The following notes come directly from Wikipedia:
IPv5 was not a successor to IPv4, but an experimental flow-oriented streaming protocol similar to IPv4 intended to support video and audio.
IPv6 addresses are normally written as eight groups of four hexadecimal digits. For example,
IPv4 mapped IPv6 addresses constitute a special class of IPv6 addresses. Such an IPv6 address has its first 80 bits set to zero, the next 16 set to one, while its last 32 bits represents an IPv4 address. For example,
It is common to see examples that attempt to show that the IPv6 address space is absurdly large. For example, IPv6 supports 2128 (about 3.4×1038) addresses, or approximately 5×1028 addresses for each of the roughly 6.5 billion people alive today. In a different perspective, this is 252 addresses for every star in the known universe - a million times as many addresses per star than IPv4 supported for our single planet.
As of October 2008, IPv6 accounts for a minuscule percentage of the live addresses in the publicly-accessible Internet, which is still dominated by IPv4. A study by Google indicates that penetration is less than one percent of Internet traffic in any country. The leaders are Russia (0.76%), France (0.65%), Ukraine (0.64%), Norway (0.49%), and the United States (0.45%). Although Asia leads in terms of absolute deployment numbers, the relative penetration is smaller (e.g. China: 0.24%). However, in terms of software, IPv6 is implemented on all major operating systems in use in commercial, business, and home consumer environments.
Estimates as to when the pool of available IPv4 addresses will be exhausted vary widely, and should be taken with caution. In 2003, Paul Wilson (director of APNIC) stated that, based on then-current rates of deployment, the available space would last for one or two decades. In September 2005 a report by Cisco Systems reported that the pool of available addresses would be exhausted in as little as 4 to 5 years. In May 2009, a daily updated report projected that the IANA pool of unallocated addresses would be exhausted in June 2011, with the various Regional Internet Registries using up their allocations from IANA in March 2012.
It is expected that IPv4 will be supported alongside IPv6 for the foreseeable future. IPv4-only nodes (clients or servers) will not be able to communicate directly with IPv6 nodes, and will need to go through an intermediary.
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