On this day, ARIN handed out the last IPv4 addresses in its free pool, leaving North America with none left to give away.

ARIN — the American Registry for Internet Numbers — is the nonprofit that has assigned IP addresses across the US, Canada, and parts of the Caribbean since 1997. IPv4, the addressing scheme underlying most of the internet, allows for roughly 4.3 billion unique addresses, a number that looked inexhaustible in the 1980s and had been running low for years.

The end came in stages, not all at once. ARIN had received one last top-up from IANA, the global coordinator of address space, on September 1, 2015 — a /15 block and two /16 blocks. In IPv4 addressing the number after the slash works backwards: the smaller it is, the bigger the block, so a /15 is 131,072 addresses and a /16 is 65,536; together they went toward a backlog of requests. Three weeks later, the pool hit zero.

John Curran, ARIN’s president, announced it the same day. ARIN was the third of the world’s five regional registries to run dry, after APNIC in the Asia-Pacific region exhausted its pool in April 2011 and RIPE NCC, covering Europe and the Middle East, reached its last /8 block — over 16 million addresses — in September 2012.

Running out did not mean ARIN stopped issuing addresses. New requests went onto a wait list, to be filled only as ARIN recovered or received more space — and organizations could still buy addresses from each other on the IPv4 transfer market, a practice ARIN’s own policy had anticipated since 2010. A narrow set of exceptions survived: a /24 block — 256 addresses — for networks actively transitioning to IPv6, and small allocations for critical infrastructure like internet exchange points and core DNS operators.

What changed was simple. Before September 24, an organization in ARIN’s region could ask for IPv4 space and, if it qualified, get it for free. After that date, it could only wait or pay — a scarcity that had been theoretical for years and was now the operating reality of the internet’s oldest addressing system.

See also Tracing the Origins of the Internet: The First RFC Series Begins (1970).