Question 1

What is a CIDR prefix?

Accepted Answer

It is the number of leading bits shared by every address in the subnet, written after a slash, for example /24 in 192.168.1.0/24. A larger prefix means a smaller subnet.

Question 2

What is the difference between the network and broadcast address?

Accepted Answer

The network address is the first address in the subnet and identifies it. The broadcast address is the last one and reaches every host. Neither can normally be assigned to a device.

Question 3

Why are there fewer usable hosts than total hosts?

Accepted Answer

Two addresses are reserved — the network address and the broadcast address — so the usable count is the total minus two.

Question 4

Does my address leave my device?

Accepted Answer

No. All calculations happen locally in your browser and nothing is uploaded.

IP Subnet Calculator

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