VLSM calculator
Enter a base network and how many devices each segment needs. The calculator gives every segment a subnet of the right size, with room to grow and no overlap.
Result
| Segment | VLAN | Devices | Subnet | Netmask | Gateway | Host range | Broadcast | Usable | Growth |
|---|---|---|---|---|---|---|---|---|---|
| Students | 30 | 600 | 10.10.0.0/22 | 255.255.252.0 | 10.10.0.1 | 10.10.0.2 – 10.10.3.254 | 10.10.3.255 | 1,022 | +70 % |
| Guests | 40 | 250 | 10.10.4.0/23 | 255.255.254.0 | 10.10.4.1 | 10.10.4.2 – 10.10.5.254 | 10.10.5.255 | 510 | +104 % |
| Staff | 20 | 180 | 10.10.6.0/24 | 255.255.255.0 | 10.10.6.1 | 10.10.6.2 – 10.10.6.254 | 10.10.6.255 | 254 | +41 % |
| Printers | 50 | 25 | 10.10.7.0/26 | 255.255.255.192 | 10.10.7.1 | 10.10.7.2 – 10.10.7.62 | 10.10.7.63 | 62 | +144 % |
| Network devices | 99 | 20 | 10.10.7.64/27 | 255.255.255.224 | 10.10.7.65 | 10.10.7.66 – 10.10.7.94 | 10.10.7.95 | 30 | +45 % |
| Servers | 70 | 12 | 10.10.7.96/27 | 255.255.255.224 | 10.10.7.97 | 10.10.7.98 – 10.10.7.126 | 10.10.7.127 | 30 | +142 % |
The plan uses 1,920 of 4,096 addresses in 10.10.0.0/20.
What is VLSM?
VLSM (Variable Length Subnet Masking) means the subnets in a plan have different sizes, matched to need. Instead of giving every segment a /24, the student network gets a /22 and the network devices a /27. That saves addresses and makes the plan more realistic.
How the calculator allocates
- The device count is increased by the growth margin, and one address is added for the gateway.
- Each segment gets the smallest subnet that fits: a /26 has 62 usable addresses, a /25 has 126, and so on.
- Segments are placed from largest to smallest. That way every subnet automatically lands on a valid boundary without gaps between the large networks.
- The first usable address is suggested as the gateway.
Tips for a good plan
- Allow at least 30% growth in client networks. Renumbering later is much more work than using a few extra addresses now.
- Leave free space in the base network for segments you do not know about yet.
- Use the same VLAN number for the same function at every site, and the VLAN number in the third octet where possible.
- Keep network devices and management in a small, separate network that clients cannot reach.
ipmanager has the same planner with templates for school, office, data centre and healthcare – and the plan can be created as subnets with one click. See also the network segmentation guide.
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