单项选择题 MultiProtocolLabelSwitching（MPLS）isadata-carryingmechanismthatbelongstothefamilyofpacket-switchednetworks.ForanMPLSlabel，ifthestackbitissetto1，whichoptionistrue？（）
单项选择题 TheOSPFRFC3623GracefulRestartfeatureallowsyoutoconfigureIETFNSFinultivendornetworks.WhenusingOSPFGracefulRestart，whichmechanismisusedtocontinueforwardingpacketsduringaswitchover？（）
问答题 AAAauthenticationlogin做什么用？