Obtaining Router Advertisement

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

Routers send router advertisements periodically. However, the delay between successive advertisements is generally longer than a host that performs autoconfiguration can 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 that indicate 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).