What is SLAAC and what makes it "stateless"?

SLAAC = Stateless Address Autoconfiguration: a host builds its own IPv6 address from a router-advertised prefix, with no DHCP server tracking who has which address.

A host can come online and get a working global address without any server keeping state:

• No DHCP needed — the router just advertises the network prefix
• The host combines that prefix with its own interface ID to form the address
• No ARP needed — neighbor information is derived via Neighbor Discovery (and historically the interface ID came from the MAC)
• Automatic router discovery and a duplicate-address check happen as part of the process
• For extra info not carried by SLAAC (e.g. NTP servers), a DHCPv6 add-on can supplement it

"Stateless" means nobody maintains a lease table mapping addresses to hosts — contrast with DHCP, which is stateful.

Tip: SLAAC is the preferred IPv6 autoconfiguration method and is why an IPv6 host can self-address on a network that has only a router and no DHCP server at all.

Go deeper:

• IPv6 explained — SLAAC and DHCPv6 (OneMarcFifty, 2022) — walks the RA/RS exchange and contrasts SLAAC with stateless and stateful DHCPv6.
• RFC 4862 — IPv6 Stateless Address Autoconfiguration — the primary spec for the whole self-configuration sequence.