SLAAC

Stateless Address Autoconfiguration (SLAAC) is an IPv6 mechanism that allows a device to automatically configure its own network layer address and related parameters using information received from local routers, without requiring a dedicated DHCPv6 server for address assignment. It is described in RFC 4862 and relies on Router Advertisement messages to convey prefix information and other configuration cues.

In operation, an IPv6-enabled device connects to a network and listens for Router Advertisements. If a Prefix Information Option is present, the host can construct a global unicast address by combining the advertised IPv6 prefix with a 64-bit interface identifier. The interface identifier may be generated from the device’s MAC address using an EUI-64 method or produced randomly for privacy. The Router Advertisement also carries flags, commonly the M (Managed) and O (Other Configuration) bits, which indicate whether DHCPv6 should be consulted for addresses or other information, respectively.

Configuration beyond the address itself is not mandated by SLAAC. The default gateway is obtained from the router’s address in the RA, and other settings such as DNS server addresses are typically delivered via DHCPv6 or configured manually. Thus SLAAC provides address autoconfiguration on a stateless basis, while allowing complementary mechanisms to supply additional data.

Security and privacy considerations include the risk of trackability when interface identifiers are derived from hardware IDs; privacy extensions (temporary or randomized addresses) mitigate this risk. Potential vulnerabilities also arise from rogue Router Advertisements, which can be mitigated by measures such as RA-Guard and Secure Neighbor Discovery.

SLAAC is commonly used alone or in combination with DHCPv6, where SLAAC provides addressing and DHCPv6 supplies additional information like DNS settings.