The stateless mechanism allows a node to generate its own addresses using a combination of locally available information and information advertised by routers. Routers advertise prefixes that identify the subnet(s) associated with a link, while nodes generate an Interface ID that uniquely identifies an interface on a subnet. An address is formed by combining the two. In the absence of routers, a node can only generate link-local addresses. However, link-local addresses are sufficient for allowing communication among nodes attached to the same link.
So the first node generates its own link-local address. Before the link-local address can be assigned to an interface and used, however, a node must attempt to verify that this "tentative" address is not already in use by another node on the link. Specifically, it sends a NS message containing the tentative address as the target. If another node is already using that address, it will return a NA message saying so. If a node determines that its tentative link-local address is not unique, auto-configuration stops and manual configuration of the interface is required. This mechanism is called Duplicate Address Detection. Duplication of addresses is also tested in the cases of manual and stateful address auto-configuration.
Once a node ascertains that its tentative link-local address is unique, it assigns the address to the interface. At this point, the node has IP-level connectivity with neighboring nodes. The next phase of auto-configuration involves obtaining a RA messages or determining that no routers are present. If routers are present, they will send RA messages that specify what sort of auto-configuration a node can do. Note that the DHCPv6 service for address auto-configuration may still be available even if no routers are present. It should be noted that a node may use both stateless address auto-configuration and DHCPv6 simultaneously. The A flag indicates whether or not the option even applies to stateless auto-configuration. If it does, additional option fields contain a subnet prefix, together with lifetime values, indicating how long addresses created from the prefix remain preferred and valid.
Routers send RA messages periodically, but the delay between successive advertisements will generally be longer than a node performing auto-configuration will want to wait. To obtain an advertisement quickly, a node sends one or more RS messages to the all-routers multicast group.
Because routers generate RA messages periodically, nodes will continually receive new advertisements. Nodes process the information contained in each advertisement as described above, adding to and refreshing information received in previous advertisements.