IPv4 VLSM Calculator
Split an IPv4 network into variable-size subnets based on host requirements.
Accepted format: Name: number or just a number. Largest subnets are allocated first.
Use the result with confidence
Recommended workflow
- Use measured or documented input values and consistent units.
- Calculate a baseline, then add redundancy, peak-load and growth margins where relevant.
- Validate the result against the real environment before changing production.
What to verify
- Confirm the scope, units and input values before interpreting the output.
- Separate the observed result from the operational decision that follows from it.
- Validate the conclusion against the real target system, logs or configuration before changing production.
Questions about this tool
Which addresses matter when working on VLSM address planning?
Check network prefix, usable range, gateway convention and reserved/broadcast semantics appropriate to IPv4 or IPv6.
Can I apply the result directly to production?
Validate it against the existing routing, DHCP, VLAN and address-management plan first to avoid overlap.
What is the most common planning error?
Reusing or overlapping a prefix that is already routed, assigned or reserved elsewhere in the environment.