A network technician is configuring a new IPv6 network. After enabling IPv6 on the routers and ensuring all interfaces are correctly configured with IPv6 addresses, the technician notices that the routers are not discovering each other's presence on the link. Which protocol must be correctly implemented on the network to facilitate the discovery of neighboring devices on the same link in an IPv6 environment?
Internet Group Management Protocol (IGMP)
Internet Control Message Protocol for IPv4 (ICMPv4)
Address Resolution Protocol (ARP)
Neighbor Discovery Protocol (NDP)