Internet Protocol version 4 is the fourth iteration of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed. IPv4 is the dominant network layer protocol on the internet and when ignoring its successor — IPv6 — it is the only protocol used on the internet.

It is described in IETF RFC 791 (September 1981) which obsoleted RFC 760 (January 1980). The United States Department of Defense also standardized it as MIL-STD-1777.

IPv4 is a data-oriented protocol to be used on a packet switched internetwork (e.g., Ethernet). It is a best effort protocol in that it doesn't guarantee delivery. It doesn't make any guarantees on the correctness of the data; it may result in duplicated packets and/or packets out-of-order. All of these things are addressed by an upper layer protocol (e.g., TCP, UDP).

The entire purpose of IP is to provide unique global computer addressing to ensure that two computers over the internet can uniquely identify one another.