IPv4 and IPv6 do the same job — give interfaces an address so packets can find them. IPv6 has a far larger address space, which matters because the central IPv4 pool ran out in 2011 (ARIN). Many networks run both at once.
Side-by-side comparison
| IPv4 | IPv6 | |
|---|---|---|
| Defined in | RFC 791 | RFC 8200 |
| Address size | 32 bits | 128 bits |
| Example | 203.0.113.42 |
2001:db8::8a2e:370:7334 |
| Format | 4 decimal numbers, dots | 8 hex groups, colons, shortened with :: (RFC 5952) |
| Total addresses | 232 ≈ 4.3 billion | 2128 ≈ 3.4 × 1038 |
| Central pool | Exhausted 3 Feb 2011 (ARIN) | Not exhausted |
| NAT | Widely used to share addresses (RFC 3022) | Not needed for address sharing |
| Address setup | DHCP (RFC 2131) or manual | SLAAC (RFC 4862), DHCPv6 (RFC 8415) or manual |
| Header | Variable length, with header checksum (RFC 791) | Fixed 40 bytes, no header checksum (RFC 8200) |
| IPsec | Optional | SHOULD be supported (RFC 8504) |
| Loopback | 127.0.0.1 |
::1 (RFC 4291) |
Why do I have both?
This is called dual stack. When a site supports both, many clients use Happy Eyeballs (RFC 8305): they try IPv6 first and, if it hasn't connected after a short delay (250 ms recommended), start an IPv4 attempt in parallel and use whichever connects. Each connection uses only one protocol, which is why the home page checks each separately.
Is IPv6 more secure?
Not automatically. With IPv4, NAT means outside hosts can't start connections to your devices unless the router is configured to forward them. With IPv6, devices have globally reachable addresses, so the router's firewall does that job: RFC 6092 recommends that home routers don't forward unsolicited inbound connections to the home network by default. Check your router's firewall settings.
Should I disable IPv6?
For Windows, Microsoft says: “We don't recommend that you disable IPv6 or IPv6 components … If you do, some Windows components might not function.” It suggests preferring IPv4 in prefix policies instead (Microsoft).
Check which ones you have
curl -4 https://forgotmyip.com # your IPv4 address
curl -6 https://forgotmyip.com # your IPv6 address (fails if you have no IPv6)