VLSM subnet planner
Allocate differently sized IPv4 networks inside one parent prefix without alignment mistakes.
IPv4 allocation arithmetic only; no VLANs, VRFs, DHCP reservations, imported overlaps or IPv6 prefix delegation.
Subnets are packed largest-first to reduce fragmentation; equal-size requests keep their entered order.
Remaining CIDR blocks
10.0.0.112/28, 10.0.0.128/25
Included
- Every visible input and selected unit
- Reconciled intermediate values and result breakdown
- Reproducible URL state
Not included
- IPv4 allocation arithmetic only; no VLANs, VRFs, DHCP reservations, imported overlaps or IPv6 prefix delegation.
What this means
Allocate differently sized IPv4 networks inside one parent prefix without alignment mistakes.
IPv4 allocation arithmetic only; no VLANs, VRFs, DHCP reservations, imported overlaps or IPv6 prefix delegation.
Intermediate values are not rounded; only the localized display formats the result.
Formula & worked example
block size = next power of two at or above hosts + 2
50, 20 and 10-host LANs inside 10.0.0.0/24
- Inputs
- 50 + 2 → 64 addresses; 20 + 2 → 32; 10 + 2 → 16
- Calculation
- Allocate 10.0.0.0/26, 10.0.0.64/27 and 10.0.0.96/28
112 of 256 addresses are allocated; 10.0.0.112/28 and 10.0.0.128/25 remain.
How this calculation works
The calculation follows the formulas, definitions and assumptions explained on this page. The references below support the method and any stated boundaries.
Official sources
- RFC 4632 — CIDR address strategy — Public definitions and technical semantics used by this calculation