How to use this tool
- Enter one IPv4 or IPv6 address. Leave out brackets, ports, zone identifiers and CIDR suffixes.
- Select Check address to validate the syntax and find the most specific matching reservation.
- Read the purpose and address range. Classification describes address space; it does not test whether a host is online.
Public and private are only part of the picture
Private IPv4 ranges are used inside networks, while IPv6 unique-local addresses serve a similar local purpose. Loopback addresses refer to the local machine, and link-local addresses apply to a local network link. Multicast addresses identify groups rather than an ordinary unicast host.
Carrier-shared IPv4 space, 100.64.0.0/10, is separate from the familiar private ranges. Providers can use it upstream of a customer router. Documentation and benchmarking ranges also have special purposes and should not be treated as ordinary public destinations.
Most specific reservations matter
Some small globally reachable reservations sit inside broader special-purpose blocks. The checker matches the longest prefix first, using a reviewed snapshot of the IANA IPv4 and IPv6 special-purpose registries. This avoids labelling every address in a broad block the same way.
IPv4-mapped IPv6 forms are displayed with their embedded IPv4 value. Such a representation is not, by itself, evidence of an independently working IPv6 internet route. Ordinary IPv6 global-unicast space currently comes from 2000::/3; other allocations need their own interpretation.
Classification does not test routing
A public address can be unused, filtered or unreachable. A registry's global-reachability flag describes the reservation's intended properties rather than a measurement of the entered host. Your network may also route special-use addresses in a local context.
The calculation runs in the browser. For actual public-address geolocation and network details, use IP lookup; for a router WAN mismatch, use the CGNAT troubleshooting helper.