OpenVPN is designed to operate optimally over UDP, but TCP capability is provided for situations where UDP cannot be used.
兼容TCP可以让OpenVPN运行在UDP不能用的环境中(比如不支持UDP的NAT实现)。
There are certain cases, however, where using TCP may be advantageous from a security and robustness perspective, such as tunneling non-IP or application-level UDP protocols, or tunneling protocols which don't possess a built-in reliability layer.