多项选择题 An802.1Qtrunkisnotcomingupbetweentwoswitches.Theportsonbothswitchesareconfiguredas"switchportmodedesirable."Assumingthatthereisnophysicalissue，choosetwopossiblecauses.（）

单项选择题 YoureplacedyourLayer3switch，whichisthedefaultgatewayoftheendusers.Manyuserscannotaccessanythingnow，includingemail，Internet，andotherapplications，althoughotherusersdonothaveanyissues.Alloftheapplicationsarehostedinanoutsourceddatacenter.Inordertofixtheproblem，whichoneoftheseactionsshouldyoutake？（）

问答题 在R2的show ip route ospf中，关于R1的loopback0的路由条目下一跳指向哪个路由器。