VLSM Planner
Divide a network block into subnets of different sizes, with extra room for growth and an overview of what's still available.
| Subnet name | Number of devices |
|---|
With VLSM (variable subnet masks) you give each part of your network exactly as many addresses as it needs, instead of using the same format everywhere. That way a large LAN, a small administration network, and a few connections between routers fit in one block, without wasting addresses.
The tool allocates subnets from largest to smallest. That prevents gaps, because each subnet must start on its own boundary. For each subnet, the network address and the broadcast address are subtracted (2 addresses), and you can choose extra room for growth.
Want to divide a network into equal parts? Use the Subnet Splitter. Check your plan for overlap with the CIDR Overlap Tool, or calculate a single network with the Subnet Calculator. Everything happens in your browser. For IPv6 use the IPv6 Calculator.