单项选择题 A user reports sporadic connectivity with their wireless connection. A technician determines the wireless speed reported by the laptop to be 1Mbps. Which of the following is the MOST likely cause of this issue?（）

单项选择题 At which of the following layers does the ICMP protocol operate?（）

单项选择题 Which of the following security devices would MOST likely be used on a network to screen and prevent malicious traffic?（）