CWNP CWNP Certifications CWNA-109 Questions & Answers

• Question 41:

  You are implementing a multi-AP WLAN and fast secure roaming is essential. Which one of the following methods is an IEEE 802.11 standard method for fast roaming?

  A. FT

  B. OKC

  C. Load balancing

  D. Band steering

  Correct Answer: A

  FT (Fast Transition) is an IEEE 802.11 standard method for fast roaming. FT is defined in the IEEE 802.11r amendment and is also known as Fast BSS Transition (FBT) or Fast Secure Roaming. FT is a feature that allows a client station to quickly switch from one AP to another within the same ESS (Extended Service Set) without having to re-authenticate and re-associate with each AP. This reduces the latency and packet loss that may occur during roaming, thus improving the user experience and maintaining the security of the connection. FT works by using pre-authentication and key caching mechanisms that allow the client station and the APs to exchange security information before the actual roaming occurs. This way, when the client station decides to roam to a new AP, it can use a fast reassociation request and response that contain only a few fields, instead of a full authentication and association exchange that require more time and data. References: 1, Chapter 9, page 367; 2, Section 6.3

• Question 42:

  A client complains of low data rates on his computer. When you evaluate the situation, you see that the signal strength is -84 dBm and the noise floor is -96 dBm. The client is an 802.11ac client and connects to an 802.11ac AP. Both the client and AP are 2x2:2 devices. What is the likely cause of the low data rate issue?

  A. Weak signal strength

  B. CAT5e cabling run to the AP

  C. Too few spatial streams

  D. Lack of support for 802.11n

  Correct Answer: A

  Weak signal strength is the likely cause of the low data rate issue for the client that has a signal strength of -84 dBm and a noise floor of -96 dBm. The client is an 802.11ac client and connects to an 802.11ac AP. Both the client and AP are 2x2:2 devices. Signal strength 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 traffic. The higher the signal strength, the better the signal quality and the higher the data rate. The lower the signal strength, the worse the signal quality and the lower the data rate. The data rate of an 802.11ac connection depends on several factors, such as channel bandwidth, modulation and coding scheme (MCS), spatial streams, guard interval, and beamforming. However, these factors are also influenced by the signal strength, as they require a certain signal-to-noise ratio (SNR) to operate properly. SNR is the ratio of the signal strength to the noise floor, which is the measure of the background noise or interference in the RF environment. The higher the SNR, the more robust and efficient the communication. The lower the SNR, the more prone and vulnerable to errors and retries. According to the CWNA Official Study Guide , Table 3.7, page 112, an 802.11ac connection with a channel bandwidth of 80 MHz, an MCS of 9, two spatial streams, a short guard interval, and no beamforming can achieve a maximum data rate of 867 Mbps. However, this data rate requires a minimum SNR of 30 dB to maintain a sufficient signal quality. If the signal strength is -84 dBm and the noise floor is -96 dBm, then the SNR is only 12 dB (-84 dBm - (-96 dBm) = 12 dB), which is far below the required SNR for this data rate. Therefore, the data rate will drop significantly to match the lower SNR and signal quality. To solve this problem, the signal strength should be increased to improve the SNR and data rate. This can be done by adjusting the output power or channel assignment of the AP or client, relocating or reorienting some APs or antennas to reduce attenuation or interference, updating or replacing some faulty oroutdated hardware or software components, etc. References: , Chapter 3, page 112; , Section 3.2

• Question 43:

  In a mesh BSS (MBSS), according to the 802.11 standard, what device connect the mesh to an Ethernet network?

  A. Mesh Gate

  B. Mesh Switch

  C. Mesh Router

  D. Mesh Portal

  Correct Answer: D

  a mesh portal is a device that connects a mesh BSS (MBSS) to an Ethernet network, such as the Internet. A mesh portal acts as a bridge between the wired and wireless domains, and allows the mesh stations to communicate with external networks. A mesh portal is also a mesh point, which means it can forward traffic within the MBSS. The other options are not correct. Option A. Mesh Gate is a device that connects a mesh BSS (MBSS) to another mesh BSS or another wireless network, such as an infrastructure BSS or an ad hoc network2. A mesh gate acts as a gateway between different wireless domains, and allows the mesh stations to communicate with other wireless networks. A mesh gate is also a mesh point, which means it can forward traffic within the MBSS. Option B. Mesh Switch is not a valid term in the 802.11 standard. Option C. Mesh Router is also not a valid term in the 802.11 standard.

• Question 44:

  You are managing a wireless access point in autonomous mode using the Web based interface. You capture traffic during this management task and notice that you can see the HTML code of the Web pages used for access point management. What error in administration could be the cause of this security concern?

  A. IPsec is not in use of the management connection as recommended

  B. A VPN with the AP is not established

  C. WPA2 is disabled on the WLAN

  D. HTTP is in use instead of HTTPS

  Correct Answer: D

  The error in administration that could be the cause of this security concern is that HTTP is in use instead of HTTPS. HTTP is an unencrypted protocol that transfers data in plain text over the network. This means that anyone who captures the traffic can see the HTML code of the Web pages used for access point management, as well as any sensitive information such as passwords or configuration settings. HTTPS is an encrypted protocol that uses SSL/TLS to secure the data transmission between the Web browser and the Web server. HTTPS prevents anyone from snooping on or tampering with the Web traffic. Therefore, HTTPS should always be used for Web based management of wireless access points, especially in autonomous mode where there is no centralized controller to enforce security policies. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 431; [HTTP vs HTTPS: What's The Difference And Why Should You Care?].

• Question 45:

  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

  Correct Answer: B

  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 46:

  You are performing a post-implementation validation survey. What basic tool can be used to easily locate areas of high co-channel interference?

  A. Throughput tester

  B. Laptop-based spectrum analyzer

  C. Access point spectrum analyzer

  D. Wi-Fi scanner

  Correct Answer: D

  A Wi-Fi scanner is a basic tool that can be used to easily locate areas of high co-channel interference. A Wi-Fi scanner is a software application that can run on a laptop, tablet, smartphone, or other device that has a Wi-Fi adapter. A Wi-Fi scanner can scan the wireless environment and display information about the detected access points and client stations, such as their SSID, BSSID, channel, signal strength, security, and data rate. A Wi-Fi scanner can also show the channel utilization and overlap of different access points, which can indicate the level of co-channel interference. Co-channel interference is a type of interference that occurs when multiple access points use the same or adjacent channels within the same coverage area. Co-channel interference can reduce the throughput and performance of the WLAN, as the access points and client stations have to contend for the channel access and avoid collisions. To identify areas of high co-channel interference, a Wi-Fi scanner can be used to measure the signal strength and channel utilization of different access points and compare them with a threshold or a baseline. Alternatively, a Wi-Fi scanner can also use a color-coded heat map to visualize the co-channel interference level in different locations. References: 1, Chapter 7, page 279; 2, Section 4.3

• Question 47:

  You are implementing a VHT-capable AP. Which one of the following channels is available in the 802.11-2016 standard that was not available before the ratification of 802.11 ac?

  B. 161

  C. 153

  D. 144

  Correct Answer: D

  Channel 144 is a new channel that was added to the 5 GHz band by the 802.11ac amendment, which defines the VHT (Very High Throughput) PHY for WLANs. Channel 144 has a center frequency of 5720 MHz and a bandwidth of 20 MHz. It can also be combined with adjacent channels to form wider channels of 40 MHz, 80 MHz, or 160 MHz. Channel 144 is available in some regions, such as North America and Europe, but not in others, such as Japan and China . References: [CWNA-109 Study Guide], Chapter

  3: Antennas and Accessories, page 121; [CWNA-109Study Guide], Chapter 3: Antennas and Accessories, page 115; [Wikipedia], List of WLAN channels.

• Question 48:

  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

  Correct Answer: B

  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 49:

  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

  Correct Answer: B

  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 50:

  What facts are true regarding controllers and APs in a Split MAC architecture?

  A. An IP tunnel is established between the AP and controller for AP management and control functions.

  B. Using centralized data forwarding, APs never tag Ethernet frames with VLAN identifiers or 802.1p CoS.

  C. With 802.1X/EAP security, the AP acts as the supplicant and the controller acts as the authenticator.

  D. Management and data frame types must be processed locally by the AP, while control frame types must be sent to the controller.

  Correct Answer: A

  The fact that is true regarding controllers and APs in a Split MAC architecture is that an IP tunnel is established between the AP and controller for AP management and control functions. A Split MAC architecture is a WLAN architecture where some of the MAC layer functions are performed by the APs (such as encryption, decryption, and frame acknowledgement) and some are performed by the controllers (such as authentication, association, roaming, and QoS). To communicate with each other, the APs and controllers establish an IP tunnel that carries the management and control frames between them. The IP tunnel can use protocols such as Lightweight Access Point Protocol (LWAPP) or Control And Provisioning of Wireless Access Points (CAPWAP). References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 372; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 362.