Ccna certification Practice Tests

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Appendix 

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  Answers to Practice Test Questions

 17.  B.  The store and forward method of switching allows the switch to receive the entire 

frame and calculate the CRC against the data contained in the frame. If the CRC does 

not match, the frame is dropped, and the sending node must retransmit after an expiry 

timer or upper-protocol timer times out. Switches cannot perform error correction 

from the CRC calculation; they can only detect that there are errors and discard the 

frame. Switches will never send a frame back; they will discard the frame and wait for 

retransmission from upper layer protocols. Switches do not store frames for longer than it 

would take for a forward filter decision to be made.

 18.  A.  In the exhibit, a broadcast storm is occurring due to improper configuration of 

Spanning Tree Protocol (STP) for loop avoidance. MAC table thrashing could occur due to 

the loop in the exhibit; however, the exhibit does not show evidence to prove MAC table 

thrashing is occurring. Although STP is not configured, duplication of unicast frames is 

not evident in the exhibit. STP is a loop avoidance mechanism; it will not propagate loops.

 19.  B.  The command to show the current MAC address entry count in the MAC address 

table is 

show mac address-table count. This command will also show the maximum 

number of entries the table can hold. The command 

show mac address-table is 

incorrect, as it will show the contents of the MAC address table in the switch. The 

command 

show mac count is incorrect. The command show cam count is incorrect.

 20.  A.  Forward filter decisions are made upon the destination MAC address in the frame. The 

source MAC address is used for MAC address learning to build the forward/filter table. 

The source and destination IP address in the frame is no concern of the switch. Only a 

router would decapsulate the frame further to make routing decisions upon the destination 

IP address.

 21.  C.  The computer is on another switch connected via a trunk link since there are multiple 

VLANs on the interface of Gi0/1. This is also evidence that the computer is not the only 

device on port Gi0/1. It cannot be concluded that the computer is on a hub connected to 

port Gi0/1. The computer’s MAC address has not aged out of the table yet because it can 

still be seen in the exhibit.

 22.  B.  Access ports strip all VLAN information before the frame egresses the destination 

interface. The endpoint on an access switch port will never see any of the VLAN 

information that was associated with the frame. A trunk port will carry the frame along 

with the VLAN information until it gets to the other side of the trunk link. Voice ports 

also carry the frame along with VLAN tagging information. A Dynamic Trunking 

Protocol (DTP) port will form a trunk port to another switch; therefore, it is a trunking 

protocol, not a switch port type.

 23.  B.  The switch has negotiated with the adjacent switch to become a trunk and set its 

trunking protocol to 802.1Q. The letter n in front of 802.1Q specifies it was negotiated. 

When a switch is set to auto for the Dynamic Trunking Protocol (DTP), it will respond 

to trunking requests but will not initiate DTP messages. The adjacent switch must be set 

to desirable since the desirable mode will send DTP messages. The native VLAN does not 

show it has been changed, since VLAN 1 is the default native VLAN as it is configured 

in the exhibit. The exhibit does not show evidence that the switch is sending DTP frames. 

Evidence also does not exist in the exhibit to support the theory that the adjacent switch is 

also set for auto DTP.

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Chapter 7: Practice Exam 1