To avoid the situation where two IPv6 systems use the same address, systems perform Duplicate Address Detection for (nearly) all new IPv6 addresses before they’re used. DAD is done for global unicast addresses—and not just those created using stateless address autoconfiguration, but also for link-local addresses. For obvious reasons, there is no DAD for anycast addresses, as the whole point of anycast is that multiple systems have the same address. It’s also permitted to skip DAD for addresses that have an (EUI-64-based) interface identifier that was already tested for uniqueness. So if a host just uses stateless address autoconfiguration with an EUI-64 interface identifier, it only needs to perform DAD for the link-local address.
