What is IPv4?

IPv4 (Internet Protocol version 4) is the fourth version of the Internet Protocol. It was first deployed in the ARPANET in 1983 and remains the dominant routing protocol on the Internet today, despite being decades old and technically exhausted.

Key facts:

• 32-bit addresses — total 2³² = 4,294,967,296 (≈ 4.3 billion) unique addresses
• Format — four dot-separated decimal numbers, 0–255 each (e.g. 198.51.100.7)
• Exhaustion — IANA allocated its last unassigned /8 blocks in February 2011
• Replacement — IPv6 (128-bit) coexists with IPv4; most devices support both

See our IPv4 exhaustion tracker for live statistics, or compare IPv4 vs IPv6.