Network guide
What is IPv4?
Reviewed 10 September 2026 · 5-minute read
IPv4 is the fourth version of the Internet Protocol. It identifies interfaces with 32-bit addresses commonly written as four decimal numbers, such as 192.0.2.1.
How an IPv4 address is written
Each of the four decimal octets represents eight bits and ranges from 0 to 255. A prefix length such as /24 states how many leading bits describe the network.
Public, private and shared ranges
Globally routed addresses can communicate across the public internet. RFC 1918 reserves private ranges for internal networks, while RFC 6598 reserves 100.64.0.0/10 for carrier-grade NAT. A router or carrier may therefore translate many private devices to one public address.
Why IPv4 is still used
Its address space is limited, but extensive compatibility and network address translation keep it widely deployed. IPv6 expands the address space and often runs alongside IPv4 during transition.