CIDR Overlap Detector
Check whether two IPv4 CIDR ranges overlap.
What is CIDR overlap?
Two CIDR ranges overlap when they share at least one IP address. Every CIDR block is a continuous range of addresses — from its network address to its broadcast address. Two blocks overlap when one range begins before the other one ends.
Why check CIDR overlap?
- AWS VPC peering: VPCs cannot be peered if their CIDR blocks overlap. AWS rejects overlapping peering configurations, so check before you connect.
- VPN networks: If a remote network uses the same or an overlapping range as your local network, routes collide and traffic is sent to the wrong place.
- Office and data center planning: When you merge networks or connect new sites, overlapping subnets cause routing conflicts that are hard to debug later.
Example
10.0.0.0/24 covers 10.0.0.0 – 10.0.0.255. 10.0.0.128/25 covers 10.0.0.128 – 10.0.0.255. Every address in the second range is also in the first, so they overlap. The shared range is 10.0.0.128 – 10.0.0.255.
Related Tools
- CIDR Summarizer — Coming soon
- IP Range to CIDR — Coming soon
- VLSM Planner — Coming soon
- Wildcard Mask Calculator — Coming soon