IPv4 address exhaustion

IPv4 address exhaustion is the depletion of the pool of unallocated IPv4 addresses. Because the original Internet architecture had fewer than 4.3 billion addresses available, depletion has been anticipated since the late 1980s when the Internet started experiencing dramatic growth. This depletion is one of the reasons for the development and deployment of its successor protocol, IPv6.^[1] IPv4 and IPv6 coexist on the Internet.

The IP address space is managed globally by the Internet Assigned Numbers Authority (IANA), and by five regional Internet registries (RIRs) responsible in their designated territories for assignment to end users and local Internet registries, such as Internet service providers. The main market forces that accelerated IPv4 address depletion included the rapidly growing number of Internet users, always-on devices, and mobile devices.

The anticipated shortage has been the driving factor in creating and adopting several new technologies, including network address translation (NAT), Classless Inter-Domain Routing (CIDR) in 1993, and IPv6 in 1998.^[2]

The top-level exhaustion occurred on 31 January 2011.^[3][4][5][6] All RIRs have exhausted their address pools, except those reserved for IPv6 transition; this occurred on 15 April 2011 for the Asia-Pacific (APNIC),^[7][8][9] on 10 June 2014 for Latin America and the Caribbean (LACNIC),^[10] on 24 September 2015 for North America (ARIN),^[11] on 21 April 2017 for Africa (AfriNIC),^[12] and on 25 November 2019 for Europe, Middle East and Central Asia (RIPE NCC).^[13] These RIRs still allocate recovered addresses or addresses reserved for a special purpose. Individual ISPs still have pools of unassigned IP addresses, and could recycle addresses no longer needed by subscribers.

Vint Cerf co-created TCP/IP thinking it was an experiment, and has admitted he thought 32 bits was enough.^{[14][15][16][17]}