单项选择题 An administrator attempts a traceroute but receives a "Destination Unreadable" message. Which protocol is responsible for that message?（）

单项选择题 When a host transmits data across a network to another host, which process does the data go through?（）

单项选择题 A network admin wants to know every hop the packets take when he accesses cisco.com. Which command is the most appropriate to use?（）