Worked example
10.5.0.0/16 overlaps 10.0.0.0/8 because every address in the /16 is already inside the /8.
Subnet Overlap Detector
Identify collisions and containment between CIDR blocks. Paste a list of subnets to find which ones overlap, helping you prevent routing conflicts and firewall rule shadowing.
Paste a list of IPv4 subnets above to check for overlaps and containment.
Why check for subnet overlaps?
Overlapping subnets cause major issues in enterprise networks. They can lead to non-deterministic routing, where traffic for a specific destination might be sent to different gateways depending on where it originates. In firewall configuration, overlapping blocks can lead to rule shadowing, where a broader rule inadvertently blocks or permits traffic meant for a more specific subnet.
How to use Overlap Detector
Paste network lists from routing tables, VPNs, or cloud environments to identify containment, collisions, and duplicates.
Common mistake
Adjacent networks are not overlapping; duplicates and parent-child containment are.