Address Uniqueness

For safety, all addresses must be tested for uniqueness prior to their assignment to an interface. In the case of addresses created through stateless autoconfiguration, however, the uniqueness of an address is determined primarily by the portion of the address formed from an interface identifier. Thus, if a node has already verified the uniqueness of a link-local address, additional addresses created from the same interface identifier need not be tested individually. In contrast, all addresses obtained manually or by stateful address autoconfiguration should be tested individually for uniqueness. To accommodate sites that believe the overhead of performing duplicate address detection outweighs its benefits, the use of duplicate address detection can be disabled through the administrative setting of a per-interface configuration flag.

To speed up the autoconfiguration process, a host can generate its link-local address (and verify its uniqueness) in parallel with waiting for a router advertisement. Because a router might delay responding to a router solicitation for a few seconds, the total time needed to complete autoconfiguration can be significantly longer if the two steps are done serially.