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🎯 CIDR Contains Check
You have an IP and a CIDR block. You want to know if the IP is inside. Common when reading firewall rules, debugging VPC route tables, or checking abuse logs against your own subnets. This tool does the bitwise AND for you across one or many IPs.
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Examples
Standard check
Input
10.0.5.42 in 10.0.0.0/16?Output
✓ Yes (inside)Frequently asked questions
How does the check work?
Apply the subnet mask to both the IP and the network address. If the masked results match, the IP is inside the block.
About this calculator
CIDR Contains Check runs entirely in your browser using standard formulas. No data is sent to any server. We don't share your inputs with lenders, brokers, or anyone else — there's no funnel and no follow-up email.
Related tools
- 🧮 Subnet / CIDR Calculator — Calculate network, broadcast, host range, mask from any CIDR notation.
- 🏷️ IP Class Identifier — Identify class (A, B, C, D, E) of any IPv4 address. Private vs public.
Why this tool
vs typical free network-tools sites
| NetToolset | Typical free site | |
|---|---|---|
| Price | Free | Free |
| Signup required | No | Often (for advanced features) |
| Ads inside the tool | No | Yes (banner + interstitial) |
| Logs your IP / queries | No | Yes (often resold) |
| Data sent to a server | Math runs in browser; lookups hit Cloudflare DoH directly | Yes (all goes through their server) |
| Open source | Yes | No |
| Bookmarkable URL per tool | Yes | Mixed |
| Multilingual | EN / ES / PT / FR / DE | Usually EN only |
| Loads in under 1s | Yes (static) | Often slow (ad tracking) |