Vint Cerf, also known as the father of the Internet, warned that we'd run out of IP addresses by 2010. That didn't happen. Now some pundits are predicting 2012 as the new doom-and-gloom date for the World Wide Web.

No one knows for sure when the original pool of IP addresses will be depleted, but one thing is certain: The continued growth of the Internet and the increasing use of machine-to-machine communications makes it likely -- and soon.

Here's how it works in a nutshell: IP version 4, or IPv4, addresses are allocated by the Internet Assigned Numbers Authority (IANA) to regional registries. The registries then allocate IPv4 addresses to individual customers. As it stands, the last free pool at IANA is tracking for September 2011 -- and the last address would be offered to an individual customer about a year later, or about 700 days from now.

"As with all scarce resources, occupation of new address resources will slow down as the free pool shrinks, just as oil consumption decreases as the price goes up," said Dr. Milton Mueller, a professor at the Syracuse University School Of Information Studies' Internet Governance Project. "But sooner or later, the free pool will be gone. IPv4 addresses are fixed in number and most of them have already been handed out to organizations and ISPs."

Exhausting the Pool

Several factors contribute to address scarcity. First, the Internet address space is a fixed quantity, set by the basic Internet protocol standard of 1981. It allows for about four billion unique bit combinations. In the early years of Internet development, address blocks were handed out too easily, Mueller said, because no one knew the Internet would become so large. By 1993, about 40 percent of the addresses had already been given out.

"The regional address registries don't have effective reclamation policies, so once they give out an address block, it never comes back, regardless of how efficiently it is used," Mueller said. "A more fundamental cause of inefficient address usage is the need for aggregation of routes. This is difficult to explain simply, but the current system of routing makes it difficult and sometimes impossible for users to carve up their address blocks into smaller pieces and move them around to different users, so there is a lot of underutilized address space."

What happens when we run out of IPv4 addresses? The impact of an IPv4 address exhaust can manifest itself in a number of ways -- technical and business, according to Pravin Mahajan, marketing manager for Cisco's Core Solutions. There's a possibility of a 'last-chance' rush on the registries, he said, along with industry talk about the possibility of trading IPv4 addresses. However no such model exists today or is forecast to be built.

"Apart from these issues which relate to the procurement of addresses, there's the issue of optimization with available addresses. Optimization involves reuse of existing addresses with translation and tunneling techniques," Mahajan said. "The business impact of the exhaust is already being felt in some market opportunities. Smart grid involves IP-enabling the electric power infrastructure."

According to Mueller, when the world runs out of IPv4 addresses, it will force network operators to use their address resources more carefully and promote two structural adjustments. First, it will promote the use of network address translators (NATs) that put an entire organizational network in a private address space. Second, it will, hopefully, eventually drive ISPs and others to adopt the new Internet protocol, IPv6, which has a very large address space.

Crimping the Internet's Growth

Meeting the challenge means understanding the distinction between IPv4 addresses (the established Internet protocol) and IPv6 addresses, which are not widely used yet.

The Internet itself is unlikely to run out of IP addresses because IPv6 offers a virtually infinite pool. However, the challenge is to make the transition from IPv4 to IPv6. Eventually providers will adopt IPv6 addressing, and the IPv4 exhaust could prompt them to move faster on its adoption.

"The migration to IPv6 will take years, and that will require both standards to be in place for a long time," Mueller said. "If we really develop shortages of IP addresses, it could crimp the growth of the Internet and undermine its performance in various ways."

Shifting to IPv6

As Mueller sees it, the best solution in the short term is for the regional address registries to allow market trading of address resources -- with some restrictions to maintain aggregation -- and to institute more effective policies to reclaim unused address resources. "Longer term," he said, "we must either standardize NAT arrangements in a way that allows a huge expansion of the address space, or migrate to IPv6."

Mahajan has a similar take. Any technology transition usually involves periods of coexistence before the complete shift. In this case, the transition is expected to occur over many years and possibly decades. That points to an industry need for a coherent plan during this long migration.

"The plan needs to incorporate preservation of the existing mode of operations, preparation for the new technology coexisting with the old, and maintain or enhance business prosperity along the process," Mahajan said. "Industry participants may move at a different pace based on their vertical segment -- wireline, mobile, cable, etc. -- geography and other drivers. The best solution for the transition needs to factor in all of these dynamic components."