单项选择题 You have been asked to use a 23-bit network mask to segment the network block 209.18.12.0, How many usable host address will there e per subnet?（）

单项选择题 Which statement is true about the routing table?（）

单项选择题 You want to log into the router and make a configuration change.After loggin in as the root user, what is the next command you must enter?（）