VPN-Tunnel

Anatomy of a Tunnel

A VPN tunnel is the logical, encrypted pathway that carries your data between your device and a VPN endpoint. Physically, data still travels over ordinary internet infrastructure — routers, cables, and fiber optics — but each packet is encapsulated inside an outer packet addressed to the VPN server, and the inner payload is encrypted. To any observer on the path, the traffic looks like communication with the VPN server's Public IP AddressA globally unique IP address assigned by an ISP that is routable on the public internet. Every device directly accessible from the internet must have a public IP address., not with the final destination.

Encapsulation Process

Tunneling works by wrapping one protocol inside another. When you send data, your VPN client takes the original IP packet, encrypts it, and wraps it inside a new packet using a tunneling protocol such as IPSecInternet Protocol Security. A suite of protocols that authenticates and encrypts IP packets at the network layer. Used in site-to-site VPNs and as the transport layer for L2TP/IPSec and IKEv2 VPN connections., OpenVPNAn open-source VPN protocol that uses SSL/TLS for key exchange and can operate over UDP or TCP. Known for its flexibility, strong security, and wide platform support, though slower than WireGuard., or WireGuardA modern, lightweight VPN protocol that uses state-of-the-art cryptography (ChaCha20, Curve25519) with a minimal codebase (~4,000 lines). Designed for simplicity, high performance, and low latency compared to OpenVPN and IPSec.. The VPN server at the other end decapsulates the outer packet, decrypts the inner packet, and forwards it to the real destination. Responses follow the reverse path.

Tunnel Lifetime and Rekeying

VPN tunnels are not permanent connections in the traditional sense — they rely on session keys that must be periodically rotated (rekeyed) to maintain EncryptionThe process of converting plaintext data into ciphertext using a cryptographic algorithm and key, making it unreadable without the corresponding decryption key. The foundation of secure communication on the internet. security. IPSecInternet Protocol Security. A suite of protocols that authenticates and encrypts IP packets at the network layer. Used in site-to-site VPNs and as the transport layer for L2TP/IPSec and IKEv2 VPN connections. uses IKEv2 for this rekeying process. WireGuardA modern, lightweight VPN protocol that uses state-of-the-art cryptography (ChaCha20, Curve25519) with a minimal codebase (~4,000 lines). Designed for simplicity, high performance, and low latency compared to OpenVPN and IPSec. uses a one-minute handshake interval. If a tunnel drops unexpectedly, a kill switch in the VPN client should block all traffic until the tunnel is re-established, preventing DNS LeakA privacy flaw where DNS queries bypass the VPN tunnel and are sent to the ISP's default DNS resolver, revealing the websites a user visits despite using a VPN. DNS leak tests help detect this issue. or WebRTC LeakA privacy vulnerability where WebRTC (a browser API for real-time communication) reveals a user's real public and local IP addresses through STUN requests, even when connected to a VPN. exposure.