ExpressVPN’s version of OpenVPN supports both UDP and TCP ports. In the ExpressVPN app, OpenVPN is actually referred to as “UDP” or “TCP,” two internet protocols that can greatly affect performance.
What is UDP?
UDP stands for User Datagram Protocol. Though it can be configured to run on any port, OpenVPN runs best on a UDP port. UDP does not allow the recipient to acknowledge receipt of the data or request information to be resent. This allows UDP to establish connections and transfer data faster. Your ExpressVPN app is likely to choose UDP when using OpenVPN. By default, you will experience faster speeds over UDP. On unreliable networks, however, you may have a better experience switching to TCP.
What is TCP?
TCP stands for Transmission Control Protocol. Unlike UDP, TCP carefully checks whether data is received by the recipient in the correct form and order and can request it again. This results in increased reliability at the expense of latency.