This is a simple tool to check if your internet connection supports IPv6. It will display your current IPv4 and IPv6 addresses, as well as the status of your DNS servers for both protocols.
If you see "IPv6: Not detected", you do not have an IPv6 connection on your current network. The most likely cause is that your ISP does not support IPv6 yet, but it could also be a configuration issue with your router or device.
If you see "IPv6 DNS: Not Working", it means that your DNS servers cannot reach IPv6 nameservers, which could also be a configuration issue or your DNS provider (usually your ISP) does not support IPv6. It is not uncommon to see IPv6 DNS working even if you do not have an IPv6 connection. If IPv6 DNS isn't working, but your IPv6 connection is, try a resolver that supports IPv6, such as Cloudflare, Quad9, or many of the others.
For each of the connection tests (IPv4 and IPv6), your browser makes a request to both 4.ip.c48.uk and 6.ip.c48.uk, and requests your IP from both. Each server respectively only has a record in the
DNS for the protocol it is testing, so if your browser can reach the server and get a response, it means that your connection supports that protocol.
For the ASN lookups, your browser makes requests to iptoasn at https://ip.c48.uk/v1/as/ip/ with your IP address(es).
For the PTR lookups, your browser makes requests to https://dnsapi.c48.uk/dns-query with the reverse DNS hostname for your IP address(es).
DNS works slightly differently: the browser makes a request to dns.4.ip.c48.uk and dns.6.ip.c48.uk. From there, your DNS server looks up these hostnames. dns.4.ip.c48.uk only has IPv4 nameservers
(v4.ns1.c48.uk and v4.ns2.c48.uk), whereas dns.6.ip.c48.uk only has IPv6 nameservers (ns1.c48.uk and ns2.c48.uk). If your DNS server can resolve the hostname, it means that it supports that protocol.