Calculator
Example Data Table
This example shows a typical VLSM plan inside 192.168.10.0/24.
| Team | Hosts | Planned CIDR | Usable hosts | Gateway |
|---|---|---|---|---|
| Guest WiFi | 80 | 192.168.10.0/25 | 126 | 192.168.10.1 |
| IT | 60 | 192.168.10.128/26 | 62 | 192.168.10.129 |
| HR | 30 | 192.168.10.192/27 | 30 | 192.168.10.193 |
| CCTV | 10 | 192.168.10.224/28 | 14 | 192.168.10.225 |
Formula Used
- Total addresses = 2^(32 − prefix).
- Usable hosts: total − 2 for /0 to /30, 2 for /31, 1 for /32.
- Equal subnets: newPrefix = basePrefix + ceil(log2(subnetCount)).
- Plan by hosts: blockSize = nextPow2(hosts + 2), then newPrefix = 32 − log2(blockSize).
- VLSM: sort host needs descending, then allocate aligned blocks sequentially.
How to Use This Calculator
- Enter your base network in CIDR notation.
- Choose a planning mode that matches your design.
- Set the gateway preference for each subnet.
- Provide subnet count, hosts, or a VLSM list.
- Press Submit to generate the full plan table.
- Use the download buttons for CSV or PDF exports.
FAQs
1) Why does my network change after I enter CIDR?
If the IP is not on a subnet boundary, the tool aligns it to the correct network address. This prevents incorrect range math and keeps exports consistent.
2) What is the difference between equal subnets and VLSM?
Equal subnets divide the base network into same-size blocks. VLSM creates different-size blocks to match each team’s host needs more efficiently.
3) Why does the tool add two addresses to host needs?
Traditional IPv4 subnets reserve the network and broadcast addresses. So, a request for H hosts needs at least H+2 total addresses to fit cleanly.
4) When should I allow /31 and /32?
Use /31 for point-to-point links where both addresses are usable. Use /32 for single-host routes or loopbacks. Many LAN segments still prefer /30 or larger.
5) Why is broadcast shown as N/A sometimes?
A /31 link has no broadcast address in the usual sense, and both IPs are usable. A /32 represents one host address only, so broadcast is not meaningful.
6) How does the planner pick a gateway address?
You can choose the first usable or last usable address per subnet. The suggestion is included for convenience and can be adjusted to your standards.
7) Can I plan more subnets than the base network supports?
No. The tool checks capacity based on prefix and block size. If the request exceeds available space, it returns a clear limit message.
8) Is this calculator suitable for production network design?
It is a strong planning aid for IPv4 ranges, exports, and reviews. Always validate with your routing, security policies, and address management standards before deployment.