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VLSM Planner

Plan variable-length subnet allocations from a base CIDR.

Last validated: 2026-02-14

VLSM Planner allocates variable-length subnets from a parent block based on host requirements. It is useful when designing efficient address plans for mixed-size network segments. The tool helps reduce wasted space while keeping subnet boundaries valid. Use it to build a clear addressing scheme before implementation.

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Input Pattern

Enter values in the left panel, keep units explicit, run the calculation, then copy or share the result. Invalid fields are highlighted immediately.

VLSM Inputs

Enter base CIDR and required hosts per subnet.

Result

Fits base block: Yes

Used IPs: 240 / 256

Remaining IPs: 16

SubnetCIDRHosts
Subnet 110.0.0.0/25126
Subnet 210.0.0.128/2662
Subnet 310.0.0.192/2730
Subnet 410.0.0.224/2814

How to use this tool

  1. Enter parent CIDR and host counts per required subnet.
  2. Run the planner to generate subnet assignments.
  3. Review allocations and reserve growth room for critical segments.

Worked Example

Auto-generated from the tool's current default or entered inputs.

Example Inputs

  • Base cidr: 10.0.0.0/24
  • Requirements: 120, 60, 28, 12
  • Fits: true
  • Used ips: 240
  • Remaining ips: 16

Expected Outputs

  • Parsed requirements 0: 120
  • Parsed requirements 1: 60
  • Parsed requirements 2: 28
  • Parsed requirements 3: 12

Interpretation

Scenario Compare (A vs B)

Use this to compare two input sets and quantify change in key outputs.

Scenario A

Scenario B

Formula References

Assumptions

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