IPv4 Fundamentals

Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). This is one of the core protocols of standard-based Internetworking methods in the Internet, and was the first version deployed for production in ARPANET in 1983. It still routes most Internet traffic today [1] despite the ongoing deployment of 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 in packet-switched networks. It operates as a best effort delivery model, in that it does not guarantee delivery, nor does it ensure 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). 

IPv4 uses 32-bit (four-byte) addresses, which limits address space to 4294967296 (232) addresses. This limitation stimulated the development of IPv6 in the 1990s, which has been in commercial deployment since 2006.