多项选择题
A.Listening
B.Learning
C.Forwarding
D.Blocking
E.Discarding
F.Disabled
问答题 r1isthehub，multipointmodesubinterface，r2andr3isspoke，whenr2downatthespoke，Whatwillr1react？howaboutr3？
单项选择题 TheclassicSpanningTreeProtocol（802.1D1998）useswhichsequenceofvariablestodeterminethebestreceivedBPDU？（）
问答题 Inarunsparse-dense-modemulticastnetwork，whenrendezvouspointdown，willtherecipientreceivethepacketssendbythesource？why？