An IPv4 subnet is a logically segmented portion of an IP network that shares a common address prefix. The IPv4 Subnet Split Calculator lets you explore how larger networks divide into smaller segments. You provide one address and two CIDR values; the tool instantly shows network, broadcast, and usable ranges.

You often need to split an allocated block to fit departmental, security, or host-count requirements. This calculator automates that complex task in seconds. It validates inputs, derives every child subnet, and presents address summaries side by side. You avoid manual binary math and reduce errors while planning network infrastructure changes.

Imagine redesigning a /24 office network into /26 segments for production, guest, and laboratory zones. Enter the address, pick /24 as current and /26 as target, then review four equal subnets with usable ranges. The summary card highlights total new networks and addresses, informing routing and firewall rules in advance.

Technical Details:

Review the core capabilities before running your calculations.

• Accepts any dotted-decimal IPv4 address input.
• Supports current masks /1–/30 and target masks up to /30.
• Rejects target masks shorter than the current mask.
• Calculates network, broadcast, and usable host addresses.
• Generates a complete list of child subnets.
• Displays total new networks and total usable addresses.
• Shows validation errors in a red alert for quick correction.
• Updates results instantly as you edit inputs.

Calculations and Scoring:

Understand the logic that drives every figure.

Formula Breakdown

The table above shows how the tool derives each subnet statistic using bitwise operations and exponentiation.

Worked Example

Split 192.168.0.1/24 into /26 networks:

1. Mask difference = 2 bits, so New Networks = 4.
2. Child size = 64 addresses; usable each = 62.
3. First child network: 192.168.0.0/26; last: 192.168.0.192/26.
4. Total usable addresses = 248.

Interpretation

• More host bits yield larger ranges.
• Network and broadcast addresses are not assignable.
• Equal-size subnets simplify routing summarisation.

Recommendations

• Reserve the first subnet for infrastructure to standardise documentation.
• Apply separate VLANs to keep broadcast domains manageable.
• Document each allocation to maintain audit trails.
• Use CIDR notation consistently in firewall rules.

Step-by-Step Guide:

Follow these steps to generate accurate subnet plans.

1. Enter an IPv4 address in the IP Address field.
2. Select the current prefix length under Current CIDR.
3. Choose the desired longer prefix under Target CIDR.
4. Review any messages in the red alert box Caution.
5. Scroll to the Summary card for overall statistics.
6. Browse the Subnets table and copy needed ranges Tip.

FAQ:

Find answers to common questions.

Troubleshooting:

Resolve issues quickly with these checks.

• Invalid address alert: Verify each octet is 0–255.
• Redundant mask error: Ensure target mask is longer than current mask.
• No output generated: Address and masks must pass validation before calculations run.
• Unexpected network results: Confirm address belongs to the stated current CIDR block.
• Table scrolling clipped: Widen your browser or use the horizontal scrollbar.