Detect overlapping IP address ranges between CIDR blocks. Check a single pair or scan an entire list for conflicts.
Enter two or more CIDR blocks to check for overlaps
The CIDR Overlap Checker detects IP address range conflicts between subnets. Overlapping CIDRs cause routing problems in VPCs, BGP configurations, and any network design requiring non-overlapping address spaces. In single-pair mode, enter two CIDR blocks to instantly see whether they overlap and what the shared range is. In batch mode, paste an entire list of subnets (one per line) to find all conflicting pairs at once.
The checker normalizes CIDRs to their network address before comparing (e.g. 10.0.0.5/24 becomes 10.0.0.0/24). Containment is also detected as overlap: 10.0.0.0/8 and 10.1.2.0/24 overlap because the /24 is entirely inside the /8. All processing runs in your browser with no data sent to any server.