OpenVPN is an application to securely tunnel IP networks over a single UDP or TCP port. It can be used to access remote sites, make secure point-to-point connections, enhance wireless security, etc.

OpenVPN uses all of the encryption, authentication, and certification features provided by the OpenSSL library (any cipher, key size, or HMAC digest).

OpenVPN may use static, pre-shared keys or TLS-based dynamic key exchange. It also supports VPNs with dynamic endpoints (DHCP or dial-up clients), tunnels over NAT or connection-oriented stateful firewalls (such as Linux's iptables).