IPv4

Internet Protocol version 4 (IPv4) is the fourth revision in the development of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet, and is still by far the most widely deployed Internet Layer protocol.

IPv4 uses 32-bit (four-byte) addresses, which limits the address space to 4,294,967,296 possible unique addresses. However, some are reserved for special purposes such as private networks (~18 million addresses) or multicast addresses (~16 million addresses). This reduces the number of addresses that can be allocated as public Internet addresses. As the number of addresses available are consumed, an IPv4 address shortage appears to be inevitable, however network address translation (NAT) has significantly delayed this inevitability.

This limitation has helped stimulate the push towards IPv6.

IPv4 addresses are usually written in dot-decimal notation, which consists of the four octets of the address expressed in decimal and separated by periods. For example:

208.94.149.4 

IPv4 addresses are represented in the Domain Name System by A records.