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Choose Single or Bulk Mode
Select "Single IP" to classify one address, or "Bulk List" to classify multiple IPs at once by pasting one address per line.
Public or Private IP Checker |
Classify any IPv4 or IPv6 address as public, private (RFC 1918), loopback, link-local (APIPA), or CGNAT (RFC 6598). Single address or bulk list supported.
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Public or Private IP Checker — Classify Any IP Address Instantly
Public or private IP classification determines whether an IPv4 or IPv6 address is internet-routable or restricted to a local network. Classification is performed by checking the address against IANA-reserved blocks defined in RFC 1918, RFC 1122, RFC 3927, and RFC 6598 for IPv4; and RFC 4193 and RFC 4291 for IPv6. Results include six categories: Public, Private (RFC 1918), Loopback, Link-Local (APIPA), CGNAT (RFC 6598), and Invalid IP. All checks run in the browser — no address data is transmitted or stored.
Single address mode classifies one IP immediately. Bulk list mode accepts any number of addresses — one per line — and returns a classification table in one operation. Both IPv4 and IPv6 addresses are supported in either mode.
How to Check if an IP is Public or Private
Classify any IPv4 or IPv6 address as public, private (RFC 1918), loopback, link-local, CGNAT, or invalid in seconds.
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Enter the IP Address
Type an IPv4 or IPv6 address into the input field (single mode), or paste a list with one IP per line into the text area (bulk mode).
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Click Classify IP Address
Click the "Classify IP Address" button. The tool checks the input against all IANA-reserved ranges immediately — no server request is made.
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Read the Classification Result
Each IP is labeled: Public, Private (RFC 1918), Loopback, Link-Local (APIPA), CGNAT (RFC 6598), or Invalid IP. In bulk mode, results appear in a table with one row per address.
What Each Classification Result Means
| Classification | What It Means | Example |
|---|---|---|
| Public | Internet-routable address — visible to external servers and services. | 8.8.8.8 |
| Private (RFC 1918) | Internal network address — not routable on the public internet. Used in home and enterprise LANs. | 192.168.1.1 |
| Loopback | Refers to the local machine itself. Packets never leave the host. Used for local service testing. | 127.0.0.1 |
| Link-Local (APIPA) | Auto-assigned by a host when DHCP fails (RFC 3927). Only reachable within the local network segment — never routed. | 169.254.1.5 |
| CGNAT (RFC 6598) | ISP Carrier-Grade NAT shared address space (100.64.0.0/10). Your ISP holds the public IP — your router does not. Port forwarding and hosting are typically blocked. | 100.64.0.1 |
| Invalid IP | Input is not a valid IPv4 or IPv6 address format — octet exceeds 255, contains illegal characters, or is malformed. | 999.0.0.1 |
How IP Address Classification Works
IP address classification is a deterministic range-membership check against blocks
published by IANA. For IPv4, RFC 1918 (February 1996) reserves three blocks for
private internets: 10.0.0.0/8, 172.16.0.0/12, and
192.168.0.0/16. These addresses are guaranteed never to appear as
globally routable public IP addresses. RFC 1122 reserves 127.0.0.0/8
for loopback. RFC 3927 (May 2005) reserves 169.254.0.0/16 for
zero-configuration link-local addressing (APIPA on Windows). RFC 6598 (April 2012)
carves out 100.64.0.0/10 for Carrier-Grade NAT shared address space —
distinct from RFC 1918 because it is assigned by ISPs between their infrastructure
and subscribers, not within a private LAN.
For IPv6, RFC 4193 defines Unique Local Addresses (ULA) in the fc00::/7
block (the fc and fd prefixes) — the IPv6 equivalent of
RFC 1918 private space. RFC 4291 defines the loopback address ::1/128
and link-local addresses in fe80::/10. All classification in this tool
runs client-side; no address is transmitted to any server.
Common Uses for IP Classification
Firewall rule validation: A DevOps engineer writing AWS security group rules encounters the range 100.64.0.0/10 in a configuration file. Before treating it as a trusted internal range, the tool confirms it is CGNAT address space — assigned by an ISP, not a private LAN. The rule is updated accordingly to avoid unintentional trust of ISP-level infrastructure.
Server log analysis: A sysadmin reviewing Nginx access logs finds repeated requests from 169.254.x.x addresses. The link-local classification immediately identifies these as APIPA addresses — devices that failed to obtain a DHCP lease and are operating on the local segment only. These requests are originating from internal infrastructure, not external users.
Bulk IP audit: An IT administrator exports 150 IP addresses from a network scan and needs to separate public-facing addresses from internal ones for a security review. Using bulk list mode, the full list is pasted and classified in one operation — no manual range lookup required. The results table is then filtered for "Public" entries to scope the external attack surface.
Frequently Asked Questions
What IP address ranges are classified as private?
Three address blocks are reserved for private use by RFC 1918: 10.0.0.0/8 (Class A, ~16.7 million addresses), 172.16.0.0/12 (Class B, ~1 million addresses), and 192.168.0.0/16 (Class C, 65,536 addresses). These addresses are guaranteed never to be assigned as public internet addresses. This tool also classifies 127.0.0.0/8 as Loopback, 169.254.0.0/16 as Link-Local (APIPA), and 100.64.0.0/10 as CGNAT — ranges that are non-routable on the public internet but are not part of RFC 1918.
What does "Link-Local (APIPA)" mean in the result?
A 169.254.0.0/16 address is a link-local address assigned automatically by a host when it cannot reach a DHCP server — a process called Automatic Private IP Addressing (APIPA), defined in RFC 3927. These addresses are only reachable within the local network segment and are never routed beyond it. If a device in your network shows a 169.254.x.x address, it typically means DHCP failed — check your router's DHCP settings or the network connection on that device.
What is CGNAT and why does my result show CGNAT instead of Public?
Carrier-Grade NAT (CGNAT) is a technique where an ISP shares a single public IP address among multiple subscribers. The CGNAT range — 100.64.0.0/10, defined in RFC 6598 — sits between your private home network and the public internet. If your router's WAN IP falls in this range (100.64.0.0 to 100.127.255.255), your ISP holds the real public IP, not your router. This can prevent port forwarding, peer-to-peer connections, and self-hosted server access. Contact your ISP to request a dedicated public IP if CGNAT causes problems.
What is the difference between a public IP and a private IP address?
A public IP address is globally unique and internet-routable — assigned by an ISP and visible to external servers when your device connects online. A private IP address (RFC 1918) is reused across millions of local networks and is not routable on the public internet; your router translates between them using NAT (Network Address Translation). Every device on a home network has a private IP, while the router itself holds one public IP shared by all devices on that network.
How accurate is the IP classification result?
Classification is 100% deterministic for valid IP addresses — it is based solely on numeric range comparisons against IANA-reserved blocks defined in published RFCs. There is no probability involved: an address either falls within a reserved range or it does not. The only source of inaccuracy is an invalid or malformed input, which the tool labels as "Invalid IP."
Do you store or log the IP addresses I check?
No. All classification runs entirely in your browser using JavaScript. No IP address — single or bulk — is transmitted to any server. No data is stored or logged at any point during or after the check.