"When the Internet registries run out of addresses, life will still appear like normal, e-mail will still work, and you won't be forced to start using IPv6 all of a sudden." You will still be able to get addresses, if you pay for them, because a market will appear.

"Anyone that is a clever economic unit will buy and sell. Anyone with class B addresses will figure out that if they band up behind a NAT, they can sell off all spare addresses. So scarcity is just a pricing function and there will be a market in address compression."

With this second stage of the IPv4 market, he said, it could be 2050 before all the IPv4 addresses run out, depending on what modelling method is used.

Cisco's senior technical leader for IPv6 technologies, Tony Hain, begs to differ.

"Network Address Translation (NAT) and CIDR (Classless Inter-Domain Routing) did their jobs and bought the 10 years needed to get IPv6 standards and products developed," he said.