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. IPv4 and IPv6 coexist on the Internet.
The IP address space is managed globally by the Internet Assigned Numbers Authority, and by five regional Internet registries 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, Classless Inter-Domain Routing in 1993, and IPv6 in 1998.
The top-level exhaustion occurred on 31 January 2011. All RIRs have exhausted their address pools, except those reserved for IPv6 transition; this occurred on 15 April 2011 for the Asia-Pacific, on 10 June 2014 for Latin America and the Caribbean, on 24 September 2015 for North America, on 21 April 2017 for Africa, and on 25 November 2019 for Europe, Middle East and Central Asia. 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.

IP addressing

Every node of an Internet Protocol network, such as a computer, router, or network printer, is assigned an IP address for each network interface, used to locate and identify the node in communications with other nodes on the network. Internet Protocol version 4 provides 232 addresses. However, large blocks of IPv4 addresses are reserved for special uses and are unavailable for public allocation.
The IPv4 addressing structure provides an insufficient number of publicly routable addresses to provide a distinct address to every Internet device or service. This problem has been mitigated for some time by changes in the address allocation and routing infrastructure of the Internet. The transition from classful network addressing to Classless Inter-Domain Routing delayed the exhaustion of addresses substantially. In addition, network address translation permits Internet service providers and enterprises to masquerade private network address space with only one publicly routable IPv4 address on the Internet interface of a main Internet router, instead of allocating a public address to each network device.

Address depletion

While the primary reason for IPv4 address exhaustion is insufficient capacity in the design of the original Internet infrastructure, several additional driving factors have aggravated the shortcomings. Each of them increased the demand on the limited supply of addresses, often in ways unanticipated by the original designers of the network.
;Mobile devices: As IPv4 increasingly became the de facto standard for networked digital communication and the cost of embedding substantial computing power into hand-held devices dropped, mobile phones have become viable Internet hosts. New specifications of 4G devices require IPv6 addressing.
;Always-on connections: Throughout the 1990s, the predominant mode of consumer Internet access was telephone modem dial-up. The rapid increase in the number of the dial-up networks increased address consumption rates, although it was common that the modem pools, and as a result, the pool of assigned IP addresses, were shared amongst a large customer base. By 2007, however, broadband Internet access had begun to exceed 50% penetration in many markets. Broadband connections are always active, as the gateway devices are rarely turned off, so that the address uptake by Internet service providers continued at an accelerating pace.
;Internet demographics: The developed world consists of hundreds of millions of households. In 1990, only a small fraction of these had Internet access. Just 15 years later, almost half of them had persistent broadband connections. The many new Internet users in countries such as China and India are also driving address exhaustion.
;Inefficient address use: Organizations that obtained IP addresses in the 1980s were often allocated far more addresses than they actually required, because the initial classful network allocation method was inadequate to reflect reasonable usage. For example, large companies or universities were assigned class A address blocks with over 16 million IPv4 addresses each, because the next smaller allocation unit, a class B block with 65,536 addresses, was too small for their intended deployments.

Mitigation efforts

Efforts to delay address space exhaustion started with the recognition of the problem in the early 1990s, and the introduction of a number of stop-gap refinements to make the existing structure operate more efficiently, such as CIDR methods and strict usage-based allocation policies.
The Internet Engineering Task Force created the Routing and Addressing Group in November 1991 to respond to the scalability problem caused by the classful network allocation system in place at the time.
IPv6, the successor technology to IPv4, was designed to address this problem. It supports approximately network addresses. Although the predicted depletion was already approaching its final stages, most providers of Internet services and software vendors were just beginning IPv6 deployment at that time.
Other mitigation efforts and technologies include:
  • use of network address translation which allows a private network to use one public IP address and permitting private addresses in the private network;
  • use of private network addressing;
  • name-based virtual hosting of web sites;
  • tighter control by regional Internet registries on the allocation of addresses to local Internet registries;
  • network renumbering and subnetting to reclaim large blocks of address space allocated in the early days of the Internet, when the Internet used inefficient classful network addressing.

    Exhaustion dates and impact

On 31 January 2011, the last two unreserved IANA address blocks were allocated to APNIC according to RIR request procedures. This left five reserved but unallocated blocks. In accord with ICANN policies, IANA proceeded to allocate one of those five s to each RIR, exhausting the IANA pool, at a ceremony and press conference on 3 February 2011.
The various legacy address blocks with administration historically split among the RIRs were distributed to the RIRs in February 2011.
APNIC was the first regional Internet registry to run out of freely allocated IPv4 addresses, on 15 April 2011. This date marked the point where not everyone who needed an IPv4 address could be allocated one. As a consequence of this exhaustion, end-to-end connectivity as required by specific applications will not be universally available on the Internet until IPv6 is fully implemented. However, IPv6 hosts cannot directly communicate with IPv4 hosts, and have to communicate using special gateway services. This means that general-purpose computers must still have IPv4 access, for example through NAT64, in addition to the new IPv6 address, which is more effort than just supporting IPv4 or IPv6.
In early 2011, only 16–26% of computers were IPv6 capable, while only 0.2% preferred IPv6 addressing with many using transition methods such as Teredo tunneling. About 0.15% of the top million websites were IPv6 accessible in 2011. Complicating matters, 0.027% to 0.12% of visitors could not reach dual-stack sites, but a larger percentage could not reach IPv4-only sites. IPv4 exhaustion mitigation technologies include IPv4 address sharing to access IPv4 content, IPv6 dual-stack implementation, protocol translation to access IPv4 and IPv6-addressed content, and bridging and tunneling to bypass single protocol routers. Early signs of accelerated IPv6 adoption after IANA exhaustion are evident.

Regional exhaustion

All the RIRs have set aside a small pool of IP addresses for the transition to IPv6, from which each LIR can typically get at most 1024 in total. ARIN and LACNIC reserves the last for IPv6 transition. APNIC, and RIPE NCC have reserved the last obtained block for IPv6 transition. AFRINIC reserves a block for this purpose. When only this last block remains, the RIR's supply of IPv4 addresses is said to be "exhausted".
APNIC was the first RIR to restrict allocations to 1024 addresses for each member, as its pool reached critical levels of one block on 14 April 2011. The APNIC RIR is responsible for address allocation in the area of fastest Internet expansion, including the emerging markets of China and India.
RIPE NCC, the regional Internet registry for Europe, was the second RIR to deplete its address pool on 14 September 2012.
On 10 June 2014, LACNIC, the regional Internet registry for Latin America and the Caribbean, was the third RIR to deplete its address pool.
ARIN was exhausted on 24 September 2015. ARIN has been unable to allocate large requests since July 2015, but smaller requests were still being met. After IANA exhaustion, IPv4 address space requests became subject to additional restrictions at ARIN, and became even more restrictive after reaching the last in April 2014.
On 31 March 2017, AFRINIC became the last regional Internet registry to run down to its last block of IPv4 addresses, thus triggering the first phase of its IPv4 exhaustion policy. "On 13 January 2020, AFRINIC approved an IPv4 prefix that resulted in no more than a /11 of non-reserved space to be available in the Final /8," which triggered its IPv4 Exhaustion Phase 2.
On 25 November 2019, RIPE NCC announced that it had made its "final IPv4 allocation from the last remaining addresses in our available pool. We have now run out of IPv4 addresses." RIPE NCC will continue to allocate IPv4 addresses, but only "from organisations that have gone out of business or are closed, or from networks that return addresses they no longer need. These addresses will be allocated to our members according to their position on a new waiting list…" The announcement also called for support for the implementation of the IPv6 roll-out.