VLSM Calculator Online IPv4 Subnetting Tool

How to calculate VLSM with this online calculator

1. 1

   Enter your base IPv4 network and CIDR prefix, for example 192.168.100.0/24 to divide a Class C block into multiple VLSM subnets.

2. 2

   List host requirements largest to smallest (one per line or comma-separated). For six subnets, enter six host counts such as 50, 30, 20, 10, 5, 2.

3. 3

   Press calculate. The VLSM CIDR subnet calculator allocates each block, shows the subnet mask / prefix, and builds a VLSM table with network, broadcast, and usable host ranges, no download required.

VLSM subnet calculator vs FLSM (and why CCNA cares)

A fixed-length subnetting approach (FLSM) gives every segment the same size. An advanced VLSM calculator / VLSM and FLSM comparison shows why that wastes addresses: a head office may need hundreds of hosts while a point-to-point WAN link only needs two. This Cisco-style VLSM calculator for CCNA sequences requirements largest-first, picks the correct block size and CIDR mask for each subnet, and helps you practise VLSM subnet mask calculation examples before the exam, all in the browser as a quick online IP CIDR VLSM subnet calculator.

VLSM calculation example, 192.168.100.0/24 into 6 subnets

Save your VLSM table for labs and hand-ins

Once the calculator builds your addressing plan, copy the network, mask, broadcast, and usable ranges into your Packet Tracer or CCNA lab notes. Many learners keep those notes in Markdown (a README, gist, or study doc). When a mentor or portfolio site needs a normal web page instead of raw Markdown, you can turn the file into standalone HTML with a free Markdown to HTML converter that runs in the browser—handy for sharing a clean VLSM write-up without installing Pandoc or a desktop app.

Guides and next steps

• CIDR notation explained (with worked examples)
• Private network IP address ranges
• Free CCNA practice tests