What is IPv4?
IPv4, short for Internet Protocol version 4, is the addressing system that identifies devices on most networks today. It assigns each connected device a 32-bit address written as four decimal numbers separated by dots, such as 192.0.2.1. Every packet sent across the internet carries a source and destination IPv4 address, which is how routers know where to deliver data.
The protocol was specified in RFC 791, published in 1981, and it has outlasted every attempt to replace it at scale.
How IPv4 addresses are structured
An IPv4 address is 32 bits long. Those bits split into a network portion and a host portion, and the split point is defined by the subnet mask or the CIDR prefix length.
- 32 bits total, which allows about 4.29 billion unique addresses
- Written in dotted-decimal notation, four groups of 0 to 255
- Prefix lengths such as /24 or /16 show how many bits identify the network
- Earlier class-based rules (Class A, B, C) were replaced by CIDR in 1993
Why the world ran out of IPv4 addresses
The original design assumed a few large networks, not billions of phones, servers, and sensors. Address blocks were handed out generously in the early years, and demand outgrew supply. The global pool reached its final allocation stage in 2011, and the regional registries that distribute addresses have been working from remaining stock, recovered blocks, and transfer markets since then.
Exhaustion does not mean the protocol stopped working. It means new networks have to be economical with the addresses they can get.
How networks cope
Three techniques keep IPv4 running well past its original capacity.
- NAT (Network Address Translation): a router shares one public address among many internal devices
- CIDR: variable-length prefixes let a block be divided into right-sized pieces
- Address transfers: organizations that hold unused ranges can sell or reassign them
IPv4 compared with IPv6
IPv6 uses 128-bit addresses, which removes the shortage problem and simplifies routing. IPv4 and IPv6 run side by side on many networks, a setup called dual stack. IPv4 traffic still dominates on older infrastructure, while mobile carriers and large cloud providers lean heavily on IPv6.
- IPv4: 32-bit, about 4.29 billion addresses, mature tooling
- IPv6: 128-bit, effectively unlimited addresses, simpler header format
IPv4 ranges worth knowing
- 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are private and not routed on the public internet
- 127.0.0.0/8 is the loopback range, where 127.0.0.1 means this device
- 169.254.0.0/16 is link-local, used when a device cannot reach a DHCP server
- 224.0.0.0/4 is reserved for multicast
Frequently asked questions
Is IPv4 still in use?
Yes. Most websites, VPNs, and enterprise networks still run IPv4 alongside IPv6, and many internal networks rely on it entirely.
How many IPv4 addresses exist?
The 32-bit space holds 4,294,967,296 addresses, though reserved and special-use ranges reduce how many are available for ordinary assignment.
Does IPv4 slow down a connection?
Not by itself. Latency depends on routing, distance, and congestion rather than on the address version.