IPv4 (Internet Protocol version 4) is the fourth version of the Internet Protocol and the foundation of internet communication. Every device connected to the internet uses IPv4 to send and receive data.
What is IPv4?
IPv4 (Internet Protocol version 4) is the fourth revision of the Internet Protocol and the first version to be widely deployed. It provides the addressing system that identifies devices on a network and routes traffic across the internet.
An IPv4 address is a 32-bit number typically displayed in dotted-decimal notation—four numbers separated by periods, where each number represents 8 bits (one octet) and ranges from 0 to 255.
192.168.1.1
IPv4 Address Format
An IPv4 address consists of four octets (8-bit numbers) separated by periods. Each octet can have a value between 0 and 255.
Octet
Each octet represents 8 bits, giving 256 possible values (0-255)
The total address space of 32 bits allows for approximately 4.3 billion unique addresses (2^32 = 4,294,967,296). While this seemed enormous when IPv4 was designed in 1981, internet growth has exhausted this pool.
IPv4 Address Classes
Historically, IPv4 addresses were organized into classes based on their leading bits. While classful networking is largely obsolete (replaced by CIDR), understanding classes helps interpret legacy configurations.
Large networks with millions of hosts. First octet identifies the network.
Medium-sized networks with thousands of hosts. First two octets identify the network.
Small networks with up to 254 hosts. First three octets identify the network.
Special IPv4 Address Ranges
Several IPv4 ranges are reserved for special purposes and cannot be used for public internet addressing.
| Range | Purpose |
|---|---|
| 10.0.0.0/8 | Private network (Class A) - Large organizations |
| 172.16.0.0/12 | Private network (Class B) - Medium organizations |
| 192.168.0.0/16 | Private network (Class C) - Home/small office |
| 127.0.0.0/8 | Loopback (localhost) - Testing and development |
| 169.254.0.0/16 | Link-local - Automatic private IP addressing |
Why IPv4 Addresses Are Exhausted
The 4.3 billion IPv4 addresses seemed infinite when the protocol was designed in 1981. However, the explosive growth of the internet—smartphones, IoT devices, cloud services—quickly depleted this pool.
IANA (Internet Assigned Numbers Authority) allocated the last blocks of IPv4 addresses to Regional Internet Registries in 2011. Today, new IPv4 addresses can only be obtained through the secondary market.
IPv4 Scarcity
With no new IPv4 addresses available from registries, businesses must lease or purchase addresses from existing holders. This has created a thriving secondary market.