IPv4

What IPv4 is

IPv4 (Internet Protocol version 4) is the addressing scheme that powered most of the early internet and still carries enormous traffic today. It uses 32-bit addresses, which are normally written as four decimal numbers from 0 to 255 separated by dots, a format called dotted-decimal notation.

Why it matters

A 32-bit space allows roughly 4.3 billion unique addresses. That sounded like plenty in the 1980s, but the explosion of phones, servers, and smart devices exhausted the free pool. This shortage drove the adoption of techniques like NAT, which lets many devices share one public address, and pushed the long migration toward IPv6.

How it is structured

An IPv4 address splits into a network part and a host part, defined by a subnet mask or CIDR notation:

• 203.0.113.42 is a single host address.
• 192.168.0.0/16 describes a private range of many addresses.
• 10.0.0.0/8 is another common private block.

For example, a small office router might hand out addresses in 192.168.1.0/24, giving up to 254 usable host addresses. You can inspect any IPv4 address with the WhatIP ip-lookup tool to see its owner and location.