Public IP address
A public address is routable on the internet. At home, several devices often share the router’s public address through network address translation, or NAT.
A site sees the public address from which the connection reaches it. Without a VPN, this is often the one assigned by your internet service provider. With a VPN, it is generally the exit server’s address.
Private addresses and local networks
In IPv4, ranges such as 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are reserved for private networks. They can be reused in many homes and organisations and are not routed as-is on the public internet.
An address such as 192.168.1.24 therefore distinguishes a device on its local network, but not globally. The router keeps track of the mapping between internal connections and the public address.
Sources and references
IPv6 and multiple addresses
IPv6 provides a much larger address space. Depending on its configuration, a device may simultaneously have a global address, a link-local address and a unique local address.
A global address does not automatically mean that the device is reachable from the internet: firewalls and network policies still apply. While using a VPN, IPv6 must be routed through the tunnel or explicitly blocked to prevent a different path.
Sources and references
What the VPN changes—and what it does not
The VPN changes the exit address seen for covered traffic. It does not necessarily change the private address used on the local Wi-Fi network, and it does not remove other browser identifiers.
An IP address indicates a network or an approximate geolocation, not a certain identity or GPS position. Several users may share the same address, and its estimated location may be inaccurate.
How to read an IP address test
Compare the test before and after connecting, in the application that is actually covered. A browser extension may change the result in that browser without affecting other software.
If IPv4 changes but an IPv6 test shows the usual path, check the IPv6 configuration. If the browser is signed in to an account, changing the address does not sign out of the account or remove its cookies.