In the Neighbor Discovery Protocol, which message is used to inform nodes about the presence of a router?

The Router Advertisement message is a key component of the Neighbor Discovery Protocol (NDP) utilized mainly in IPv6 networks. This message is sent by routers to inform local devices or nodes about their presence on the network. When a router sends out Router Advertisements, it includes various essential information, such as the router's IP address, network prefix, and other configuration details necessary for devices to properly manage their connectivity and routing.

Router Advertisements allow nodes on the network to automatically discover routers and receive information about available links and their attributes, thereby enabling efficient communication and data transmission. This feature supports stateless address autoconfiguration, allowing devices to configure their own IPv6 addresses based on the prefix information provided in the Router Advertisement.

In contrast, the other messages play different roles in the NDP. Router Solicitation messages are sent by nodes to request Router Advertisements actively. Neighbor Advertisement and Neighbor Solicitation messages are used for informing nodes about the presence of other nodes and resolving addresses within the same link, rather than for router discovery.