CWNP CWNA-109 Online Practice Questions and Exam Preparation

CWNP CWNA-109 Online Questions & Answers

• Question 11:

  You are configuring an access point to use channel 128. What important fact should be considered about this channel?

  A. It is a 2.4 GHz frequency band 40 MHz channel, so it should not be used
  B. It is a 22 MHz channel so it will overlap with the channels above and below it
  C. It is a channel that may require DFS when used
  D. It is a channel that is unsupported by all access points in all regulatory domains
  C. It is a channel that may require DFS when used

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  Explanation/Reference:

  It is a channel that may require DFS when used is an important fact that should be considered about channel 128. Channel 128 is a 5 GHz frequency band 20 MHz channel that has a center frequency of 5.64 GHz. Channel 128 is one of the channels that are subject to DFS (Dynamic Frequency Selection) rules, which require Wi-Fi devices to monitor and avoid using channels that are occupied by radar systems or other primary users. DFS is a feature that is defined in the IEEE 802.11h amendment and is mandated by some regulatory bodies, such as the FCC and the ETSI, to protect the licensed users of the 5 GHz band from interference by unlicensed Wi-Fi devices. DFS works by using a mechanism called channel availability check (CAC), which requires Wi-Fi devices to scan a channel for a certain period of time before using it. If a radar signal is detected during the CAC or while using the channel, the Wi-Fi devices must switch to another channel that is free from radar interference. When configuring an access point to use channel 128, it is important to consider the implications of DFS rules, such as: The access point must support DFS and comply with the local regulations and standards that apply to DFS channels. The access point may experience delays or interruptions in its operation due to CAC or channel switching. The access point may have limited channel selection or availability due to radar interference or other Wi-Fi devices using DFS channels. The access point may have compatibility or interoperability issues with some client devices that do not support DFS or use different DFS parameters. The access point may have performance or quality issues due to co-channel or adjacent-channel interference from other Wi-Fi devices using non-DFS channels. Therefore, it is advisable to use channel 128 only when necessary and after performing a thorough site survey and spectrum analysis to determine the best channel for the access point. References: 1, Chapter 3, page 117; 2, Section 3.2

• Question 12:

  What statement about 802.11 WLAN performance is true?

  A. In modem networks, both centralized and distributed data forwarding work well for most standard office deployments
  B. In most WLANs, no special skill or tuning is required to get peak performance
  C. WLANs perform better as more wireless clients connect with each AP
  D. To get the best performance out of an AP, you should disable data rates of 72 Mbps and lower
  A. In modem networks, both centralized and distributed data forwarding work well for most standard office deployments

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  Explanation/Reference:

  The statement that in modern networks, both centralized and distributed data forwarding work well for most standard office deployments is true about WLAN performance. Data forwarding refers to how wireless frames are transmitted from wireless clients to wired networks or vice versa through wireless access points (APs). Centralized data forwarding means that all wireless frames are sent to a central controller or gateway before being forwarded to their destinations. Distributed data forwarding means that wireless frames are forwarded directly by the APs to their destinations without going through a central controller or gateway. Both methods have their advantages and disadvantages, depending on the network size, topology, traffic pattern, security, and management requirements. However, in modern networks, both methods can achieve high performance and scalability for most standard office deployments, as they can leverage advanced features such as fast roaming, load balancing, quality of service, and encryption. The other statements about WLAN performance are false. In most WLANs, special skill or tuning is required to get peak performance, such as selecting the appropriate channel, power, data rate, and antenna settings. WLANs perform worse as more wireless clients connect with each AP, as they cause more contention and interference on the wireless medium. To get the best performance out of an AP, you should not disable data rates of 72 Mbps and lower, as they are needed for backward compatibility and range extension. References: CWNA-109 Study Guide, Chapter 9: Wireless LAN Architecture, page 2811

• Question 13:

  You are using a tool that allows you to see signal strength for all Aps in the area with a visual representation. It shows you SSIDs available and the security settings for each SSID. It allows you to filter by frequency band to see only 2.4 GHz networks or only 5 GHz networks. No additional features are available.

  What kind of application is described?

  A. Protocol analyzer
  B. Site survey utility
  C. Spectrum analyzer
  D. WLAN scanner tool
  D. WLAN scanner tool

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  Explanation/Reference:

  The tool described is a WLAN (Wireless Local Area Network) scanner tool. WLAN scanner tools are designed to provide information about the wireless networks in a given area, including: Signal Strength: They show the signal strength of all access points (APs) in the vicinity, which is crucial for understanding the coverage area and potential interference.

  SSID Visualization: These tools display the SSIDs (Service Set Identifiers) of available networks, allowing users to identify different wireless networks easily. Security Settings Information: WLAN scanner tools often show the type of security

  implemented on each network, such as WPA2, WEP, etc. Frequency Band Filtering: They allow users to filter and view networks based on the frequency band (2.4 GHz or 5 GHz), which is useful for analyzing network distribution and

  planning.

  While protocol analyzers, site survey utilities, and spectrum analyzers are also used in wireless networking, their functions are distinct from what is described:

  Protocol Analyzersare more sophisticated and are used to capture and analyze network traffic.

  Site Survey Utilitiesare used to map signal coverage and plan network layouts, often with more advanced features for detailed site surveys. Spectrum Analyzersprovide a detailed view of the frequency spectrum and non- Wi-Fi interference

  but don't typically focus on SSIDs or security settings. Thus, the correct answer is D, a WLAN scanner tool, based on the functionalities described.

  References:

  CWNA Certified Wireless Network Administrator Official Study Guide: Exam PW0- 105, by David D. Coleman and David A. Westcott.

  Tools and techniques for wireless network analysis and troubleshooting.

• Question 14:

  You are evaluating access points for use in the 5 GHz frequency band. What PHY supports this band and supports 80 MHz channels?

  A. HT
  B. VHT
  C. ERP
  D. OFDM
  B. VHT

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  Explanation/Reference:

  VHT stands for Very High Throughput, which is a physical layer (PHY) specification that supports the 5 GHz frequency band and supports 80 MHz channels. VHT is used by the IEEE 802.11ac standard, which is also known as Wi-Fi 5. VHT allows for higher data rates and more spatial streams than the previous HT (High Throughput) PHY, which is used by the IEEE 802.11n standard, also known as Wi-Fi 4. HT supports the 2.4 GHz and 5 GHz bands, but only supports up to 40 MHz channels12 The other options are not correct because: ERP (option C) stands for Extended Rate PHY, which is a physical layer specification that supports the 2.4 GHz frequency band and supports up to 20 MHz channels. ERP is used by the IEEE 802.11g standard, which is also known as Wi- Fi

  3. ERP allows for higher data rates than the previous DSSS (Direct Sequence Spread Spectrum) PHY, which is used by the IEEE 802.11b standard, also known as Wi-Fi 234 OFDM (option D) stands for Orthogonal Frequency Division Multiplexing, which is a modulation technique that divides a signal into multiple subcarriers that are spaced orthogonally to each other. OFDM is not a physical layer specification, but a common feature of many PHY specifications, including ERP, HT, and VHT. OFDM allows for higher spectral efficiency and robustness against multipath interference than the previous CCK (Complementary Code Keying) modulation technique used by DSSS34

• Question 15:

  When a client station sends a broadcast probe request frame with a wildcard SSID, how do APs respond?

  A. Each AP responds in turn after preparing a probe response and winning contention.
  B. For each probe request frame, only one AP may reply with a probe response.
  C. Each AP checks with the DHCP server to see if it can respond and then acts accordingly.
  D. After waiting a SIFS, all APs reply at the same time with a probe response.
  A. Each AP responds in turn after preparing a probe response and winning contention.

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  Explanation/Reference:

  In the 802.11 wireless networking protocols, when a client station sends a broadcast probe request frame with a wildcard SSID (Service Set Identifier), it is essentially asking for any nearby access points (APs) to identify themselves. The way

  APs respond to such a probe request is governed by standard 802.11 behavior, which includes:

  Probe Request Handling: Upon receiving a broadcast probe request, each AP that can serve the client prepares a probe response. The response includes information about the AP, such as its SSID, supported data rates, and other

  capabilities.

  Contention-Based Mechanism: Wireless networks use a contention-based mechanism (CSMA/CA - Carrier Sense Multiple Access with Collision Avoidance) for medium access. Each AP must wait for a clear channel and win the contention

  process before it can send its probe response.

  Independent Responses: Each AP operates independently in responding to the probe request. There is no coordination between APs to decide which one responds first or at all, leading to multiple APs sending probe responses, each after

  winning the contention for the medium.

  Option A accurately reflects this process, indicating that each AP prepares and sends a probe response in turn, contingent upon winning the medium contention. The other options suggest mechanisms (such as coordination with a DHCP

  server or simultaneous responses after a Short Interframe Space (SIFS)) that do not align with standard 802.11 procedures for handling broadcast probe requests.

  References:

  IEEE 802.11 Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.

  CWNA Certified Wireless Network Administrator Official Study Guide: Exam PW0- 105, by David D. Coleman and David A. Westcott.

• Question 16:

  You are troubleshooting a problem with interference from a non-802.11 device. Given that the device is not a WLAN device, you cannot use a protocol analyzer and have chosen to use a spectrum analyzer. You want to view the signal from the interfering device over time to see the activity that is generating.

  What common spectrum analyzer view should you use for this analysis?

  A. APs
  B. Waterfall/Spectrogram
  C. Real-time FFT
  D. Clients
  B. Waterfall/Spectrogram

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  Explanation/Reference:

  The common spectrum analyzer view that you should use for this analysis is the Waterfall/Spectrogram view. The Waterfall/Spectrogram view shows the signal from the interfering device over time on a three-dimensional graph. The x-axis

  represents frequency, the y-axis represents time, and the z-axis represents amplitude or power. The color of each pixel indicates the signal strength at a given frequency and time. The Waterfall/Spectrogram view can help you identify the

  characteristics of the interference source, such as its frequency range, duty cycle, modulation type, and pattern. References: [CWNP Certified Wireless Network Administrator Official Study Guide:

  ExamCWNA-109], page 524; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 494.

• Question 17:

  802. 11ax (HE) introduces Resource Units that can be used to allow communications with multiple devices at the same time, on the same channel, in the same BSS. What feature of 802.1 lax provides this functionality?

  A. 6 GHz support
  B. TWT
  C. Wi-Fi-LTE
  D. OFDMA
  D. OFDMA

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  Explanation/Reference:

  The feature of 802.11ax (HE) that provides this functionality is OFDMA. OFDMA stands for Orthogonal Frequency Division Multiple Access and is a technology that allows multiple devices to communicate simultaneously on the same channel in the same BSS. OFDMA works by dividing a channel into smaller subchannels called Resource Units (RUs), which are composed of groups of subcarriers or tones. Each RU can be assigned to a different device based on its bandwidth requirement and signal quality. This way, OFDMA can increase the efficiency and capacity of the channel by reducing overhead, contention, and latency. OFDMA can also support both uplink and downlink multi-user transmissions using trigger frames and buffer status reports. 6 GHz support, TWT, and Wi-Fi-LTE are not features of 802.11ax that provide this functionality. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 226; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 216.

• Question 18:

  You recently purchased four laptops containing dual-band 802.11ac adapters. The laptops can connect to your 2.4 GHz network, but they cannot connect to the 5 GHz network. The laptops do not show the 5 GHz SSIds, which are different than the 2.4 GHz SSIDs. Existing devices can connect to the 5 GHz SSIDs with no difficulty. What is the likely problem?

  A. Interference from non-Wi-Fi sources
  B. Faulty drivers
  C. DoS attack
  D. Interference from other WLANs
  B. Faulty drivers

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  Explanation/Reference:

  The likely problem that causes this scenario is faulty drivers. Drivers are software components that enable the communication between the operating system and the hardware devices, such as the wireless adapters. Faulty drivers can cause various issues with the wireless connectivity, such as not detecting or connecting to certain networks, dropping connections, or reducing performance. Faulty drivers can be caused by corrupted files, outdated versions, incompatible settings, or hardware defects. To fix faulty drivers, you can try to update, reinstall, or roll back the drivers, or contact the manufacturer for support. Interference from non-Wi-Fi sources, DoS attack, or interference from other WLANs are not likely to cause this scenario, as they would affect all devices in the same area, not just the new laptops. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 562; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 532.

• Question 19:

  What can cause excessive VSWR in RF cables used to connect a radio to an antenna?

  A. High gain yagi antenna
  B. Radio output power above 100 mW but below 400 mw
  C. High gain parabolic dish antenna
  D. Impedance mismatch
  D. Impedance mismatch

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  Explanation/Reference:

  Impedance is the measure of opposition to the flow of alternating current (AC) in a circuit. Impedance mismatch occurs when the impedance of the radio does not match the impedance of the antenna or the cable. This causes some of the transmitted or received signal to be reflected back, resulting in a loss of power and efficiency. The voltage standing wave ratio (VSWR) is a metric that indicates the amount of impedance mismatch in a transmission line. A higher VSWR means a higher impedance mismatch and a lower signal quality. A VSWR of 1:1 is ideal, meaning there is no impedance mismatch and no reflected power. A VSWR of 2:1 means that for every 2 units of forward power, there is 1 unit of reflected power12. The other options are not correct because they do not affect the VSWR in RF cables. A high gain yagi antenna or a high gain parabolic dish antenna can increase the signal strength and directionality, but they do not cause impedance mismatch in the cable. Radio output power above 100 mW but below 400 mW is within the acceptable range for most WLAN devices and does not cause excessive VSWR in the cable3. References: 1:CWNA-109Official Study Guide, page 77

  2: VSWR 3:CWNA-109Official Study Guide, page 81

• Question 20:

  As an RF wave propagates through space, the wave front experiences natural expansion that reduces its signal strength in an area. What describes the rate at which this expansion happens?

  A. Fresnel zone thinning
  B. Ohm's law
  C. Inverse square law
  D. MU-MIMO
  C. Inverse square law

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  Explanation/Reference:

  The inverse square law states that the signal strength of an RF wave is inversely proportional to the square of the distance from the source. This means that as the distance from the transmitter increases, the signal strength decreases rapidly. References: Wireless Network Administrator Official Study Guide, Chapter 3, page 64.