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VLSM subnet planner
Allocate unequal subnets from one IPv4 base, largest-first, with every sizing decision shown as a step and failures named per subnet.
workerless environment, same engine, this tab · up to 64 subnets
Set the base and rows, then press Plan.
- Deterministic largest-first (classic VLSM): same inputs, same plan, every time. Equal sizes keep entry order. It is a teaching/planning layout, not a claim of optimality.
- "Usable hosts" is the IPv4 convention (network + broadcast reserved; RFC 3021 /31 and /32 exact). The same rule the subnet calculator prints.
- A request the base cannot satisfy is a named failure on its row: the plan never silently drops or shrinks it.
- Caps: 64 subnet rows per plan. Bulk tables run in the network family worker so planning never blocks the page.
Paste, drop, or type to begin. Everything stays on this device.