self-proclaimed internet enthusiast!

ipv4 subnets

CIDR | Addresses     | Netmask         | Size            | Comment
---- | ------------- | --------------- | --------------- | -------
/32  | 1             | 255.255.255.255 |    1/256 of /24 | A single host
/31  | 2             | 255.255.255.254 |    1/128 of /24 | 0 usable addresses
/30  | 4             | 255.255.255.252 |     1/64 of /24 |
/29  | 8             | 255.255.255.248 |     1/32 of /24 |
/28  | 16            | 255.255.255.240 |     1/16 of /24 |
/27  | 32            | 255.255.255.224 |      1/8 of /24 |
/26  | 64            | 255.255.255.192 |      1/4 of /24 |
/25  | 128           | 255.255.255.128 |      1/2 of /24 |
/24  | 256           | 255.255.255.0   |         1 x /24 | Class C
/23  | 512           | 255.255.254.0   |         2 x /24 |
/22  | 1.024         | 255.255.252.0   |         4 x /24 |
/21  | 2.048         | 255.255.248.0   |         8 x /24 |
/20  | 4.096         | 255.255.240.0   |        16 x /24 |
/19  | 8.192         | 255.255.224.0   |        32 x /24 |
/18  | 16.384        | 255.255.192.0   |        64 x /24 |
/17  | 32.768        | 255.255.128.0   |       128 x /24 |
/16  | 65.536        | 255.255.0.0     |       256 x /24 | Class B
/15  | 131.072       | 255.254.0.0     |         2 x /16 |
/14  | 262.144       | 255.252.0.0     |         4 x /16 |
/13  | 524.288       | 255.248.0.0     |         8 x /16 |
/12  | 1.048.576     | 255.240.0.0     |        16 x /16 |
/11  | 2.097.152     | 255.224.0.0     |        32 x /16 |
/10  | 4.194.304     | 255.192.0.0     |        64 x /16 |
/9   | 8.388.608     | 255.128.0.0     |       128 x /16 |
/8   | 16.777.216    | 255.0.0.0       |       256 x /16 | Class A
/7   | 33.554.432    | 254.0.0.0       |         2 x /8  |
/6   | 67.108.864    | 252.0.0.0       |         4 x /8  |
/5   | 268.435.456   | 248.0.0.0       |         8 x /8  |
/4   | 268.435.456   | 240.0.0.0       |        16 x /8  |
/3   | 536.870.912   | 224.0.0.0       |        32 x /8  |
/2   | 1.073.741.824 | 192.0.0.0       |        64 x /8  |
/1   | 2.147.483.648 | 128.0.0.0       |       128 x /8  |
/0   | 4.294.967.296 | 0.0.0.0         |       256 x /8  |

Amount of **usable addresses** in a subnet, is 2 less than total addresses.

IETF RFC1878: Variable Length Subnet Table For IPv4