What is IPv4?
// the protocol that built the internet
Overview
IPv4 (Internet Protocol version 4) is the fourth revision of the Internet Protocol and the first to be widely deployed. Defined in 1981 by RFC 791, it remains the dominant protocol for routing traffic across the internet today — though IPv6 is rapidly growing alongside it.
Address format
An IPv4 address is a 32-bit number, typically written in dotted-decimal notation: four groups of numbers from 0 to 255, separated by dots.
192.168.1.1 203.0.113.42 8.8.8.8
32 bits allows for 2³² = 4,294,967,296 unique addresses — just over 4.3 billion. In the early days of the internet, this seemed more than enough.
Address exhaustion
As the internet grew explosively in the 1990s and 2000s, it became clear that 4.3 billion addresses would not be sufficient for a world where every phone, thermostat, and car might need its own address. The last blocks of unallocated IPv4 addresses were distributed to regional registries by IANA in 2011.
Several techniques were developed to slow exhaustion:
- NAT (Network Address Translation) — allows many devices on a private network to share a single public IPv4 address. This is why your home router can serve a dozen devices with one ISP-assigned address.
- CIDR (Classless Inter-Domain Routing) — more efficient allocation of address blocks.
These are stopgaps. The long-term solution is IPv6.
Private address ranges
Certain IPv4 ranges are reserved for private networks and are not routable on the public internet:
10.0.0.0 – 10.255.255.255 172.16.0.0 – 172.31.255.255 192.168.0.0 – 192.168.255.255
If your device shows a private address (e.g., 192.168.x.x), that is your local network address — not the public IP the internet sees.