What advantage does IPv6 provide over IPv4?

The advantage that IPv6 provides over IPv4 is indeed the increased security features. IPv6 was designed with security in mind from the outset. It includes the mandatory use of IPsec, a suite of protocols for securing Internet Protocol (IP) communications, which allows for data integrity, authentication, and confidentiality. This inherent security feature facilitates secure connections between devices, which is a significant improvement over IPv4, where security was added later as an option rather than being integral to its design.

In contrast to IPv4, IPv6's broader address space also allows for a much larger number of unique IP addresses, accommodating the exponential growth of devices connected to the internet, particularly with the rise of mobile devices and the Internet of Things (IoT). However, this relates to capacity rather than security directly.

The other options relate to drawbacks or limitations rather than advantages. Thus, the significant enhancement in security through built-in mechanisms in IPv6 sets it apart from its predecessor, making it a crucial advancement in internet technology.