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IPv4 address exhaustion is the depletion of the pool of unallocated Internet Protocol Version 4 (IPv4) addresses, which has been anticipated since the late 1980s. This depletion is the reason for the development and deployment of its successor protocol, IPv6. The IP address space is managed by the Internet Assigned Numbers Authority (IANA) globally, and by five regional Internet registries (RIR) responsible in their designated territories for assignment to end users and local Internet registries, such as Internet service providers. The top-level exhaustion occurred on 31 January 2011.〔(Available Pool of Unallocated IPv4 Internet Addresses Now Completely Emptied ), (Major Announcement Set on Dwindling Pool of Available IPv4 Internet Addresses )〕〔(【引用サイトリンク】title=Five /8s allocated to RIRs – no unallocated IPv4 unicast /8s remain )〕 Four of the five RIRs have exhausted allocation of all the blocks they have not reserved for IPv6 transition; this occurred on 15 April 2011 for the Asia-Pacific, on 14 September 2012 for Europe, on 10 June 2014 for Latin America and the Caribbean, and on 24 September 2015 for North America. IPv4 provides approximately 4.3 billion addresses; a subset of these have been distributed by IANA to the RIRs in blocks of approximately 16.8 million addresses each. The depletion of the IPv4 allocation pool has been a concern since the late 1980s, when the Internet started to experience dramatic growth. The Internet Engineering Task Force (IETF) created the Routing and Addressing Group (ROAD) in November 1991 to respond to the scalability problem caused by the classful network allocation system in place at the time.〔RFC 4632〕 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.〔 IPv6, the successor technology to IPv4 which was designed to address this problem, supports approximately network addresses〔(【引用サイトリンク】title=World IPv6 Day: Working Together Towards a New Internet Protocol )〕 Although the predicted depletion was already approaching its final stages in 2008, most providers of Internet services and software vendors were just beginning IPv6 deployment. ==IP addressing== Every node of an Internet Protocol (IP) network, such as a computer, router, or network printer, is assigned an IP address that is used to locate and identify the node in communications with other nodes on the network. Internet Protocol version 4 provides 232 (4,294,967,296) addresses. However, large blocks of IPv4 addresses are reserved for special uses and are unavailable for public allocation. More precisely, if a device has several network interfaces, then each interface must have at least one distinct IP address assigned to it. For example, a laptop might have a wireless network interface and a wired network interface using a network cable, and this would require a total of two IP addresses, one per interface. Another example is a mobile phone with a 3G network interface and an interface to a wireless LAN. All routers have to have several network interfaces and typically will have several IP addresses associated with them. It is also possible that an interface can be assigned more than one IP address, for various reasons. 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 (NAT) 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 customer premises router, instead of allocating a public address to each network device. Complicating matters, IPv6-unaware NAT devices break native and 6to4 IPv6 connectivity, and a large fraction break 6in4 tunnels. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「IPv4 address exhaustion」の詳細全文を読む スポンサード リンク
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