单项选择题 1. （）

单项选择题 Hardware networking devices operate within the protocol stack just like protocols them-selves.Thus，hardware networking devices can be associated with an OSI model layerrelated to the protocols they manage or control.At which layer of the OSI model does arouter operate？（）

单项选择题 Unfortunately，attackers have many options of attacks to perform against their targets. Which of the following is considered a denial-of-service （DoS）attack？（）