CWNP CWNP Certifications CWNA-108 Questions & Answers

• Question 171:

  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

  Correct Answer: D

  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-108 Official Study Guide, page 77 2: VSWR 3: CWNA-108 Official Study Guide, page 81

• Question 172:

  What security solution is required to be used in place of Open System Authentication for all open network 802.11 implementations in the 6 GHz band?

  A. OWE

  B. Kerberos

  C. WPA3-Enterprise

  D. WPA3-SAE

  Correct Answer: A

• Question 173:

  You are troubleshooting a problem with a new 802.11ax AP. While the AP supports four spatial streams, most clients are only achieving maximum data rates of 150 Mbps. What is the likely cause?

  A. The clients are 802.11n devices

  B. The clients are only two stream 802.11ax clients

  C. Contention caused by an overlapping BSS

  D. Non-Wi-Fi interference in the channel

  Correct Answer: A

  The clients are 802.11n devices. 802.11n devices can only support a maximum of four spatial streams, and the maximum data rate for a single spatial stream is 150 Mbps. Therefore, if most clients are only achieving 150 Mbps, it means they are using only one spatial stream, which is typical for 802.11n devices. To achieve higher data rates, the clients would need to support more spatial streams, which is possible with 802.11ax devices12. The other options are not correct because they do not explain why most clients are only achieving 150 Mbps. Option B is incorrect because two stream 802.11ax clients can achieve data rates of up to 574 Mbps in a 20 MHz channel1. Option C is incorrect because contention caused by an overlapping BSS would affect all clients, not just most of them, and it would also reduce the throughput, not the data rate. Option D is incorrect because non-Wi-Fi interference in the channel would also affect all clients, not just most of them, and it would also cause errors and retransmissions, not lower data rates. References: 1: CWNA-108 Official Study Guide, page 144 2: 802.11ax data rates

• Question 174:

  What is required when operating 802.11ax APS in the 6 GHz band using passphrase- based authentication?

  A. VHT PHY

  B. HT PHY

  C. SAE

  D. CCMP

  Correct Answer: C

  Explanation: SAE (Simultaneous Authentication of Equals) is required when operating 802.11ax APs in the 6 GHz band using passphrase-based authentication. SAE is a secure and robust authentication method that is defined in the IEEE 802.11s amendment and is also known as WPA3-Personal or WPA3-SAE. SAE is based on a cryptographic technique called Dragonfly Key Exchange, which allows two parties to establish a shared secret key using a passphrase, without revealing the passphrase or the key to an eavesdropper or an attacker. SAE also provides forward secrecy, which means that if the passphrase or the key is compromised in the future, it does not affect the security of past communications. SAE is required when operating 802.11ax APs in the 6 GHz band using passphrase-based authentication because of the new regulations and standards that apply to this band. The 6 GHz band is a new frequency band that was opened for unlicensed use by the FCC and other regulatory bodies in 2020. The 6 GHz band offers more spectrum and less interference than the existing 2.4 GHz and 5 GHz bands, which can enable higher performance and efficiency for Wi-Fi devices. However, the 6 GHz band also has some restrictions and requirements that are different from the other bands, such as: The 6 GHz band is divided into two sub-bands: U-NII-5 (5925-6425 MHz) and U- NII-7 (6525-6875 MHz). The U-NII-5 sub-band is 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. The U- NII-7 sub-band is not subject to DFS rules, but it has a lower maximum transmit power limit than the U-NII- 5 sub-band. The Wi-Fi devices that operate in the 6 GHz band are called 6E devices, which stands for Extended Spectrum. 6E devices must support 802.11ax technology, which is also known as Wi-Fi 6 or High Efficiency (HE). 802.11ax is a new standard that improves the performance and efficiency of Wi-Fi networks by using features such as OFDMA (Orthogonal Frequency Division Multiple Access), MU- MIMO (Multi-User Multiple Input Multiple Output), BSS Coloring, TWT (Target Wake Time), and HE PHY and MAC enhancements. The 6E devices that operate in the 6 GHz band must also support WPA3 security, which is a new security protocol that replaces WPA2 and provides stronger encryption and authentication for Wi-Fi networks. WPA3 has two modes: WPA3Personal and WPA3-Enterprise. WPA3-Personal uses SAE as its authentication method, which requires a passphrase to establish a secure connection between two devices. WPA3-Enterprise uses EAP (Extensible Authentication Protocol) as its authentication method, which requires a certificate or a credential to authenticate with a server. Therefore, SAE is required when operating 802.11ax APs in the 6 GHz band using passphrase-based authentication because it is part of WPA3-Personal security, which is mandatory for 6E devices in this band. References: , Chapter 3, page 120; , Section 3.2 9of30

• Question 175:

  Which unit of measurement, as formally defined, is an absolute unit that is used to quantify received signal power levels on a logarithmic scale?

  A. SNI

  B. VSWR

  C. dBm

  D. dBi

  Correct Answer: C

  Explanation: The unit of measurement that is an absolute unit and is used to quantify received signal power levels on a logarithmic scale is dBm. dBm stands for decibel-milliwatt and represents the power level relative to 1 milliwatt (mW). dBm is an absolute unit because it has a fixed reference point and does not depend on the input power level. dBm is used to measure the received signal power levels on a logarithmic scale because it can express large variations in power levels with small numbers and make calculations easier. For example, a 10 dB increase in power level means a 10-fold increase in power, and a 20 dB increase means a 100-fold increase in power. References: [CWNP Certified Wireless Network Administrator Official Study Guide: WNA-107], page 66; [CWNA: Certified Wireless Network Administrator Official Study Guide: WNA-106], page 56.

• Question 176:

  What security option for 802.11 networks supports SAE and requires protected management frames?

  A. WPA

  B. WPA2

  C. WPA3

  D. OWE

  Correct Answer: C

  The security option for 802.11 networks that supports SAE and requires protected management frames is WPA3. WPA3 stands for Wi-Fi Protected Access version 3 and is the latest security standard for WLANs. WPA3 supports two modes: WPA3-Personal and WPA3-Enterprise. WPA3-Personal uses Simultaneous Authentication of Equals (SAE) as the key exchange protocol, which provides stronger protection against offline dictionary attacks and password guessing than WPA2-Personal. WPA3 also requires protected management frames, which are encrypted frames that prevent spoofing, replay, or denial- of-service attacks on management frames such as deauthentication or disassociation frames. WPA, WPA2, and OWE do not support SAE or require protected management frames. References: [CWNP Certified Wireless Network Administrator Official Study Guide: WNA-107], page 307; [CWNA: Certified Wireless Network Administrator Official Study Guide: WNA-106], page 297.

• Question 177:

  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: WNA-107], page 81; [CWNA: Certified Wireless Network Administrator Official Study Guide: WNA-106], page 71.

• Question 178:

  What feature of 802.1 lax (HE) is managed with beacon and trigger frames and is primarily a power management method, but also provides more efficient access to the channel used within a BSS?

  A. TWT

  B. BSS Color

  C. UL-MU-MIMO

  D. OFDMA

  Correct Answer: A

  TWT is the feature of 802.11ax (HE) that is managed with beacon and trigger frames and is primarily a power management method, but also provides more efficient access to the channel used within a BSS. TWT stands for target wake time, which is a mechanism that allows an access point and a client device to negotiate and schedule specific times for data transmission and reception. This enables the client device to enter a low-power sleep mode when it is not expected to communicate with the access point, which saves battery life and reduces power consumption. TWT also reduces contention and interference on the channel used within a BSS, as it coordinates the transmissions of multiple client devices and avoids collisions. TWT is managed with beacon and trigger frames, which are two types of management frames that are used to announce and initiate data exchanges. A beacon frame is a frame that is periodically sent by an access point to advertise its presence, capabilities, and parameters to client devices. A trigger frame is a frame that is sent by an access point or a client device to request or initiate a data transmission with another device. BSS color, UL-MU-MIMO, and OFDMA are other features of 802.11ax (HE) that are not primarily power management methods, but rather performance enhancement methods. BSS color is a feature that assigns a color code to each BSS to differentiate it from other BSSs that use the same channel. This reduces interference and improves spatial reuse of the channel. UL-MU-MIMO is a feature that allows an access point to receive multiple simultaneous transmissions from different client devices using multiple spatial streams. This increases capacity and throughput of the uplink direction. OFDMA is a feature that divides a channel into smaller subchannels called resource units (RUs) that can be allocated to different devices for concurrent transmissions. This increases efficiency and flexibility of the channel utilization. References: CWNA-109 Study Guide, Chapter 10: Wireless LAN Operation, page 323

• Question 179:

  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

  Correct Answer: D

  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: WNA-107], page 226; [CWNA: Certified Wireless Network Administrator Official Study Guide: WNA-106], page 216.

• Question 180:

  A natural disaster has occurred in a remote area that is approximately 57 miles from the response team headquarters. The response team must implement a local wireless network using 802.11 WLAN access points. What is the best method, of those listed, for implementation of a network back-haul for communications across the Internet in this scenario?

  A. 802.11 bridging to the response team headquarters

  B. Cellular/LTE/5G

  C. Turn up the output power of the WLAN at the response team headquarters

  D. Temporary wired DSL

  Correct Answer: B

  Explanation: Cellular/LTE/5G is the best method for implementing a network backhaul for communications across the Internet in a remote area that is affected by a natural disaster. This is because cellular/LTE/5G networks are wireless and do not depend on physical infrastructure that may be damaged or unavailable in such scenarios. Cellular/LTE/5G networks also offer high-speed data transmission and wide coverage area, which are essential for emergency response operations. 802.11 bridging to the response team headquarters is not feasible because it requires line-of-sight and has limited range. Turning up the output power of the WLAN at the response team headquarters is not effective because it may cause interference and does not guarantee reliable connectivity. Temporary wired DSL is not practical because it requires installing cables and equipment that may not be available or accessible in a remote area. References: CWNA- 109 Study Guide, Chapter 7: Wireless LAN Topologies, page 2031