Specifying IPs In CIDR Notation
These days, CIDR notation is used in a lot of places especially in various configurations like firewall rules in almost all popular cloud providers. But what exactly is CIDR?
Classless inter-domain routing (CIDR) is a set of Internet protocol (IP) standards that is used to create unique identifiers for networks and individual devices
| IPv4 CIDR IP/CIDR | Difference to last IP | Subnet Mask | Hosts | Class |
|---|---|---|---|---|
| a.b.c.d/32 | +0.0.0.0 | 255.255.255.255 | 1 | 1/256 C |
| a.b.c.d/31 | +0.0.0.1 | 255.255.255.254 | 2 | 1/128 C |
| a.b.c.d/30 | +0.0.0.3 | 255.255.255.252 | 4 | 1/64 C |
| a.b.c.d/29 | +0.0.0.7 | 255.255.255.248 | 8 | 1/32 C |
| a.b.c.d/28 | +0.0.0.15 | 255.255.255.240 | 16 | 1/16 C |
| a.b.c.d/27 | +0.0.0.31 | 255.255.255.224 | 32 | 1/8 C |
| a.b.c.d/26 | +0.0.0.63 | 255.255.255.192 | 64 | 1/4 C |
| a.b.c.d/25 | +0.0.0.127 | 255.255.255.128 | 128 | 1/2 C |
| a.b.c.0/24 | +0.0.0.255 | 255.255.255.000 | 256 | 1 C |
| a.b.c.0/23 | +0.0.1.255 | 255.255.254.000 | 512 | 2 C |
| a.b.c.0/22 | +0.0.3.255 | 255.255.252.000 | 1,024 | 4 C |
| a.b.c.0/21 | +0.0.7.255 | 255.255.248.001 | 2,048 | 8 C |
| a.b.c.0/20 | +0.0.15.255 | 255.255.240.000 | 4,096 | 16 C |
| a.b.c.0/19 | +0.0.31.255 | 255.255.224.000 | 8,192 | 32 C |
| a.b.c.0/18 | +0.0.63.255 | 255.255.192.000 | 16,384 | 64 C |
| a.b.c.0/17 | +0.0.127.255 | 255.255.128.000 | 32,768 | 128 C |
| a.b.0.0/16 | +0.0.255.255 | 255.255.000.000 | 65,536 | 256 C = 1 B |
| a.b.0.0/15 | +0.1.255.255 | 255.254.000.000 | 131,072 | 2 B |
| a.b.0.0/14 | +0.3.255.255 | 255.252.000.000 | 262,144 | 4 B |
| a.b.0.0/13 | +0.7.255.255 | 255.248.000.000 | 524,288 | 8 B |
| a.b.0.0/12 | +0.15.255.255 | 255.240.000.000 | 1,048,576 | 16 B |
| a.b.0.0/11 | +0.31.255.255 | 255.224.000.000 | 2,097,152 | 32 B |
| a.b.0.0/10 | +0.63.255.255 | 255.192.000.000 | 4,194,304 | 64 B |
| a.b.0.0/9 | +0.127.255.255 | 255.128.000.000 | 8,388,608 | 128 B |
| a.0.0.0/8 | +0.255.255.255 | 255.000.000.000 | 16,777,216 | 256 B = 1 A |
| a.0.0.0/7 | +1.255.255.255 | 254.000.000.000 | 33,554,432 | 2 A |
| a.0.0.0/6 | +3.255.255.255 | 252.000.000.000 | 67,108,864 | 4 A |
| a.0.0.0/5 | +7.255.255.255 | 248.000.000.000 | 134,217,728 | 8 A |
| a.0.0.0/4 | +15.255.255.255 | 240.000.000.000 | 268,435,456 | 16 A |
| a.0.0.0/3 | +31.255.255.255 | 224.000.000.000 | 536,870,912 | 32 A |
| a.0.0.0/2 | +63.255.255.255 | 192.000.000.000 | 1,073,741,824 | 64 A |
| a.0.0.0/1 | +127.255.255.255 | 128.000.000.000 | 2,147,483,648 | 128 A |
| 0.0.0.0/0 | +255.255.255.255 | 000.000.000.000 | 4,294,967,296 | 256 A |