Ccna certification Practice Tests

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Appendix 

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  Answers to Practice Test Questions

 150.  A.  You will create a temporary switching loop until the BPDUs are heard from each 

interface over the hub. However, during this period you will have a switching loop and 

degrade traffic over the entire switching topology until convergence happens. This is risky 

because the CPU could spike to 100% and not be able to detect the BPDUs and the loops 

will continue. With PortFast configured, the ports will not enter an err-disable state; 

they will forward traffic until the network connection is fully saturated with bandwidth. 

The port will not disable itself via Spanning Tree since the port transitions between 

forwarding, listening, learning, and then possibly changing into a blocking mode.

 151.  A.  BPDU Guard will turn the interface to err-disable as soon as a BPDU is heard on the 

interface. This feature should be enabled on access switches when configuring PortFast. 

There is no feature called BPDU Detection. Loop Guard is used in conjunction with BPDU 

Guard for additional protection by monitoring and tracking BPDUs. UplinkFast is a Cisco 

proprietary feature that improves convergence times for Spanning Tree.

 152.  A.  PortFast mode allows an interface to bypass the blocking state and begin forwarding 

immediately. It then listens and learns of BPDUs on the interface and can make a decision 

to continue to forward frames or enter into a blocking state. All of the other options are 

incorrect.

 153.  C.  The correct command to configure BPDU Guard on a single interface is 

spanning-

tree bpduguard enabled entered into the interface you want to turn it on for. The 

command 

switchport mode bpduguard is incorrect. The command switchport 

bpduguard enable is incorrect. The command spanning-tree bpduguard is incorrect.

 154.  C.  BPDU Guard was turned on the trunk link. When the BPDU of the adjacent switch 

was seen, the switch turned the port into err-disabled mode. A Spanning Tree loop will 

not err-disable an interface; it will simply block the offending port. A switch uplink cable 

that is bad will not place the interface into an err-disable state. Flow control will not have 

any effect in placing an interface into an err-disable state.

 155.  B.  Configuring BPDU Guard along with PortFast ensures that the end device will always 

be forwarding. BPDU Guard ensures that in the event a BPDU is heard on the interface, 

the interface will enter into an err-disable mode. You should only configure PortFast mode 

on access links. BPDU Guard should never be configured on a trunk line since it will place 

the interface into an err-disable state when a BPDU is seen. BPDU Guard and UplinkFast 

perform similar functions, such as preventing network loops.

 156.  D.  Using the command 

show spanning-tree interface fa 0/1 will show the 

spanning tree configuration for an interface. If PortFast has been configured, the last 

line will display 

The port is in the PortFast mode. The command show portfast 

is incorrect. The command 

show interface fa 0/1 is incorrect. The command show 

spanning-tree is incorrect.

 157.  D.  One way to disable BDPU Guard is to enter the command 

spanning-tree bpduguard 

disable. Another way is to negate the command with no spanning-tree bpduguard. 

The command 

switchport bdpugaurd disable is incorrect. The command spanning-

tree bpduguard disable is incorrect. The command no switchport bpduguard is 

incorrect.

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Chapter 2: Network Access (Domain 2)