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IPv4 Subnet Calculator
Calculate exact IPv4 network masks, endpoints, usable ranges and ordered address membership.
IPv4/CIDR text, Optional IPv4 lines
JSON subnet report
Browser only
Runs locally in your browser. Your files, pasted content and generated output are not uploaded. Reset clears this tool’s working data.
This tool needs JavaScript. If it does not load, refresh the page and try again.
How to use this tool
- Enter IPv4 CIDR and optional addresses, one per line. Blank membership lines are ignored; nonblank values must be strict dotted decimal.
- Select Calculate IPv4 subnet. Inspect the declared host policy, endpoints and inside/outside membership results.
- Select Download result for ipv4-subnet.json. Editing or Reset clears prior output.
Examples
192.0.2.129/24 reports network 192.0.2.0, last address 192.0.2.255 and 254 conventional usable addresses; /31 instead has two point-to-point addresses.
Limitations
- CIDR at most 18 UTF-16 units; prefixes0–32; at most 1,000 optional addresses,256 KiB combined UTF-8 input,1 MiB JSON and 30 seconds.
- No leading-zero octets, shorthand, alternate bases, ports, IPv6, DNS, route checks or network requests.
- Usable range is the stated subnet convention, not a guarantee that an address is assigned or routable. Host bits are accepted and explicitly reported.
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