Out of the box, the appliance is set to let all traffic pass, leaving the user to specify which types of traffic are blocked (via packet filtering).
盒子之外，设备被设为允许任何流量通过，让用户指定阻塞哪些流量(通过包过滤)。
2
UDP packet or user datagram: UDP is an unreliable, connectionless protocol.
UD p包或用户数据报：udp是不可靠、无连接的协议。
3
Transport Layer protocols, such as the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), specify a source and destination port number in their packet headers.