Internet policymakers are considering sweeping changes to the way they distribute IP addresses that could allow network operators to make money by transferring unused blocks of IPv4 address space to others in need. One result could be lessened incentive to move to IPv6 any time soon.

The American Registry for Internet Numbers (ARIN) is expected to post proposed changes to its IPv4 address space transfer policy on its Web site this week. ARIN is a nonprofit group in Chantilly, Va., that doles out IPv4 and IPv6 address space to ISPs operating in the United States, Canada and the Caribbean.

Under the proposal, ARIN would allow ISPs to transfer IPv4 address registrations, and ARIN would provide a list of IPv4 address blocks that are available for transfer.

Until now, IPv4 addresses have not been tradeable goods. When an organization was done using IPv4 address space, it was supposed to return it to one of five regional registries such as ARIN in North America. The only time ISPs can transfer IPv4 address space is when they are acquired.

Click to see: How IP addresses are assigned

ARIN's proposed changes are designed to help network operators cope when the Internet runs out of IPv4 address space, which is expected to occur in 2012. 

"Industry demand for IPv4 addresses will not stop, but the current supply channel, namely the unallocated IPv4 address pool will have run out," says Geoff Huston, an expert on IPv4 address depletion and chief scientist at the Asia Pacific Network Information Centre, the Australian counterpart to ARIN. "So, as with any other commodity out there, trading and pricing gets included into the distribution function."

IPv4 is the Internet's main communications protocol. IPv4 uses 32-bit addresses and can support around 4 billion IP addresses. IPv6 is a long-anticipated upgrade to IPv4. IPv6 uses a 128-bit addressing scheme and can support so many billions of IP addresses that the number is too big for most non-techies to understand. (IPv6 supports 2 to the 128th power of IP addresses.)

The IETF designed IPv6 in the mid-1990s to expand the available IP address space. However, few ISPs or enterprises have upgraded to IPv6. 

The issue of IPv4 address depletion has received a great deal of attention in the last few months. Experts say more than 80% of IPv4 addresses have been distributed.