IPv6 refers to Internet Protocol version 6, a new set of specifications computers can use to identify themselves and communicate with other computers over the Internet. It is the immediate planned successor to the current specification, IPv4 (Internet Protocol version 4). IPv6 is expected to become the common standard for Internet connections in the next several years as a result of the impending shortage of IPv4 addresses.
The Internet Protocol (IP) is a standard which computers use to identify themselves and exchange groups of data, known as packets, over the Internet. When the first version of the Internet, the ARPANet, was first designed, it was intended to be decentralized enough to cope with the destruction of a nuclear war - meaning that two computers could communicate with one another through a vast web of interconnections without having to follow a single specific path, or even to follow the same path twice. Today that system is used to cope with the complexity of hundreds of millions of users connecting with each other and with websites through thousands of service providers, but the principle remains the same.
The most important part of this system at the present, and particularly relating to the transition from IPv4 to IPv6, relates to how computers identity themselves. In order to ensure that packets reach their destination (regardless of the path they travel in between), each computer receives a specific and unique identification number when it connects to the Internet, analogous to a telephone number. These unique numbers, known as IP addresses, are allocated both to end users, such as readers of this web page, as well as to the servers that power Helium.com. A separate system, known as the Domain Name System (DNS), then links IP addresses to domain names (like Helium.com), so that Internet users do not have to remember the IP addresses the way they do telephone numbers.
The IPv4 system allocates addresses using a system of four digits, each equal to a number between 0 and 255. For instance, a computer's IP address might be 59.40.255.0, or 210.210.210.210. In total, about four billion unique IP addresses are thus available. These are currently administered by the U.S.-based Internet Assigned Numbers Authority (IANA). IANA allocates blocks, each of about 17 million IP addresses, to five regional Internet registries (respectively covering North America, the Asia-Pacific, Africa, Europe, and South and Central America). These registries then subdivide them further and parcel out numbers to governments, universities, large corporations, and Internet service providers, which can then assign those numbers to end users as they see fit.
Unfortunately, while four billion IPv4 addresses seemed like a lot in the 1980s, it is no longer so impressive when a single user could plausibly require multiple IP addresses: for instance, one for a desktop PC at home, another for a laptop or notebook PC which they shuttle back and forth between home and work, another address for their work computer, and one or more for Internet-capable cell phones. Even with a variety of measures available to create subnetworks and save address space, the time before the existing IPv4 system simply runs out of addresses is limited. Of the 221 blocks (of 17 million addresses each) of IP addresses which IANA can assign, 205 have now been allocated, and each of the regional registries has been promised one of the last five. At the current rate of new allocations, no new IP addresses will be available from IANA beginning some time next year. After that, it will take some time before all of the addresses are in demand from end users, but given current progress, address exhaustion is inevitable.
IPv6 escapes this problem by introducing a different and far larger system of IP addresses. An IPv6 address consists of eight blocks of four digits, each of them hexadecimal (base-16, rather than base-10). An IPv6 address, then, would appear as (for instance) 2001:0DB8:AC10:FE01:1000:0000:0000:0000. In total, the IPv6 system would theoretically support the simultaneous connection of 340 undecillion, or the number 34 followed by thirty-seven zeroes. Each individual alive today could purchase trillions of computers without threatening the integrity of the address system. How the transition will occur is another matter; currently, there are some doubts about how smoothly the world's Internet service providers can make the transition from communicating through IPv4 to communicating with IPv6.
Aside from solving the IP address problem, there were no compelling critical matters when the first planning groups began to meet to decide on the IPv6 standards during the early 1990s. There are some incremental improvements, like multicasting (so that computers can send data to multiple recipients simultaneously), some new provisions for communications security, and the capacity to send much larger packets of data than those in IPv4, currently known by the bemusing term "jumbograms." Overall, however, the principal reason for developing IPv6 is to overcome the limitations of the IPv4 address system. Hopefully, as the actual transition occurs over the coming several years, it should seem more or less seamless from the perspective of end users.