That's why some, including Labovitz, expect companies to trade unused addresses with each other, on a black market if the activity isn't officially sanctioned. "I think an IPv4 market is inevitable," he wrote.

BT's Ford said he wasn't surprised by the results, but he cautioned that the figures may not be completely accurate. Arbor acknowledged that it did not distinguish between native and tunneled IPv6 use, he noted, and the figures may also be skewed towards what's happening in the U.S., where many of Arbor Networks' customers are.

"The US has historically been quite sluggish, and most IPv6 research and implementation has been in Europe and Asia," said Ford, who previously chaired the IPv6 Cluster of the European Commission.

Nevertheless, the adoption has clearly been slow and the study should be a further wake-up call that widespread adoption of IPv6 needs to begin quickly, Ford said.

"Two or three years ago you could make the argument that [the exhaustion of IPv4 addresses] is far enough away that we don't need to make the investment," he said. But given that widespread adoption will take about two years to implement, "now is the time for large ISPs and content providers to begin their migration."

Arbor Networks said money is the main reason for the delay. The U.S. Department of Commerce has estimated it will cost US$25 billion for ISPs to upgrade to native IPv6. "This massive expense comes without the lure of additional revenue, since IPv6 offers diminishingly few incentives nor new competitive features to attract or upsell customers," Labovitz wrote.

Ford said enterprises may be among the earlier adopters because they can suffer the most from having to use IPv4.

"They can suffer problems through corporate mergers, because both parties might be using the same address space, or they find they have a lot of network address translators, which can make it challenging to deploy new applications. IPv6 helps both those problems," he said.

In addition, deploying IPv6 within the enterprise can be easier than it is for ISPs, which have to make more connections to outside networks.

"While it is easy to poke fun at predictions of the 'Imminent Collapse of the Internet', the eventual exhaustion of IPv4 allocations is real," the Arbor report states. "We need to do something. And IPv6 is our best bet."