Python VLSM Subnetting Tool

Overview

This project is a fully automated Variable Length Subnet Masking (VLSM) calculator built in Python.
It accepts a base network and a list of subnet requirements (defined in usable hosts), then:

• Calculates optimal subnet sizes
• Allocates subnets in descending order (true VLSM)
• Computes network/broadcast addresses, usable ranges, masks, and wildcard masks
• Displays results in the CLI (simple line format)
• Exports a clean, tabulated report to output.txt using tabulate

It is designed for networking students, practitioners, and anyone needing dependable programmatic VLSM planning. I made this tool for my CS Degree's first year's networking assignment.

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Features

• ✔ VLSM allocation by sorting requirements from largest → smallest
• ✔ Automatic subnet size calculation from usable host counts
• ✔ Outputs:
  • Network address
  • Broadcast address
  • Usable host range
  • Subnet mask
  • Wildcard mask
  • (Optional) wasted IPs
• ✔ CLI-friendly output (simple pipe-separated format)
• ✔ Formatted table output saved to output.txt (tabulate grid format)
• ✔ Error handling for invalid networks and overlapping allocations
• ✔ Uses Python’s built-in ipaddress module for reliable subnet math

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Installation & Setup

1. Clone the repository

   git clone https://github.com/lak-git/VLSM-Calculator.git
   cd VLSM-Calculator

2. Install required Python packages

   pip install -r requirements.txt

3. Run the script

   python vlsm.py

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Usage

1. When prompted, enter the base network (CIDR format), e.g.:

192.168.1.0/24

2. Enter the number of subnets you want to create.
3. For each subnet, provide:
   • Name/label
   • Required number of usable hosts
   • The tool automatically determines the correct subnet size.
4. The program will:
   • Print each subnet in this format:

Name | Network | Broadcast | Usable Range | Subnet Mask | Wildcard Mask |

- Save a grid-formatted table into output.txt

Example CLI output:

Sales | 192.168.1.0 | 192.168.1.63 | 192.168.1.1 - 192.168.1.62 | 255.255.255.192 | 0.0.0.63 |
IT | 192.168.1.64 | 192.168.1.95 | 192.168.1.65 - 192.168.1.94 | 255.255.255.224 | 0.0.0.31 |

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License

This project is licensed under the MIT License.