The long-awaited depletion of the Internet's primary address space came one step closer to reality on Tuesday with the announcement that fewer than 10 per cent of IPv4 addresses remain unallocated.

The Number Resource Organization (NRO), the official representative of the five Regional Internet Registries, made the announcement. The Regional Internet Registries allocate blocks of IP addresses to ISPs and other network operators.

The NRO is urging Internet stakeholders — including corporations, government agencies, ISPs, IT vendors and users — to take immediate action and begin deploying the next-generation Internet Protocol known as IPv6, which has vastly more address space than today's IPv4.

"This is a key milestone in the growth and development of the global Internet," said Axel Pawlik, Chairman of the NRO, in a statement. "With less than 10 per cent of the entire IPv4 address range still available for allocation to RIRs, it is vital that the Internet community take considered and determined action to ensure the global adoption of IPv6."

IPv4 is the Internet's main communications protocol. IPv4 uses 32-bit addresses and can support around 4 billion IP addresses.

Designed as an 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.)IPv6 has been available since the mid-1990s, but deployment of IPv6 began in earnest last year.

The NRO recommends IPv6 as a way of ensuring that the Internet can support billions of additional people and devices.The NRO recommends the following actions:

* Businesses should provide IPv6-capable services and platforms.

* Software and hardware vendors should sell products that support IPv6.

* Government agencies should provide IPv6-enabled content and services, encourage IPv6 deployment in their countries, and purchase IPv6-compliant hardware and software.

*Users should request IPv6 services from their ISPs and IT vendors.

NRO officials warned of "grave consequences in the very near future" if the Internet community fails to recognize the rapid depletion of IPv4 addresses.

Experts predict that the rest of the available IPv4 addresses will be distributed to the Regional Internet Registries in 2011.