ystems. There are four main approaches for sending both A and AAAA queries: A first and, after response, AAAA: This approach, used by a popular desktop operating system, is the safest in the sense that the A query is finished before the AAAA is started, and issues described in RFC 4074 are avoided [146]. In the past, networks used to have old and buggy recursive DNS resolvers that could misbehave if they received an AAAA query from a client while resolution for an A query was not complete. Effectively the A query failed to resolve correctly. However, with this approach, if the A resolution takes time, the AAAA query will be delayed. AAAA first and, after response, A: A popular open source operating system utilizes this approach. While this order is not very useful as of today, in the future when the world is IPv6 dominant this may become the main approach - but at that time the A query may not be sent at all unless AAAA has failed to resolve a usable address. This approach has issues if the AAAA query does not resolve as expected [146] - the sending of an A query would be delayed. A first and AAAA immediately after: Essentially the parallel DNS queries are needed for the fastest resolution of both, or either, of IPv4 and IPv6 addresses. This approach is used by another popular desktop operating system in an attempt to resolve both address families faster - roughly in half of the time - than in the two approaches described above. On some occasions issues described by RFC 4074 may also cause problems for this approach [146], but luckily the issues with AAAA records and name servers have been significantly diminishing during recent years, as IPv6 deployments have become more common and server software has been updated. AAAA first and A immediately after: This approach does not have significant difference from the one above, other than that the small preference is given to IPv6 over IPv4. On some occasions issues described by RFC 4074 may also cause problems for this approach [146]. Once the DNS results are available