| SLAAC | Stateless DHCPv6 | Stateful DHCPv6 | |
|---|---|---|---|
| Address from | client itself | client (RA prefix) | server |
| DNS | no | yes | yes |
| RA flags | M=0 O=0 | M=0 O=1 | M=1 |
SLAAC: Router Solicitation → Router Advertisement (prefix + gateway as the router’s link-local) → client builds its Interface ID (EUI-64 or privacy random) → DAD. No server, no logs, and only works on /64.
The CCNA/CCNP law: the IPv6 default gateway always comes from RA — even under stateful DHCPv6. That’s why RA can never be switched off.
ipv6 nd other-config-flag ! stateless
ipv6 nd managed-config-flag ! stateful
ipv6 dhcp relay destination 2001:db8::10DHCPv6 uses UDP 546/547. Security companions: RA Guard, DHCPv6 Guard, ND Inspection.