单项选择题 When a local loopback is activated on a PPP serial link, what indicates that the local interface is good?（）

单项选择题 Which command would initiate a loopback on a Gigabit Ethernet interface ge-0/0/0?（）

多项选择题 If you want to test if fragmentation is causing problems on the network, which two ping command options are useful?（）