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Compares every pair of IPv4 CIDR blocks to find where address ranges overlap, listing each conflicting IP range and host count for subnet and VPC planning.

📘 How to Use

  1. Paste your CIDR ranges into the input box, one per line
  2. Read the network-to-broadcast address span and overlap status for each range
  3. Inspect the overlapping IP range and host count when a collision is reported

CIDR Range Overlap Checker

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Enter CIDR ranges to check for overlaps

Enter CIDR ranges to check for overlaps
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CIDR Range Overlap Checker | Instantly Detect IP Address Conflicts

Paste a list of CIDR blocks and instantly see the address span of each range, plus exactly which ranges collide, with the overlapping IP range and host count spelled out. Validate your subnet plan entirely in the browser.

💡 Catch silent subnet collisions before they ship

When you carve up a network or design VPC subnets, it's surprisingly easy to allocate two blocks that look distinct but actually overlap, like 10.0.0.0/24 and 10.0.0.128/25. Overlapping address space leads to ambiguous routing, firewall rules that never match, rejected VPC peering, and DHCP scopes that fight each other, and these problems usually surface only after deployment.

This checker expands every CIDR into its integer network and broadcast boundaries, then compares all pairs to find where the ranges intersect. Instead of doing subnet-mask arithmetic by hand or tracking allocations in a spreadsheet, you get a deterministic answer you can drop into a design review or an IPAM pre-check. Everything runs in your browser, so the address plan you paste is never sent to a server.

🧐 Frequently Asked Questions

How many CIDR blocks can I check at once? There is no hard limit. List them one per line and the tool compares every pair. More entries mean more comparisons, but it all runs locally in the browser.

Does it support IPv6? No. This tool is built for IPv4 dotted-decimal notation such as 192.168.1.0/24. IPv6 CIDR blocks are not parsed.

Can it handle edge prefixes like /0 and /32? Yes. /0 covers the entire address space and /32 represents a single host; both have their ranges computed correctly.

What exactly counts as an overlap? Two ranges overlap if they share even a single address. That includes the case where one block fully contains another, such as a /25 nested inside a /24.

What happens if a line is malformed? Any line that doesn't match four dotted octets plus a prefix is flagged as an error, while the valid lines are still parsed and compared.

📚 Why overlap detection matters

CIDR (Classless Inter-Domain Routing) replaced the old fixed classful scheme (Class A/B/C) precisely so that address blocks could be sized to the organization rather than forced into rigid boundaries. The flexibility of variable-length prefixes is also its trap: shift a prefix by a single bit, say from a /24 to two /25s, and an off-by-one in the math leaves you either overlapping the next block or with an unintended gap. Comparing ranges as raw integer boundaries removes that human error, which is why automated boundary checks are a standard step in network change reviews and infrastructure-as-code linting.