A study this week has revealed just how slow is the rate of adoption for IPv6, the next version of the Internet's main communications protocol, and some experts say black markets where companies trade unused IP addresses may be only a few years away.

The report, from Arbor Networks, claims to be the most comprehensive study of IPv6 use to date. It includes few surprises for those who follow the area closely, but the results provide a sobering measure of how just slowly the technology has been adopted.

"At its peak, IPv6 represented less than one hundredth of 1 percent of Internet traffic" over the past year, Arbor Networks' Craig Labovitz wrote in a summary of the findings, adding wryly: "This is somewhat equivalent to the allowed parts of contaminants in drinking water."

Arbor said it put together the study over the past year, working with the University of Michigan and almost 100 ISPs (Internet service providers) and content providers, including a quarter of the biggest ISPs in the U.S. and Europe. It used commercial traffic probes to monitor about 2,400 peering and backbone routers and 278,000 customer and peering interfaces.

"We believe this is the largest study of IPv6 and Internet traffic in general to date (by several orders of magnitude)," Labovitz wrote.

IPv6 is the successor to the current version of the Internet's underlying protocol, IPv4. Its adoption is important because IPv4 can support only about 4 billion IP (Internet Protocol) addresses and they are fast running out, while IPv6 will be able to support many trillions more (2 to the 128th power). It also offers advantages in security and network management.

Some experts say the supply of IPv4 addresses will run out in the next few years. Matthew Ford, a principal researcher with BT's Networks Research Centre in the U.K., operates a Web site that counts down the days until IPv4 addresses are used up. As of Tuesday, it predicts that the central registry of addresses will be exhausted in 904 days.

Few people expect disaster to ensue. The Arbor report notes that IPv6 adoption is growing, albeit at a slow pace. Since July last year IPv6 traffic has grown by nearly a factor of five, to an average of 100M bps (bits per second) per day. "Though not a landslide of adoption, it is still something," the report says.

What's more, there are already creative ways to get around the shortages, like using network address translators, or NATs, which essentially allow many computers to share the same IP address. There are also many addresses that were allocated to organizations and are not being used.