Neighbor Discovery Protocol

Correct Answer: Neighbor Solicitation message

The Neighbor Solicitation message is the correct answer because it is used in the Neighbor Discovery Protocol to request the link-layer address of a neighbor or to verify that a neighbor is still reachable via a cached link-layer address. The other options, Router Solicitation, Router Advertisement and Neighbor Advertisement messages, are types of NDP messages, but they perform different functions. A Router Solicitation message is sent by a host to request for immediate router advertisements, instead of waiting for the next periodic ones. A Router Advertisement message is sent by a router to advertise its presence and contains Internet Layer configuration parameters. The Neighbor Advertisement message is a response to the Neighbor Solicitation message and is used to announce network address changes.

Correct Answer: Neighbor Solicitation

Neighbor Solicitation is the correct answer. In a scenario where a device wants to send a packet to another device on the same network, the Neighbor Solicitation (NS) message under the Neighbor Discovery Protocol (NDP) is used. The NS message is sent to determine the link-layer address of a neighbor, or to verify that a neighbor is still reachable via a cached link-layer address. The other choices are incorrect as they serve different purposes: - Router Solicitation is a message sent by a host to request that routers in the network identify themselves. In this scenario, we are interested in direct communication between two nodes, not necessarily involving routers - Multicast Listener Discovery is a component of the Internet Protocol Version 6 (IPv6) suite, used by a node to report its IP multicast listening state to any neighboring multicast routers. This is not related to sending a packet to another device on the same network - Router Advertisement is a message that routers periodically send announcing their presence along with various link and Internet parameters. Even though it is part of NDP, in this specific scenario it would not be used for direct communication between two devices.

Correct Answer: Router Solicitation message

The correct answer is 'Router Solicitation message.' When a device boots up and is unable to obtain the default gateway's IPv6 address, it can use the Router Solicitation message to solicit the address from routers on the network. A device sends this message to request that all routers on the network immediately advertise their presence instead of waiting for the next scheduled advertisement. 'Router Advertisement message' is not the right answer because this is the message that routers send in response to a Router Solicitation message or at regular intervals to announce their availability to devices on the network. Both 'Neighbor Solicitation message' and 'Neighbor Advertisement message' are used for address resolution, Duplication Address Detection (DAD), and Neighbor Unreachability Detection (NUD), not for finding a default gateway’s IPv6 address.