Subnetting Visualizer
Move the CIDR slider or type any IPv4 — every value (network address, broadcast, host range, masks, magic number) updates live. Then split your subnet with VLSM and test yourself.
Practice — subnetting at the speed of conversation
Random IP + CIDR every round. Pick the right answer — instant feedback. CCNA exam questions are 30–45 seconds each; aim for under 30. Scroll down for the visualizer if you need a hint.
Tip — the magic-number method
256 − (interesting octet of the mask) = block size. Subnets land at multiples of the block size in the interesting octet. Example: /26 = mask 255.255.255.192 → 256−192 = 64. So /26 subnets start at .0, .64, .128, .192.
Inputs
- Network address
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- Broadcast address
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- First usable host
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- Last usable host
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- Subnet mask
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- Wildcard mask
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- Total addresses
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- Usable hosts
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- Class (legacy)
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- Type
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32-bit view — where the boundary lives
The vertical line between teal and grey cells is the prefix boundary. Drag the CIDR slider — it slides right (more networks, fewer hosts) or left (fewer networks, more hosts).
VLSM splitter — break this block into child subnets
Steal bits from the host portion. Each stolen bit doubles the number of child subnets and halves their size.
| # | Network | First host | Last host | Broadcast | Hosts |
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Subnetting in your head, no calculator
1:1 mentorship with timed drills, real-job scenarios, and US interview prep. Free first session. No card on file until you decide.