IPv4 is version 4 of the Internet Protocol (IP). It was the first version of the Internet Protocol to be widely deployed, and forms the basis for the current (as of 2004) Internet.

IPv4 addresses are written in Dot-decimal notation. Here's an example: 127.0.0.1.

IPv4 uses 32-bit addresses, limiting it to 4,294,967,296 unique addresses, many of which are dedicated to local networks. This limitation has helped stimulate the push towards IPv6, which is currently in the early stages of deployment, and is expected to eventually replace IPv4.