Network planning / BROWSER TOOL
VLSM Calculator
Plan several IPv4 networks inside one parent allocation. Give each network a name and a host requirement; get aligned, non-overlapping subnets and see what remains.
PARENT NETWORK
- Addresses in parent
- 256
- Addresses allocated
- 128
- Addresses unallocated
- 128
Unallocated means unused by this mathematical plan. It does not mean available on your live network. VLAN tags, DHCP reservations and routing must be configured separately.
Subnet allocations
| Name | Requested | Network | Mask | First endpoint | Last endpoint | Broadcast | Capacity |
|---|---|---|---|---|---|---|---|
| Servers | 50 | 192.168.10.0/26 | 255.255.255.192 | 192.168.10.1 | 192.168.10.62 | 192.168.10.63 | 62 |
| Home | 25 | 192.168.10.64/27 | 255.255.255.224 | 192.168.10.65 | 192.168.10.94 | 192.168.10.95 | 30 |
| IoT | 10 | 192.168.10.96/28 | 255.255.255.240 | 192.168.10.97 | 192.168.10.110 | 192.168.10.111 | 14 |
| Guests | 10 | 192.168.10.112/28 | 255.255.255.240 | 192.168.10.113 | 192.168.10.126 | 192.168.10.127 | 14 |
Capacity excludes the network and broadcast address for ordinary LANs; optional /31 and /32 allocations use their special endpoint semantics.
How VLSM allocation works
Variable Length Subnet Masking lets networks use different prefix lengths within one parent. The planner finds the smallest fitting block for each request, sorts blocks largest first, and allocates each at its required alignment. It produces a fresh plan; it cannot preserve existing reservations or determine which addresses are already occupied.
Example: four networks inside a /24
Starting with 192.168.10.0/24, requests for 50, 25, 10 and 10 hosts receive /26, /27, /28 and /28 blocks. They provide 62, 30, 14 and 14 conventional host addresses. Allocated blocks consume 128 of the parent's 256 addresses; unused host capacity within a block is still part of that allocation.
Frequently asked questions
Should the requested count include the gateway?
Yes. Include every interface that needs an address in the subnet, not just client devices. Add your own expected growth before entering the request. The tool does not automatically invent a growth margin.
Why does a request for one host normally receive /30?
In ordinary LAN mode, the model reserves network and broadcast addresses. A /30 is the smallest block in this model with conventional usable endpoints. Enable the separate small-link option only when the request represents a /31 point-to-point link or a /32 host route; it is not a shortcut for an ordinary multi-access LAN.
What happens if the plan does not fit?
The entire result is rejected. The tool does not silently drop later networks or return a partly valid plan. Choose a larger parent, reduce requests, or split the design across separate address allocations.
Does a subnet plan isolate VLANs?
No. Different addresses alone do not enforce access policy. You still need appropriate VLAN membership, routing and firewall rules. Review Proxmox bridges and VLANs before applying a plan to a virtualized network.
Can labels contain private names?
Calculations and labels stay in your browser. This page does not submit host counts, network labels or address plans to an application backend or analytics. Clipboard contents are only written when you press Copy plan.
Related tools
Inspect a single block with the IPv4 subnet calculator, convert an existing range with IP Range to CIDR, or plan a separate IPv6 allocation with the IPv6 calculator. For DHCP cutovers, use the migration checklist.