IP in CIDR Range Checker
Check a list of IPv4 and IPv6 addresses against a list of CIDR ranges, such as a CDN's published ranges or a trusted proxy list, and see which range matched.
Free · No sign-up · Your inputs stay in your browser
Input
Check whether IPs fall inside CIDR ranges
Output
3 of 4 inside
| IP | Inside | Matched range |
|---|---|---|
| 172.20.4.9 | yes | 172.16.0.0/12 |
| 8.8.8.8 | no | - |
| 2606:4700:10::6816:1 | yes | 2606:4700::/32 |
| 173.245.63.255 | yes | 173.245.48.0/20 |
The same check a TrustProxies list, a security group or set_real_ip_from makes. Trusting too wide a range (0.0.0.0/0) lets any client forge X-Forwarded-For and appear to come from anywhere.
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About this tool
Method, assumptions, practical next steps, and limits.
Trusted proxies
Behind a load balancer or a CDN, the client IP arrives in X-Forwarded-For, which any client can also send. Frameworks only believe it from proxies you list: Laravel's trustProxies(at: [...]), Nginx's set_real_ip_from. Listing the provider's published ranges, rather than 0.0.0.0/0, is what stops a visitor from choosing their own IP.
Keeping lists current
CDNs publish their ranges and change them: Cloudflare at cloudflare.com/ips, AWS in ip-ranges.json. Fetch them on a schedule rather than pasting them once into a config file.