Obtaining Router Advertisement

The next phase of autoconfiguration involves obtaining a router advertisement or determining that no routers are present. If routers are present, they send router advertisements that specify what sort of autoconfiguration a host should perform. If no routers are present, stateful autoconfiguration is invoked.

Routers send router advertisements periodically, but the delay between successive advertisements are generally longer than a host performing autoconfiguration wants to wait. To obtain an advertisement quickly, a host sends one or more router solicitations to the all-routers multicast group. Router advertisements contain two flags indicating what type of stateful autoconfiguration (if any) should be performed. A managed address configuration flag indicates whether hosts should use stateful autoconfiguration to obtain addresses. An other stateful configuration flag indicates whether hosts should use stateful autoconfiguration to obtain additional information (excluding addresses).