Some of what you see here is sample content. While the community forms, part of the members, reviews, ratings and discussions are seeded examples. Every one is badged Sample, and they do count towards the totals on this site. Vendor pages, the security data and the tools are real.
CIDR and subnet calculator
Network address, broadcast, usable range, mask and host count for any IPv4 prefix, plus what you get if you split it. Useful when a firewall change request says 10.0.0.0/22 and nobody wants to be the one who asks what that covers.
Everything you type stays in this tab. Share copies a link, never your inputs, unless the tool says it encodes them in the URL.
| Subnet | Range | Usable |
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A /31 carries two addresses and no broadcast, which RFC 3021 allows for point-to-point links, and a /32 is a single host. Both are shown as they really behave rather than as the arithmetic would suggest.