IPv4, short for Internet Protocol version 4, is the addressing system that has powered the internet since 1983. It’s the format behind every standard IP address you’ve ever seen: four numbers separated by dots, like 192.168.1.1. Each section can range from 0 to 255, giving IPv4 a total pool of approximately 4.3 billion unique addresses.

Every device that connects to the internet needs an IP address, and for decades, those addresses were IPv4. Your ISP assigns one to you each time you go online, routing data to you and not someone else. Each IP address contains two embedded pieces of information: a network ID identifying which network you’re on, and a host ID identifying your specific device within it.

The problem is that 4.3 billion addresses turned out to be nowhere near enough. Smartphones, tablets, smart home devices, and cloud infrastructure consumed the global supply faster than anyone anticipated, and the last unallocated IPv4 blocks were distributed in 2011. The industry has been transitioning to IPv6 ever since. IPv6 is a next-generation format with a vastly larger address space. Many ISPs now run a dual-stack setup, supporting both formats simultaneously. You can check whether you’re connecting with an IPv4 address, an IPv6 address, or both using an IP lookup tool.