Enter IPv4 CIDR notation, e.g. 10.0.0.0/8
Load example:
No ranges analyzed yet
Paste CIDRs on the left and click Check Overlaps// detect subnet overlaps and containment issues instantly
Instantly detect overlapping and contained CIDR ranges. Paste multiple IPv4 subnets and find all conflicts, containments, and duplicates in one click.
No ranges analyzed yet
Paste CIDRs on the left and click Check OverlapsEnter IPv4 CIDR ranges, one per line, in the input box on the left.
Click the button to analyze all pairs for overlaps, containments, and duplicates.
See a color-coded summary of all conflicts and a detailed breakdown of each CIDR range.
A CIDR Overlap Checker analyzes a list of IPv4 subnet ranges to detect when two or more ranges share IP addresses. It identifies three conflict types: overlaps (partial sharing), containment (one range fully inside another), and duplicates (identical ranges).
CIDR (Classless Inter-Domain Routing) notation represents an IP address and its associated network mask. For example, 192.168.1.0/24 means the network starts at 192.168.1.0 and the prefix length of 24 bits leaves 8 bits for host addresses (256 IPs total).
An overlap means two ranges partially share IP addresses ā neither contains the other. Containment means one range is entirely within another, like 10.0.1.0/24 being inside 10.0.0.0/8. Both are conflict types that can cause routing issues.
There's no hard limit. The tool compares every pair (O(nĀ²) complexity), so performance remains fast for typical use cases of up to a few hundred ranges. Very large lists (500+) may take a moment to process.
Currently, this tool supports IPv4 CIDR ranges only. IPv6 support is on the roadmap. For IPv6, ensure your subnets use the correct prefix length format (e.g., ::/0 to ::/128).
Overlapping subnets cause routing ambiguity ā routers may not know which path to forward packets to. In cloud environments like AWS VPCs, overlapping CIDRs prevent peering entirely. In firewalls, they can cause rule ordering conflicts and security holes.
The CIDR analysis is processed server-side via a lightweight PHP API on our own servers, but no data is stored or logged. Your IP ranges are discarded immediately after the response is returned.
A CIDR Overlap Checker is a diagnostic tool used by network engineers, DevOps teams, and cloud architects to identify conflicting IP address ranges within a given set of subnets. When two CIDR blocks share one or more IP addresses ā whether partially (overlap) or entirely (containment) ā it creates routing ambiguity, security policy conflicts, and connectivity failures across networks, VPNs, and cloud infrastructure.
This tool accepts a list of IPv4 subnets in CIDR notation and automatically scans every pair for three distinct conflict types: partial overlaps, full containment, and exact duplicates. Results are presented with clear visual indicators, so you can immediately understand which ranges are in conflict and take corrective action.
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CIDR stands for Classless Inter-Domain Routing. It's the standard method for specifying IP address ranges on modern networks. A CIDR block is written as an IP address followed by a slash and a prefix length ā for example, 10.0.0.0/8. The prefix length indicates how many leading bits are fixed (the "network" portion), while the remaining bits define the available host addresses.
A /24 prefix has 256 total addresses (254 usable hosts), a /16 has 65,536 addresses, and a /8 spans over 16 million. The smaller the prefix number, the larger the network. This flexibility is what makes CIDR the foundation of modern IP address management ā and the source of common misconfiguration errors when ranges are assigned without checking for conflicts.
This checker identifies three distinct relationship types between CIDR pairs:
192.168.1.0/24 and 192.168.1.128/25 overlap because the second range is within the address space of the first.10.0.0.0/24 is contained within 10.0.0.0/8. The smaller block's entire address space is a subset of the larger block. While not always a problem in routing hierarchies, containment can be unintentional and cause rule duplication in firewalls and security groups.Overlapping subnets might seem harmless on paper, but they cause concrete failures in production environments:
Preventing CIDR conflicts starts at the design phase. Here are proven strategies used by network and cloud architects:
After clicking Check Overlaps, the tool returns three sections. The summary bar at the top shows a color-coded count of clean ranges, overlaps, containments, and duplicates at a glance. The conflict list enumerates every detected issue, naming the specific pair of CIDRs involved and the type of conflict. Finally, the range details table shows computed metadata for each valid CIDR: network address, broadcast address, first and last usable host, and total host count.
A result showing zero overlaps, zero containments, and zero duplicates means your subnet plan is clean ā no routing conflicts were detected among the provided ranges. Note that this tool validates the ranges you provide; it doesn't know about subnets that exist in your environment but weren't included in the input.