简答题 port-security的restrict action是什么意思？

问答题spanning-tree关于listeningandlearningtime如何adjustandchangeamountoftime？

问答题WhichOSPFnetworktypeisidealforpartiallymeshedNBMAnetworksbecauseitiseasytoconfigure（requiresnoconfigurationofneighborcommands），consumesonlyoneIPsubnet，andrequiresnodesignatedrouterelection？

问答题WhichOSPFfeatureallowsaroutertocontinuetoforwardpacketswhileundergoingspecific，well-knownfailureconditions？

问答题WhyareRegistermessagesneededinPIMSM？

问答题switchortport-securityviolation选择shutdown表示什么意思？