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IPv4 CIDR Splitter

Subnets:

  • 192.168.1.0/26
  • 192.168.1.64/26
  • 192.168.1.128/26
  • 192.168.1.192/26

About This Tool

The IPv4 CIDR Splitter (also known as subnet calculator or VLSM calculator) divides a larger network into multiple smaller subnets with a specified prefix length. This tool is essential for Variable Length Subnet Masking (VLSM) and hierarchical network design, allowing network administrators to efficiently allocate IP address space by creating subnets of appropriate sizes for different departments, VLANs, or network segments.

How to Use

  1. Enter the parent network in CIDR notation (e.g., 192.168.1.0/24)
  2. Specify the new prefix length for the subnets you want to create (must be larger than the original)
  3. The tool automatically calculates and displays all resulting subnets
  4. Copy the subnet list for use in network diagrams, VLAN assignments, or router configurations
  5. Example: Splitting 192.168.1.0/24 with /26 creates four /26 subnets

Features

  • Split any IPv4 network into smaller, equal-sized subnets
  • Real-time calculation as you adjust the new prefix length
  • Displays complete list of all resulting subnets
  • Validates input to ensure new prefix is larger than original
  • Supports all valid IPv4 prefix lengths (0-32)
  • Shows all subnets in CIDR notation ready for configuration
  • Efficient for VLSM and hierarchical network design

Common Use Cases

  • Dividing a Class C network into multiple VLANs
  • Implementing Variable Length Subnet Masking (VLSM) schemes
  • Creating subnets for different departments or locations
  • Planning hierarchical network addressing for branch offices
  • Allocating address space efficiently in enterprise networks
  • Designing multi-tier network architectures
  • Subnetting for cloud VPC networks (AWS, Azure, GCP)
  • Creating DMZ and security zones with appropriate subnet sizes

Technical Details

Subnet splitting works by incrementing the network address by the size of each new subnet until the entire original network is covered.

Splitting Formula: Number of subnets created = 2^(new prefix - old prefix)

Example Calculations:

  • Split 192.168.1.0/24 into /26 → 2^(26-24) = 4 subnets:
    • 192.168.1.0/26 (64 addresses: .0 to .63)
    • 192.168.1.64/26 (64 addresses: .64 to .127)
    • 192.168.1.128/26 (64 addresses: .128 to .191)
    • 192.168.1.192/26 (64 addresses: .192 to .255)
  • Split 10.0.0.0/16 into /24 → 2^(24-16) = 256 subnets (10.0.0.0/24 through 10.0.255.0/24)
  • Split 172.16.0.0/22 into /24 → 2^(24-22) = 4 subnets (172.16.0.0/24, 172.16.1.0/24, 172.16.2.0/24, 172.16.3.0/24)

VLSM Benefits:

  • Efficient use of IP address space by creating right-sized subnets
  • Reduces address wastage compared to fixed-length subnetting
  • Enables hierarchical routing and summarization
  • Supports complex network topologies with varying subnet requirements

The tool ensures all generated subnets are contiguous and fully cover the original network without gaps or overlaps.