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 to 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 gray 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 |
|---|
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.