The IPv4 Exhaustion Counter ran out last week, indicating that the central global pool of IPv4 addresses administered by Internet Assigned Numbers Authority (IANA) has hit depletion, according to Latif Ladid, president of the IPv6 Forum .

There are still IPv4 addresses available through five regional registries, although those number-assigning entities are expected to run out in the next six to 12 months, with the North American, European and Asia-Pacific registries expected to hit depletion first.

This is just the latest milestone in what is expected to be the year of IPv6, the Internet addressing option that replaces IPv4. IPv6 advocates, such as Ladid and Vint Cerf, continue to urge the Internet community to adopt IPv6 more rapidly, as Cerf did at a Linux conference in Australia yesterday.

"It is necessary for everybody to start implementing IPv6 as soon as possible," Ladid says, via an e-mail interview.

In particular, Internet Society (ISOC) is urging major content and service providers to participate in the June 8 "IPv6 Day," which will include a 24-hour test drive of IPv6, as a final dress rehearsal for the major transition happening later in the year. Google, Facebook and other major Web companies have committed to participate.

Part of the challenge IPv6 organizers face is that the Internet continues to rock along, even as dire predictions of IPv4 addresses are issued. But wireless operators, in particular, may want to pay attention to the latest warnings because they will be affected earlier -- the proliferation of smart phones needing IP addresses will likely mean a lot of IPv6-only devices very soon.

For more To see how service providers are preparing for IPv6, check out these stories:

— Carol Wilson, Chief Editor, Events, Light Reading