// Ars Technica
For some time now, we've been writing about how IPv4 addresses are running out. Very soon, ARIN, the American Registry for Internet Numbers, which distributes IP addresses in North America, will have to say "no" to a member requesting IPv4 addresses, even though they qualify for getting them.
In Asia, Europe, and Latin America/the Caribbean, the local Regional Internet Registries handed out IPv4 addresses in accordance with the governing policies until they reached a "final /8" or "final /10" limit of 16,777,216 or 4,194,304 in 2011, 2012, and 2014, respectively. At that point, each member (mostly Internet Service Providers) got to request one last block of 1,024 addresses.
ARIN has adopted a slightly different approach: rather than reserve a final block of addresses that are distributed under different rules, ARIN attacked the depletion of the IPv4 address space in four phases, where each phase increased the scrutiny given to requests. We're currently in phase four, and so far, ARIN has been able to meet all qualifying requests. But at this time, the largest block of IPv4 addresses in ARIN's vaults is a /11, or 2(32-11) = 2.09 million addresses. Although requests for such large blocks don't come in every day, the largest ISPs in North America do request blocks of this size at somewhat regular intervals. Soon, that last /11 will be gone. Then there's a /12 (1.04 million addresses), a /17 (131 thousand addresses), and a /20 (4,096 addresses). After that, it's basically scraps, with only /21s (2,048 addresses) and smaller left.