What is the fundamental technical difference between a VPN and a proxy from the perspective of the OSI network model?

The main technological difference between a VPN and a proxy lies in the OSI network model layer at which they function and how exactly they process outgoing traffic from your device. Proxy servers, such as HTTP, HTTPS, or SOCKS5, operate primarily at the application or session layer. They act as an intermediary for specific requests from certain programs or browsers, redirecting exclusively web traffic or data of a specific application configured to work through this proxy.

Virtual Private Networks function much lower, usually at the network or data link layer, creating a secure virtual tunnel on top of your existing internet connection. Because of this, a VPN intercepts absolutely all traffic generated by the device's operating system, including background services, system updates, and requests from any installed programs, regardless of whether they support proxying or not.

In addition, classical proxy servers rarely apply data encryption between your device and the proxy itself, with the exception of secured HTTPS proxies. This means that the internet service provider can theoretically see the contents of transmitted packets. A VPN obligatorily encapsulates the entire data stream into a cryptographic container, protecting it from eavesdropping and tampering at the local network or provider level.

For developers and system administrators, the choice between these technologies depends on specific tasks. If you need to route only the traffic of a single utility or browser through a remote IP address for testing web interfaces, a proxy is ideal due to minimal overhead. If you need to completely isolate a device on the network and protect all outgoing connections, a VPN is used.