CIDR

CIDR stands for Classless Inter-Domain Routing.

In simple words, CIDR is a shorter way to write subnet information.

Instead of writing:

IP Address  : 192.168.1.10
Subnet Mask : 255.255.255.0

we can write:

192.168.1.10/24

The /24 is the CIDR prefix.

What does /24 mean?

IPv4 has 32 bits.

/24 means:

First 24 bits  → Network part
Remaining 8    → Host part

So:

192.168.1.10/24

usually means:

Network: 192.168.1.0
Host   : 10

Common CIDR Values

Why is CIDR useful?

CIDR makes it easier to describe network ranges.

Example:

192.168.1.0/24

This represents the network:

192.168.1.0 to 192.168.1.255

In practice, not every address is usable by a device because some addresses are reserved for network and broadcast purposes.

Interview Answer

If an interviewer asks:

What is CIDR?

You can answer:

CIDR is slash notation used to describe how many bits of an IP address belong to the network part. For example, 192.168.1.10/24 means the first 24 bits are the network part and the remaining 8 bits are the host part. It is a compact way to represent subnet masks and network ranges.