Final answer:
IPv6 is the only protocol among those listed that has organic security mechanisms, such as IPsec, designed to protect data packets from network attacks.
Step-by-step explanation:
Among the protocols listed—UDP, IPv4, ICMP, IPv6, and ARP—the one with some built-in security mechanisms is IPv6. IPv6 includes IPsec (Internet Protocol Security) which can provide confidentiality, integrity, and authenticity to the data packets being transmitted over the network. It is designed to prevent various network attacks. IPv4, UDP, ICMP, and ARP do not have organic security mechanisms; these protocols rely on other measures for security, like firewalls or additional protocols like TLS for securing communications.