GLOSSARY · INTERNET PROTOCOL VERSION 4
IPv4
IPv4 is the older and still most common version of the internet's addressing system. Its addresses are 32-bit numbers written as four groups separated by dots, such as 203.0.113.25. That format allows about 4.3 billion distinct addresses in total.
Why it matters
There are more devices than IPv4 addresses, so providers share addresses among many customers through techniques such as NAT and CGNAT, and run IPv6 alongside. For you, this means one IPv4 address may represent many people at once, which makes it a weaker signal of who you are than it used to be, and can cause shared-address problems such as blocks that hit innocent neighbours.
In practice
Most websites still work over IPv4 alone, and many older systems, including some blacklist services, only understand IPv4. If you run a server or check reputation lists, you will mainly deal with IPv4. A device that has both versions is called dual-stack, and you can see how yours behaves with the IPv6 test.
Related terms
- IPv6: IPv6 is the newer version of the addressing system, built to replace IPv4.
- NAT: NAT is a technique where a router rewrites the addresses on outgoing traffic so that many devices with private addresses can share one public IP address.
- CGNAT: Carrier-grade NAT is NAT performed by an internet provider, not by your own router.
- Subnet and CIDR: A subnet is a block of consecutive IP addresses treated as one network.