In a ceremony in Miami this morning, the final five blocks of IPv4 addresses were given out to the five Regional Internet Registries that further distribute IP addresses to the far corners of the planet. The five RIRs still have tens of millions of addresses as working inventory, but once those addresses are given out, it's over. Internet Protocol addresses are a prerequisite for all Internet communication—both the sender and the receiver need one. As such, additional addresses are necessary whenever new users are connected to the Internet.

Without access to more IP addresses, service providers are forced to have their customers share an address. For most types of communication, that's a workable solution, but it makes it much harder for two end-users to communicate directly, such as when making a VoIP call, video chatting, or transferring files directly using an instant messaging program, or through a peer-to-peer filesharing system.

A more permanent solution than sharing addresses is the new version of the Internet Protocol: IP version 6 or IPv6. IPv4 addresses in use today are 32 bits long, or up to 12 digits. This allows for a total of 4.3 billion addresses; 3.7 billion of them are usable. IPv6 has 128-bit addresses, which are 39 digits, allowing for an almost unlimited number of addresses. With IPv6, a single home can have billions of addresses, so each Internet-connected device can have its own IP.

Running on fumes

The RIRs have various policies governing the last scraps of IPv4 address. For instance, some will be held in reserve to allow for IPv6-to-IPv4 translators, and some for currently unforeseen future needs. So there won't be a moment when the very last IPv4 address is given out. Also, every year some millions of addresses are returned because they're not needed anymore or the organization holding them ceases to exist. What will happen instead is that at some point, a big ISP will ask for a large block of IPv4 addresses—for instance, Comcast wants another block of 16,777,216 addresses—and there simply isn't enough space left to fulfill that request.

This is going to happen within months for the Asia-Pacific RIR, APNIC, which has been using up around 10 million addresses per month for the past year, managing to burn through almost 24 million in January alone. With somewhere south of 100 million IPv4 addresses left, APNIC may have to say "no" within three or four months, and certainly before the year is out.

ARIN (North America) and the RIPE NCC (Europe, the Middle East and the former Soviet Union) aren't going through addresses quite as fast. The RIPE NCC could run out by the end of the year, but ARIN should be able to finish 2011 without having to refuse requests due to lack of space. The moment of truth for ARIN will very likely come at some point in 2012.

LACNIC (Latin America and the Caribbean) and especially AfriNIC (Africa) are in a more comfortable position and may be able to continue giving out IPv4 addresses for a few more years. Of course, all of this is predicated on existing usage patterns continuing.

The last /8 blocks, identified by the first number of the four-number IP address, were doled out as follows: 102 went to AfriNIC, 103 to APNIC, 104 to ARIN, 179 to LACNIC, and finally, 185 to the RIPE NCC.

The Internet Engineering Task Force is responsible for technical Internet standards such as IPv6—IPv4 predates the formation of the IETF. The IETF BEHAVE (Behavior Engineering for Hindrance Avoidance) working group works on NAT (address sharing) and NAT traversal, including translation between IPv6 and IPv4. These mechanisms will allow the Internet to keep working during the transition of IPv4 to IPv6.

"The IETF has actually been preparing for this day for a long time. In the Behave WG, we've developed transition technologies to ease the transition to IPv6, while also looking at the impact of carrier-grade NATs. In short, the depletion of the IANA IPv4 address pool is not a crisis, and will not have any notable short-term effects," Dave Thaler, software architect at Microsoft and IETF BEHAVE co-chair told Ars.

Thaler noted that the depletion of the global pool means that the pace of IPv6 deployment really needs to increase. "The urgency for IPv6 deployment will be strongest in areas of major growth, such as deployments of new Internet technologies," he said. "For others, the IANA depletion is a call to action to ensure that everyone is on track to support such worldwide growth while still keeping with the original principles that generated the Internet's success."

Many people already use NAT at home, but the carrier-grade version that is implemented in a service provider network will be more disruptive, because local computers can no longer reach out to the NAT device and have incoming packets directed to them.

"To continue to grow their businesses, ISPs will need to deploy some form of IPv4 address sharing—NAT44, NAT64, or similar technologies," Dan Wing, distinguished engineer at Cisco Systems and the other BEHAVE chair told Ars. "IPv4 address sharing will be necessary until all of the content and servers on the Internet support IPv6, which will take many years. Users will still need to run servers at home—for webcams, television place shifting, and so on. To accommodate that need, the IETF is working on a protocol, PCP, which allows operating a server behind an IPv6 firewall and a carrier's NAT44 or NAT64."

(NAT44 is sharing an IPv4 address, NAT64 is sharing an IPv4 address along with translation between IPv6 and IPv4, so users who only have IPv6 may reach IPv4 servers.)

Even though the pool of available IPv4 addresses is running dry, that doesn't mean that each and every address is in actual use. There are many places around the 'Net where large swaths of IP addresses remain unused. But for various reasons, ranging from having to audit firewalls to the expectations that money can be made from them in the future, these addresses aren't being released back to the RIRs for redistribution. The fact that addresses are given out in hierarchical fashion doesn't help. The same is true for the phone system: if New York needs more phone numbers, it can't get some unused Wyoming numbers.

Researchers at the Information Sciences Institute have created an interactive map of the IPv4 address space that clearly shows how lopsided the distribution of IP addresses is.

Ars has covered IPv6 exetensively the past four years; have a look at our previous articles so you can start planning your own transition to IPv6.