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?
A. 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.
B. To improve security by hiding the SSID, the AP and client stations must both be configured to remove the SSID from association request and response frames. Most WLAN products support this.
C. Any tenants in the same building using advanced penetration testing tools will be able to obtain the SSID by exploiting WPA EAPOL-Key exchanges. This poses an additional risk of exposing the WPA key.
D. This security practice prevents manufacturers' client utilities from detecting the SSID. As a result, the SSID cannot be obtained by attackers, except through social engineering, guessing, or use of a WIPS.
Correct Answer: A
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. References: 1, Chapter 4, page 133; 2, Section 4.1
Question 62:
ABC Company is planning to install a new 802.11ac WLAN, but wants to upgrade its wired infrastructure first to provide the best user experience possible. ABC Company has hired you to perform the RF site survey. During the interview with the network manager, you are told that the new Ethernet edge switches will support VoIP phones and 802.11 access points, both using 802.3 PoE.
After hearing this information, what immediate concerns do you note?
A. The power budget in the edge switches must be carefully planned and monitored based on the number of supported PoE devices.
B. The edge Ethernet switches should support Ether-channel to get the best results out of the network.
C. VoIP phones and 802.11 access points should not be powered by the same edge switch due to distortion.
D. If the switches are in optimal locations for VoIP phones, they are likely to be suboptimal locations for 802.11 APs
Correct Answer: A
An immediate concern that you note after hearing this information is that the power budget in the edge switches must be carefully planned and monitored based on the number of supported PoE devices. PoE stands for Power over Ethernet and is a technology that allows Ethernet switches to deliver power along with data to devices such as VoIP phones and 802.11 access points. PoE devices are classified into different classes based on their power consumption and output. The edge switches have a limited power budget that determines how many PoE devices they can support simultaneously. If the power budget is exceeded, some PoE devices may not receive enough power or may shut down unexpectedly. Therefore,it is important to plan and monitor the power budget in the edge switches based on the number and class of PoE devices connected to them. Using Ether- channel, placing switches in optimal locations, or avoiding distortion are not immediate concerns related to PoE devices. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 234; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 224.
Question 63:
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.
Correct Answer: B
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 64:
When using a spectrum to look for non Wi-Fi interference sources, you notice significant interference across the entire 2.4 GHz band (not on a few select frequencies) within the desktop area of a users workspace, but the interference disappears quickly after just 2 meters. What is the most likely cause of this interference?
A. USB 3 devices in the user's work area
B. Bluetooth devices in the user's work area
C. Excess RF energy from a nearby AP
D. Unintentional radiation from the PC power supply
Correct Answer: A
USB 3 devices in the user's work area are the most likely cause of this interference when using a spectrum analyzer to look for non-Wi-Fi interference sources. A spectrum analyzer is a tool that measures and visualizes the radio frequency activity and interference in the wireless environment. A spectrum analyzer can show the spectrum usage and energy levels on each frequency band or channel and help identify and locate the sources of interference. Interference is any unwanted signal that disrupts or degrades the intended signal on a wireless channel. Interference can be caused by various sources, such as other Wi-Fi devices, non-Wi-Fi devices, or natural phenomena. Interference can affect WLAN performance and quality by causing signal loss, noise, distortion, or errors. USB 3 devices are non-Wi-Fi devices that use USB 3.0 technology to transfer data at high speeds between computers and peripherals, such as hard drives, flash drives, cameras, or printers. USB 3 devices can generate electromagnetic radiation that interferes with Wi-Fi signals in the 2.4 GHz band, especially when they are close to Wi-Fi devices or antennas. USB 3 devices can cause significant interference across the entire 2.4 GHz band (not on a few select frequencies) within the desktop area of a user's workspace, but the interference disappears quickly after just 2 meters. This is because USB 3 devices emit broadband interference that affects all channels in the 2.4 GHz band with a high intensity near the source but a low intensity at a distance due to attenuation. The other options are not likely to cause this interference pattern when using a spectrum analyzer to look for non-Wi-Fi interference sources. Bluetooth devices in the user's work area are non-Wi-Fi devices that use Bluetooth technology to communicate wirelessly between computers and peripherals, such as keyboards, mice, headphones, or speakers. Bluetooth devices can cause interference with Wi-Fi signals in the 2.4 GHz band, but they use frequency hopping spread spectrum (FHSS) technique that changes frequencies rapidly and randomly within a range of 79 channels. Therefore, Bluetooth devices do not cause significant interference across the entire 2.4 GHz band (not on a few select frequencies), but rather intermittent interference on some channels at different times. Excess RF energy from a nearby AP is not a non-Wi-Fi interference source but rather a Wi-Fi interference source that occurs when an AP transmits more power than necessary for its coverage area. Excess RF energy from a nearby AP can cause co-channel interference (CCI) with other APs or client devices that use the same channel within range of each other. CCI reduces performance and capacity because it causes contention and collisions on the wireless medium,
Question 65:
You are attempting to explain RF shadow and how it can cause lack of coverage. What common building item frequently causes RF shadow and must be accounted for in coverage plans?
A. Wooden doors
B. Carpeted floors
C. Elevators
D. Cubicle partitions
Correct Answer: C
Elevators are a common building item that frequently causes RF shadow and must be accounted for in coverage plans. RF shadow is a term that describes an area where wireless signals are blocked or significantly weakened by an obstacle or an object that absorbs or reflects RF energy. RF shadow can cause lack of coverage or poor performance in a WLAN because wireless devices in those areas may not be able to communicate with access points or other devices. RF shadow can be mitigated by adjusting access point placement, antenna orientation, transmit power level, or channel selection to avoid or overcome the obstacle or object that causes it. Elevators are a common building item that frequently causes RF shadow because they are made of metal and they move up and down within a shaft. Metal is a material that has high attenuation and reflection values, which means it can block or bounce off wireless signals very effectively. A moving elevator can create dynamic RF shadow that changes depending on its position and direction. Therefore, elevators must be accounted for in coverage plans to ensure adequate WLAN coverage and performance throughout the facility. The other options are not common building items that frequently cause RF shadow or must be accounted for in coverage plans. Wooden doors are not likely to cause RF shadow because they are made of wood, which is a material that has low attenuation and reflection values, which means it can pass through or slightly weaken wireless signals. Carpeted floors are not likely to cause RF shadow because they are made of fabric, which is a material that has low attenuation and reflection values, which means it can pass through or slightly weaken wireless signals. Cubicle partitions are not likely to cause RF shadow because they are made of thin plastic or cardboard, which are materials that have low attenuation and reflection values, which means they can pass through or slightly weaken wireless signals. References: CWNA-109 Study Guide, Chapter 13: Wireless LAN Site Surveys - Types and Processes , page 433
Question 66:
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.
Correct Answer: A
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 67:
An IEEE 802.11 amendment is in the daft state. What impact does this draft amendment have on the 802.11 standard?
A. Devices will be released based on the draft amendment and the draft amendment features are part of the standard.
B. No impact: Until an amendment is ratified, it does not become part of the standard.
C. No impact: Draft amendments do not become part of the standard until a working group is formed.
D. The standard is changed to reflect the new capabilities as soon as an amendment enters the draft stage.
Correct Answer: B
An IEEE 802.11 amendment is a proposed change or addition to the existing 802.11 standard, which defines the specifications and protocols for wireless LANs. An amendment goes through several stages of development, such as draft, sponsor ballot, and final approval, before it is ratified by the IEEE Standards Association and becomes part of the standard. Until then, it has no official impact on the standard, although some vendors may release products based on draft amendments to gain a competitive edge or to influence the final outcome of the amendment . References: [CWNA-109 Study Guide], Chapter 1: Overview of Wireless Standards, Organizations, and Fundamentals, page 25; [CWNA-109Study Guide], Chapter 1: Overview of Wireless Standards, Organizations, and Fundamentals, page 23; [IEEE website], IEEE-SA Standards Development Process.
Question 68:
A WLAN is implemented using wireless controllers. The APs must locate the controllers when powered on and connected to the network. Which one of the following methods is commonly used to locate the controllers by the APs?
A. NTP
B. DHCP
C. SNMP
D. GRE
Correct Answer: B
DHCP (Dynamic Host Configuration Protocol) is a commonly used method to locate the controllers by the APs in a WLAN that is implemented using wireless 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 APs 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. This way, the APs can discover the wireless controller and establish a connection with it. Alternatively, the APs can also use other methods to locate the wireless controller, such as DNS (Domain Name System), broadcast or multicast discovery, or manual configuration. References: 1, Chapter 8, page 309; 2, Section 5.2
Question 69:
What statement about the IEEE 802.11-2016 QoS facility is true?
A. 802.11 control frames are assigned to the 802.11 EF priority queue.
B. When the Voice queue has frames awaiting transmission, no data will be transmitted from the Best Effort queue.
C. 802.11 QoS is achieved by giving high priority queues a statistical advantage at winning contention.
D. Four 802.1p user priorities are mapped to eight 802.11 transmit queues.
Correct Answer: C
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. References: , Chapter 10, page 403; , Section 6.1
Question 70:
Your consulting firm has recently been hired to complete a site survey for a company desiring an indoor coverage WI-AN. Your engineers use predictive design software for the task, but the company insists on a pre-design site visit.
What task should be performed as part of the pre-design visit to prepare for a predictive design?
A. Install at least one AP on each side of the exterior walls to test for co-channel interference through these walls
B. Collect information about the company's security requirements and the current configuration of their RADIUS and user database servers
C. Test several antenna types connected to the intended APS for use in the eventual deployment
D. Evaluate the building materials at the facility and confirm that the floor plan documents are consistent with the actual building
Correct Answer: D
A pre-design site visit in preparation for a predictive wireless LAN design is essential for gathering physical and environmental data about the site. The key tasks to be performed during such a visit include:
Evaluating Building Materials: Different materials (concrete, glass, wood, etc.) have varying effects on RF signal propagation. Understanding the materials present helps in accurately predicting how signals will behave within the environment.
Floor Plan Verification: Ensuring that the floor plan documents are an accurate representation of the actual building layout is crucial. Discrepancies between the floor plans and the physical layout can lead to inaccuracies in the predictive
design.
The other options, while potentially valuable in other contexts, are not directly related to preparing for a predictive design:
Installing APs(option A) for testing co-channel interference is more aligned with an active site survey rather than a pre-design visit for a predictive design. Collecting information about security requirements(option B) is important but is not
directly related to the physical aspects of the site that would impact a predictive design.
Testing antenna types(option C) would typically be part of an active site survey or the actual deployment phase, not a pre-design visit for predictive modeling. Therefore, option D is the correct answer, focusing on evaluating physical aspects
crucial for accurate predictive modeling.
References:
CWNA Certified Wireless Network Administrator Official Study Guide:
ExamCWNA-109, by David D. Coleman and David A. Westcott. Best practices for conducting pre-design site visits in wireless network planning.
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