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 waiting list for unmet requests, where an organization agreed to accept a smaller block than it needed and then waited for space ARIN recovered — through returns, revocations for unpaid fees, or further IANA distributions — with no guarantee of when, or whether, its turn would come. The faster route was the transfer market: an organization sitting on more IPv4 than it used could sell blocks, no smaller than a /24, to one that could show ARIN a documented 24-month need, with brokers matching buyers to sellers and ARIN approving each deal and updating the registry — a practice ARIN’s own policy had anticipated since 2010. A narrow set of exceptions survived outside both paths: 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.
More than a decade later, almost nobody gets a fresh IPv4 address the way organizations once did from ARIN’s free pool — they get access to the internet without one at all. Mobile and broadband carriers route most subscriber traffic through carrier-grade NAT (CGNAT), sharing one public IPv4 address among thousands of customers rather than assigning each a unique one; a home or phone connection typically sees only a private address handed out by the carrier. New devices reach the outside world over IPv6 instead, which has no exhaustion problem — its address space is 4.3 billion times larger than all of IPv4 combined — and by the mid-2020s a majority of traffic to major content networks such as Google’s arrives over IPv6. Organizations that still need IPv4 space for servers or infrastructure buy it on the transfer market ARIN’s 2010 policy anticipated: brokers list blocks for sale, prices settled in the tens of dollars per address, and ARIN records the transfer once a buyer documents its need. The waiting list from 2015 still exists and still moves, slowly, as addresses are reclaimed, but it has become a minor path next to purchase and IPv6.
See also Tracing the Origins of the Internet: The First RFC Series Begins (1970).