Subnet / CIDR
Network range, mask and host count from CIDR notation.
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Step by step
The formula
hosts = 2^(32 − prefix) − 2
The number after the slash says how many leading bits identify the network; the rest address individual hosts. Two addresses in every block are reserved — the first names the network itself, the last is the broadcast address — which is why usable hosts is always two short.
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Frequently asked questions
Why subtract 2 from host count?+
The first address is the network identifier and the last is the broadcast address, so neither can be assigned to a host.
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