Router discovery differs from neighbor resolution
Router Solicitation and Advertisement discover local routers and carry prefixes and parameters such as link MTU. Neighbor Solicitation and Advertisement handle address resolution and probing, while Redirect identifies a better first hop for a destination.
These are ICMPv6 functions rather than one broadcast address table. Multicast-capable links support targeted multicast requests and later unicast probing, not a requirement to broadcast every query to every host.
References: [1]
Neighbor entries and on-link prefixes are separate
The Neighbor Cache stores next-hop link-layer addresses and reachability state. The Destination Cache maps destinations to next hops, while the Prefix List and Default Router List support forwarding decisions. These linked structures have different meanings.
RFC 5942 clarifies that assigning an IPv6 address does not automatically make a matching-looking prefix on-link. A learned neighbor entry is not itself permission to enlarge the on-link prefix list; advertisements, configuration and redirects have distinct rules.
Resolution does not end reachability checks
Neighbor Unreachability Detection concerns whether outgoing packets reach the next hop. New TCP acknowledgments can supply progress evidence; otherwise solicitation probes may be needed. An unsolicited advertisement alone demonstrates only one direction, not a working round trip.
Reachability is not identity authentication. Base Neighbor Discovery is exposed to forged addresses and router advertisements. Local-link origin, address resolution and permission to advertise remain different questions requiring suitable security and link-management measures.
References: [1]