IPv4 and IPv6 are two versions of the Internet Protocol. IPv4 is the original, with addresses like 203.0.113.7. IPv6 is the successor, with addresses like 2001:db8:85a3::8a2e:370:7334. Your connection probably uses both.
Why there are two
IPv4 addresses are 32 bits long, giving about 4.3 billion of them. That was plenty in the 1980s and not enough for today's phones, laptops and gadgets. The central pool of unassigned IPv4 addresses ran out in 2011, and regional registries followed. IPv6 uses 128-bit addresses, about 340 undecillion, so there is no shortage. Providers also stretch IPv4 with CGNAT.
Key differences
| IPv4 | IPv6 | |
|---|---|---|
| Length | 32 bits | 128 bits |
| Written as | Four numbers, dotted | Eight groups of hex, with :: shortening |
| NAT needed | Usually | No: devices can have their own public address |
| Address configuration | DHCP | Automatic (SLAAC) or DHCPv6 |
Dual stack: why you probably have both
Most networks run both side by side. Your device prefers IPv6 when a site supports it and falls back to IPv4. Some carriers, such as Reliance Jio, deploy IPv6 widely, so many mobile users reach large sites over IPv6 without knowing. The home page shows both of your addresses.
IPv6 and privacy
With IPv6 the part of the address that identifies your network (the prefix) is stable, so it can serve as a long-lived identifier. To reduce tracking, operating systems generate rotating temporary addresses for outgoing connections (privacy extensions), usually changing them daily. You can check what a site sees with the IPv6 line on our home page.
Do you have IPv6?
Open the home page: if the IPv6 line shows an address, your connection supports it. If it says "not detected", your provider, router or network may not offer it, which is common and harmless. Most websites still work over IPv4, so you lose nothing, and you have no IPv6 leak to worry about.
The IPv6 leak
This is the part that matters if you use a VPN. If a VPN only tunnels IPv4, your device may still reach IPv6-enabled sites directly, revealing your real IPv6 address and location while your IPv4 address shows the VPN's. Signs of this: our home page shows a VPN IPv4 but a home-provider IPv6, or the WebRTC test reports a different address. Fixes: use a VPN that supports IPv6 or blocks it, or disable IPv6 on your device or router.