🌐 Simple CIDR Calculator

A clean, fast command-line tool written in Go that calculates and displays comprehensive subnet information for CIDR notation inputs. Perfect for network engineers, system administrators, and anyone working with IP subnetting.

✨ Features

• 🔍 CIDR Parsing: Parse and validate CIDR notation (e.g., 192.168.1.0/24)
• 📊 Network Information: Display network ID, broadcast address, subnet mask, and wildcard mask
• 🏠 Host Information: Show first/last usable IP addresses and total host count
• 🔀 Subnet Analysis: Calculate and list all possible subnets for the next prefix level
• 📄 Multiple Output Formats: Support for console text output and HTML file generation
• ⚡ Edge Case Handling: Proper handling of /31 (point-to-point) and /32 (host route) networks
• 🌍 Cross-Platform: Works on Linux, macOS, and Windows

🚀 Installation

Prerequisites

• Go 1.19 or later

Build from Source

1. Clone the repository:

git clone https://github.com/marc-poljak/simple-cidr-calculator.git
cd simple-cidr-calculator

2. Build the binary:

go build -o simple-cidr-calculator

3. (Optional) Install globally:

go install

Using Make

If you have Make installed, you can use the provided Makefile:

# Build for current platform
make build

# Build for all platforms
make build-all

# Clean build artifacts
make clean

# Run tests
make test

📖 Usage

Basic Usage

simple-cidr-calculator <CIDR>

Command Line Options

Usage:
  simple-cidr-calculator [OPTIONS] <CIDR>

Arguments:
  CIDR                 Network in CIDR notation (e.g., 192.168.1.0/24)

Options:
  -o, --output FILE    Save output to specified file
  -h, --html          Generate HTML formatted output
  --help              Show help message

Examples

Basic Network Analysis

simple-cidr-calculator 192.168.1.0/24

Output:

Network Information:
  CIDR:           192.168.1.0/24
  Network ID:     192.168.1.0
  Broadcast:      192.168.1.255
  Subnet Mask:    255.255.255.0
  Wildcard Mask:  0.0.0.255

Host Information:
  First Usable:   192.168.1.1
  Last Usable:    192.168.1.254
  Total Hosts:    254

Subnet Information:
  Possible /25 Subnets: 2

  Subnet List:
    192.168.1.0/25     (192.168.1.0 - 192.168.1.127)
    192.168.1.128/25   (192.168.1.128 - 192.168.1.255)

Save to Text File

simple-cidr-calculator -o network-report.txt 172.16.0.0/16

Generate HTML Report

simple-cidr-calculator --html -o network-report.html 10.0.0.0/8

Edge Cases

Point-to-Point Link (/31):

simple-cidr-calculator 192.168.1.0/31

Host Route (/32):

simple-cidr-calculator 192.168.1.1/32

📋 Output Formats

Text Output

The default text output provides a clean, aligned format suitable for terminal viewing and text file storage.

HTML Output

HTML output generates a professional-looking report with:

• Responsive design for mobile and desktop viewing
• CSS styling with gradient headers and clean tables
• Collapsible sections for large subnet lists
• Print-friendly formatting
• Self-contained file with embedded CSS

🧮 Subnet Calculation Logic

The tool calculates subnets by adding exactly one bit to the network prefix, creating two equal-sized subnets that together comprise the original network:

• Input: 192.168.1.0/24 → Output: Two /25 subnets (each with 128 addresses)
• Input: 10.0.0.0/16 → Output: Two /17 subnets (each with 32,768 addresses)
• Input: 172.16.0.0/20 → Output: Two /21 subnets (each with 2,048 addresses)

This approach shows the most common subnetting scenario - dividing a network into two equal halves. Each resulting subnet has exactly half the address space of the original network.

🔧 Supported Network Types

• Standard Networks: /8, /16, /24, /28, etc.
• Point-to-Point Links: /31 networks (RFC 3021)
• Host Routes: /32 networks (single host)
• Large Networks: Efficiently handles /8 networks with performance optimizations

⚠️ Error Handling

The tool provides clear error messages for common issues:

• Invalid CIDR format
• Invalid IP addresses
• Invalid prefix lengths
• File writing permissions
• Flag combination errors

⚡ Performance

• Optimized for large networks (e.g., /8 networks)
• Efficient memory usage
• Fast startup time
• Subnet listing limited for very large networks to maintain performance

🛠️ Development

Running Tests

# Run all tests
go test ./...

# Run tests with coverage
go test -cover ./...

# Run integration tests
go test -tags=integration ./...

Building for Multiple Platforms

# Linux
GOOS=linux GOARCH=amd64 go build -o simple-cidr-calculator-linux

# macOS
GOOS=darwin GOARCH=amd64 go build -o simple-cidr-calculator-macos

# Windows
GOOS=windows GOARCH=amd64 go build -o simple-cidr-calculator-windows.exe

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🤝 Contributing

Contributions are welcome! Please feel free to submit a Pull Request. For major changes, please open an issue first to discuss what you would like to change.

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add some amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

🙏 Credits

Enhanced and improved with assistance from Kiro AI - an AI-powered development assistant that helped optimize the codebase, improve documentation, and add comprehensive testing.