CIDR Overlap Detector
Check whether multiple CIDR blocks overlap with each other. The detector analyzes every pair of subnets and classifies the relationship as identical, contains, contained, overlapping, or completely separate.
Why Detect CIDR Overlaps?
CIDR overlap detection is a critical step in network planning and troubleshooting. When two subnets overlap, devices in the overlapping range may have ambiguous routing or IP assignment conflicts. This is especially important when connecting multiple networks through VPNs, VPC peering, or direct connect links — overlapping CIDRs are one of the most common causes of connectivity failures in hybrid and multi-cloud architectures.
The tool classifies each pair of CIDRs into one of five relationship types:
- Identical — both CIDRs represent exactly the same address range.
- Contains — the first CIDR fully contains the second.
- Contained — the first CIDR is fully contained within the second.
- Overlapping — the ranges partially overlap but neither fully contains the other.
- None — the ranges are completely separate with no conflict.
Common Use Cases
Cloud architects use this tool when planning VPC peerings in AWS, Azure, and GCP to ensure CIDR ranges do not conflict. Network engineers use it when designing multi-site VPNs, SD-WAN deployments, and campus network migrations. It is also essential for MPLS L3VPN route validation and IPAM (IP Address Management) audits. Before deploying any new subnet, run it through the overlap detector against existing allocations to avoid costly re-addressing work.
Overlap Detection for Multi-Cloud and Hybrid Networks
As organisations adopt multi-cloud strategies, CIDR overlap detection becomes a recurring challenge. AWS, Azure, and GCP each assign default VPC CIDR ranges that can easily collide when you peer across clouds. For example, two teams that each independently chose 10.0.0.0/16 will discover the conflict only when they try to establish connectivity. Running a quick overlap check before provisioning peering connections or VPN tunnels saves hours of troubleshooting and avoids redesigning address allocations after deployment.
The overlap detector also handles partial overlaps, which are more subtle than identical or contained ranges. A partial overlap occurs when two CIDRs share only a portion of their address space, such as 10.0.0.0/20 and 10.0.8.0/21. These are particularly dangerous because they may go unnoticed during manual review but will cause intermittent routing failures for the overlapping segment. The tool explicitly flags these partial overlaps so you can resolve them before they reach production.
Use this tool together with the Subnet Calculator to design non-overlapping address plans, or the Supernet Calculator to find a parent CIDR that encompasses multiple ranges.