CIDR

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 AN!Wiki :: CIDR

CIDR is short for 'Classless Internet Domain Routing'. The Wikipedia article below does a great job at explaining CIDR in detail.

For most cases, however, CIDR IPv4 notation is used as a short-form way of expressing a subnet mask.

Conversion table:

CIDR Notation Network Mask Total number

of addresses

Description
/0 0.0.0.0 4,294,967,296 Every Address
/1 128.0.0.0 2,147,483,648 128 /8 networks
/2 192.0.0.0 1,073,741,824 64 /8 networks
/3 224.0.0.0 536,870,912 32 /8 networks
/4 240.0.0.0 268,435,456 16 /8 networks
/5 248.0.0.0 134,217,728 8 /8 networks
/6 252.0.0.0 67,108,864 4 /8 networks
/7 254.0.0.0 33,554,432 2 /8 networks
/8 255.0.0.0 16,777,214 1 /8 net
/9 255.128.0.0 8,388,608 128 /16 networks
/10 255.192.0.0 4,194,304 64 /16 networks
/11 255.224.0.0 2,097,152 32 /16 networks
/12 255.240.0.0 1,048,576 16 /16 networks
/13 255.248.0.0 524,288 8 /16 networks
/14 255.252.0.0 262,144 4 /16 networks
/15 255.254.0.0 131,072 2 /16 networks
/16 255.255.0.0 65,536 1 /16 network
/17 255.255.128.0 32,768 128 /24 networks
/18 255.255.192.0 16,384 64 /24 networks
/19 255.255.224.0 8,192 32 /24 networks
/20 255.255.240.0 4,096 16 /24 networks
/21 255.255.248.0 2,048 8 /24 networks
/22 255.255.252.0 1,024 4 /24 networks
/23 255.255.254.0 512 2 /24 networks
/24 255.255.255.0 256 1 /24 network
/25 255.255.255.128 128 Half of a /24 network
/26 255.255.255.192 64 Fourth of a /24/span> network
/27 255.255.255.224 32 Eighth of a /24/span> network
/28 255.255.255.240 16 1/16th of a /24/span> network
/29 255.255.255.248 8 5 Usable addresses
/30 255.255.255.252 4 1 Usable address
/31 255.255.255.254 2 Unusable
/32 255.255.255.255 1 Single host

 

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