Subnet Overlap Checker

The subnet overlap checker finds every pair of CIDR blocks in your list that share addresses. Paste your subnets, one per line or separated by commas, and it flags each conflicting pair so you can resolve it before it causes duplicate IPs, ambiguous routing, or DHCP conflicts.

Overlapping subnets are one of the most common and least visible problems in network planning. They appear when two sites are merged, when a cloud VPC is added on top of existing address space, when DHCP scopes are resized by hand, or when a spreadsheet of allocations is edited by two people at once. Because both networks can legitimately use the same addresses, the conflict is invisible until traffic goes somewhere unexpected.