netmask), and in the technical jargon used in network administrators' discussions.Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be uniquely assigned to a particular computer or device. The IP address space is managed globally by the Internet Assigned Numbers Authority (IANA), and by five regional Internet registries (RIRs) responsible in their designated territories for assignment to end users and local Internet registries, such as Internet service providers.
The smallest possible individual allocation is a subnet for 2 hosts, which is the square of the size of the entire IPv4 Internet.
IPv4 addresses are usually represented in dot-decimal notation, consisting of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., network administrators interpreted an IP address in two parts: network number portion and host number portion.
The highest order octet (most significant eight bits) in an address was designated as the network number and the remaining bits were called the rest field or host identifier, and were used for host numbering within a network.
This early method soon proved inadequate as additional networks developed that were independent of the existing networks already designated by a network number.
In 1981, the Internet addressing specification was revised with the introduction of classful network architecture.