was designed in the early 1980s, 4.3 billion addresses seemed limitless. The explosion of phones, laptops, servers, and smart devices proved otherwise. Workarounds like NAT stretched IPv4 further by letting many devices share one public address, but they add complexity. IPv6 solves the shortage permanently and restores true end-to-end addressing.
Do they work together?
Yes — most networks run dual-stack, supporting both protocols at once. Your device automatically prefers IPv6 when both ends support it, and falls back to IPv4 otherwise. This is why you might see either type of address depending on the site and network you use.
Which one am I using?
Open ifconfig.is and look at the address shown — if it contains colons, you're on IPv6; if it's four dot-separated numbers, you're on IPv4. Curious what an IP reveals about you? Read What is an IP address?