单项选择题 A network administrator must configure 200 switch ports to accept traffic from only the currently attached host devices. What would be the most efficient way to configure MAC-level security on all these ports?（）

单项选择题 Which type of attack is characterized by a flood of packets that are requesting a TCP connection to a server（）。

单项选择题 V．24接口工作在同步方式下最高传输速率是（）。