IPv4 vs IPv6: the differences explained

IPv4 uses 32-bit addresses, which gives about 4.3 billion addresses. In the 1980s that seemed endless; today there are more phones than people, and every home has dozens of connected devices. The regional registries ran out of IPv4 between 2011 and 2019, and IPv4 addresses are now bought and sold at market prices.

IPv6 was designed in the 1990s to solve this: its addresses are 128 bits long, about 340 undecillion (3.4 × 10³⁸). That is enough to give billions of networks to every person on the planet without ever running out.

• Size: 32 bits in IPv4 versus 128 bits in IPv6.
• Format: IPv4 is written in dotted decimal (192.168.1.10); IPv6 in hexadecimal with colons (2001:db8::10).
• NAT: in IPv4, every device in a home shares one public IP thanks to the router's NAT. In IPv6 each device can have its own public address and NAT is no longer needed.
• Configuration: IPv6 lets every device configure itself (SLAAC), with no DHCP server.
• Broadcast: IPv4 uses broadcast; IPv6 replaces it with more efficient multicast.
• Header: IPv6's is simpler and fixed-size, which makes routers' work easier.
• Masks: IPv6 has no dotted masks, only prefixes (/64, /48…).

IPv4 and IPv6 are not compatible with each other: a device with only IPv6 cannot talk directly to one with only IPv4. That is why the transition relies on dual stack: devices and websites have one address of each version, and the operating system picks the best one for each connection (usually IPv6, using the «Happy Eyeballs» algorithm).

Some mobile carriers give IPv6 only and translate to IPv4 when needed (NAT64/DNS64), and many fiber providers share one IPv4 address among several customers (CGNAT) while giving full IPv6. In many countries, more than half of the traffic Google receives already arrives over IPv6.

Neither, by itself. IPsec was born with IPv6, but it is now available in both versions, and almost all traffic is encrypted with TLS on top of IP anyway. What matters is that your router has a firewall blocking incoming connections by default, which every home router with IPv6 does.

As for speed, IPv6 can be slightly faster when it avoids the carrier's CGNAT, but the difference is usually small. Its big advantage is something else: it brings back direct connections between devices, useful for online gaming, video calls or home servers.

Open the «What is my IP» tool: if your connection has IPv6, you will see both addresses. If only IPv4 appears, your provider or router does not have it enabled; many routers ship with IPv6 turned off and you just need to switch it on in their settings.

To practice with IPv6 addresses, use the IPv6 calculator (prefixes and subnets) and the IP converter, which shows the expanded and compressed forms and any IPv4 embedded in an IPv6 address.