Guide
Telling private, public and special-purpose IP addresses apart
Whether an address is private matters more often than most people expect. It decides whether a server can be reached from the Internet, whether a log entry shows a real visitor or an internal host, and whether a firewall rule is too broad. The page classifies a list of IPv4 and IPv6 addresses at once and says which block each belongs to.
Three groups, not two
The page does not use only “private” and “public”. Private covers addresses meant for internal use: the three RFC 1918 blocks for IPv4, the shared carrier-grade NAT block (RFC 6598), and unique local addresses for IPv6. Public means globally routable unicast space. Special-purpose covers everything the IANA registries reserve for a specific job: loopback (127.0.0.0/8, ::1), link-local (169.254.0.0/16, fe80::/10), documentation ranges such as 192.0.2.0/24, 198.51.100.0/24 and 203.0.113.0/24, multicast, benchmarking and others. A final column says whether the address is routed on the Internet, which is “No” for the first two groups of non-public space.
Reading the result
Paste addresses separated by new lines, commas or spaces. The summary shows counts of public, private and special-purpose addresses, and the table lists each address with its scope, its kind (with the RFC and the exact block, for instance Private use (RFC 1918) (10.0.0.0/8)) and the routing answer. The table can be copied as CSV. IPv4-mapped IPv6 addresses such as ::ffff:a00:1 are classified by the IPv4 address inside them, which is how a dual-stack server logs its IPv4 clients.
The ranges people get wrong
172.16.0.0/12 spans 172.16.0.0 to 172.31.255.255, not the whole 172 range. 192.168.0.0/16 is private but 192.169.0.0 is not. 169.254.x.x is link-local, the address a PC assigns itself when DHCP fails, and indicates a configuration problem rather than a private network design. 100.64.0.0/10 looks private but is reserved for provider NAT, so it should not be used inside a home or office network. IPv6 has no NAT-based private space by design; unique local addresses starting fc or fd serve internal use and are not routed on the Internet.
A worked example
The sample list contains thirteen addresses and gives 3 public, 6 private and 4 special-purpose. 10.4.5.6, 172.20.1.1 and 192.168.0.10 are private (RFC 1918). 100.64.12.1 is scoped Private as shared CGN space. 172.32.0.1 is Public because it is outside the /12. 8.8.8.8 and 2606:4700:4700::1111 are public. 169.254.10.20, 127.0.0.1, 203.0.113.5 and fe80::1 are special-purpose, and fd12:3456:789a::1 is a unique local address, so private. ::ffff:a00:1 is private because it embeds 10.0.0.1.
Limits
The classification follows the IANA special-purpose address registries as built into the page; the registries can change, though rarely. “Public” means only that the address is in globally routable space. It does not mean the address is allocated, announced in routing or in use, and the page does not look anything up on the network. For allocation owners and AS numbers use an RIR lookup or the ASN Number Checker for the number side.
Related tools
- Subnet Calculator works out blocks around any address.
- IPv4 to IPv6 Converter shows how IPv4 addresses are embedded in IPv6.
- Reverse DNS Lookup asks for the host name of a public address.
- ASN Number Checker tells private and reserved AS numbers apart.
Checked against the current version of the Private IP Checker on .