Quiz Entry - updated: 2026.07.14
How do the RA's M and O flags tell a host which dynamic addressing method (SLAAC, SLAAC + stateless DHCPv6, or stateful DHCPv6) to use?
M=0, O=0 → pure SLAAC. M=0, O=1 → SLAAC builds the address, stateless DHCPv6 supplies other info (DNS). M=1 → stateful DHCPv6 assigns the address itself.
RA flag decision matrix:
| M (Managed) | O (Other) | Host behavior | Method |
|---|---|---|---|
| 0 | 0 | Build own GUA from RA prefix; no DHCPv6 at all | SLAAC |
| 0 | 1 | Build own GUA via SLAAC; ask a stateless DHCPv6 server for DNS/domain | SLAAC + stateless DHCPv6 |
| 1 | — | Get the GUA (and other info) from a stateful DHCPv6 server | Stateful DHCPv6 |
In all three cases:
- The default gateway is the router's link-local address (the RA's source address).
- The prefix/prefix length comes from the RA.
Gotcha: SLAAC needs a /64 prefix to build the 64-bit Interface ID — this is why /64 is the recommended LAN prefix.
Go deeper:
RFC 4861 §4.2 — Router Advertisement message (M & O flags) — defines the Managed (M) and Other (O) configuration flags carried in the RA.- Stateless DHCPv6 vs SLAAC (NetworkAcademy.IO) — how the flag combinations map to SLAAC, SLAAC + stateless DHCPv6 and stateful DHCPv6.