CWNP CWNA-109 Online Practice Questions and Exam Preparation

CWNP CWNA-109 Online Questions & Answers

• Question 101:

  You are a small business wireless network consultant and provide WLAN services for various companies. You receive a call from one of your customers stating that their laptop computers suddenly started experiencing much slower data transfers while connected to the WLAN. This company is located in a multi-tenant office building and the WLAN was designed to support laptops, tablets and mobile phones. What could cause a sudden change in performance for the laptop computers?

  A. The sky was not as cloudy that day as it typically is and the sun also radiates electromagnetic waves.
  B. A new tenant in the building has set their AP to the same RF channel that your customer is using.
  C. The antennas in the laptops have been repositioned.
  D. A few of your customer's users have Bluetooth enabled wireless headsets.
  B. A new tenant in the building has set their AP to the same RF channel that your customer is using.

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  Explanation/Reference:

  A possible cause of a sudden change in performance for the laptop computers is that a new tenant in the building has set their AP to the same RF channel that your customer is using. This can create co-channel interference (CCI), which is a situation where two or more APs or devices use the same or overlapping channels in the same area. CCI can degrade the performance of WLANs by increasing contention, collisions, retransmissions, and latency. CCI can also reduce the effective range and throughput of WLANs by lowering the signal-to-noise ratio (SNR). To avoid or mitigate CCI, it is recommended to use non- overlapping channels, adjust transmit power levels, or implement channel management techniques such as dynamic frequency selection (DFS) or load balancing. The sky condition, antenna position, or Bluetooth headset are not likely to cause a sudden change in performance for the laptop computers. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 81; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 71.

• Question 102:

  What factors will have the most significant impact on the amount of wireless bandwidth available to each station within a BSS? (Choose 2)

  A. The number of clientstations associated to the BSS
  B. The power management settings in the access point's beacons
  C. The presence of co-located (10m away) access points on non-overlapping channels
  D. The layer 3 protocol used by each station to transmit data over the wireless link
  A. The number of clientstations associated to the BSS

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  Explanation/Reference:

  The factors that will have the most significant impact on the amount of wireless bandwidth available to each station within a BSS are: The number of client stations associated to the BSS The presence of co-located (10m away) access points on non-overlapping channels The number of client stations associated to the BSS affects the wireless bandwidth because each station shares the same channel and medium with other stations in the same BSS. The more stations there are, the more contention and collision there will be for the channel access, which reduces thethroughput and efficiency of the wireless communication. The wireless bandwidth available to each station depends on how the access point allocates the channel resources and how the stations use the channel time. For example, if the access point uses a round-robin scheduling algorithm, each station will get an equal share of the channel time regardless of its data rate or traffic demand. However, if the access point uses a proportional fair scheduling algorithm, each station will get a share of the channel time that is proportional to its data rate and traffic demand, which may result in higher or lower bandwidth for different stations. The presence of co-located (10m away) access points on non-overlapping channels affects the wireless bandwidth because even though they use different channels, they may still cause interference and noise to each other due to channel leakage or imperfect filtering. The interference and noise can degrade the signal quality and SNR of the wireless communication, which reduces the data rate and throughput of the wireless communication. The wireless bandwidth available to each station depends on how well the access point and the station can cope with the interference and noise from other channels. For example, if the access point and the station support dynamic frequency selection (DFS) or adaptive radio management (ARM), they can switch to a less congested channel or adjust their output power or antenna gain to avoid or minimize interference from other channels. References:1, Chapter 3, page 94;2, Section 3.2

• Question 103:

  XYZ Company has decided to install an 802.11 WLAN system that will support 1083 wireless users, but they are concerned about network security. XYZ is interested in deploying standardized security features. In addition to WPA2-Enterprise with PEAP and role-based access control, XYZ would like to support management frame protection as well as a fast secure roaming protocol for future mobile handsets.

  As XYZ Company selects a product to deploy, what two IEEE amendments, which are included in 802.11-2016, and 802.11-2020 should be supported to provide the management frame protection and fast secure roaming security features?

  A. 802.11j and 802.11z
  B. 802.11r and 802.11w
  C. 802.11j and 802.11k
  D. 802.11k and 802.11v
  B. 802.11r and 802.11w

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  Explanation/Reference:

  The two IEEE amendments that should be supported to provide the management frame protection and fast secure roaming security features are 802.11r and 802.11w12. 802.11r (Fast BSS Transition): This amendment to the IEEE 802.11 standard permits continuous connectivity aboard wireless devices in motion, with fast and secure client transitions from one Basic Service Set to another1. 802.11w (Management Frame Protection): This amendment increases the security of its management frames2.

• Question 104:

  A string of characters and digits is entered into an AP and a client STA for WPA2 security. The string is 8 characters long. What is this string called?

  A. MSK
  B. WEP key
  C. Passphrase
  D. PSK
  C. Passphrase

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  Explanation/Reference:

  The string of characters and digits that is entered into an AP and a client STA for WPA2 security and is 8 characters long is called a passphrase. A passphrase is a human- readable text that is used to generate a Pre-Shared Key (PSK) for WPA2-Personal security. A passphrase can be between 8 and 63 characters long and can include any ASCII character. The PSK is a 256-bit key that is derived from the passphrase using a hashing algorithm called PBKDF2. The PSK is used to encrypt and decrypt the data frames between the AP and the client STA. A MSK is a Master Session Key that is generated by an authentication server for WPA2-Enterprise security. A WEP key is a 40-bit or 104-bit key that is used for Wired Equivalent Privacy (WEP) security, which is deprecated and insecure. A PSK is not a string of characters and digits, but a binary key. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 303; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 293.

• Question 105:

  The requirements for a WLAN you are installing state that it must support unidirectional delays of less than 150 ms and the signal strength at all receivers can be no lower than -67 dBm. What application is likely used that demands these requirements?

  A. VoIP
  B. E-Mail
  C. FTP
  D. RTLS
  A. VoIP

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  Explanation/Reference:

  VoIP (Voice over Internet Protocol) is an application that is likely used that demands the requirements of unidirectional delays of less than 150 ms and the signal strength at all receivers can be no lower than -67 dBm. VoIP is an application that allows users to make and receive voice calls over a network, such as the Internet or a WLAN. VoIP is a real-time and interactive application that requires high quality of service (QoS) to ensure good user experience and satisfaction. One of the QoS metrics for VoIP is delay, which is the time it takes for a voice packet to travel from the sender to the receiver. Delay can affect the quality and intelligibility of the voice conversation, as well as the synchronization and naturalness of the dialogue. The ITU-T G.114 recommendation suggests that the maximum acceptable one-way delay for VoIP should be less than 150 ms, as anything higher than that can cause noticeable degradation and annoyance to the users. Another QoS metric for VoIP is signal strength, which is the measure of how strong the RF signal is at the receiver. Signal strength can affect the reliability and performance of the wireless connection, as well as the data rate and throughput of the VoIP traffic. The CWNA Official Study Guide recommends that the minimum signal strength for VoIP should be -67 dBm, as anything lower than that can cause packet loss, retries, jitter, and other issues that can impair the voice quality. References: 1, Chapter 10, page 398; 2, Section 6.1

• Question 106:

  Option 43 must be configured to allow access points to locate controllers. In what network service should this option be configured?

  A. DNS
  B. LDAP
  C. DHCP
  D. RADIUS
  C. DHCP

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  Explanation/Reference:

  DHCP (Dynamic Host Configuration Protocol) is the network service where option 43 must be configured to allow access points to locate controllers. DHCP is a protocol that allows a device to obtain an IP address and other network configuration parameters from a server. In a wireless controller scenario, the access points can use DHCP to request an IP address from a DHCP server, which can also provide the IP address or hostname of the wireless controller as an option in the DHCP response. Option 43 is a vendor-specific option that can be used to encode custom information for different types of devices. For example, Cisco access points can use option 43 to receive the IP address of the wireless controller from the DHCP server, while Aruba access points can use option 43 to receive the hostname of the wireless controller from the DHCP server. This way, the access points can discover the wireless controller and establish a connection with it. References: 1, Chapter 8, page 309; 2, Section 5.2

• Question 107:

  You are using a site survey tool for post-implementation validation. You have installed the appropriate adapter driver and imported a floor plan. Now, you want to take the next step in proper tool use. What must you do before gathering survey data after the floor plan is imported?

  A. Calibrate the floor plan
  B. Install WinPCAP
  C. Nothing, you can simply start capturing signal readings
  D. Install iPerf
  A. Calibrate the floor plan

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  Explanation/Reference:

  Calibrating the floor plan is what you must do before gathering survey data after the floor plan is imported when using a site survey tool for post-implementation validation. A site survey tool is a software application that can run on a laptop, tablet, smartphone, or other device that has a Wi-Fi adapter and a GPS receiver. A site survey tool can scan the wireless environment and collect information about the detected access points and client stations, such as their SSID, BSSID, channel, signal strength, security, and data rate. A site survey tool can also measure and display various metrics of network performance, such as throughput, jitter, packet loss, delay, and SNR. A site survey tool can also use a floor plan to visualize the wirelesscoverage and quality in different locations on a map. A floor plan is an image file that shows the layout and dimensions of a building or an area where the WLAN is deployed. A floor plan can be imported from various sources, such as a CAD file, a PDF file, an image file, or a Google Maps screenshot. After importing a floor plan into a site survey tool, it is necessary to calibrate the floor plan before gathering survey data. Calibrating the floor plan means adjusting the scale and orientation of the floor plan to match the actual size and direction of the area. Calibrating the floor plan can be done by using a reference point or a reference line that has a known distance or angle in the real world. Calibrating the floor plan ensures that the survey data is accurate and consistent with the physical environment. References: 1, Chapter 7, page 290; 2, Section 4.3

• Question 108:

  You are troubleshooting a controller-based AP that is unable to locate the controller. DHCP is not use and the controller is located at 10.10.10.81/24 while the AP is on the 10.10.16.0/24 network. What should be inspected to verify proper configuration?

  A. NTP
  B. BOOTH
  C. DNS
  D. AP hosts file
  C. DNS

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  Explanation/Reference:

  What should be inspected to verify proper configuration is DNS. DNS stands for Domain Name System and is a service that resolves hostnames to IP addresses. In a controller- based AP deployment, DNS can be used to help the AP locate the controller by using a predefined hostname such as CISCO-CAPWAP-CONTROLLER or aruba-master. The AP sends a DNS query for this hostname and receives an IP address of the controller as a response. Therefore, if DNS is not configured properly or if there is no DNS entry for the controller hostname, the AP may not be able to locate the controller. NTP, BOOTP, and AP hosts file are not relevant for this scenario. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 374; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 364.

• Question 109:

  The center frequency of channel 1 in the 2.4 GHz band is 2.412 GHz (2412 MHz). What is the center frequency of channel 4?

  A. 2.427
  B. 2.422
  C. 2.413
  D. 2.417
  A. 2.427

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  Explanation/Reference:

  The center frequency of channel 4 in the 2.4 GHz band is 2.427 GHz (2427 MHz). The center frequency of a channel is the midpoint of its frequency range, where the signal strength is highest and most concentrated. The center frequency of channel 1 in the 2.4 GHz band is 2.412 GHz (2412 MHz), as given in the question. The center frequency of each subsequent channel is obtained by adding 5 MHz to the previous channel's center frequency, since the channels are spaced 5 MHz apart from each other in this band. Therefore, to find the center frequency of channel 4, we need to add 15 MHz (5 MHz x 3) to the center frequency of channel 1:

  2.412 GHz + 0.015 GHz = 2.427 GHz

  Alternatively, we can use a formula to calculate the center frequency of any channel in the 2.4 GHz band:

  Center frequency (GHz) = 2.407 + (0.005 x Channel number) Using this formula for channel 4, we get:

  Center frequency (GHz) = 2.407 + (0.005 x 4)

  Center frequency (GHz) = 2.407 + 0.02

  Center frequency (GHz) = 2.427 References: 1, Chapter 3, page 85; 2, Section 3.2

• Question 110:

  Three access points are used within a facility. One access point is on channel 11 and the other two are on channel 1. The two access points using channel 1 are on either side of the access point using channel 11 and sufficiently apart so that they do not interfere with each other when they transmit frames. Assuming no other APs are in the vicinity, is CCI still a possibility in this network and why?

  A. Yes, because the client devices connected to one of the channel 1 APs will transmit frames that reach the other channel 1 AP as well as clients connected to the other channel 1 AP.
  B. No, because the APs are far enough apart that no CCI will occur.
  C. No, because CCI only occurs in the 5 GHz frequency band.
  D. Yes, because channel 11 loops around and causes CCI with channel 1.
  A. Yes, because the client devices connected to one of the channel 1 APs will transmit frames that reach the other channel 1 AP as well as clients connected to the other channel 1 AP.

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  Explanation/Reference:

  CCI is still a possibility in this network because the client devices connected to one of the channel 1 APs will transmit frames that reach the other channel 1 AP as well as clients connected to the other channel 1 AP. CCI stands for co-channel interference, which is a type of interference that occurs when two or more devices transmit on the same channel within range of each other. CCI reduces performance and capacity because it causes contention and collisions on the wireless medium, which leads to retransmissions and delays. CCI can be mitigated by increasing physical separation between devices using the same channel or byreducing transmit power levels to limit coverage area. In this scenario, three access points are used within a facility. One access point is on channel 11 and the other two are on channel 1. The two access points using channel 1 are on either side of the access point using channel 11 and sufficiently apart so that they do not interfere with each other when they transmit frames. However, this does not prevent CCI from occurring between their client devices that are connected on channel 1. For example, if a client device connected to one of the channel 1 APs sends a frame to another device on the wired network or on another wireless network (such as an Internet server or a VoIP phone), that frame will be heard by both channel 1 APs as well as any other client devices connected to either of them on channel 1. This will cause CCI because these devices will have to wait for the channel to be clear before they can transmit their own frames. The answer that CCI only occurs in the 5 GHz frequency band is incorrect; CCI can occur in any frequency band where devices use the same channel. The answer that channel 11 loops around and causes CCI with channel 1 is also incorrect; channel 11 does not loop around and it operates in a different frequency band than channel 1. References: CWNA- 109 Study Guide, Chapter 5: Radio Frequency Signal and Antenna Concepts, page 147