After a host has generated an IPv6 address by using the DHCPv6 or SLAAC process, how does the host verify that the address is unique and therefore usable?

Question:
After a host has generated an IPv6 address by using the DHCPv6 or SLAAC process, how does the host verify that the address is unique and therefore usable?

• The host sends an ICMPv6 echo request message to the DHCPv6 or SLAAC-learned address and if no reply is returned, the address is considered unique.
• The host sends an ICMPv6 neighbor solicitation message to the DHCP or SLAAC-learned address and if no neighbor advertisement is returned, the address is considered unique.
• The host checks the local neighbor cache for the learned address and if the address is not cached, it it considered unique.
• The host sends an ARP broadcast to the local link and if no hosts send a reply, the address is considered unique.

Explanation: Before a host can actually configure and use an IPv6 address learned through SLAAC or DHCP, the host must verify that no other host is already using that address. To verify that the address is indeed unique, the host sends an ICMPv6 neighbor solicitation to the address. If no neighbor advertisement is returned, the host considers the address to be unique and configures it on the interface.

Exam with this question: CCNA 2 v7 Modules 7 – 9 Exam Answers
Exam with this question: Switching, Routing, and Wireless Essentials ( Version 7.00) - SRWE Final Exam