Final answer:
The correct answer is Option D: Router Solicitation (RS) message. When a host is booting up and needs to acquire an IPv6 configuration, it sends out a Router Solicitation (RS) message.
Step-by-step explanation:
The correct answer is Option D: Router Solicitation (RS) message. When a host is booting up and needs to acquire an IPv6 configuration, it sends out a Router Solicitation (RS) message. This message is used to request the presence of a router on the network, which can provide IPv6 configuration details such as the prefix, default gateway, and DNS server.
Once a router receives the RS message, it responds with a Router Advertisement (RA) message. The RA message contains the necessary information for the host to configure itself with an IPv6 address and other network parameters.