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Chapter 3
IP Addressing
Classless Interdomain Routing
Classless Interdomain Routing (CIDR) is an industry standard for display-
ing the number of subnet bits used with the IP address of a host or a network.
Let's say you have a 172.16.10.1 address with a 255.255.255.0 mask.
Instead of writing the IP address and subnet mask separately, you can com-
bine them. For example, 172.16.10.1/24 means that the subnet mask has 24
out of 32 bits on.
The following list shows all the possible CIDRs:
255.0.0.0 = /8
255.128.0.0 = /9
255.192.0.0 = /10
255.224.0.0 = /11
255.240.0.0 = /12
255.248.0.0 = /13
255.252.0.0 = /14
255.254.0.0 = /15
255.255.0.0 = /16
255.255.128.0 = /17
255.255.192.0 = /18
255.255.224.0 = /19
255.255.240.0 = /20
255.255.248.0 = /21
255.255.252.0 = /22
255.255.254.0 = /23
255.255.255.0 = /24
255.255.255.128 = /25
255.255.255.192 = /26
255.255.255.224 = /27
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