v4 What is IPv4?

IPv4 carries most internet traffic using 32-bit addresses. Learn about address classes, CIDR notation, private ranges, and why IPv4 is running out.

What is IPv4?

IPv4 (Internet Protocol version 4) is the fourth revision of the Internet Protocol and the foundation of most internet traffic today. It defines how data packets are addressed, routed, and delivered across networks.

An IPv4 address is a 32-bit number represented as four decimal octets separated by dots — for example, 192.168.1.1. Each octet ranges from 0 to 255. This gives a theoretical maximum of 2³² = 4,294,967,296 (about 4.3 billion) unique addresses.

Address structure

192      .168      .1        .1
11000000  10101000  00000001  00000001
↑ octet 1  ↑ octet 2  ↑ octet 3  ↑ octet 4

Each address consists of a network portion and a host portion. The subnet mask (or CIDR prefix) tells you how many bits belong to the network — the rest identify individual hosts within that network.

Private address ranges (RFC 1918)

Three blocks are reserved for private networks and are never routed on the public internet. Every home router, corporate network, and cloud VPC uses addresses from these ranges:

Range	CIDR	Hosts
`10.0.0.0 – 10.255.255.255`	`10.0.0.0/8`	16,777,216
`172.16.0.0 – 172.31.255.255`	`172.16.0.0/12`	1,048,576
`192.168.0.0 – 192.168.255.255`	`192.168.0.0/16`	65,536

Address exhaustion

IANA (the global IP address authority) allocated the last block of IPv4 addresses in February 2011. Regional registries followed — APNIC (Asia-Pacific) in 2011, RIPE NCC (Europe) in 2012, LACNIC (Latin America) in 2014, ARIN (North America) in 2015, AFRINIC (Africa) in 2017.

Two mechanisms have extended IPv4's life:

NAT (Network Address Translation) — lets millions of devices share a single public IP, multiplying the effective address space at the cost of complexity.
IPv6 — the long-term replacement, with a 128-bit address space (3.4 × 10³⁸ addresses). Adoption is gradual; most servers run both protocols simultaneously.

CIDR notation

Classless Inter-Domain Routing (CIDR) notation replaces the old class system and describes a range of addresses as a base address and a prefix length:

192.168.1.0/24
            ↑ network address  ↑ prefix length (24 bits = network, 8 bits = host)

A /24 network has 2⁸ = 256 addresses (254 usable hosts — one is the network address, one is the broadcast address). See the subnet reference or use the subnet calculator for quick calculations.

Frequently asked questions

What is the difference between IPv4 and IPv6?

IPv4 uses 32-bit addresses (about 4.3 billion unique addresses); IPv6 uses 128-bit addresses (effectively unlimited). IPv4 is written in dotted decimal (192.168.1.1); IPv6 uses colon-separated hexadecimal (2001:db8::1). IPv6 also has built-in features like auto-configuration and improved security headers.

Is IPv4 being replaced by IPv6?

Gradually, yes. IPv6 adoption has grown significantly (Google sees around 40-45% of traffic over IPv6), but IPv4 still handles the majority of internet traffic. Both protocols will likely coexist for many years. Most servers and CDNs now support both (dual-stack).

What is a /24 network?

A /24 network has a 24-bit prefix, leaving 8 bits for host addresses. It contains 256 IP addresses (254 usable, since the first is the network address and the last is the broadcast address). It's one of the most common subnet sizes for small networks.