OpenVPN — Open-Source SSL VPN Solution

Introduction

OpenVPN is an open-source VPN solution that uses SSL/TLS for key exchange and encryption. It creates secure tunnels between clients and servers over UDP or TCP, supporting both routed and bridged configurations. OpenVPN runs on Linux, Windows, macOS, and most mobile platforms.

What OpenVPN Does

• Creates encrypted point-to-point or site-to-site VPN tunnels using TLS
• Supports both UDP (faster) and TCP (firewall-friendly) transport modes
• Routes or bridges entire network subnets through the tunnel
• Authenticates clients via certificates, username/password, or multi-factor methods
• Compresses traffic and shapes bandwidth per client or group

Architecture Overview

OpenVPN operates as a user-space daemon that creates a virtual TUN/TAP network interface. It uses the OpenSSL library for encryption (AES-256-GCM by default) and TLS for the control channel. The server maintains a client table mapping virtual IPs to authenticated sessions. Configuration is file-based, with separate server and client configs referencing PKI certificates generated via EasyRSA or another CA tool.

Self-Hosting & Configuration

• Install from package managers on most Linux distributions, or compile from source
• Generate a PKI with EasyRSA: CA certificate, server key, client certificates
• Configure server.conf with network ranges, DNS push directives, and logging
• Open UDP port 1194 (default) or TCP 443 for firewall traversal
• Distribute .ovpn client profiles bundling certificates and connection settings

Key Features

• Battle-tested encryption with TLS 1.3 and AES-256-GCM cipher support
• Split tunneling to route only specific traffic through the VPN
• Client certificate revocation (CRL) for immediate access removal
• Plugin interface for custom authentication via LDAP, RADIUS, or PAM
• Cross-platform clients available for every major desktop and mobile OS

Comparison with Similar Tools

• WireGuard — newer, simpler protocol with lower overhead; OpenVPN offers more configuration flexibility and broader firewall compatibility
• SoftEther VPN — multi-protocol server; OpenVPN uses its own protocol but has a larger deployment base
• IPsec (StrongSwan) — kernel-level VPN standard; OpenVPN is easier to configure and works better through NAT
• Tailscale/Headscale — mesh VPN built on WireGuard; OpenVPN follows a traditional client-server model

FAQ

Q: Is OpenVPN still relevant with WireGuard available? A: Yes. OpenVPN supports TCP transport (useful behind restrictive firewalls), has a mature PKI model, and is still widely deployed in enterprise environments.

Q: What throughput can I expect? A: Typical throughput is 100-500 Mbps depending on hardware and cipher choice. DCO (Data Channel Offload) in newer versions improves kernel-level performance.

Q: Can I run it in a Docker container? A: Yes. Community images like kylemanna/openvpn bundle server setup into a single container with persistent PKI storage.

Q: How do I handle client certificate management at scale? A: Use EasyRSA or integrate with an existing CA. Tools like Pritunl add a web UI for managing users and certificates.

Sources

• https://github.com/OpenVPN/openvpn
• https://openvpn.net/community-resources/