<P> At the design stage of the IPv6 DNS architecture, the AAAA scheme faced a rival proposal . This alternate approach, designed to facilitate network renumbering, uses A6 records for the forward lookup and a number of other innovations such as bit - string labels and DNAME records . It is defined in RFC 2874 and its references (with further discussion of the pros and cons of both schemes in RFC 3364), but has been deprecated to experimental status (RFC 3363). </P> <P> IPv6 is not foreseen to supplant IPv4 instantaneously . Both protocols will continue to operate simultaneously for some time . Therefore, IPv6 transition mechanisms are needed to enable IPv6 hosts to reach IPv4 services and to allow isolated IPv6 hosts and networks to reach each other over IPv4 infrastructure . </P> <P> According to Silvia Hagen a dual - stack implementation of the IPv4 and IPv6 on devices is the easiest way to migrate to IPv6 . Many other transition mechanisms use tunneling to encapsulate IPv6 traffic within IPv4 networks . This is an imperfect solution, which reduces the maximum transmission unit (MTU) of a link and therefore complicates Path MTU Discovery, and may increase latency . </P> <P> Dual - stack IP implementations provide complete IPv4 and IPv6 protocol stacks in the same network node on top of the common physical layer implementation, such as Ethernet . This permits dual - stack hosts to participate in IPv6 and IPv4 networks simultaneously . The method is defined in RFC 4213 . </P>

Number of bits used by ipv4 & ipv6