单项选择题
A. To enhance Spanning Tree troubleshooting on multilayer switches
B. To reduce the total number of spanning tree instances necessary for a particular topology
C. To provide faster convergence when topology changes occur in a switched network
D. To provide protection for STP when a link is unidirectional and BPDUs are being sent but not received
E. None of the other alternatives apply
多项选择题 The Company network utilizes the Multiple-instance Spanning Tree protocol in its switched LAN. Which three statements about the MST protocol （IEEE 802.1S） are true？ （）
单项选择题 On switch R1 you issue the "udld enable" global command. What does this command accomplish？ （）
单项选择题 Switch R1 has been configured with the root guard feature. What statement is true if the spanning tree enhancement Root Guard is enabled？ （）