Free CIDR Subnet Calculator
Enter CIDR notation like 10.0.0.0/24 and get the full picture · network, broadcast, usable range, mask, and how many hosts fit.
Frequently asked
What does the /24 in CIDR notation mean?
The number of leading bits fixed as the network part. /24 fixes 24 bits, leaving 8 for hosts · 256 addresses, 254 usable. Each step down doubles the network: /23 is 512 addresses.
Why do security groups use CIDR ranges?
Firewall and cloud security-group rules allow traffic by CIDR block. A rule for 0.0.0.0/0 means "the entire internet" · fine for a public website's port 443, a serious finding on a database port.
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