Refer to the exhibit. For what purpose is the command show ip cef used？（）

单项选择题Refer to the exhibit. Which statement is true about the output？（）

A.The port on switch CAT1 is forwarding and sending BPDUs correctly.
B.The port on switch CAT1 is blocking and sending BPDUs correctly.
C.The port on switch CAT2 is forwarding and receiving BPDUs correctly.
D.The port on switch CAT2 is blocking and sending BPDUs correctly.
E.The port on switch CAT3 is forwarding and receiving BPDUs correctly.
F.The port on switch CAT3 is forwarding， sending， and receiving BPDUs correctly.

单项选择题Refer to the exhibit.  What does the command channel-group 1 mode desirable do？ （）

A.enables LACP unconditionally
B.enables PAgP only if a PAgP device is detected
C.enables PAgP unconditionally
D.enables Etherchannel only
E.enables LACP only if a LACP device is detected

多项选择题Refer to the exhibit. Initially， LinkA is connected and forwarding traffic. A new LinkB is then attached between SwitchA and HubA.  Which two statements are true about the possible result of attaching the second link？（）

A.The switch port attached to LinkB will not transistion to up.
B.One of the two switch ports attached to the hub will go into blocking mode when a BPDU is received.
C.Both switch ports attached to the hub will transition to the blocking state.
D.A heavy traffic load could cause BPDU transmissions to be blocked and leave a switching loop. 
E.The switch port attached to LinkA will immediately transition to the blocking state.

单项选择题HowareSTPtimersandstatetransitionsaffectedwhenatopologychangeoccursinanSTPenvironment？（）

A.All ports will temporarily transition to the learning state for a period equal to the max age timer plus the forward delay interval.
B.All ports will transition temporarily to the learning state for a period equal to the forward delay interval.
C.The default aging time for MAC address entries will be reduced for a period of the max age timer plus the forward delay interval.
D.The default hello time for configuration BDPUs will be reduced for the period of the max age timer.

多项选择题WhattwothingswilloccurwhenanedgeportreceivesaBPDU？（）

A.The port immediately transitions to the Forwarding state.
B.The switch generates a Topology Change Notification （TCN） BPDU.
C.The port immediately transitions to the err-disable state.
D.The port becomes a normal STP switch port.