Connection essentials
IPv4 vs IPv6: addresses and test results.
IPv4 and IPv6 are two versions of Internet Protocol. Both carry internet traffic, but they use different address formats. A connection may support one or both.
| Feature | IPv4 | IPv6 |
|---|---|---|
| Example | 203.0.113.42 | 2001:db8::42 |
| Format | Four decimal numbers separated by dots. | Hexadecimal groups separated by colons. |
| Address size | 32 bits. | 128 bits. |
| Common home setup | Private device addresses translated to a public address. | Devices can have global addresses as well as local ones. |
Both examples above are reserved for documentation. In an IPv6 address, :: compresses consecutive zero groups and can appear only once. Address format and IPv6 address types are defined in RFC 4291.
What does an IPv6 prefix such as /64 mean?
The number after the slash is the number of bits that identify the network prefix. The remaining bits span the address range. For example, a /64 contains 264 addresses mathematically; that is not a count of usable devices. Use the IPv6 subnet calculator to find the first and last addresses, count addresses exactly, or split a larger prefix into smaller subnets.
Why your browser can show either address
IPv4's address space is limited. IPv6 provides a much larger one, but deployment is gradual. Networks that support both are called dual-stack. Your browser can use one family to load the home page and another for a different destination. Seeing an IPv4 address on a page therefore does not mean IPv6 is unavailable.
What our connection test measures
The IPv6 test makes separate requests to an IPv4-only hostname and an IPv6-only hostname. Each successful endpoint returns the address it observed. These are our service's endpoints; the test does not use a third-party IP checker.
- Both detected: both endpoints were reachable from this browser during the test.
- Only IPv4 detected: IPv4 worked here; the failed IPv6 request needs further investigation if you expected IPv6.
- Only IPv6 detected: IPv6 worked here; the IPv4 result can be affected by translation, filtering or endpoint problems.
- Neither detected: check ordinary browsing and endpoint availability before diagnosing both address families as broken.
Reaching both endpoints does not establish native dual-stack connectivity. For example, NAT64 translation can let an IPv6-only client reach an IPv4 server. The test records what each endpoint observed, not every protocol used along the path.
An IPv6 address is not a complete connectivity test
A link-local address in fe80::/10 works only on its local link. Having one does not establish IPv6 internet access. Even a global address does not prove a working route, DNS configuration or permission for incoming traffic. Firewalls remain relevant with IPv6.
A timeout can come from DNS, a VPN, filtering, your network or our test server. Follow IPv6 no internet access: what to check to separate these possibilities.