单项选择题
Which one of the following protocols uses both UDP and TCP ports for the transport layer operation?（）
A.FTP B.TFTP C.SMTP D.Telnet E.DNS
多项选择题 Which of the following protocols utilize UDP as the layer 4 transport mechanism?（）
多项选择题 Which of the protocols below use TCP at the transport layer?（）
单项选择题 You have just configured a static default route on router TK1. What is the purpose of a default route?（）
