Editing IPv4 (section)

==Address space exhaustion==
{{Main|IPv4 address exhaustion}}
[[File:IPv4 exhaustion time line-en.svg|thumb|upright=2|IPv4 address exhaustion timeline]]
In the 1980s, it became apparent that the pool of available IPv4 addresses was depleting at a rate that was not initially anticipated in the original design of the network.<ref>{{cite web|title=World 'running out of Internet addresses'|url=http://technology.inquirer.net/infotech/infotech/view/20110121-315808/World-running-out-of-Internet-addresses|access-date=2011-01-23|url-status=dead|archive-url=https://web.archive.org/web/20110125195711/http://technology.inquirer.net/infotech/infotech/view/20110121-315808/World-running-out-of-Internet-addresses|archive-date=2011-01-25}}</ref> The main market forces that accelerated address depletion included the rapidly growing number of Internet users, who increasingly used mobile computing devices, such as [[laptop computers]], [[personal digital assistant]]s (PDAs), and [[smart phone]]s with IP data services. In addition, high-speed Internet access was based on always-on devices. The threat of exhaustion motivated the introduction of a number of remedial technologies, such as:
*[[Classless Inter-Domain Routing]] (CIDR), for smaller ISP allocations 
*[[#Unnumbered interface|Unnumbered interfaces]] removed the need for addresses on transit links.
*[[Network address translation]] (NAT) removed the need for the [[end-to-end principle]].
By the mid-1990s, NAT was used pervasively in network access provider systems, along with strict usage-based allocation policies at the regional and local Internet registries.

The primary address pool of the Internet, maintained by IANA, was exhausted on 3 February 2011, when the last five blocks were allocated to the five [[Regional Internet registry|RIR]]s.<ref>{{cite web|url=http://www.nro.net/news/ipv4-free-pool-depleted|title=Free Pool of IPv4 Address Space Depleted|last=Smith|first=Lucie|author2=Lipner, Ian|date=3 February 2011|publisher=[[Number Resource Organization]]|access-date=3 February 2011}}</ref><ref>{{cite web|url=http://mailman.nanog.org/pipermail/nanog/2011-February/032107.html|title=Five /8s allocated to RIRs&nbsp;– no unallocated IPv4 unicast /8s remain|author=ICANN, nanog mailing list}}</ref> [[APNIC]] was the first RIR to exhaust its regional pool on 15 April 2011, except for a small amount of address space reserved for the transition technologies to IPv6, which is to be allocated under a restricted policy.<ref>{{cite web|title=APNIC IPv4 Address Pool Reaches Final /8|url=http://www.apnic.net/publications/news/2011/final-8|access-date=15 April 2011|author=Asia-Pacific Network Information Centre|date=15 April 2011|url-status=dead|archive-url=https://web.archive.org/web/20110807162057/http://www.apnic.net/publications/news/2011/final-8|archive-date=7 August 2011}}</ref>

The long-term solution to address exhaustion was the 1998 specification of a new version of the Internet Protocol, [[IPv6]].{{Ref RFC|2460}} It provides a vastly increased address space, but also allows improved route aggregation across the Internet, and offers large subnetwork allocations of a minimum of 2<sup>64</sup> host addresses to end users. However, IPv4 is not directly interoperable with IPv6, so that IPv4-only hosts cannot directly communicate with IPv6-only hosts. With the phase-out of the [[6bone]] experimental network starting in 2004, permanent formal deployment of IPv6 commenced in 2006.{{Ref RFC|3701}} Completion of [[IPv6 deployment]] is expected to take considerable time,<ref>{{Cite book|title=2016 IEEE International Conference on Emerging Technologies and Innovative Business Practices for the Transformation of Societies (EmergiTech)|publisher=University of Technology, Mauritius, Institute of Electrical and Electronics Engineers|date=August 2016|isbn=9781509007066|location=Piscataway, NJ|oclc=972636788}}</ref> so that intermediate [[IPv6 transition mechanism|transition technologies]] are necessary to permit hosts to participate in the Internet using both versions of the protocol.