Prefix Information

Router advertisements also contain zero or more prefix information options that contain information that stateless address autoconfiguration uses to generate site-local and global addresses. The stateless address and stateful address autoconfiguration fields in router advertisements are processed independently of one another. A host can use both stateful address and stateless address autoconfiguration simultaneously. One option field that contains prefix information, the autonomous address-configuration flag, indicates whether the option even applies to stateless autoconfiguration. If the option field does apply, additional option fields contain a subnet prefix with lifetime values. These values indicate how long addresses that are created from the prefix remain preferred and valid.

Because routers generate router advertisements periodically, hosts continually receive new advertisements. Hosts process the information that is contained in each advertisement as described previously. Hosts add to the information. Hosts also refresh the information that is received in previous advertisements.