Network, broadcast, mask, and usable host range - plus the parts a plain subnet calculator skips: security-zone templates and an overlap checker for actually planning a network, not just doing the math.
Most subnet calculators stop at broadcast addresses. Security architects actually need the block divided into zones - pick a template and it slices the CIDR above into non-overlapping subnets sized for that architecture.
Paste two or more CIDR blocks (one per line) - useful before a VPC peering connection, a network merge, or an M&A cloud integration, where an undetected overlap breaks routing.
The "usable hosts" count is total addresses minus 2 (network and broadcast) for anything /30 or larger. A /31 is a special case (RFC 3021) reserved for point-to-point links - both addresses are usable since there's no broadcast concept between exactly two hosts. A /32 is a single host route.
The zone templates split your block into equal-sized pieces (adding enough bits for at least as many pieces as zones, so 3 zones become 4 equal quarters with one held in reserve for growth) - a reasonable default, though a real design should size each zone to its actual expected host count rather than assume they're equal.
Related terms: IPv4 • VLAN • DMZ
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