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VLSM Planner

Allocate real host requirements with optional RFC 3021 /31 point-to-point support.

Plan VLSM allocations

Replace the examples with your own values. Nothing is calculated until you provide a parent network and at least one host requirement.

1 Parent network2 Host requirements3 Calculate

Step 1 — Enter your parent IPv4 networkEnter the IPv4 block you actually own or want to subdivide.

Step 2 — Enter your subnet requirementsOne requirement per line. Use Label: number of hosts or just a number. Maximum 200 requirements.

Waiting for your values.

Allow RFC 3021 /31 for exactly two-host point-to-point requirementsOff by default. /32 is never used as a generic one-host LAN allocation.

Enter a parent network and at least one host requirement.

VLSM without hidden assumptions

VLSM is not only a “hosts-to-prefix” conversion. The allocation order, alignment boundaries and treatment of point-to-point links change the final layout. This planner shows request IDs, the allocated subnet, endpoint range, utilization and remaining CIDRs.

For ordinary LANs, a request for one or two hosts still needs a /30 because network and broadcast addresses remain reserved. If the link is genuinely point-to-point and both endpoints support RFC 3021 semantics, explicitly enable /31 mode.