What it's for
Detecting overlap between two CIDR ranges matters when planning networks, static routes, site-to-site VPNs or firewall rules — two overlapping subnets often cause routing conflicts that are hard to diagnose.
How it's checked
The tool computes the first and last address of each range (network and broadcast) and checks whether the numeric intervals intersect — including when one range is fully contained within the other.
Frequently asked questions
Do two identical subnets count as overlapping?
Yes — if the two CIDRs are exactly the same, they overlap completely.
What about a range fully inside another (e.g. a /25 inside a /24)?
That also counts as overlap — the tool detects both partial overlap and a range entirely contained within another.