Public vs Private IP Addresses

Private IPv4 addresses belong to 10.0.0.0/8, 172.16.0.0/12 or 192.168.0.0/16. An address outside those ranges is not automatically a usable public address.

Examples at a glance

Private IPv4 blocks

10.x.x.x: 10.0.0.0/8
10.0.0.0 through 10.255.255.255.
172.16–31.x.x: 172.16.0.0/12
172.16.0.0 through 172.31.255.255.
192.168.x.x: 192.168.0.0/16
192.168.0.0 through 192.168.255.255.

Different special uses

Shared carrier space: 100.64.0.0/10
Shared space, separate from the three private blocks.
Loopback: 127.0.0.1
Your own device.
Documentation: 192.0.2.10
Reserved for examples.

The boundaries matter

172.16.0.0 through 172.31.255.255 is private; 172.15.255.255 and 172.32.0.0 fall outside this private block. Private addresses are reused inside different networks.

Other special ranges

100.64.0.0/10 is shared address space, often used for carrier-grade NAT, not RFC1918 private space. Loopback, link-local, multicast and documentation addresses also need their own labels.

IPv6 uses different ranges

fc00::/7 is unique-local space, fe80::/10 is link-local and ::1 is loopback. Global classification is based on registry entries and address architecture, not simply “not private.”