CIDR/Subnet Overlap Checker

How it works

Each CIDR is converted to a 32-bit integer network address and broadcast address using bitwise masking, kept unsigned via >>> 0 since JavaScript's bitwise operators are otherwise signed 32-bit and would break on ranges near 255.255.255.255 or a /0. Every range is then checked against every other range — an O(n²) comparison — flagging two as overlapping whenever one's network address falls at or before the other's broadcast address and vice versa.

FAQ

Does it check IPv6 ranges?

No — it only parses IPv4 CIDR notation (dotted-quad plus a /0-32 prefix); IPv6 addresses or invalid lines are silently excluded from the overlap check and counted separately as unparseable.

Does a /24 fully contained inside a /16 count as an overlap?

Yes — any two ranges are flagged if their address spans intersect at all, regardless of whether one is fully nested inside the other or they only partially cross, since both cases represent a real allocation conflict.