Enter a CIDR block or an IP plus subnet mask to get the network address, broadcast address, usable host range, and address counts — including how many addresses AWS and GCP actually reserve out of the "textbook" usable count. Supports IPv4 and IPv6. Everything runs in your browser; nothing is looked up or sent anywhere.
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Network address
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Broadcast / last address
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First usable host
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Last usable host
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Total addresses
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Usable (standard)
Two IPs → smallest covering CIDR
Enter two addresses of the same family (both IPv4 or both IPv6) to find the smallest CIDR block that contains both.