As the final allocation took place, new rules immediately went into effect at the American Registry for Internet Numbers, the RIR for North America. In the past, ARIN has allowed its customers to forecast their need for addresses over the next 12 months and apply for a year's allocation. Now they will have to apply every 90 days, showing a forecast for that period.
"We don't want to have a circumstance where organizations come in and we give one a year's worth, and someone else has none," Curran said.
When APNIC's supply is reduced to its final block of 16 million addresses, it will restrict its customers to just one much smaller block of addresses. It expects this supply to last approximately five years.
Thursday's action will have no noticeable short-term effects, Internet Architecture Board Chairman Olaf Kolkman said during a press conference following the Miami ceremony. But over time, the Internet will be severely limited if network administrators don't migrate to IPv6, he said.
"Such an Internet is likely to grow increasingly less capable of serving our needs than it is today," Kolkman said. Because of the need for adaptation tools within the network, the end-to-end model that makes many Internet applications work will break down. For example, it might become hard to make a Skype call or to trade files, he said.
For businesses, migrating to IPv6 will cost money, but not making the move eventually could cost revenue, he said. "The next 2 or 3 billion customers will use IPv6 only, and they will not be able to do business with you," Kolkman said.
As the pool of IPv4 addresses shrinks, it's possible that a black market will form, but it probably won't be large, said Raul Echeberria, chairman of the Number Resource Organization. All the RIRs have set procedures for transfers between address holders, which are designed to make sure that addresses only go to entities that need them. Echeberria believes most addresses will change hands through those mechanisms.
Despite the small portion of Internet traffic that uses IPv6 today -- recently estimated at less than one-tenth of 1 percent -- Echeberria is optimistic about the work done so far by vendors and network operators.
"All conditions are in place for a successful IPv6 transition," he said.
"A crisis has been averted," ICANN's Beckstrom said. The collaborative culture of the Internet allowed ICANN, the RIRs, the Internet Engineering Task Force and other entities to deal with the declining address space and create IPv6, he said. "This model is working incredibly well for the world."