多项选择题
Which three Layer 2 access designs have all of their uplinks in an active state？（）
A.Flex Links B.loop-free U C.looped square D.looped triangle E.loop-free inverted U
单项选择题 WhenBGPtuningisused，howispacketflowintothee-commercemodulecontrolled？（）
单项选择题 Whatismeantbytheterm"firewallsandwich"？（）
单项选择题 WhichstatementiscorrectregardingNBARandNetFlow？（）
