My IP Help

IPv4

Also known as: Internet Protocol version 4

The original 32-bit Internet Protocol address format, providing about 4.3 billion unique addresses in dotted-decimal notation like 192.0.2.1.

Last updated:

What is IPv4?

IPv4 (Internet Protocol version 4) is the fourth revision of the Internet Protocol and the first version to be widely deployed. Defined in RFC 791 in 1981, it uses 32-bit addresses, which allows for about 4.3 billion unique addresses. Addresses are written in dotted-decimal notation: four 8-bit numbers separated by dots, like 192.0.2.1.

How IPv4 addresses are structured

Each IPv4 address has two parts: a network portion and a host portion. The split is defined by a subnet mask or, more commonly today, by CIDR notation like 192.0.2.0/24. The network portion identifies the subnet, and the host portion identifies a device within that subnet. Routers use only the network portion to forward packets between networks.

Certain address blocks are reserved for special uses: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 for private networks; 127.0.0.0/8 for loopback; 169.254.0.0/16 for link-local auto-configuration; and 224.0.0.0/4 for multicast.

Address exhaustion and NAT

IANA allocated the last unreserved /8 blocks to the regional internet registries in February 2011, and APNIC, the Asia-Pacific registry, ran out of general IPv4 allocations shortly after. The practical workaround is Network Address Translation — a single public IPv4 address can front thousands of devices on a private network by rewriting addresses on the fly. The long-term fix is migration to IPv6, which provides 340 undecillion addresses.

You can check whether your connection uses IPv4, IPv6, or both with our IP lookup tool.

Frequently Asked Questions

IPv4 stands for Internet Protocol version 4. It was the first widely deployed version of the Internet Protocol, standardized in RFC 791 in 1981.
IPv4 uses 32-bit addresses, giving a theoretical maximum of 2^32 — about 4.3 billion unique addresses. Hundreds of millions are reserved for private networks, loopback, and multicast, leaving roughly 3.7 billion usable on the public internet.
Yes. IPv4 is still widely used, typically alongside IPv6 in dual-stack deployments. A growing share of networks are IPv6-only, but IPv4-only and dual-stack configurations remain the norm on home ISPs and enterprise networks.
With only 4.3 billion addresses for tens of billions of connected devices, supply was mathematically insufficient. IANA exhausted its central pool in February 2011, and most regional registries followed within a decade.
IPv4 uses 32-bit addresses written as four decimal octets (192.0.2.1); IPv6 uses 128-bit addresses written as eight hexadecimal groups (2001:db8::1). IPv6 provides vastly more addresses and removes the need for NAT in typical home networks.
Back to glossary