Subnet and CIDR calculator
Network, broadcast, usable range, mask and wildcard for any IPv4 prefix — including the /31 and /32 cases most calculators get wrong.
The address
A prefix typed here wins over the field below.
What that means
- Network
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- First usable host
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- Last usable host
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- Broadcast
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- Subnet mask
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- Wildcard mask
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- Usable hosts
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- Addresses in total
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- Range belongs to
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Split
| Subnet | Range | Broadcast |
|---|
The cases most calculators get wrong
- /31 has two usable addresses, not zero. RFC 3021 does away with the network and broadcast addresses on point-to-point links, so both addresses are assignable. Anything that tells you a /31 has no hosts is applying the classful rule where it no longer belongs.
- /32 is a host route. One address, no network, no broadcast — normal for loopbacks and for a single address in a routing table, and not a mistake.
- The mask is not a filter. It tells a host which addresses it can reach directly instead of via the gateway. Two hosts with the same address and different masks will disagree about that, and the symptom is traffic that works one way only.
- 100.64.0.0/10 is not private. It is carrier-grade NAT space, which is why overlay networks use it — and why it collides badly with an ISP that also uses it.
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