MB Networks
VLAN · IP · Subnets
VLAN & subnet planner
Enter a parent block and the number of subnets needed — get a ready-to-configure VLAN table with addresses and host counts.
Subnets
0
Prefix
/—
Hosts/subnet
—
Wasted subnets
—
Configuration
Subnets are equal-sized. The tool allocates the next power-of-2 number of subnets — requesting 5 allocates 8. Edit VLAN IDs and names in the table.
Subnet table
| VLAN | Name | Network | Prefix | Gateway (suggestion) | First host | Last host | Usable hosts |
|---|
A VLAN and a subnet are two different things that travel together
A VLAN (802.1Q tag) is a Layer 2 concept — it segments a physical switch into isolated broadcast domains, so traffic on VLAN 20 never reaches a port assigned to VLAN 10 even though both run over the same physical cabling. A subnet is Layer 3 — an IP address range. They're independent ideas, but in almost every real network each VLAN gets exactly one subnet, because routing between VLANs happens at Layer 3 and that requires each VLAN to have its own address range to route between. This tool plans both halves together: give it a parent block and a number of VLANs, and it slices out equal-size subnets and assigns each one a VLAN ID in the same step.
Why every subnet comes out the same size
Splitting a parent block into VLANs works in powers of 2, not arbitrary counts — each split either halves or doubles the number of subnets, there's no way to carve a block into, say, exactly 5 equal pieces. Ask for 5 subnets and the tool allocates 8 (the next power of 2), with 3 going unused. This is the same constraint behind any subnetting scheme, not a limitation specific to this tool — if you actually need unequal subnet sizes (a few large VLANs and several small ones from the same parent block), that's VLSM (Variable Length Subnet Masking), a manual technique this tool deliberately doesn't attempt, because the moment subnets aren't equal size, "how many subnets do you need" stops being a single number.
VLAN ID ranges worth knowing
| Range | Status |
|---|---|
| 0 | Reserved (used internally in 802.1Q frames, not assignable) |
| 1 | Default VLAN on most switches — often left unused deliberately, since every unconfigured port lands here |
| 2–1001 | Normal usable range on nearly all hardware |
| 1002–1005 | Reserved on Cisco hardware for legacy Token Ring/FDDI |
| 1006–4094 | Extended range — usable on modern hardware, worth checking your specific switch's support before relying on it |
| 4095 | Reserved |
Starting your allocation at VLAN 10 or 20 instead of 1 or 2 is a common convention, not a technical requirement — it leaves room to insert VLANs later and avoids any ambiguity with the switch's default VLAN 1.
Worked example
Parent block 10.0.0.0/16, 6 VLANs needed, starting at VLAN 10. Six isn't a power of 2, so the tool allocates 8 subnets (2 wasted) at a /19 each (65,536 ÷ 8 = 8,192 addresses per subnet, 8,190 usable hosts). The result: VLAN 10 gets 10.0.0.0/19, VLAN 11 gets 10.0.32.0/19, VLAN 12 gets 10.0.64.0/19, and so on in steps of /19 — each with room for far more hosts than a typical VLAN needs, which is the real cost of the power-of-2 constraint: the more your subnet count doesn't line up with a power of 2, the more address space gets allocated per subnet just to make the split even.
What's the difference between a VLAN and a subnet?
A VLAN is a Layer 2 tag that isolates traffic on a switch; a subnet is a Layer 3 IP address range. They're independent concepts that are almost always paired one-to-one in practice, because routing between VLANs requires each one to have its own address range.
Why did I ask for 5 subnets and get 8?
Equal-size subnetting only works in powers of 2 — splitting a block always halves or doubles the subnet count, there's no clean way to produce exactly 5 equal pieces. The tool rounds up to the next power of 2 (8) and reports the 3 unused subnets as wasted. If you need genuinely unequal subnet sizes, that's VLSM, a manual technique outside what an equal-split tool can do.
What VLAN ID should I start numbering from?
There's no technical requirement, but starting at 10 or 20 instead of 1 is common practice — VLAN 1 is the default on most switches, so every unconfigured port lands there, and starting higher avoids any confusion with that default plus leaves low numbers free to insert a VLAN later.
What's the maximum number of VLANs I can have?
The 802.1Q standard allows IDs 1–4094 (0 and 4095 are reserved), so 4,094 VLANs is the theoretical ceiling. In practice your switch hardware usually has a much lower practical limit, and IDs 1002–1005 are reserved on Cisco gear specifically for legacy protocols.
Do I need a managed switch to use VLANs?
Yes — VLAN tagging (802.1Q) is a managed-switch feature. Unmanaged switches pass all traffic through untagged with no VLAN awareness at all. If you're planning VLANs, confirm your switch explicitly supports 802.1Q tagging before building out the plan.
Can different VLANs be different sizes?
Not with this tool, deliberately — it does equal-size splitting only. Unequal VLAN/subnet sizes from one parent block is VLSM (Variable Length Subnet Masking), a manual planning technique where you subnet different portions of the block at different prefix lengths. That's a real and common approach for networks with a few large VLANs and many small ones, but it has to be planned by hand, one split at a time.
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