CWNA-109 Certification Exam Questions with AI Explanations

QUESTION: 21

What security solution is deprecated in the 802.11 standard and should never be used in any modern WLAN deployment?

Shared Key Authentication
Open System Authentication
CCMP
AES

Answer(s): A

Explanation:

Shared Key Authentication is a security solution that was defined in the original 802.11 standard as an alternative to Open System Authentication, which does not provide any security at all. Shared Key Authentication uses WEP (Wired Equivalent Privacy) to encrypt and authenticate data frames between the client station and the AP. However, WEP has been proven to be extremely vulnerable to various attacks that can easily crack the encryption key and compromise the network security. Therefore, Shared Key Authentication is deprecated in the 802.11 standard and should never be used in any modern WLAN deployment .

Reference:

[CWNA-109 Study Guide], Chapter 10: Wireless LAN Security, page 401; [CWNA-109 Study Guide], Chapter 10: Wireless LAN Security, page 391; [Wikipedia], Wired Equivalent Privacy.

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QUESTION: 22

You are reconfiguring an AP to use the short guard interval. How long will the new guard interval duration be after the change?

800 ns
400 ns
104 ms
10 ms

Answer(s): B

Explanation:

The short guard interval is an optional feature of 802.11n and 802.11ac that reduces the time between OFDM symbols from 800 ns to 400 ns. This can increase the data rate by about 11%, but also requires more precise timing and synchronization between the transmitter and the receiver. The short guard interval is only used when both the AP and the client support it and agree to use it .

Reference:

[CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page 163; [CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page 157.

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QUESTION: 23

What statement about the IEEE 802.11-2016 QoS facility is true?

802.11 control frames are assigned to the 802.11 EF priority queue.
When the Voice queue has frames awaiting transmission, no data will be transmitted from the Best Effort queue.
802.11 QoS is achieved by giving high priority queues a statistical advantage at winning contention.
Four 802.1p user priorities are mapped to eight 802.11 transmit queues.

Answer(s): C

Explanation:

802.11 QoS is achieved by giving high priority queues a statistical advantage at winning contention. 802.11 QoS is based on the Enhanced Distributed Channel Access (EDCA) mechanism, which defines four access categories (ACs) for different types of traffic: Voice, Video, Best Effort, and Background. Each AC has its own transmit queue and contention parameters, such as Arbitration Interframe Space (AIFS), Contention Window (CW), and Transmission Opportunity (TXOP). These parameters determine how long a station has to wait before transmitting a frame and how long it can occupy the channel. Higher priority ACs have shorter AIFS, smaller CW, and longer TXOP, which means they have more chances to access the channel and send more data than lower priority ACs. However, this does not guarantee that higher priority ACs will always win the contention, as there is still a random backoff process involved. Therefore, 802.11 QoS is a statistical service that provides different levels of service quality based on traffic categories.

Reference:

, Chapter 10, page 403; , Section 6.1

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QUESTION: 24

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?

All clients implement single spatial stream radios
The clients are all 802.11n STAs or lower
The AP is improperly configured to use only 40 MHz of the 80 MHz allocated bandwidth
The short guard interval is also enabled

Answer(s): B

Explanation:

https://7signal.com/802-11ac-migration-part-2-whats-nobodys-telling-you-about-80mhz-and- 160mhz-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

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QUESTION: 25

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

Legacy Power Save mode was removed in the 802.11ac amendment.
VHT TXOP power save allows the WLAN transceiver to disable more components when in a low power state.
VHT TXOP power save uses the partial AID in the preamble to allow clients to identify frames targeted for them.
VHT TXOP power save allows stations to enter sleep mode and legacy Power Save does not.

Answer(s): 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.

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QUESTION: 21

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QUESTION: 23

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QUESTION: 25

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