New CCNA – Troubleshooting

Question 1

Refer to the exhibit:

Assuming that the entire network topology is shown, what is the operational status of the interfaces of R2 as indicated by the command output shown?

A. One interface has a problem.
B. Two interfaces have problems.
C. The interfaces are functioning correctly.
D. The operational status of the interfaces cannot be determined from the output shown.

 

Answer: C

Explanation

The subnet of Fa0/0 of R2 is 172.16.109.0/26 (range from 172.16.109.0 to 172.16.109.63) which covers the subnet of S0/1 interface 172.16.109.4/30 so in fact the answer C is not correct. But from the output of the “show ip interface brief” command we see both Fa0/0 and S0/1 interfaces’ statuses are ‘up/up’ -> they are working normally. So we think there is a typo in the subnet mask of Fa0/0. It should not be ‘/26′ but longer one, ‘/28′, for example. So you should still choose answer C in this question.

Question 2

Refer to the exhibit:

Switch port FastEthernet 0/24 on AlSwitch1 will be used to create an IEEE 802.1Q-complaint trunk to another switch. Based on the output shown, What is the reason the trunk does not form, even thought the proper cabling has been attached?

A. VLANs have not been created yet.
B. An IP address must be configured for the port.
C. The port is currently configured for access mode.
D. The correct encapsulation type has not been configured.
E. The no shutdown command has not been entered for the port.

 

Answer: C

Explanation

The “Operational Mode” is “static access” so this port is currently in access mode.

Question 3

Refer to the exhibit:

The Bigtime router is unable to authenticate to the Littletime router. What is the cause of the problem?

A. The usernames are incorrectly configured on the two routers.
B. The passwords do not match on the two routers.
C. CHAP authentication cannot be used on a serial interface.
D. The routers cannot be connected from interface S0/0 to interface S0/0.
E. With CHAP authentication, one router must authenticate to another router. The routers cannot be configured to authenticate to each other.

 

Answer: B

Explanation

Both routers must use the same password for CHAP to authentication.

Question 4

Refer to the exhibit. Hosts in network 192.168.2.0 are unable to reach hosts in network 192.168.3.0. Based on the output from RouterA, what are two possible reasons for the failure? (Choose two)

A. The cable that is connected to S0/0 on RouterA is faulty.
B. Interface S0/0 on RouterB is administratively down.
C. Interface S0/0 on RouterA is configured with an incorrect subnet mask.
D. The IP address that is configured on S0/0 of RouterB is not in the correct subnet.
E. Interface S0/0 on RouterA is not receiving a clock signal from the CSU/DSU.
F. The encapsulation that is configured on S0/0 of RouterB does not match the encapsulation that is configured on S0/0 of RouterA.

 

Answer: E F

Explanation

From the output we see the Serial0/0 of RouterA is in “status up/protocol down” state which indicates a Layer 2 problem so the problem can be:

+ Keepalives mismatch
+ Encapsulation mismatch
+ Clocking problem

Question 5

Which command can be used from a PC to verify the connectivity between hosts that connect through a switch in the same LAN?

A. pingaddress
B. tracertaddress
C. tracerouteaddress
D. arpaddress

 

Answer: A

Question 6

Two routers named Atlanta and Brevard are connected by their serial interfaces as illustrated, but there is no connectivity between them. The Atlanta router is known to have a correct configuration. Given the partial configurations, identify the problem on the Brevard router that is causing the lack of connectivity.

A. transmission unit size too large
B. no loopback set
C. an incorrect subnet mask
D. incompatible encapsulation at each end
E. an incorrect IP address
F. incompatible bandwidth between routers

 

Answer: E

Question 7

Refer to the exhibit. HostA cannot ping HostB. Assuming routing is properly configured, what could be the cause of this problem?

A. HostA is not on the same subnet as its default gateway.
B. The address of SwitchA is a subnet address.
C. The Fa0/0 interface on RouterA is on a subnet that can’t be used.
D. The serial interfaces of the routers are not on the same subnet.
E. The Fa0/0 interface on RouterB is using a broadcast address.

 

Answer: D

Explanation

Now let’s find out the range of the networks on serial link:

For the network 192.168.1.62/27:

Increment: 32
Network address: 192.168.1.32
Broadcast address: 192.168.1.63

For the network 192.168.1.65/27:

Increment: 32
Network address: 192.168.1.64
Broadcast address: 192.168.1.95

-> These two IP addresses don’t belong to the same network and they can’t see each other -> D is the correct answer.

Question 8

Router# show interface s0/0 Serial 0/0/0 is administratively down, line protocol is down

What is the reason that the interface status is “administratively down, line protocol down”?

A. There is no encapsulation type configured.
B. There is a mismatch in encapsulation types.
C. The interface is not receiving any keepalives.
D. The interface has been configured with the shutdown command.
E. The interface needs to be configured as a DTE device.
F. The wrong type of cable is connected to the interface.

 

Answer: D

Question 9

Refer to the exhibit. A network administrator configures a new router and enters the copy startup-config running-config on the router. The network administrator powers down the router and sets it up at a remote location. When the router starts, it enter the system configuration dialog as shown. What is the cause of the problem?

— System Configuration Dialog — Would you like to enter the initial configuration dialog? [yes/no]: % Please answer yes’ or ‘no’. Would you like to enter the initial configuration dialog? [yes/ho]: n Would you like to terminate autoinstall? [yes]: Press RETURN to get started!

A. The network administrator failed to save the configuration.
B. The configuration register is set to 0×2100.
C. The boot system flash command is missing from the configuration.
D. The configuration register is set to 0×2102.
E. The router is configured with the boot system startup command.

 

Answer: A

Explanation

The “System Configuration Dialog” appears only when no startup configuration file is found. The network administrator has made a mistake because the command “copy startup-config running-config” will copy the startup config (which is empty) over the running config (which is configured by the administrator). So everything configured was deleted.

Note: We can tell the router to ignore the start-up configuration on the next reload by setting the register to 0×2142. This will make the “System Configuration Dialog” appear at the next reload.