Europe has run out of its original block of Internet addresses, forcing a transition that could prove a major roadblock to online growth.
Any computer that connects to the Internet requires a unique Internet Protocol (IP) address to send and receive data.
But when the old IP system (known as IPv4) was built in the 1960s and standardised in the 1980s, it allowed for only 4.2 billion unique addresses.
It was thought that number would prove inexhaustible - but instead the rapid growth of the Internet has seen the addresses all but run out.
There is now just one block of addresses left, and strict rationing means that they will not be allocated without commitments to switch to a new system.
The successor to IPv4 - IPv6 - does allow for an almost limitless (340 trillion, trillion, trillion) supply of addresses, and many major internet services including Microsoft, Google and Facebook already support it.
But the transition from IPv4 will still prove taxing - and could prove "vital to the future growth of the Internet", according to Europe's online registry.
Anyone applying for a some of the last remaining 16 million IPv4 addresses will be allocated just 1,024 of them - and will have to show they are already moving over to IPv6.
Making that switch will require businesses and ISPs to invest in new equipment, but internet users should not notice the change.
Before reaching the latest milestone, Ripe NCC - which distributes addresses in Europe - was giving out about four million every ten days.
At the formal launch of IPv6 earlier this year, Axel Pawlik, MD of Ripe, told HuffPost that ISPs had dragged their feet on the switch for too long.
"They all had more important things to do next week, next month and next year," he said. "Like get money from customers. Ad those customers never asked for IPv6... The pressure from the market wasn't there."