How does a VPN work?

The short path

1. You authenticate (account, key, or device credential).
2. Your client and the server perform a handshake and derive session keys.
3. Your OS routes selected traffic into a virtual network interface.
4. Packets are encrypted and encapsulated toward the VPN server’s public endpoint.
5. The server decrypts, applies its policy (DNS, firewall, bandwidth), and forwards traffic to destinations.
6. Replies return through the same tunnel.

Handshake and keys

Modern protocols such as WireGuard use public-key cryptography so each side proves identity without shipping a long-lived password on every packet. After the handshake, symmetric keys encrypt bulk traffic efficiently.

If keys or peer records are wrong, the tunnel simply fails to pass traffic—prefer fail-closed behavior (see kill switch).

Encapsulation

Think of your original IP packet as a letter. The VPN puts that letter inside a locked envelope addressed to the VPN server. Observers on your local network see envelopes to the VPN IP and port (for WireGuard, typically UDP), not every inner destination in cleartext.

Exit and return path

At the server, the envelope is opened. The inner packet goes out via the provider’s uplink with network address translation in most consumer setups, so destinations see the VPN’s address. Return traffic is mapped back into your tunnel.

DNS inside the tunnel

Name lookups should also go through the provider’s resolver while connected; otherwise you can suffer a DNS leak. VeritasVPN pushes an in-tunnel DNS gateway and blocks common bypasses for peers.

Failure modes worth knowing

• Tunnel up, DNS elsewhere — sites load but resolvers still see queries.
• IPv6 or WebRTC bypass — some apps punch outside the tunnel; test with a VPN leak check.
• Split tunnel — some traffic intentionally skips the VPN; see split tunneling.

Understanding the path makes marketing claims easier to evaluate—and makes honest products easier to trust.