Handitab

VLSM Calculator

Split an IPv4 network into subnets of different sizes with VLSM: enter the hosts needed per subnet and get each range and mask.

About VLSM Calculator

Variable Length Subnet Masking (VLSM) divides one IPv4 network into subnets of different sizes, so each gets only as many addresses as it needs. This calculator sorts your requirements from largest to smallest, gives each the smallest block that holds the hosts plus a network and a broadcast address, and assigns blocks in order from the start of the network. It reports the range, prefix, and mask of each subnet and the addresses left unused.

How to use VLSM Calculator

  1. Type or paste into the "Subnets needed (one per line: name, number of hosts)" box, or press "Use example" to try it with sample data.
  2. Set "Network to divide" if the defaults do not fit.
  3. The result appears below and updates as you type.
  4. Copy the result with the copy button, or download it as a file where that is offered.

Questions about VLSM Calculator

Why are subnets allocated from largest to smallest?

Each block must start on a boundary that is a multiple of its own size. Placing the largest blocks first keeps every later, smaller block aligned without leaving gaps, which wastes the fewest addresses.

Runs in your browser. Page last updated .

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