Internet Protocol version 6 is an IP protocol with a much larger address space than IPv4 and its own packet structure and networking arrangements. Networks and applications can support both versions, sometimes choosing different paths. IPv6 capability therefore needs to work across the relevant client, access network and destination rather than only appearing in one device's settings.
A practical example
A website or service hostname can offer both IPv4 and IPv6 destinations. A device may select one supported route, while another device or application uses the other, potentially exposing different routing or configuration problems during a comparison.
A common misunderstanding
Do not disable a protocol permanently merely because one test changes behaviour. Establish whether the actual IPv6 path, DNS response or endpoint configuration is failing and follow the network operator's supported guidance.
Related terms
Further reading
Stable technical definition. Editorial approach