VLSM planner: split a network into right-sized subnets
Split one network into right-sized subnets for each department, VLAN or link.
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Enter the block you have to work with, such as 10.20.0.0/22 or 192.168.1.0/24, and list the subnets you need with the number of hosts in each. The planner allocates the largest subnets first, aligns each one on a valid boundary and shows the network, mask, usable range and broadcast for every VLAN, plus the space left over.
How the planner allocates
Variable Length Subnet Masking (VLSM) gives each subnet only the size it needs. The planner adds two addresses to each host count (network and broadcast), rounds up to the next power of two, then places the largest subnets first so every block starts on a boundary that matches its size. This is the same method used in CCNA-style subnetting and avoids overlaps.
Plan for growth
Size each VLAN for the devices you expect in two to three years, not today. Phones, cameras, access points and IoT sensors grow fast. Leaving the free space at the end of the block makes it easy to add VLANs later without renumbering.
Common questions
Why are larger subnets allocated first?
Placing the largest blocks first keeps every subnet aligned to its natural boundary, which avoids gaps and overlaps and leaves the free space in one contiguous range.
How many hosts should a router link have?
Two. The planner gives a /30. If your equipment supports /31 on point-to-point links you can save two more addresses per link.
What if my subnets do not fit?
The planner tells you which subnet does not fit. Use a larger base network, for example a /22 instead of a /24, or reduce the host counts.
