The emergence of the United States as a leader in IPv6 deployment comes at a time when both Asia and Europe have run out of all but small reserves of their IPv4 address space.

The European Internet registry - RIPE NCC - [Sept 14] that it had distributed all but its last /8 block of IPv4 addresses, which has around 16.7 million addresses. RIPE NCC has gone into conservation mode and will now allocate only 1,024 IPv4 addresses at a time to European network operators. Asia reached a in April 2011.

The United States, however, is relatively flush with IPv4 address space. The American Registry for Internet Numbers (ARIN) has three /8 blocks of , which equals more than 50 million IPv4 addresses.

Many U.S. organizations also have that they received at the dawn of the Internet, before anyone realized IPv4 addresses would become so valuable.

Peter Thimmesch, chairman of IPv4 address trading firm , says carriers around the globe continue to need IPv4 addresses for their dual-stack IPv6 deployments. "Carriers are taking a strategic view: they need to acquire enough IPv4 address space to support their customers for the many years it's going to take to deploy IPv6," he says. "It's about IPv4 and IPv6, not one or the other."