A complete guide to how the VLAN/Subnet Planner allocates non-overlapping subnets by host count, and how to use it for real network design work.
Launch the VLAN / Subnet Planner →The VLAN/Subnet Planner takes a single parent network block (for example, 10.0.0.0/16) and a list of named VLANs, each with a specified number of hosts it needs to support, and automatically calculates a complete, non-overlapping subnet allocation plan carving that parent block into appropriately sized pieces for each VLAN. The output is a table showing each VLAN's assigned network address, CIDR prefix, usable host range, broadcast address, and usable host count.
This directly extends the subnet-splitting logic already proven out in the IP Subnet Calculator's VLSM (Variable Length Subnet Masking) feature, but adds the ability to assign a VLAN ID and a human-readable name to each subnet, and to specify sizing by "how many hosts does this need" rather than requiring you to manually work out the correct CIDR prefix length yourself.
The IP Subnet Calculator's VLSM splitter already answers the question "if I split this parent network into N equally-sized or appropriately-sized pieces, what do those pieces look like?" The VLAN/Subnet Planner exists to answer a related but distinct, more specific question that comes up constantly in actual network design work: "I have several different purposes — management traffic, staff workstations, guest Wi-Fi, and so on — each needing a different number of hosts, and I want each one to have a name and a VLAN ID I can actually use in my switch configuration, not just an anonymous numbered subnet."
Real-world network planning almost always starts from a list of purposes and host-count requirements, not from a predetermined number of equal-sized subnets. A typical small business network might need 20 addresses for network infrastructure devices, 100 for staff workstations, and 50 for a separate guest Wi-Fi network that should never be able to reach the internal file server. Each of those needs a different-sized subnet, and manually calculating the correct CIDR prefix for an arbitrary host count, then manually verifying none of the resulting ranges overlap, is tedious and error-prone work to do by hand — exactly the kind of calculation this tool exists to automate correctly.
Given a list of VLANs each with a required host count, the tool first calculates the minimum subnet size needed for each one. For any given number of required usable hosts, the smallest adequate subnet is found by determining how many host bits are needed such that 2 raised to that power, minus 2 (to account for the network and broadcast addresses that cannot be assigned to a host), is at least as large as the requested host count.
Once each VLAN's required size is known, the tool sorts all VLANs from largest to smallest and allocates address space to them in that order, packing each one into the next available position within the parent block. Allocating from largest to smallest first is a standard and important technique: because every subnet's size must be a power of two, and every subnet must start at an address boundary aligned to its own size, allocating larger blocks first and smaller blocks into the remaining gaps produces a tightly packed, non-wasteful result. Allocating in the opposite order, smallest first, can leave oddly-sized unusable gaps that are too small to fit any subnet that needs to go in afterward.
After all VLANs have been assigned their address ranges in size order, the tool re-sorts the final results back into the original order you entered them in, so the output table matches the order you listed your VLANs, not the internal allocation order used during calculation. If the total requested address space exceeds what the parent block can actually provide, the tool reports this clearly rather than producing an invalid or silently incorrect plan.
Planning three VLANs — Management (20 hosts), Staff (100 hosts), and Guest Wi-Fi (50 hosts) — against a parent block of 10.0.0.0/16 would allocate Staff first (needing a /25, the largest requirement), then Guest Wi-Fi (needing a /26), then Management (needing a /27, the smallest requirement), fitting all three into the beginning of the parent block with zero wasted or overlapping address space between them.
It's worth being clear about something that can be confusing to anyone newer to networking: the VLAN ID (a number from 1 to 4094, used by network switches to tag and separate traffic at the data-link layer) and the IP subnet assigned to that VLAN (an entirely separate addressing scheme used at the network layer) are two completely independent numbering systems that happen to be configured together as a matter of convention and convenience, not because they're mathematically related in any way.
Many organizations follow a loose convention where, for memorability, VLAN 10 might use a subnet ending in .10.0/24, or similar numeric patterns, but this is purely an organizational choice some network administrators adopt to make configurations easier to remember and audit, not a technical requirement of VLANs or IP subnetting themselves. This tool lets you assign any VLAN ID to any subnet size independently, matching how real switch and router configuration actually works.
A few recurring situations illustrate when this kind of structured VLAN planning tends to matter most:
10.0.0.0 with a /16 prefix.All subnet planning calculations happen entirely within your browser using standard binary arithmetic on the address ranges and host counts you enter. No network request of any kind is made by this tool. The network topology and VLAN names you plan here are never transmitted, logged, or stored anywhere outside your own browser session.
The tool detects this condition and reports it clearly, suggesting you either choose a larger parent CIDR block (a smaller number after the slash) or reduce the host-count requirements for one or more VLANs.
Internally, the tool allocates larger subnets before smaller ones to pack the address space efficiently without gaps, but it always displays the final results back in the exact order you originally entered your VLANs, for readability.
The tool accepts any VLAN ID from 1 to 4094, which is the full valid range defined by the IEEE 802.1Q standard. Some organizations reserve certain VLAN IDs (like 1) for default or management purposes by convention, but that's a site-specific policy choice, not a technical restriction enforced by this tool.
No. This tool only calculates and displays a planning document showing which addresses each VLAN should use. Applying that plan to real network hardware requires separately configuring your switches, routers, or firewall according to your own equipment's configuration process.