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Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet, and was the first version deployed for production in the ARPANET in 1983. It still routes most Internet traffic today,〔(【引用サイトリンク】title=BGP Analysis Reports )〕 despite the ongoing deployment of a successor protocol, IPv6. IPv4 is described in IETF publication RFC 791 (September 1981), replacing an earlier definition (RFC 760, January 1980). IPv4 is a connectionless protocol for use on packet-switched networks. It operates on a best effort delivery model, in that it does not guarantee delivery, nor does it assure proper sequencing or avoidance of duplicate delivery. These aspects, including data integrity, are addressed by an upper layer transport protocol, such as the Transmission Control Protocol (TCP). ==Addressing == IPv4 uses 32-bit (four-byte) addresses, which limits the address space to (232) addresses. This limitation stimulated the development of IPv6 in the 1990s, which has been in commercial deployment since 2006. Because of the demand of the growing Internet, the small address space finally suffered exhaustion on February 3, 2011, after having been significantly delayed by classful network design, Classless Inter-Domain Routing, and network address translation (NAT). IPv4 reserves special address blocks for private networks (~18 million addresses) and multicast addresses (~270 million addresses). ===Address representations=== IPv4 addresses may be represented in any notation expressing a 32-bit integer value. They are most often written in the dot-decimal notation, which consists of four octets of the address expressed individually in decimal numbers and separated by periods. The CIDR notation standard combines the address with its routing prefix in a compact format, in which the address is followed by a slash character (/) and the count of consecutive ''1'' bits in the routing prefix (subnet mask). For example, the quad-dotted IP address 192.0.2.235 represents the 32-bit decimal number 3221226219, which in hexadecimal format is 0xC00002EB. This may also be expressed in dotted hex format as 0xC0.0x00.0x02.0xEB, or with octal byte values as 0300.0000.0002.0353. 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」の詳細全文を読む スポンサード リンク
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