Multi-Cloud CIDR Overlap Checker
Compare entered cloud network allocations.
Multi-Cloud CIDR Overlap Checker: inputs and results
Enter an IP address, CIDR prefix, or range. Then check its first and last address below.
Calculated Boundaries & ParametersReady
Key Capabilities
- •100% Client-Side: Zero telemetry or server latency.
- •RFC Compliant: Exact 32-bit and 128-bit integer precision.
- •Quick Copy: Instant access to CIDR, mask, and range bounds.
- •Cross-Platform: Works on desktop, tablet, and mobile browsers.
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IP-in-Subnet Checker
Test membership within a CIDR block.
How Multi-Cloud CIDR Overlap Checker Works?
This tool works by comparing every network CIDR entered for AWS, Azure, Google Cloud, and on-premises sites against every other entry, and flagging each overlapping pair.
Enter networks per provider
Add entries such as "AWS prod VPC 10.0.0.0/16" and "Azure hub VNet 10.0.128.0/17".
Compare all pairs
The checker tests each pair with the CIDR overlap rule.
Group conflicts by provider pair
Conflicts are grouped as AWS–Azure, Azure–GCP, and similar.
Suggest free space
The checker lists unused blocks inside the shared parent range for renumbering.
Multi-Cloud CIDR Overlap Checker Formula
The formula is Conflict(A, B) = (N_A AND Mask(min(p_A, p_B))) = (N_B AND Mask(min(p_A, p_B))) for each pair across providers.
Pair test
mask both with the shorter prefix and compareSame rule as single-list CIDR overlap.
Pairs compared
n × (n − 1) ÷ 28 networks → 28 pairs.
Shared addresses
size of the longer prefixNested CIDRs share the whole smaller block.
Worked example: AWS 10.0.0.0/16 vs Azure 10.0.128.0/17
Shorter prefix = /16 10.0.128.0 AND 255.255.0.0 = 10.0.0.0 = AWS network Conflict: the Azure VNet sits inside the AWS VPC Shared addresses = 32,768
Multi-Cloud CIDR Overlap Checker Conversion Table
The table compares 6 cloud and on-premises networks and lists every overlapping pair.
| Network A | Network B | Relationship | Shared Addresses |
|---|---|---|---|
| AWS prod VPC 10.0.0.0/16 | Azure hub VNet 10.0.128.0/17 | A contains B | 32,768 |
| AWS dev VPC 10.1.0.0/16 | GCP shared VPC 10.1.64.0/18 | A contains B | 16,384 |
| On-prem DC 172.16.0.0/12 | Azure spoke VNet 172.20.0.0/16 | A contains B | 65,536 |
Pairs not listed, such as AWS prod VPC and AWS dev VPC, do not overlap.
What is Multi-Cloud CIDR Overlap Checker?
The Multi-Cloud CIDR Overlap Checker is a tool that detects address conflicts between networks in different cloud providers and on-premises data centers.
Teams in different clouds often pick the same default ranges, such as 10.0.0.0/16. The conflict stays hidden until the networks need to connect through VPC peering, Transit Gateway, Azure Virtual WAN, or an interconnect. At that point, overlapping CIDRs block the connection or force NAT.
The checker compares every entered network across every provider at once and lists each conflicting pair, before any connection is built.
What are the uses of Multi-Cloud CIDR Overlap Checker?
There are 4 main uses of the Multi-Cloud CIDR Overlap Checker, including interconnect planning, landing zone design, and mergers.
Planning cloud interconnects
AWS Direct Connect, Azure ExpressRoute, and Google Cloud Interconnect need unique ranges on both sides.
Designing landing zones
Landing zone address plans reserve non-overlapping blocks per provider.
Integrating acquired companies
Cloud estates from 2 companies are checked before connecting.
Enforcing address governance
Central teams check new VPC and VNet requests against all existing networks.