OpenVPN is open-source commercial software that implements VPN techniques to create secure point-to-point or site-to-site connections in routed or bridged configurations and remote access facilities. It uses a custom security protocol that utilizes SSL/TLS for key exchange. OpenVPN implements TLS using the open source OpenSSL library, utilizing X.509 certificates (or clientpacks) to create encrypted connections between machines, oftentimes a users laptop and a device like VNS3.

OpenVPN supports both TCP and UDP but works best over UDP.