How to Use the Public vs Private IP Address Classifier
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Enter an IPv4 or IPv6 address.
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The classifier checks the address against all standard IANA reserved blocks.
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View status: Public (Internet Routable), RFC 1918 Private (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), CGNAT (100.64.0.0/10), Loopback, or Link-Local.
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Inspect default gateway and subnet implications.
Practical Example & Use Case
Common Real-World Scenario
Recognizing that an IP `100.72.15.4` is behind a Carrier-Grade NAT (CGNAT) ISP proxy and cannot accept incoming port-forwarded traffic.
Technical Notes & Limitations
Browser Engine Architecture
Validates against RFC 1918, RFC 6598, RFC 3927, RFC 5771, and RFC 6890 registries.
Frequently Asked Questions
What is CGNAT (Carrier-Grade NAT)?
The 100.64.0.0/10 block reserved by RFC 6598 for ISPs to share a single public IPv4 address across multiple residential subscribers.