VLAN Subnet Planner
Assign prefixes to requested VLAN capacities.
VLAN Subnet Planner: inputs and results
Enter an IP address, CIDR prefix, or range. Then check its first and last address below.
Calculated Boundaries & ParametersReady
Key Capabilities
- •100% Client-Side: Zero telemetry or server latency.
- •RFC Compliant: Exact 32-bit and 128-bit integer precision.
- •Quick Copy: Instant access to CIDR, mask, and range bounds.
- •Cross-Platform: Works on desktop, tablet, and mobile browsers.
Related Planning, VLSM & CloudAll Tools
VLSM Calculator
Allocate differently sized subnets.
VLSM Allocation Validator
Check alignment, capacity, and overlaps.
Supernet Calculator
Find a covering parent prefix.
Exact CIDR Aggregator
Merge prefixes without adding addresses.
Route Summary Calculator
Summarize networks and identify included gaps.
DHCP Scope Calculator
Plan allocation boundaries within a subnet.
How VLAN Subnet Planner Works?
The VLAN Subnet Planner works by sizing a subnet for each VLAN from its device count plus growth, then allocating the subnets from a parent block in largest-first order.
Enter the parent block
Type the site block, such as
10.100.0.0/20.List the VLANs
Enter VLAN ID, name, and device count for each VLAN.
Add growth
The planner adds a growth margin, such as 25 %, to each count.
Allocate and output
Each VLAN receives a prefix, gateway, and range, ready for switch and DHCP configuration.
VLAN Subnet Planner Formula
The VLAN Subnet Planner formula is Prefix = 32 − ceil(log2(ceil(Devices × (1 + Growth)) + 2)), with subnets placed largest first.
Planned hosts
H = ceil(D × (1 + g))g is the growth margin.
Prefix
32 − ceil(log2(H + 2))Smallest fitting subnet.
Gateway
Network + 1SVI or router subinterface address.
Worked example: VLAN 10 Users, 300 devices, 25 % growth
Planned = ceil(300 × 1.25) = 375 hosts Host bits = ceil(log2(377)) = 9 → /23 (510 hosts) Gateway = first address + 1
VLAN Subnet Planner Conversion Table
The VLAN Subnet Planner conversion table allocates 7 VLANs from 10.100.0.0/20 with a 25 % growth margin.
| VLAN | Name | Devices | Planned | Subnet | Gateway | Capacity |
|---|---|---|---|---|---|---|
| 10 | Users | 300 | 375 | 10.100.0.0/23 | 10.100.0.1 | 510 |
| 30 | Wi-Fi | 400 | 500 | 10.100.2.0/23 | 10.100.2.1 | 510 |
| 20 | Voice | 150 | 188 | 10.100.4.0/24 | 10.100.4.1 | 254 |
| 50 | Cameras | 60 | 75 | 10.100.5.0/25 | 10.100.5.1 | 126 |
| 40 | Printers | 25 | 32 | 10.100.5.128/26 | 10.100.5.129 | 62 |
| 60 | Servers | 40 | 50 | 10.100.5.192/26 | 10.100.5.193 | 62 |
| 99 | Management | 12 | 15 | 10.100.6.0/27 | 10.100.6.1 | 30 |
What is VLAN Subnet Planner?
The VLAN Subnet Planner is a tool that assigns an IPv4 subnet to each Virtual Local Area Network (VLAN) based on its device count and planned growth.
Each VLAN is a separate broadcast domain and needs its own subnet and gateway. Users, voice, Wi-Fi, printers, cameras, and management traffic usually live in separate VLANs, each with a very different device count. The planner sizes each subnet individually and packs them into 1 site block.
The output maps directly to switch configuration: VLAN ID, Switch Virtual Interface (SVI) address, and DHCP scope boundaries.
What are the uses of VLAN Subnet Planner?
There are 4 main uses of the VLAN Subnet Planner, including campus design, switch configuration, and growth planning.
Designing campus networks
Each building gets a site block split into VLAN subnets.
Configuring switch SVIs
The gateway column becomes the
interface vlanaddress.Planning for growth
The growth margin keeps each VLAN from outgrowing its subnet in year one.
Standardizing site layouts
Every site uses the same VLAN IDs with subnets from its own block.