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IP Address Info

Public, Private, Loopback and CGNAT Classification With Integer, Hex and Binary Forms

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How the IP Address Info works

This IP address info tool says what kind of address it is. Type an IP address and learn what it is: whether it is routable on the public internet or reserved for private networks, loopback, link-local, carrier NAT, multicast or documentation; how it is written as an integer, in hex, in binary and in dotted or colon form; and what name its reverse DNS record gives. Useful when an address turns up in a log and you need to know whether to worry.

IP address info: public, private and reserved ranges

An IP address in a log, a firewall rule or an error message tells you very little on its own. The first thing to establish is what kind of address it is, because 10.0.3.7 in a request log means an internal service, 100.64.1.2 means a carrier's NAT, 127.0.0.1 means the same machine and 203.0.113.5 means someone is quoting documentation. This tool applies the IANA special-purpose registries for IPv4 and IPv6 and tells you which block the address falls in and what that block is for.

Classification. IPv4 addresses are checked against: private ranges (10/8, 172.16/12, 192.168/16), loopback (127/8), link-local (169.254/16), carrier-grade NAT (100.64/10), the documentation ranges (192.0.2/24, 198.51.100/24, 203.0.113/24), benchmarking (198.18/15), multicast (224/4), the reserved class E block (240/4), broadcast and the "this network" block. IPv6 addresses are checked against loopback (::1), unspecified (::), unique local (fc00::/7), link-local (fe80::/10), multicast (ff00::/8), documentation (2001:db8::/32), 6to4, Teredo, IPv4-mapped (::ffff:a.b.c.d), NAT64 (64:ff9b::/96), the discard prefix and global unicast. Anything else is public.

Forms. An IPv4 address is a 32-bit number, and some systems store or log it that way: 3232235777 is 192.168.1.1. The tool shows the decimal integer, hex (0xC0A80101), binary in four octets and the dotted form, and accepts any of them as input. IPv6 addresses are shown fully expanded (2606:4700:0000:0000:0000:0000:0000:1111), compressed per RFC 5952, and as a 128-bit hex integer. An IPv4-mapped IPv6 address is shown with its embedded IPv4.

Reverse DNS. The reverse name for an address is built for you — 1.1.168.192.in-addr.arpa for IPv4, the 32-nibble ip6.arpa name for IPv6 — and, unless you choose Skip, the PTR record is fetched from a public DNS-over-HTTPS resolver. The PTR name often reveals the hosting provider or ISP (ec2-…compute.amazonaws.com, …googleusercontent.com). Private and reserved addresses are not looked up because they have no public reverse zone.

No geolocation. Mapping an IP to a city needs a commercial database that changes daily and cannot run in a browser without shipping it, and its accuracy is oversold anyway. The PTR name and the block classification tell you what is knowable without one.

What to do with the answer. A private or loopback address in a public-facing log usually means a proxy is in front of your server and you should be reading X-Forwarded-For instead. A CGNAT address means many customers share it, so blocking it blocks them all. A documentation address in production configuration is a placeholder someone forgot to replace.

FAQ

Can I paste an integer or hex value instead of a dotted address?

Yes. A plain decimal number up to 4294967295, or a hex value starting with 0x, is treated as a 32-bit IPv4 address and converted. This is the reverse of the integer form shown in the result, and matches how some databases and log formats store addresses.

Why does the tool say my public address is private?

Because it is. 192.168.x.x, 10.x.x.x and 172.16–31.x.x are never routable on the internet, whatever your router shows. If you want the address the world sees, an external service must tell you; this tool does not contact one and does not report your own address.

What is CGNAT and why does it matter?

Carrier-grade NAT lets an ISP share one public IPv4 address among many customers using the 100.64.0.0/10 block internally. An address in that block seen on your own network means you are behind the ISP's NAT, which is why inbound connections and port forwarding do not work.

Does it validate IPv6 zone IDs and CIDR notation?

A zone ID such as fe80::1%eth0 is accepted and the zone is shown separately. CIDR notation such as 10.0.0.0/8 is accepted and the prefix length is reported; for subnet arithmetic — network, broadcast, host counts — use the subnet calculator, which is linked below.

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