<P> Compatibility with IPv6 networking is mainly a software or firmware issue . However, much of the older hardware that could in principle be upgraded is likely to be replaced instead . The American Registry for Internet Numbers (ARIN) suggested that all Internet servers be prepared to serve IPv6 - only clients by January 2012 . </P> <P> Host software may have only IPv4 or only IPv6 networking software, or it may support dual - stack, or hybrid dual - stack operation . The majority of personal computers running recent operating system versions support IPv6 . Many popular applications with networking capabilities are compliant . </P> <P> Some software transitioning mechanisms are outlined in RFC 4038, RFC 3493, and RFC 3542 . </P> <P> Hybrid dual - stack IPv6 / IPv4 implementations recognize a special class of addresses, the IPv4 - mapped IPv6 addresses . These addresses consist of an 80 - bit prefix of zeros, the next 16 bits are one, and the remaining, least - significant 32 bits contain the IPv4 address . These addresses are typically written with a 96 - bit prefix in the standard IPv6 format, and the remaining 32 bits written in the customary dot - decimal notation of IPv4 . For example,:: ffff: 192.0. 2.128 represents the IPv4 address 192.0. 2.128 . A deprecated format for IPv4 - compatible IPv6 addresses is:: 192.0. 2.128 . </P>

6. in ipv6 how many bits are set for the network prefix and how many bits are for the host portion