Public and private IP addresses

Public: what this website sees

CheckIP displays the source address presented by your connection. With typical home IPv4 networking, the router translates connections from local devices to a public address using network address translation (NAT). A VPN or proxy can present its own address instead.

Private: inside your network

The private IPv4 ranges are 10.0.0.0–10.255.255.255, 172.16.0.0–172.31.255.255, and 192.168.0.0–192.168.255.255. Different homes can reuse these ranges. A local address alone is not a globally unique way to reach a device.

Why several devices show the same public IP

Devices behind the same router often share a public IPv4 address. Providers can also share public addresses across customers using carrier-grade NAT (CGNAT). The shared address space 100.64.0.0/10 is distinct from the private ranges above. Seeing different router and website addresses can be a clue, but does not by itself confirm CGNAT.

IPv6 works differently

A device may have global IPv6 addresses as well as link-local or other local addresses. IPv6 privacy addresses can change over time. A global address does not mean inbound connections are allowed: firewall rules still matter. CheckIP shows the address used for a request, not every address configured on the device.

Which address should I send to support?

For an internet-facing connection issue, the public IP and timestamp are usually useful. For a printer or local network issue, support may need your local address too. Ask which one they need. Find both types of address.

References: private IPv4 ranges (RFC 1918), shared address space (RFC 6598).