Final Answer:
The RA sent to the 'All-IPv6-Routers' multicast address. (option 4)
Step-by-step explanation:
When a host doesn't possess an IPv6 address and sends a Router Solicitation (RS) message, the Router Advertisement (RA) is typically sent to the 'All-IPv6-Routers' multicast address. This address is specifically designated for routers in an IPv6 network.
In the absence of an assigned IPv6 address, the RA is directed to the 'All-IPv6-Routers' multicast address to ensure that routers within the network can respond and advertise their presence and available services. The RA contains essential network configuration information, including prefixes, hop limits, and other parameters necessary for hosts to configure their IPv6 settings.
The 'All-IPv6-Routers' multicast address enables routers to communicate and disseminate configuration details even when individual hosts initiating the RS might not have a specific IPv6 address. This ensures that essential network information reaches all potential hosts within the network, allowing them to configure their IPv6 settings dynamically.
This mechanism is fundamental in IPv6 networks, facilitating automatic configuration and communication between routers and hosts, ensuring efficient network setup and operation.