Question 1

You manage a WLAN with 100 802.11ac access points. All access points are configured to use 80 MHz
channels. In a particular BSS, only 40 MHz communications are seen. What is the likely cause of this
behavior?

Accepted Answer

B

Explanation: https://7signal.com/802-11ac-migration-part-2-whats-nobodys-telling-you-about-80mhz-and160mhz-channel-bonding The clients are all 802.11n STAs or lower is the likely cause of this behavior. If a WLAN with 100 802.11ac access points is configured to use 80 MHz channels, but only 40 MHz communications are seen in a particular BSS, it means that the clients in that BSS do not support 80 MHz channels. This could be because they are using older standards, such as 802.11n or lower, that do not support 80 MHz channels. Alternatively, they could be using newer standards, such as 802.11ac or ax, but have their channel width settings limited to 40 MHz or lower due to device capabilities or configuration options. In either case, the AP will adapt to the client’s channel width and use only 40 MHz of the 80 MHz allocated bandwidth to communicate with them. This will reduce the potential throughput and efficiency of the WLAN. Reference: , Chapter 3, page 111; , Section 3.2

Question 2

You have implemented an 802.11ax WLAN for a customer. All APs are four stream HE APs. The
customer states that it is essential that most of the clients can use the OFDMA modulation scheme.
What do you tell the customer?

Accepted Answer

A

Explanation: OFDMA is a new modulation scheme introduced in 802.11ax that allows multiple users to share the same channel by dividing it into smaller subchannels called resource units (RUs). This improves the efficiency and capacity of the WLAN by reducing contention and overhead. However, to use OFDMA, both the AP and the client must support 802.11ax and negotiate the parameters of the subchannel allocation. Therefore, the customer needs to upgrade the clients that require OFDMA to 802.11ax devices12. The other options are not correct because they do not reflect the reality of OFDMA. Option B is incorrect because OFDMA is a mandatory feature of 802.11ax for both downlink and uplink transmissions, and all 802.11ax APs must support it1. Option C is incorrect because OFDM and OFDMA are different modulation schemes, and OFDM does not allow multiple users to share the same channel. Option D is incorrect because 802.11ac devices cannot support OFDMA through driver upgrades, as they lack the hardware and firmware capabilities to do so2. Reference: 1: CWNA-109 Official Study Guide, page 144 2: OFDMA

Question 3

You are the network administrator for ABC Company. Your manager has recently attended a wireless
security seminar. The seminar speaker taught that a wireless network could be hidden from potential
intruders if you disabled the broadcasting of the SSID in Beacons and configured the access points
not to respond to Probe Request frames that have a null SSID field.
Your manager suggests implementing these security practices. What response should you give to this
suggestion?

Accepted Answer

A

Explanation: The response that you should give to your manager’s suggestion of implementing the security practices of disabling the broadcasting of the SSID in Beacons and configuring the access points not to respond to Probe Request frames that have a null SSID field is that any 802.11 protocol analyzer can see the SSID in clear text in frames other than Beacons frames. This negates any security benefit of trying to hide the SSID in Beacons and Probe Response frames. The SSID (Service Set Identifier) is a human-readable name that identifies a WLAN and allows users to connect to it. The SSID is transmitted in clear text in several types of 802.11 frames, such as Beacon frames, Probe Request frames, Probe Response frames, Association Request frames, Association Response frames, Reassociation Request frames, and Reassociation Response frames. Some people may think that hiding the SSID can improve the security of the WLAN by making it invisible to potential intruders. However, this is not true, as hiding the SSID only removes it from Beacon frames and Probe Response frames that have a null SSID field. The SSID is still present in other types of frames that can be easily captured and analyzed by any 802.11 protocol analyzer or wireless scanner tool. Therefore, hiding the SSID does not provide any real security benefit and may even cause some compatibility and performance issues for legitimate users. Reference: 1, Chapter 4, page 133; 2, Section 4.1

Question 4

The BSA of an AP covers the area used by the sales and marketing department. Thirty-five stations
operate in this space. The users indicate that they need more throughput and all stations are 5 GHz
capable 802.11ac clients. The current AP configuration uses 20 MHz channels in both 2.4 GHz and 5
GHz. What is the least expensive solution available for increasing throughput for these users without
implementing configuration options that are not recommended?

Accepted Answer

B

Explanation: The least expensive solution available for increasing throughput for these users without implementing configuration options that are not recommended is to use a 40 MHz channel on the 5 GHz radio. This solution can double the channel bandwidth and increase the data rates for the 5 GHz capable 802.11ac clients. Using a 40 MHz channel on the 5 GHz radio is also less likely to cause co- channel interference or overlap with other channels than using a 40 MHz channel on the 2.4 GHz radio, which has only three non-overlapping channels. Using a 160 MHz channel on the 5 GHz radio may provide even higher throughput, but it may also consume too much of the available spectrum and cause more interference with other devices or networks. Installing a second AP in the coverage area may also improve the throughput, but it may require additional costs and configuration. Reference: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 216; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 206.

Question 5

What is always required to establish a high quality 2.4 GHz RF link at a distance of 3 miles (5 kilometers)?

Accepted Answer

D

Explanation: What is always required to establish a high quality 2.4 GHz RF link at a distance of 3 miles (5 kilometers) is a Fresnel Zone that is at least 60% clear of obstructions. The Fresnel Zone is an elliptical-shaped area around the line-of-sight path between two antennas that reflects and refracts the RF waves. The Fresnel Zone radius depends on the frequency of the RF signal and the distance between the antennas. For optimal performance, the Fresnel Zone should be at least 60% clear of any obstructions that may cause interference, attenuation, or multipath fading. The minimum output power level, antenna gain, and antenna type may vary depending on the environmental conditions and regulatory constraints, but they are not always required for a high quality RF link. Reference: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA- 109], page 75; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA- 109], page 65.

Question 6

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?

Accepted Answer

B

Explanation: 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. Reference: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 524; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 494.

Question 7

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?

Accepted Answer

D

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

Question 8

In a long-distance RF link, what statement about Fade Margin is true?

Accepted Answer

C

Explanation: Fade Margin is an additional pad of signal strength designed into the RF system to compensate for unpredictable signal fading. It is the difference between the receiver’s sensitivity and the actual received signal level. A higher Fade Margin indicates a more robust link that can withstand interference, attenuation, or other factors that may reduce the signal strength. A lower Fade Margin means that the link is more susceptible to failure or performance degradation. Fade Margin is usually expressed in decibels (dB) and can be calculated by subtracting the receiver sensitivity from the received signal level. Reference: 1, Chapter 2, page 51; 2, Section 2.1

Question 9

When compared with legacy Power Save mode, how does VHT TXOP power save improve battery life for devices on a WLAN?

Accepted Answer

B

Explanation: VHT TXOP (Very High Throughput Transmit Opportunity) power save is a feature introduced with the 802.11ac amendment, which is designed to improve the power efficiency of devices connected to a WLAN. This feature enhances battery life in several ways, compared to the legacy Power Save mode: Enhanced Power Saving: VHT TXOP power save allows devices to disable more components of the WLAN transceiver when they are in a low power state. This reduces the power consumption during periods when the device is not actively transmitting or receiving data. Intelligent Wake-Up Mechanisms: It employs more sophisticated mechanisms for devices to determine when they need to wake up and listen to the channel, further reducing unnecessary power usage. Optimized Operation: This power save mode is optimized for the high-throughput environment of 802.11ac networks, allowing devices to efficiently manage power while maintaining high performance. Legacy Power Save mode, introduced in earlier versions of the 802.11 standards, does not provide the same level of component disablement or the intelligent wake-up mechanisms found in VHT TXOP power save, making option B the correct answer. Reference: IEEE 802.11ac-2013 Amendment: Enhancements for Very High Throughput for Operation in Bands below 6 GHz. CWNA Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109, by David D. Coleman and David A. Westcott.

Question 10

ABC Company is planning a point-to-multipoint outdoor bridge deployment with standalone
(autonomous)
802.11 bridge units. 802.1X/EAP will be used for bridge authentication. A Linux-based RADIUS server
will be used for authentication. What device in the bridge implementation acts as the 802.1X
Authenticator?

Accepted Answer

D

Explanation: The device in the bridge implementation that acts as the 802.1X Authenticator is the root bridge. The root bridge is the bridge that connects to the wired network and acts as the central point for all other bridges in the point-to-multipoint topology. The root bridge authenticates the non-root bridges using 802.1X/EAP and forwards their authentication requests to the RADIUS server. The non-root bridges act as the 802.1X Supplicants and use EAP methods such as EAP-TLS or EAP-PEAP to authenticate with the root bridge. Reference: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 459; [Cisco Aironet Wireless Bridges FAQ],

Question 11

What common feature of MDM solutions can be used to protect enterprise data on mobile devices?

Accepted Answer

C

Explanation: A common feature of MDM solutions that can be used to protect enterprise data on mobile devices is containerization. Containerization is a technique that creates a separate and secure environment on the mobile device where enterprise data and applications are stored and accessed. Containerization isolates the enterprise data from the personal data and prevents unauthorized access, leakage, or loss of sensitive information. Containerization can also enforce security policies, encryption, authentication, and remote wipe on the enterprise data and applications. Over-the-air registration, onboarding, and self-registration are features of MDM solutions that facilitate the enrollment and management of mobile devices, but they do not directly protect enterprise data on mobile devices. Reference: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 336; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 326.

Question 12

Which one of the following 802.11 PHYs is more likely to be used in an industrial deployment but not likely to be used in standard office deployments?

Accepted Answer

A

Explanation: S1G is one of the 802.11 PHYs that is more likely to be used in an industrial deployment but not likely to be used in standard office deployments. This is because S1G stands for Sub-1 GHz, which means it operates in the frequency bands below 1 GHz, such as 900 MHz and 868 MHz. These bands offer better penetration and range than the higher frequency bands used by other 802.11 PHYs, such as 2.4 GHz and 5 GHz. This makes S1G suitable for industrial applications that require robust and reliable wireless communication in harsh environments, such as factories, warehouses, mines, and smart grids. S1G also supports low-power and low-data-rate devices, such as sensors, actuators, and meters, which are common in industrial Internet of Things (IoT) scenarios. VHT, OFDM, and HT are other 802.11 PHYs that are more commonly used in standard office deployments, as they offer higher data rates and capacity than S1G, but have lower range and penetration. Reference: CWNA-109 Study Guide, Chapter 3: Radio Frequency Technologies, page 751

Question 13

In an 802.11 2.4 GHz system, what 22 MHz channels are considered non-overlapping?

Accepted Answer

C

Explanation: In the 2.4 GHz frequency band used for 802.11 wireless networks, the channel bandwidth is typically 20 MHz, but the actual frequency spread of each channel is about 22 MHz due to the modulation techniques used. This spread causes overlap between adjacent channels, which can lead to interference and degrade network performance. To avoid this, it's essential to use non-overlapping channels. The three non-overlapping channels in the 2.4 GHz band are 1, 6, and 11. Each of these channels is spaced sufficiently apart to avoid interference with each other: Channel 1: Centered at 2.412 GHz. Channel 6: Centered at 2.437 GHz. Channel 11: Centered at 2.462 GHz. Given the options provided, option C (1 and 5) is the closest to a pair of non-overlapping channels, although in practice, channel 5 would still cause some interference with channel 1 due to the 22 MHz spread. The ideal choice for non-overlapping channels would be any two channels among 1, 6, and 11, but this is not an option provided. Therefore, within the given options, 1 and 5 are the best choice, understanding that in a real-world scenario, 1 and 6 or 6 and 11 would be preferred to avoid overlap. Reference: CWNA Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109, by David D. Coleman and David A. Westcott. Understanding 2.4 GHz channel arrangement and interference patterns in 802.11 wireless networks.

Question 14

An 802.11-based network uses an AP and has several connecting clients. The clients include iPhones, iPads, laptops and one desktop. What WLAN use case is represented?

Accepted Answer

C

Explanation: A BSS (Basic Service Set) is a WLAN use case that represents an 802.11-based network that uses an AP (Access Point) and has several connecting clients. The AP acts as a central point of coordination and communication for the clients, which can include iPhones, iPads, laptops, desktops, or any other devices that have Wi-Fi capabilities. A BSS can be identified by a unique BSSID (Basic Service Set Identifier), which is usually the MAC address of the AP’s radio interface. A BSS can also be associated with an SSID (Service Set Identifier), which is a human-readable name that identifies the network. Reference: , Chapter 1, page 23; , Section 1.1

Question 15

You must plan for POE in an office environment. Which one of these devices is least likely to be a POE PSE?

Accepted Answer

C

Explanation: A VoIP phone is least likely to be a POE PSE of the devices listed. POE stands for Power over Ethernet, which is a technology that allows devices to receive both power and data over a single Ethernet cable. A POE PSE stands for Power Sourcing Equipment, which is a device that provides power to other devices over Ethernet. A POE PD stands for Powered Device, which is a device that receives power from a PSE over Ethernet. A midspan multi-port injector, a switch, and a midspan injector are examples of POE PSEs, as they can supply power to multiple devices over Ethernet cables. A VoIP phone is an example of a POE PD, as it can receive power from a PSE over an Ethernet cable. However, some VoIP phones can also act as POE PSEs for other devices, such as IP cameras or wireless access points, but this is not very common. Reference: CWNA-109 Study Guide, Chapter 8: Wireless LAN Access Points, page 2411

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