Which is a key difference between IPv4 and IPv6?

The key difference that highlights the evolution from IPv4 to IPv6 is that IPv6 uses a 128-bit address space. This significantly increases the number of possible unique addresses available in the IPv6 system compared to IPv4, which uses a 32-bit address space. The shift to a 128-bit address space in IPv6 allows for a far greater number of unique IP addresses, solving the limitations faced by the growing number of devices connected to the internet.

This transition was necessary to accommodate the expanding Internet and the increasing number of devices, applications, and users that require unique IP addresses. By providing an expansive address range, IPv6 ensures more efficient routing and address allocation, which is crucial for the future development of the internet.

The other statements either misrepresent the capabilities of IPv4 and IPv6 or are simply inaccurate, which underscores the importance of knowing the exact specifications and enhancements introduced with IPv6.