How does the material describe the use of multicast in IPv6 Neighbor Discovery (ND) when one host needs another host's Media Access Control (MAC) address?

### Why this is right The material describes IPv6 Neighbor Discovery as using a multicast group associated with an IPv6 address. A host sends a Neighbor Solicitation to that group, and the switch can forward the message only to the interested device or devices rather than flooding it to every port. ### The concept Multicast is delivery to a group of interested receivers. In the supplied explanation, an IPv6 address has an associated multicast group, and hosts join the group for their addresses. A Neighbor Solicitation sent to the target's group can therefore reach the relevant host efficiently. This differs from the IPv4 ARP request described in the material, which uses a broadcast MAC address and is flooded within the broadcast domain. The material presents the IPv6 process as a simplified refresher, so the key comparison is multicast delivery versus broadcast delivery. ### The other options - **B. The requester sends every Neighbor Solicitation to the Ethernet broadcast address, which all local hosts must process.**: This describes the broadcast behavior of an ARP request, not the multicast-based Neighbor Discovery process described here. - **C. The requester sends a unicast Neighbor Solicitation to the target's MAC address before learning that address.**: This assumes the requester already knows the address it is trying to discover. - **D. The requester sends the request to every router on the Internet, which returns the target's MAC address.**: Neighbor Discovery is used for local neighbor resolution, not for asking Internet routers to reveal a remote host's MAC address. ### Terms - **IPv6**: Internet Protocol version 6. The version of Internet Protocol that uses 128-bit addresses. - **ND**: Neighbor Discovery. IPv6 functions that include discovering local neighbors and resolving addresses. - **MAC**: Media Access Control. The address used for delivery over a local link. - **Multicast**: Delivery to a group of interested receivers. - **Neighbor Solicitation**: An IPv6 Neighbor Discovery message used to ask about a neighbor. - **Switch**: A device that forwards local frames using MAC addresses. - **ARP**: Address Resolution Protocol. It resolves an IPv4 address to a MAC address on a local network. - **Broadcast**: Delivery to all devices in the relevant broadcast domain. ### Remember In this material, IPv4 ARP requests use broadcast, while IPv6 Neighbor Discovery uses multicast.