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IPv4 CIDR subnet calculator
Find a subnet’s mask, address range and conventional host count.
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The prefix keeps the first n bits; the remaining bits describe the range. 192.0.2.17/24 belongs to 192.0.2.0/24, with mask 255.255.255.0 and 256 addresses. Conventional subnet arithmetic leaves 254 host addresses, .1 through .254.
A /31 is treated as two point-to-point endpoints under RFC 3021; /32 is one host route. For other prefixes, the reported conventional host range excludes the first and last addresses. Special-purpose ranges, local policy and device support can further restrict actual use. This is arithmetic, not an allocation or routing recommendation. See CIDR, RFC 4632.