Quiz Entry - updated: 2026.07.14
What are the four Neighbor Discovery Protocol (NDP) messages and what do they do?
Router Solicitation/Advertisement (RS/RA) handle router and prefix discovery; Neighbor Solicitation/Advertisement (NS/NA) handle address resolution and duplicate detection.
* The RS/RA half of Neighbor Discovery delivering the prefix. *
| Message | Sent by | Purpose |
|---|---|---|
| Router Solicitation (RS) | host | "Are there routers? Send me the prefix" (to ff02::2) |
| Router Advertisement (RA) | router | announces prefix(es), default router, flags (sent periodically + on request) |
| Neighbor Solicitation (NS) | host | "Who has this address?" / Duplicate Address Detection |
| Neighbor Advertisement (NA) | host | "That address is mine, here's my link-layer address" |
NDP is built on ICMPv6 and replaces ARP, ICMP Router Discovery, and ICMP Redirect from the IPv4 world in one unified mechanism.
Tip: Map them by pairs — RS/RA = router business (prefixes), NS/NA = neighbor business (address resolution & DAD).
Go deeper:
Neighbor Discovery Protocol (Wikipedia) — the RS/RA/NS/NA message types with their ICMPv6 type numbers, plus how NDP subsumes ARP, Router Discovery, and Redirect.