IP Subnet (IP Addressing and Subnetting)

4/18/22, 1:24 AM Classless Interdomain Routing (CIDR)

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Learning Topic

Classless Interdomain Routing (CIDR) Classless Interdomain Routing (CIDR) is a method to use IP addressing without being

restricted to the original grouping of IPv4 (Class A, B, and C). Using CIDR, you can create

a network (or subnetwork) and size it appropriately based on the needs.

For example, without CIDR, if you have a network with 500 hosts or systems,

you cannot use a Class C network because Class C is limited to 254 hosts, so

you are forced to use a Class B network, which leads to a waste of IP addresses.

Also, prior to CIDR, when specifying a network address, you will need to also provide the

subnet mask. For example:

Network address: 192.168.1.0

Subnet mask: 255.255.255.0

You need both to inform the size of the network.

With CIDR notation, instead of specifying the subnet mask, you note the number of bits

used for the network hosts. For example, the same network as above would be written as:

Network address: 192.168.1.0/24

For more information, review the following article:

A Linux networking guide to CIDR notation and configuration

(https://opensource.com/article/16/12/cidr-network-notation-configuration-linux)

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