What is Stateless DHCPv6 and how does it relate to SLAAC?
Stateless DHCPv6 supplements SLAAC: the host still gets its address via SLAAC, but queries a DHCPv6 server for the extra config (like NTP servers) that SLAAC can't provide.
The problem: plain SLAAC (via Router Advertisements) can convey the prefix and DNS — but not everything, e.g. NTP time servers are not delivered by SLAAC.
Stateless DHCPv6 fills that gap:
- The host configures its address via SLAAC as usual
- It then asks a DHCPv6 server for the additional parameters only
- The server hands out info but does not assign or track addresses → it remains stateless (no lease table)
Which "additional parameters"? The typical "other configuration" options a client fetches this way:
- DNS recursive name servers and the DNS search domain list (though modern RAs can also carry DNS via RDNSS/DNSSL)
- NTP / SNTP time servers — the classic example SLAAC cannot deliver
- SIP proxy/registrar servers (VoIP)
- TFTP / boot server and network boot parameters (PXE-style provisioning)
- NIS / NIS+ domain and servers
- SNTP, POSIX timezone and other vendor-specific options
The rule of thumb: addressing comes from SLAAC; everything else a host needs to be useful can come from stateless DHCPv6.
In practice: the Router Advertisement distributes the IP basics, and DHCPv6 distributes everything else, while autoconfiguration stays stateless.
Tip: "Stateless" here refers to the DHCP server keeping no per-host address state — it's purely an information desk, not an address landlord.
Go deeper:
DHCPv6 (Wikipedia) — the message exchange and the RA flag that sends clients to DHCPv6 for "other" settings.