North America has finally run out of new addresses based on IPv4, the numbering system that got the Internet where it is today but which is running out of space for the coming era of networking.

The American Registry for Internet Numbers, the nonprofit group that distributes Internet addresses for the region, said Thursday it has assigned the last addresses in its free pool. The announcement came after years of warnings from ARIN and others that IPv4 addresses were running out and that enterprises and carriers should adopt the next protocol, IPv6.

IPv4 dates back to 1981 and only has room for 4.3 billion unique addresses. IPv6, introduced in 1999, should have enough addresses to serve Internet users for generations, according to ARIN.

Anyone who still needs IPv4 addresses can request them from ARIN, but the organization won't have any to give away unless it gets more from the global Internet Assigned Numbers Authority (IANA) or returned addresses from users who don't need them anymore. ARIN already runs a waiting list for requests, which it set up earlier this year.

Users can also buy IPv4 addresses on the so-called transfer market from others who don't need them and are looking to make some money. Addresses recently were going for around US$10-$12 each, according to people who follow the transfer market.

More North American addresses may go on the market now that ARIN has exhausted its pool of fresh ones. That event triggered a change in the organization's rules for approving transfers: There is no longer any restriction on how often an address holder can request transfers to specified recipients.

Internet Protocol addresses come from IANA and are distributed through ARIN and other regional Internet registries (RIRs) around the world. Other RIRs are also running low on IPv4 addresses.

Migration from IPv4 to IPv6 can cause headaches for some types of organizations, and there is a chicken-and-egg problem as some content providers wait for consumers to start using the newer protocol. But big carriers and Internet players including Facebook and Google have helped to make IPv6 more common.