Final answer:
IPv6 has mandatory requirements for the IPSec security protocol, providing network-level authentication and encryption to ensure secure communication, unlike its predecessor IPv4.
Step-by-step explanation:
The security protocol that IPv6 has mandatory requirements built in for is IPSec (Internet Protocol Security). IPv6 was designed to include a mandatory specification for providing network-level security, which includes features for both authentication and encryption. IPSec supports these security measures by enabling encrypted communication and helping to ensure that all data transferred over an IPv6 network is secure from eavesdropping and tampering. This is a significant difference from IPv4, which does not have security measures built into its core specifications and requires additional measures for secure communication.
IPv6, in addition to having more bits allocated for each host address, has mandatory requirements built in for IPSec - Internet Protocol Security. IPSec is a protocol suite that authenticates and encrypts the data packets in IPv6 networks to ensure secure communication over the internet.