Why IPv6 matters for privacy testing
Many internet connections support both IPv4 and IPv6. If a privacy tool or VPN only changes one protocol path, traffic using the other protocol can sometimes follow a different route. That is why checking IPv6 separately can be useful.
What this test compares
The page compares the IP used to reach IP-Lookup.com with an address returned through an IPv4/IPv6-capable endpoint. If an IPv6 address is available, you can analyze the network behind it and decide whether it belongs to the route you expected.
Does a different IPv6 address mean a leak?
Not automatically. A VPN can intentionally provide its own IPv6 address, and dual-stack networks naturally use different IPv4 and IPv6 addresses. The important question is whether the returned address belongs to your intended VPN/network or unexpectedly to your normal ISP.
What if no IPv6 address appears?
Your connection, browser path, VPN or network may simply not have usable IPv6 for that request. That is not necessarily an error. It means this browser test did not observe a public IPv6 path at that moment.
Check the network, not just the address format
If IPv6 is returned, use the full IP lookup to inspect its ASN and organization. Network ownership usually provides more useful privacy context than the fact that the address contains colons instead of dots.