What Is IPv4 (Internet Protocol Version 4)?
Learn what IPv4 is, how IPv4 addressing works, and why exhaustion of IPv4 space led to the development of IPv6.
IPv4 Overview
Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol and the foundation of most networks in use today. It defines how devices identify each other and route packets across local networks and the global internet.
An IPv4 address is a 32-bit value typically written in dotted-decimal notation such as 203.0.113.42. The protocol includes mechanisms for fragmentation, checksums, and basic header information used by routers and hosts.
IPv4 Addressing and Subnetting
IPv4 divides address space into networks and hosts. Subnet masks or CIDR prefixes specify which bits represent the network portion and which represent host addresses. For example, 192.0.2.0/24 describes a network with 256 total addresses, typically 254 usable host addresses.
Subnetting allows administrators to break larger networks into smaller segments for organizational, performance, and security reasons. Private address ranges reserved by RFC 1918 further extend IPv4’s usefulness for internal networks.
Limitations of IPv4 and the Move to IPv6
IPv4’s 32-bit space provides around 4.3 billion unique addresses. While that number seemed large in the early days of the internet, the explosion of devices and services made it clear that more space would be needed. Techniques such as NAT, CIDR, and private addressing delayed exhaustion but could not prevent it entirely.
To address these limitations, IPv6 was designed with a vastly larger address space and updated features. Today, many networks run both IPv4 and IPv6 side by side as adoption continues.