问答题 TwoCiscoroutersareconnectedtoeachotherandareenabledCDP.Seriallineisup，protocolisalsoupbutcdpneighbornotworking.WhatlayeroftheOSImodeldoestheproblemmostlikelyexist？

单项选择题 The interface is up and protocol is up. What level of logging is enabled when you get these messages？（）

问答题 YouhavetwoNTPservers10.1.1.1&10.1.1.2andwanttoconfigurearoutertouse10.1.1.2asitsNTPserverbeforefallingbackto10.1.1.1.Whichcommandwillyouuse？