Worked example
A /24 can hold a 50-host /26, a 20-host /27, a 10-host /28, and a 5-host /29 with room left over.
VLSM Subnet Planner
Allocate subnets of different sizes from a parent network block. The planner sorts them largest-first and allocates address space with zero waste.
Configuration
Subnet Requirements
| Subnet Name | Required Hosts | |
|---|---|---|
What is VLSM?
VLSM allows network engineers to divide an IP block into subnets of different sizes. Unlike classful subnetting, VLSM lets you allocate a /26 for 50 hosts, a /28 for 10 hosts, and a/30 for a WAN link — all from the same parent block.
VLSM formula
To find the prefix for N hosts: find the smallest n where 2^n − 2 ≥ N. The prefix is /(32−n).
How to use VLSM Planner
Add each required network and its host count. The planner allocates the largest requirements first so address blocks stay aligned and compact.
Common mistake
Plan for growth and remember that ordinary IPv4 subnets reserve network and broadcast addresses.