OpenVPN is an open-source VPN protocol that executes virtual private network (VPN) techniques for producing safe site-to-site or point-to-point connections in remote access facilities and bridged or routed configurations.
The OpenVPN protocol is responsible for handling client-server communications. Basically, it helps establish a secure “tunnel” between the VPN client and the VPN server.OpenVPN works best over UDP (according to OpenVPN.net), which is why the OpenVPN Access Server first tries to establish UDP connections. If those connections fail, only then does the server try establishing TCP connections. Most VPN providers also offer OpenVPN over UDP by default.