The difference in one sentence
IPv4 and IPv6 are two versions of the Internet Protocol: IPv4 uses short 32-bit addresses that have run out, while IPv6 uses 128-bit addresses that will never run out. Both carry the same web pages, video and games; they're just two different addressing systems running side by side.
IPv4 vs IPv6 at a glance
| IPv4 | IPv6 | |
|---|---|---|
| Example | 203.0.113.42 | 2001:db8:85a3::8a2e:370:7334 |
| Address length | 32 bits | 128 bits |
| Number of addresses | About 4.3 billion | About 340 undecillion (3.4 × 10³⁸) |
| Written as | Four decimal numbers with dots | Eight hexadecimal groups with colons |
| Sharing | Usually one public IP per home, shared through NAT | Every device can get its own public address |
| Setup | DHCP or manual | Automatic (SLAAC) or DHCPv6 |
| Introduced | 1981 | 1998, widely used since the 2010s |
Why IPv6 exists
IPv4 has room for about 4.3 billion addresses, fewer than the number of phones in use today. The last free blocks were handed out between 2011 and 2019. Providers stretched IPv4 with NAT, which lets many devices share one public address, and with carrier-grade NAT, which lets many customers share one. IPv6 solves the shortage for good: there are enough addresses to give every device on Earth its own billions of times over.
Is IPv6 faster or more secure?
Speed: in practice they're about the same. IPv6 can be slightly faster on mobile networks because it avoids carrier-grade NAT, and slightly slower where a provider routes it poorly. You won't notice the difference when browsing.
Security: IPv6 was designed with encryption support (IPsec) built in, but IPv4 can use it too, and most traffic is protected by HTTPS either way. The real difference is privacy. Without NAT, an IPv6 address can identify a single device rather than a whole household. Modern systems use "temporary" privacy addresses that change regularly to limit this.
How to tell if you have IPv6
Open the My IP page. It shows your IPv4 and IPv6 addresses separately. If the IPv6 row shows an address, your connection supports IPv6. If it says none was found, your provider, router or device isn't using IPv6.
Around half of Google's users reach it over IPv6 today. Support is high on mobile networks and in countries such as India, France, Germany, the United States and Japan, and lower in many others.
Why IPv6 matters when you use a VPN
Many VPNs and proxies only carry IPv4. If your connection also has IPv6, websites that support IPv6 can be reached directly, outside the VPN, and they see your real IPv6 address. This is called an IPv6 leak, and it's one of the most common ways a VPN fails without telling you.
The checks on the My IP page compare your IPv4 and IPv6 networks. If they leave through different networks while you're on a VPN, one of them is going around it.
To fix an IPv6 leak:
- Turn on the VPN app's IPv6 leak protection or "block IPv6" setting, if it has one.
- Choose a VPN that supports IPv6 properly.
- As a last resort, disable IPv6 on your network adapter or router.
Read how to check if your VPN is working for the full set of leak tests.
FAQ
Should I use IPv4 or IPv6?
You don't need to choose. Devices use both automatically and prefer IPv6 when a website supports it. Leave IPv6 on unless it causes a VPN leak you can't fix another way.
Can IPv4 and IPv6 talk to each other?
Not directly. A website must have both kinds of address to reach both kinds of users, which is why most large sites are "dual stack." Providers also use translation methods such as NAT64 for IPv6-only networks.
Why does my IPv6 address keep changing?
Your device creates temporary IPv6 addresses for privacy and replaces them every few hours or days. The network part (the first half) usually stays the same while the device part changes.
Does disabling IPv6 make my internet slower?
Usually not noticeably. A few games, apps and mobile networks work better with IPv6, so only disable it if you need to stop a leak.