CIDR stands for Classless Inter-Domain Routing and is a method for allocating IP addresses as well as for IP routing.
It was introduced in 1993 by the Internet Engineering Task Force to replace the previous classful network addressing architecture on the internet.
When choosing a CIDR range for your network, the following chart will show you how many maximum IP’s you can have on that network.
For example, /32 will give you 1 usable IP, /24 will give you 256 usable IPs, while /3 will give you 512 million usable IPs.
| IP Addresses | Bits | Prefix | Subnet Mask |
| 1 | /32 | 255.255.255.255 | |
| 2 | 1 | /31 | 255.255.255.254 |
| 4 | 2 | /30 | 255.255.255.252 |
| 8 | 3 | /29 | 255.255.255.248 |
| 16 | 4 | /28 | 255.255.255.240 |
| 32 | 5 | /27 | 255.255.255.224 |
| 64 | 6 | /26 | 255.255.255.192 |
| 128 | 7 | /25 | 255.255.255.128 |
| 256 | 8 | /24 | 255.255.255.0 |
| 512 | 9 | /23 | 255.255.254.0 |
| 1 K | 10 | /22 | 255.255.252.0 |
| 2 K | 11 | /21 | 255255.248.0 |
| 4 K | 12 | /20 | 255.255.240.0 |
| 8 K | 13 | /19 | 255.255.224.0 |
| 16 K | 14 | /18 | 255.255.192.0 |
| 32 K | 15 | /17 | 255.255.128.0 |
| 64 K | 16 | /16 | 255.255.0.0 |
| 128 K | 17 | /15 | 255.254.0.0 |
| 256 K | 18 | /14 | 255.252.0.0 |
| 512 K | 19 | /13 | 255.248.0.0 |
| 1 M | 20 | /12 | 255.240.0.0 |
| 2 M | 21 | /11 | 255.224.0.0 |
| 4 M | 22 | /10 | 255.192.0.0 |
| 8 M | 23 | /9 | 255.128.0.0 |
| 16 M | 24 | /8 | 255.0.0.0 |
| 32M | 25 | /7 | 254.0.0.0 |
| 64 M | 26 | /6 | 252.0.0.0 |
| 128 M | 27 | /5 | 248.0.0.0 |
| 256 M | 28 | /4 | 240.0.0.0 |
| 512 M | 29 | /3 | 224.0.0.0 |
| 1024 M | 30 | /2 | 192.0.0.0 |
| 2048 M | 31 | /1 | 128.0.0.0 |
| 4096 M | 32 | /0 | 0.0.0.0 |