The Asia-Pacific Network Information Centre (APNIC), which is the organization responsible for distributing IP addresses in most of Asia, Australia, and the Pacific, announced that on April 15, it reached its final /8 block of IPv4 addresses. This cryptic announcement means that APNIC's supply of IPv4 addresses has been exhausted, and since the global pool of IPv4 addresses was previously exhausted, IPv4 addresses are no longer available in the APNIC region as they were before—basically, "to each according to his needs."

However, APNIC set aside one block of 16,777,216 addresses for distribution under a different regime: every network operator may obtain exactly one delegation of 1024 out of that block. The final /8 consists of the addresses 103.0.0.0 to 103.255.255.255, or 103.0.0.0/8.

A day earlier, the Chinanet Fujian Province Network managed to snag up more than a thousand small blocks adding up to nearly half a million IPv4 addresses. Interestingly, it looks like there's still a few hundred thousand regular addresses in APNIC's pool, and more will come in over time as network operators relinquish unused address space—this has amounted to several million addresses annually worldwide in recent years. Or maybe they won't be inclined to do that anymore, as apparently Microsoft is paying $7.5 million to obtain 666,000 addresses from bankrupt telecom Nortel. It's unclear what will happen to APNIC's remaining regular IPv4 addresses.

Internet Service Providers usually got the new IP addresses they need on a six-month to two-year cycle, so many of them will have enough addresses to continue connecting new users for some time to come. Also, IPv4 addresses have been moving very fast in the APNIC region, it's not unreasonable to suspect that ISPs have been more aggressive about requesting addresses to better position themselves for the day the well runs dry.

Presumably, most ISPs have also been preparing for this eventuality by investing in "carrier grade network address translation (NAT)" devices, which allow them to share one address between multiple customers, so their existing address blocks and last 1,024 addresses can be used to keep connecting more customers in the coming years.

Unfortunately, rolling out IPv6, which has no shortage of addresses, not even in Asia, is not a viable short-term solution: if Asian and Australian ISPs were to provide IPv6 connectivity instead of IPv4 connectivity to new customers—remember, existing IPv4 addresses keep working—those customers would be unable to reach destinations around the 'Net which haven't upgraded to IPv6 yet. It's possible to translate from IPv6 to IPv4, but like carrier-grade NAT, such translators also need an IPv4 address for every X users—where there is no clear consensus what the value of X should be.

However, IPv6 is an important part of the picture, as it provides an escape for peer-to-peer protocols that can't be made to work through the increasing layers of NAT that will be applied in the now IPv4-deprived region. To add insult to injury, users who have un-NATed IPv4 can set up IPv6 connectivity without cooperation from their ISP relatively easily, but those behind NAT, especially the carrier-grade variety, have a much harder time accomplishing this. So it's important that ISPs who offer NAT to their customers also provide IPv6.

Although the impending end of the IPv4 supply has been foretold for years, it's still possible that some unlucky ISP managed to miss that news, or at least the fact that it would be happening this soon in their region, and are going to be caught flat-footed when they turn to APNIC for more addresses. Such an ISP would have to turn down new customers until it can obtain and deploy a carrier-grade NAT solution. It wouldn't be surprising me if this dooms a few ISPs that are already struggling.

In the meantime, the clock is ticking for the RIPE NCC, which handles Europe, the Middle East, and the former Soviet Union. RIPE still has some 65 million addresses left—almost exactly the number it gave out last year. RIPE has a similar final /8 policy to APNIC, so Europe may be looking at a Christmas stocking with no IPv4 addresses in it by the end of 2011. Of course if ISPs rush to submit their last, big requests, it could happen sooner.

LACNIC in Latin America and the Caribbean and AfriNIC in Africa dish out relatively few IPv4 addresses every year, so they are good for several more years. ARIN, which handles North America, does give out a lot more addresses, but somehow managed to get the long end of the stick: not only does it have 61 million regular addresses left, but it also "administers" 75 million unused legacy addresses (given out before the RIPE NCC, APNIC and ARIN were formed). So North America should be good, IPv4-wise, for a couple more years. Maybe even longer.