Troubleshooting Wireless Networks

Here you will find answers to Troubleshooting Wireless Networks Questions

Question 1

What is the facility level of FTP Daemons?

A. 10
B. 11
C. 12
D. 15

 

Answer: B

Explanation

Syslog messages are broadly categorized on the basis of the sources that generate them. These sources can be the operating system, the process, or an application. These categories, called facility, are represented by integers. In other words, facility refers to the source of the message (such as a hardware device, a protocol, or a module of the system software).

The local use facilities are not reserved and are available for general use. Hence, the processes and applications that do not have pre-assigned facility values can choose any of the eight local use facilities. As such, Cisco devices use one of the local use facilities for sending syslog messages.

Question 2

Richard works as a network administrator for Fenco Auto Inc. The company has a wireless LAN network. Richard configures 802.11 authentications on all the clients present in the network. A client becomes active on the network and wants to pass traffic on the medium. Which of the following frames does the client use to search all access points in its radio range?

A. Authentication request frame
B. Association request frame
C. Probe request frame
D. Authentication response frame

 

Answer: C

Explanation

Probe request frame: A station sends a probe request frame when it needs to obtain information from another station. For example, a radio network interface cards (NIC) would send a probe request to determine which access points are within range.

Note:

Probe response frame: A station will respond with a probe response frame, containing capability information, supported data rates, etc., when after it receives a probe request frame.

Question 3

You work as a network consultant. Fenco Auto Inc. hires you to troubleshoot a communication problem and implement a functional wireless network. You check the network connection and all related issues. You find a reason why the clients do not communicate with each other, as they try to send data on the same channel at the same time. What is the best way to mitigate this problem?

A. Forces RTS/CTS control frames.
B. Remove the obstacles that are in the way
C. Reduce transmitted power of the signal.
D. Adjust the radio resources as needed.

 

Answer: A

Explanation

RTS/CTS (Request to Send / Clear to Send) is the optional mechanism used by the 802.11 wireless networking protocol to reduce frame collisions introduced by the hidden node problem.

The hidden node problem happens when two stations try to send on the same channel at the same time. If two stations are in the range of an AP but can not hear each other (because they are too far away or there is an obstacle between them), they both can start sending and the signals collide.

This is how the RTS/CTS works:

For example, station 1 has a frame to send; it initiates the process by sending an RTS frame. The RTS frame serves several purposes: in addition to reserving the radio link for transmission, it silences any stations that hear it. If the target station receives an RTS, it responds with a CTS. Like the RTS frame, the CTS frame silences stations in the immediate vicinity. Once the RTS/CTS exchange is complete, station 1 can transmit its frames without worry of interference from any hidden nodes. Hidden nodes beyond the range of the sending station are silenced by the CTS from the AP. When the RTS/CTS clearing procedure is used, any frames must be positively acknowledged.

The downsides of this method are that it slows down the network connection and that it usually sets, on a global level, for all clients in the cell.

Question 4

You work as a Network Administrator for Tech Perfect Inc. You have to implement a wireless LAN network for the company. After implementing the network, you check all the functions and find that most of its clients try to send data on the same channel at the same time. As a result, a collision occurs in the network and it affects the communication. What is the reason behind this problem?

A. The IP addresses of clients are in the same subnet.
B. The clients are not in range of one another.
C. The controller is not configured properly.
D. The access point cannot cover the required area.

 

Answer: B

Explanation

As explained at question 3, this phenomenon is called “the hidden node” problem.

Question 5

Richard works as a network administrator for Fenco Auto Inc. The company deploys a wireless LAN network but there is some problem due to the interference of signals. Which of the following tools should you use to determine signal strength, noise level, and potential sources of interference? Each answer represents a complete solution. (Choose three)

A. RSSI
B. Link Budget
C. EIRP
D. SNR

 

Answer: A B D

Explanation

RSSI is the signal strength indicator. It indicates how much power is received, usually expressed in dBm. RSSI usually a negative value, the closer to 0 the better.
SNR is signal strength relative to noise level. The higher the SNR, the better.

SNR and RSSI may be useful to detect a near/far issue or determine if the client RF conditions may be causing the issue.

The link budget determines how much power needs to be sent out of the transmitter for the receiver to get a signal that can be interpreted. It accounts for attenuation, antenna gain, and other miscellaneous losses that may occur -> it determines potential sources of interference.

Note:

Effective Isotropic Radiated Power (EIRP) determines how much energy was actually radiated from the antenna towards the main beam.

Question 6

Which two actions would you use to begin to troubleshoot an access point that fails to successfully join a wireless LAN controller? (Choose two)

A. SSH to the AP
B. SSH to the Cisco WCS
C. SSH to the Cisco WLC
D. Cisco WLC command: debuglwapp events enable
E. Cisco WLC command: showlwapp events

 

Answer: C D

Question 7

Which CLI command shows the controller configuration in a way that is similar to the way that it is displayed on Cisco IOS routers?

A. showconfig
B. show runconfig
C. show run-config
D. show runningconfig
E. show running-config

 

Answer: E