Public / Private IP Checker

Not every IPv4 address is reachable on the internet. Some ranges are reserved for special use — private networks, loopback, link-local, documentation — and are never routed on the public internet. This tool tells you which range an IP belongs to, whether it is internet-routable, and the RFC behind it.

Use it to tell whether an IP in your server logs is an internal address or an external visitor, or while reviewing firewall and proxy settings. If the IP is an external visitor, dig deeper with the IP Geolocation or IP ASN Lookup tools.

Key special ranges

• Private (RFC 1918): 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 — internal only.
• Loopback: 127.0.0.0/8 — the host itself (localhost).
• Link-local: 169.254.0.0/16 — auto-assigned when DHCP fails (APIPA).
• CGNAT: 100.64.0.0/10 — carrier shared NAT range.
• Documentation: 192.0.2.0/24 and others — examples only, not routable.

Seeing 169.254.x.x?

If a device has this address, it failed to get an IP from DHCP — a common cause of "no internet" issues.

Full special-range reference (the 16 rules this tool checks)

The tool tests these ranges using longest-prefix match (narrowest range wins). If an address matches none of them, it is classified as public. The Matched range and Referencevalues appear verbatim on the result card.

Example: how 100.64.10.5 is classified

It looks like an ordinary private IP with no external ASN, but it is actually a carrier shared-NAT address. Here is how the tool decides:

• Input 100.64.10.5 → 32-bit integer 1681915397.
• AND with the 100.64.0.0/10 mask (top 10 bits) → same base value. Match.
• Classification = CGNAT, matched range = 100.64.0.0/10, reference = RFC 6598, internet routable = No.
• The status shows as warn, alongside private/loopback/link-local — while multicast, reserved, and documentation show as danger.

Common pitfall

• Do not assume 10.x.x.x always means "our corporate LAN." The same private range is reused by countless orgs, VPNs, and container networks, so the IP alone never tells you which network it belongs to.
• It is easy to mistake 100.64.x.x for RFC 1918 private space, but it is RFC 6598 CGNAT — an address the carrier hands to subscribers, not your own internal LAN.
• An address not being in a special range does not mean it is reachable from outside. Being public is independent of firewall, NAT, and open-port status.