Classless Inter Domain Routing (CIDR) is a method for assigning IP addresses without using the standard IP address classes like Class A, Class B or Class C.
In CIDR notation, an IP address is represented as A.B.C.D /n, where "/n" is called the IP prefix or network prefix. The IP prefix identifies the number of significant bits used to identify a network. For example, 192.9.205.22 /18 means, the first 18 bits are used to represent the network and the remaining 14 bits are used to identify hosts. Common prefixes are 8, 16, 24, and 32.
Refer to the following page for the CIDR to Netmask Translation Table.
|
CIDR |
Netmask (Dot Notation) | Number of Hosts |
|---|---|---|
| /1 | 128.0.0.0 | |
| /2 | 192.0.0.0 | |
| /3 | 224.0.0.0 | |
| /4 | 240.0.0.0 | |
| /5 | 248.0.0.0 | |
| /6 | 252.0.0.0 | |
| /7 | 254.0.0.0 | |
| /8 | 255.0.0.0 | |
| /9 | 255.128.0.0 | |
| /10 | 255.192.0.0 | |
| /11 | 255.224.0.0 | |
| /12 | 255.240.0.0 | |
| /13 | 255.248.0.0 | |
| /14 | 255.252.0.0 | |
| /15 | 255.254.0.0 | |
| /16 | 255.255.0.0 | |
| /17 | 255.255.128 | |
| /18 | 255.255.192.0 | |
| /19 | 255.255.224.0 | |
| /20 | 255.255.240.0 | |
| /21 | 255.255.248.0 | |
| /22 | 255.255.252.0 | |
| /23 | 255.255.254.0 | |
| /24 | 255.255.255.0 | 256 |
| /25 | 255.255.255.128 | 128 |
| /26 | 255.255.255.192 | 64 |
| /27 | 255.255.255.224 | 32 |
| /28 | 255.255.255.240 | 16 |
| /29 | 255.255.255.248 | 8 |
| /30 | 255.255.255.252 | 4 |
| /31 | 255.255.255.254 | 2 |
| /32 | 255.255.255.255 | 1 |