IPv4 Address Classes: A, B, C, D and E
An IPv4 address is made of four numbers from 0 to 255, for example 192.168.1.1. In the original “classful” system, the first number decides which of five classes – A, B, C, D or E – the address belongs to.
Classes A, B and C are used for normal devices such as routers, computers and phones. Class D is used for multicast, and Class E is reserved for experiments.
| Class | IP range | First number | Default subnet mask | Private range | Used for |
|---|---|---|---|---|---|
| Class A | 1.0.0.0 – 127.255.255.255 | 1 – 127 | 255.0.0.0 (/8) | 10.0.0.0/8 | Very large networks. The private 10.x.x.x part is widely used by companies, VPNs and some ISP routers. |
| Class B | 128.0.0.0 – 191.255.255.255 | 128 – 191 | 255.255.0.0 (/16) | 172.16.0.0/12 | Medium-sized networks. The private 172.16.x.x – 172.31.x.x part is used by offices, Docker and iPhone hotspots. |
| Class C | 192.0.0.0 – 223.255.255.255 | 192 – 223 | 255.255.255.0 (/24) | 192.168.0.0/16 | Small networks. The private 192.168.x.x part is used by most home routers. |
| Class D | 224.0.0.0 – 239.255.255.255 | 224 – 239 | Not used | None | Multicast: one sender delivers the same data to a group of devices (IPTV, streaming, routing protocols). |
| Class E | 240.0.0.0 – 255.255.255.255 | 240 – 255 | Not used | None | Reserved for experiments and future use; not used on the public internet. |
How to find the class of an IP address
Look only at the first number of the address:
- 1 – 126: Class A (127 is reserved for loopback, e.g. 127.0.0.1)
- 128 – 191: Class B
- 192 – 223: Class C
- 224 – 239: Class D (multicast)
- 240 – 255: Class E (experimental)
Example: 192.168.1.1 starts with 192, so it is a Class C address. 10.0.0.1 starts with 10, so it is Class A.
Private IP ranges in each class
Classes A, B and C each contain one private range (RFC 1918). Private addresses are free for anyone to use inside a home or office network and are not reachable from the internet. Your router’s login address is almost always one of them.
| Class | Private range | CIDR | IP |
|---|---|---|---|
| Class A | 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | 16,777,216 |
| Class B | 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | 1,048,576 |
| Class C | 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | 65,536 |
Are IP classes still used?
Since 1993 the internet routes addresses without classes (CIDR), so a network can have any size, for example /22. The class names are still used to describe address ranges, default subnet masks and the three private ranges.