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IPv4 CIDR Split Calculator

Split IPv4 networks into smaller subnets for VLSM planning and network optimization

Network Split Configuration

How to Use the IPv4 CIDR Split Calculator

Getting Started

  • Step 1: Enter the base network IP address (e.g., 192.168.1.0)
  • Step 2: Specify the original CIDR prefix length (e.g., 24)
  • Step 3: Enter the new CIDR prefix for smaller subnets (e.g., 26)
  • Step 4: Click "Split Network" to see detailed subnet breakdown

Key Concepts

  • CIDR Splitting: Dividing a large network into multiple smaller subnets
  • VLSM: Variable Length Subnet Masking for efficient IP allocation
  • Subnet Size: Larger CIDR prefix = smaller subnet size
  • Host Calculation: Total addresses minus network and broadcast addresses

Best Practices

  • Planning First: Determine required subnet sizes before splitting
  • Growth Allowance: Plan for future expansion in subnet sizing
  • Address Efficiency: Use VLSM to minimize IP address waste
  • Documentation: Record subnet assignments and purposes

Network Design Guidelines

  • Point-to-Point: Use /30 or /31 for router interconnections
  • Small LANs: /28 provides 14 usable hosts
  • Medium LANs: /26 provides 62 usable hosts
  • Large LANs: /24 provides 254 usable hosts

Frequently Asked Questions

What is CIDR splitting and why is it useful?

CIDR splitting divides a large network into multiple smaller subnets. This improves network organization, security through segmentation, broadcast domain management, and enables more efficient IP address allocation.

How do I determine the right subnet sizes for my network?

Count the maximum number of hosts needed in each segment, add 20-30% for growth, then choose the next larger subnet size. Consider that each subnet loses 2 addresses (network and broadcast).

What does it mean that the new CIDR must be larger?

A larger CIDR number means a smaller network. /24 is larger than /16 but represents a smaller network (256 vs 65,536 addresses). To split a network, you increase the CIDR prefix to create smaller subnets.

Can I split subnets unevenly with different sizes?

This calculator creates equal-sized subnets. For unequal subnet sizes (VLSM), you'll need to plan manually by allocating the largest subnets first, then subdividing remaining space for smaller subnets.

What happens to unused subnets after splitting?

All subnet addresses are allocated even if unused. Unused subnets can be reserved for future use, assigned to other network segments, or further subdivided if needed for smaller requirements.

How does subnet splitting affect routing?

Each subnet becomes a separate network requiring its own routing entry. However, if subnets are contiguous and follow proper hierarchical design, route summarization can reduce routing table size.

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