IPv4

Internet Protocol version 4 (IPv4) is the fourth version of the (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, 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 transport protocol, such as the (TCP).

IP addresses based on IPv4 are 32-bits (four-byte) in size. This limits the address space to 4294967296 (2³²) addresses. Out of this range, IPv4 reserves special address blocks for private networks (~18 million addresses) and multicast addresses (~270 million addresses).

The limitation on IP addresses in IPv4 has lead to 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).

...
Wikipedia