OpenVPN

Architecture and Design

OpenVPN is an open-source VPNVirtual Private Network. A technology that creates an encrypted tunnel between a device and a remote server, protecting data in transit and masking the user's real IP address. Used for privacy, security, and accessing restricted networks. solution that uses the SSL/TLSSecure Sockets Layer / Transport Layer Security. Cryptographic protocols that provide encrypted, authenticated communication over a network. SSL is deprecated; modern implementations use TLS 1.2 or TLS 1.3. protocol for key exchange and 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., running over either UDPUser Datagram Protocol. A connectionless transport protocol that sends datagrams without establishing a connection or guaranteeing delivery. Faster than TCP, it is preferred for real-time applications like DNS queries, VoIP, gaming, and streaming. or TCPTransmission Control Protocol. A reliable, connection-oriented transport protocol that guarantees ordered, error-checked delivery of data through three-way handshakes, acknowledgments, and retransmission. The foundation of HTTP, SSH, and most internet services.. Because it can operate on TCP port 443 — the same port used by HTTPSHTTP Secure. The encrypted version of HTTP that uses TLS to protect data in transit between a browser and a web server. Identified by the padlock icon in browsers and the https:// URL scheme. — OpenVPN traffic is very difficult for firewalls and deep packet inspection systems to distinguish from ordinary web traffic, making it highly effective at bypassing censorship and restrictive networks.

TUN vs. TAP Modes

OpenVPN supports two device modes. TUN (tunnel) mode creates a virtual Layer 3 interface and routes IP packets through the tunnel. TAP (network tap) mode emulates a Layer 2 Ethernet adapter, allowing broadcast traffic like ARPAddress Resolution Protocol. A Layer 2 protocol that maps an IP address to a physical MAC address on a local network. When a device needs to communicate with another on the same subnet, ARP discovers the target's hardware address. and DHCPDynamic Host Configuration Protocol. A network protocol that automatically assigns IP addresses, subnet masks, gateways, and DNS servers to devices when they join a network. to flow through the tunnel. TUN mode is more efficient and is used in most point-to-point and client-to-server deployments, while TAP mode is common in bridged LAN-to-LAN scenarios.

Security Characteristics

OpenVPN supports a wide range of cipher suites and authentication methods, including certificates, pre-shared keys, and username/password combinations. Its reliance on SSL/TLSSecure Sockets Layer / Transport Layer Security. Cryptographic protocols that provide encrypted, authenticated communication over a network. SSL is deprecated; modern implementations use TLS 1.2 or TLS 1.3. means it benefits from the mature cryptographic ecosystem of OpenSSL. Compared to 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., OpenVPN has a much larger codebase (roughly 70,000 lines versus WireGuard's 4,000), which makes it harder to audit but also more configurable. It supports Split TunnelingA VPN configuration that routes only selected traffic through the VPN tunnel while allowing other traffic to access the internet directly. Reduces VPN bandwidth usage but may expose some traffic to the local network., kill switches, and DNS leak prevention through its client configuration.