CIDR Overlap Calculator

CIDR (Classless Inter-Domain Routing) ranges define contiguous blocks of IP addresses. When two or more ranges share addresses, they overlap. Overlap detection is essential for network design: merging subnets, configuring firewalls, and avoiding IP conflicts.

To determine overlap, compare the network and broadcast addresses of each range. The overlap exists if the later network address is less than or equal to the earlier broadcast address. The overlapping range itself runs from max(network1, network2) to min(broadcast1, broadcast2).

Overlapping subnets can cause routing ambiguity — a host might match multiple routes. In DHCP, overlapping scopes can assign the same IP to different devices. Firewall rules with overlapping ranges may behave unexpectedly. When migrating or consolidating networks, identifying overlaps prevents duplicate allocations and ensures clean cutover.

Use this tool before merging VPCs, consolidating office networks, or implementing complex ACLs. A quick overlap check saves hours of troubleshooting.

The bar chart maps each CIDR range onto a horizontal axis representing the IP address space. Each range appears as a bar from its network address to broadcast address. Overlapping regions are highlighted in red.

This visualization makes it easy to see containment (one range fully inside another), partial overlap, or adjacency. When planning subnet changes, the chart helps communicate design decisions to stakeholders.