VLSM (Variable Length Subnet Masking) is a subnetting technique that lets you split a base network into subnets of different sizes so you match host requirements without wasting addresses. This interactive trainer gives you a base network (e.g., 192.168.10.0/24) and a list of host counts; your job is to assign, for each requirement, a network address and a prefix (e.g., /25, /27) that fits, stays within the base, and doesn’t overlap other subnets.
Choose a difficulty or enter your own base and host list, type your proposed networks, then click Check to validate alignment, size, and overlap; use Show Hints to see the smallest valid prefix and Reveal Solution to compare with a step-by-step largest-first VLSM plan. It’s ideal for learning CIDR, planning lab topologies, or preparing for exams like the CCNA/Network+.
Tip: start with the largest host requirement first, align each subnet to its block boundary, and remember that traditional host counts exclude the network and broadcast addresses (except in /31 point-to-point links).
VLSM Practice Generator
Your plan
| # | Hosts required | Min prefix | Your network | Your prefix | Status |
|---|
One valid solution (largest-first VLSM)
| # | Hosts | Prefix | Network | Broadcast | Usable range | Mask | Wildcard | Total | Usable |
|---|
Best IP training I have ever seen for IPv4 addressing ...
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