How Does a VPN Actually Work?
A VPN builds an encrypted tunnel between your device and a VPN server, then routes your traffic through it. Anyone in between — your ISP, a café Wi-Fi snooper — sees only encrypted data to one destination, not what you actually do.
The tunnel, concretely
Your device wraps each outgoing packet inside another, encrypted packet addressed to the VPN server (this is encapsulation). The server unwraps it, forwards the inner packet to the real destination, and reverses the process on the way back. Two things change for observers: they can't read the payload (encryption) and they can't see the real destination (it's inside the tunnel).
The protocols that build it
Different VPNs use different tunnelling protocols, and the choice is a real security decision:
- IPsec — the enterprise standard for site-to-site tunnels; strong, widely supported.
- WireGuard — modern, fast, small codebase; increasingly the default.
- OpenVPN — mature, flexible, TLS-based.
- PPTP — obsolete and cryptographically broken. Never use it.
All rely on encryption to make the tunnel unreadable.
Site-to-site vs remote-access
Two jobs, same idea:
- Remote-access VPN connects one user's device to a network (working from home into the office). This is what consumer VPN apps also do — to the provider's server.
- Site-to-site VPN permanently links two whole networks over the internet — e.g. a branch office to headquarters — so they behave like one network. This is core CCNA/CCNP territory.
What a VPN does and doesn't do
Does: hide your traffic from the local network and ISP, mask your real IP from websites (they see the server's), and let you reach private network resources remotely.
Doesn't: make you anonymous (the VPN provider can see your traffic — trust moves from ISP to provider), protect against malware or phishing, or encrypt anything after the VPN server. That nuance — "a VPN moves trust, it doesn't remove it" — is a favourite security interview point.
Frequently asked questions
What does a VPN actually do?
It creates an encrypted tunnel between your device and a VPN server and routes your traffic through it, so the local network and your ISP see only encrypted data to one destination, and websites see the server's IP instead of yours.
What is the difference between site-to-site and remote-access VPN?
Remote-access connects a single device to a network (e.g. a laptop into the office). Site-to-site permanently links two entire networks over the internet, such as a branch office to headquarters, making them act as one.
Does a VPN make you anonymous?
No. It hides your traffic from your ISP and local network and masks your IP from websites, but the VPN provider can see your traffic — you are trusting them instead of your ISP. It also does not stop malware or phishing.
Which VPN protocol is most secure?
IPsec, WireGuard and OpenVPN are all strong modern choices. PPTP is broken and must never be used. WireGuard is increasingly preferred for its speed and small, auditable codebase.
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