[2024年01月最新リリース] 合格できるCWAP-404試験にはリアル問題とアンサー
合格できるCWAP-404レビューガイド、頼もしいCWAP-404テストエンジン
質問 # 25
Which one of the statements regarding the Frame Control field in an 802.11 MAC header is true?
- A. Only Control frames have a Frame Control field
- B. The Frame Control field contains subfields, and soma in 1-bit flags
- C. The Frame Control field is used to communicate the duration value
- D. The Frame Control field is always set to 0
正解：B
解説：
Explanation
The statement that the Frame Control field contains subfields, and some 1-bit flags is true. The Frame Control field is a 2-byte field in the MAC header that contains information about the type, subtype, and characteristics of a frame. The Frame Control field is divided into several subfields, each with a specific function and length.
Some of these subfields are 1-bit flags, which can be set to 0 or 1 to indicate a certain condition or status. For example, the To DS and From DS subfields are 1-bit flags that indicate whether a frame is destined for or originated from the DS (Distribution System). The other statements are not true, as they do not describe the Frame Control field correctly. All types of frames (management, control, and data) have a Frame Control field, not just control frames. The Frame Control field is not used to communicate the duration value, which is a separate field in the MAC header. The Frame Control field is not always set to 0, as it varies depending on the type, subtype, and characteristics of each frame. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 5: 802.11 MAC Sublayer, page 113-114
質問 # 26
What is the difference between a Data frame and a QoS-Data frame?
- A. QoS Data frames include a DSCP control field
- B. QoS Data frames include a QoS control field
- C. QoS Data frames include an 802.1Q VLAN tag
- D. QoS Data frames include a QoS information element
正解：B
解説：
Explanation
The difference between a Data frame and a QoS-Data frame is that QoS Data frames include a QoS control field. A Data frame is a type of data frame that is used to carry user data or upper layer protocol data between STAs and APs. A QoS Data frame is a type of data frame that is used to carry user data or upper layer protocol data between STAs and APs that support QoS (Quality of Service) features. QoS features allow different types of traffic to be prioritized and handled differently according to their QoS requirements, such as delay, jitter, throughput, etc. QoS Data frames include a QoS control field in their MAC header, which contains information such as traffic identifier (TID), queue size (TXOP), acknowledgment policy (ACK), etc., that are used for QoS purposes. The other options are not correct, as they do not describe the difference between Data and QoS Data frames. QoS Data frames do not include a DSCP (Differentiated Services Code Point) control field, which is part of the IP header in the network layer, not the MAC header in the data link layer. QoS Data frames do not include a QoS information element (IE), which is part of some management frames that indicate QoS capabilities or parameters, not data frames. QoS Data frames do not include an 802.1Q VLAN tag, which is part of some Ethernet frames that indicate VLAN membership or priority, not wireless frames. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 5: 802.11 MAC Sublayer, page 118-119
質問 # 27
A PHY Header is added to the PSDU at which layer?
- A. PHY
- B. MAC
- C. LLC
- D. Network
正解：A
解説：
Explanation
A PHY header is added to the PSDU at the PHY layer. A PHY header is a part of the PPDU that contains information such as modulation, coding, and data rate. The PHY header is added by the PHY layer when it converts a PSDU to a PPDU for transmission, or removed by the PHY layer when it converts a PPDU to a PSDU for reception. The other layers do not add or remove a PHY header. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 4: 802.11 Physical Layer, page 97-98
質問 # 28
What interframe space would be expected between a CIS and a Data frame?
- A. AIFS
- B. SIFS
- C. PIFS
- D. DIFS
正解：B
解説：
Explanation
The interframe space that would be expected between a CTS (Clear to Send) and a Data frame is SIFS (Short Interframe Space). A SIFS is the shortest interframe space that is used for high-priority transmissions, such as ACKs (Acknowledgements), CTSs, or data frames that are part of a fragmentation or aggregation process. A SIFS is a fixed value that depends on the PHY type and channel width. A CTS and a Data frame are part of a virtual carrier sense mechanism called RTS/CTS (Request to Send/Clear to Send), which is used to avoid collisions and hidden node problems in wireless transmissions. When a STA (station) wants to send a data frame, it first sends an RTS frame to the intended receiver, indicating the duration of the transmission. The receiver then responds with a CTS frame, also indicating the duration of the transmission. The other STAs in the vicinity hear either the RTS or the CTS frame and update their NAV (Network Allocation Vector) timers accordingly, deferring their access to the medium until the transmission is over. The sender then sends the data frame after waiting for a SIFS, followed by an ACK frame from the receiver after another SIFS. The other options are not correct, as they are not used between a CTS and a Data frame. A PIFS (PCF Interframe Space) is used for medium access by the PCF (Point Coordination Function), which is an optional and rarely implemented polling-based mechanism that provides contention-free service for time-sensitive traffic. An AIFS (Arbitration Interframe Space) is used for medium access by different ACs (Access Categories), which are logical queues that correspond to different QoS (Quality of Service) levels for different types of traffic. An AIFS is a variable interframe space that depends on the AIFSN (Arbitration Interframe Space Number) value of each AC. A DIFS (Distributed Interframe Space) is used for medium access by the DCF (Distributed Coordination Function), which is the default and mandatory contention-based mechanism that provides best-effort service for normal traffic. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 6: 802.11 Frame Exchanges, page 166-167; Chapter 7: QoS Analysis, page 194-195
質問 # 29
ABC International has installed a new smart ZigBee controlled lighting system. However, the network team is concerned that this new system will interfere with the existing WLAN and has asked you to investigate the impact of the two systems operating simultaneously in the 2.4 GHz band. When performing Spectrum Analysis, which question could you answer by looking at the FFT plot?
- A. Is the ZigBee system using more than 50% of the available airtime?
- B. Is the WLAN corrupting ZigBee system messages?
- C. Is the ZigBee system causing an increase in WLAN retries?
- D. Do the ZigBee channels used by the lighting system overlap with the WLAN channels?
正解：D
解説：
Explanation
The FFT plot is a spectrum analysis plot that shows the RF power present at a particular frequency over a short period of time. It can help identify the sources and characteristics of RF signals in the spectrum. By looking at the FFT plot, you can determine which ZigBee channels are used by the lighting system and whether they overlap with the WLAN channels in the 2.4 GHz band. ZigBee channels are 5 MHz wide and WLAN channels are 20 MHz or 40 MHz wide, so there is a possibility of overlap and interference between them. The other questions cannot be answered by looking at the FFT plot alone, as they require other types of plots or analysis tools, such as duty cycle plot, airtime utilization plot, or protocol analyzer. References: [Wireless Analysis Professional Study Guide], Chapter 3: Spectrum Analysis, page 69-70
質問 # 30
Why would a STA that supports 802.11k Radio Measurement send a Neighbor Request to an AP?
- A. To request a list of neighboring STAs which enables the STA to better pick the right protection mechanisms
- B. To request a list of neighboring APs which the STA can use as roaming candidates
- C. To learn about neighboring interference sources and tune its RF radio accordingly
- D. To inform the current AP about the STA's intent to roam to a neighboring AP, ensuring a seamless handover
正解：B
解説：
Explanation
A STA that supports 802.11k Radio Measurement would send a Neighbor Request to an AP to request a list of neighboring APs which the STA can use as roaming candidates. A Neighbor Request is an Action frame that contains a subelement specifying the type of information that the STA wants to receive from the AP. A Neighbor Report is an Action frame that contains a subelement with a list of neighboring APs that match the criteria specified in the Neighbor Request. The Neighbor Report provides information such as BSSID, channel, operating class, and PHY type of each neighboring AP. This information helps the STA to perform intelligent roaming decisions based on signal quality, load, and compatibility . References: CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 12: 802.11k/v/r/u/w/ai Amendments, page 434; CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 12: 802.11k/v/r/u/w/ai Amendments, page 435.
質問 # 31
How many frames make up the Group Key Handshake excluding any Ack frames that may be required?
- A. 0
- B. 1
- C. 2
- D. 3
正解：B
解説：
Explanation
The Group Key Handshake consists of two frames excluding any Ack frames that may be required. The Group Key Handshake is used to distribute and update the Group Temporal Key (GTK) for encrypting broadcast and multicast traffic. The AP initiates the Group Key Handshake by sending a Group Key Message 1 frame to a STA, which contains the new GTK and other information. The STA responds with a Group Key Message 2 frame to the AP, which confirms the receipt of the GTK and other information. After this, both the AP and the STA can use the new GTK for encryption and decryption of broadcast and multicast traffic . References:
CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 7: 802.11 Security, page 246; CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 7: 802.11 Security, page 247.
質問 # 32
As a wireless network consultant you have been called in to troubleshoot a high-priority issue for one of your customers. The customer's office is based on two floors within a multi-tenant office block. On one of these floors (floor 5) users cannot connect to the wireless network. During their own testing the customer has discovered that users can connect on floor 6 but not when they move to the floor 5. This issue is affecting all users on floor 5 and having a negative effect on productivity.
To troubleshoot this issue, you perform both Spectrum and Protocol Analysis. The Spectrum Analysis shows the presence of Bluetooth signals which you have identified as coming from wireless mice. In the protocol analyzer you see the top frame on the network is Deauthentication frames. On closer investigation you see that the Deauthentication frames' source addresses match the BSSIDs of your customers APs and the destination address is FF:FF:FF:FF:FF:FF:FF.
What do you conclude from this troubleshooting exercise?
- A. The customer should replace all their Bluetooth wireless mice as they are stopping the users on floor 5 from connecting to the wireless network
- B. The CCI from the APs on the floor 4 is the problem and you need to ask the tenant below to turn down their APs Tx power
- C. The customers APs are misbehaving and a technical support case should be open with the vendor
- D. The users on floor 5 are being subjected to a denial of service attack, as this is happening across the entire floor it is likely to be a misconfigured WIPS solution belonging to the tenants on the floor below
正解：D
解説：
Explanation
The users on floor 5 are being subjected to a denial of service attack, as this is happening across the entire floor it is likely to be a misconfigured WIPS solution belonging to the tenants on the floor below. This is because the Deauthentication frames have a source address that matches the BSSIDs of the customer's APs and a destination address that is a broadcast address (FF:FF:FF:FF:FF:FF). This indicates that someone is sending spoofed Deauthentication frames to all STAs associated with the customer's APs, causing them to disconnect from the wireless network. This is a common type of DoS attack on wireless networks, and it could be caused by a rogue device or a WIPS solution that is configured to protect the wireless network of another tenant on the floor below12. References: CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 13: Troubleshooting Common Wi-Fi Issues, page 4961; CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 14: Troubleshooting Tools, page 5272.
質問 # 33
How does a VoIP Phone, using WMM Power Save, request data frames buffered at the AP?
- A. The VoIP phone sets the More Data bit in the MAC Header to 1
- B. The VoIP phone transmits a trigger frame, which is a QoS Null frame or a QoS Data frame
- C. The VoIP phone transmits a WMM Action frame
- D. The VoIP phone transmits a PS-Poll frame
正解：B
解説：
Explanation
A VoIP phone, using WMM Power Save, requests data frames buffered at the AP by transmitting a trigger frame, which is a QoS Null frame or a QoS Data frame. WMM Power Save is a power saving mode that allows a STA (station) to conserve battery power by periodically sleeping and waking up. WMM Power Save is based on WMM (Wi-Fi Multimedia), which is a QoS (Quality of Service) enhancement that provides prioritized and differentiated access to the medium fordifferent types of traffic. When a STA sleeps, it cannot receive any data frames from the AP, so it informs the AP of its power save status by setting a bit in its MAC header. The AP then buffers any data frames destined for the sleeping STA until it wakes up. When a STA wakes up, it sends a trigger frame to the AP, indicating its AC (Access Category), which is a logical queue that corresponds to its QoS level. A trigger frame can be either a QoS Null frame or a QoS Data frame, depending on whether it has any payload or not. The AP then responds with one or more data frames from the same AC as the trigger frame, followed by an ACK or BA (Block Acknowledgement) frame from the STA. The other options are not correct, as they are not used by a VoIP phone using WMM Power Save to request data frames buffered at the AP. A PS-Poll (Power Save Poll) frame is used by a STA using legacy power save mode, not WMM Power Save mode, to request data frames buffered at the AP. A PS-Poll frame does not indicate any AC or QoS information. Setting the More Data bit in the MAC header to 1 does not request any data frames from the AP, but indicates that there are more data frames to be sent by the STA or received by the STA.
Transmitting a WMM Action frame does not request any data frames from the AP, but performs various management actions related to WMM features, such as admission control, parameter update, etc. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 7: QoS Analysis, page
198-199
質問 # 34
When configuring a long-term, forensic packet capture and saving all packets to disk which of the following is not a consideration?
- A. Total capture storage space
- B. Individual trace file size
- C. Real-time packet decodes
- D. Analyzer location
正解：C
解説：
Explanation
Real-time packet decodes are not a consideration when configuring a long-term, forensic packet capture and saving all packets to disk. Real-time packet decodes are useful for live analysis and troubleshooting, but they consume CPU and memory resources that could affect the performance of the capture process. For a long-term, forensic packet capture, it is more important to consider the analyzer location, the total capture storage space, and the individual trace file size. These factors affect the quality and quantity of the captured packets and the ease of post-capture analysis34 References:
CWAP-404 Study Guide, Chapter 2: Protocol Analysis, page 49
CWAP-404 Objectives, Section 2.1: Configure protocol analyzers
質問 # 35
The network administrator at ABC Engineering has taken a large packet capture from one of their APs running in monitor mode. She has very little knowledge of 802.11 protocols but would like to use the capture file to evaluate the overall health and performance of their wireless network. When she asks your advice, which tool do you recommend she opens the packet capture file with?
- A. Python
- B. Capture visualization tool
- C. WLAN scanner
- D. Spectrum analyzer
正解：B
解説：
Explanation
A capture visualization tool is a software application that can open a packet capture file and display various graphs, charts, tables, and statistics that illustrate the characteristics and behavior of the wireless network. A capture visualization tool can help a network administrator with little knowledge of 802.11 protocols to evaluate the overall health and performance of their wireless network by providing a visual and intuitive representation of the captured data. A spectrum analyzer is a hardware device that measures the radio frequency signals in a given frequency range and displays their amplitude, frequency, and modulation. A spectrum analyzer can help identify sources of interference and noise in the wireless environment, but it cannot open a packet capture file. Python is a programming language that can be used to write scripts or applications that manipulate or analyze packet capture files, but it requires coding skills and knowledge of
802.11 protocols. A WLAN scanner is a software application that scans for available wireless networks and displays information such as SSID, BSSID, channel, signal strength, security type, and vendor. A WLAN scanner can help discover wireless networks and their basic parameters, but it cannot open a packet capture file345 References:
CWAP-404 Study Guide, Chapter 2: Protocol Analysis, page 63
CWAP-404 Objectives, Section 2.5: Use capture visualization tools
CWAP-404 Study Guide, Chapter 4: Spectrum Analysis and Troubleshooting, page 117 CWAP-404 Objectives, Section 4.1: Use spectrum analysis tools CWAP-404 Study Guide, Chapter 2: Protocol Analysis, page 33 CWAP-404 Objectives, Section 2.2: Analyze field values
質問 # 36
Which one of the following is not a valid acknowledgement frame?
- A. RTS
- B. Ack
- C. CTS
- D. Block Ack
正解：A
解説：
Explanation
RTS is not a valid acknowledgement frame. RTS stands for Request To Send, and it is a control frame that is used to initiate an RTS/CTS exchange before sending a data frame. The purpose of an RTS/CTS exchange is to reserve the medium for a data transmission and avoid collisions with hidden nodes. An acknowledgement frame is a control frame that is used to confirm the successful reception of a data frame or a block of data frames. The valid acknowledgement frames are CTS (Clear To Send), Ack (Acknowledgement), and Block Ack (Block Acknowledgement) . References: CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 6: MAC Sublayer Frame Exchanges, page 186; CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 6: MAC Sublayer Frame Exchanges, page 187; CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 6: MAC Sublayer Frame Exchanges, page 189; CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 6: MAC Sublayer Frame Exchanges, page 190.
質問 # 37
Protocol analyzers may present field values in either binary, decimal or hexadecimal. What preceeds a hexadecimal value to indicate it is hexadecimal?
- A. 0x
- B. 16x
- C. HEX
- D. %
正解：A
解説：
Explanation
A hexadecimal value is a value that uses base 16 notation, which means it can have digits from 0 to 9 and letters from A to F. A hexadecimal value is usually preceded by 0x to indicate that it is hexadecimal and not decimal or binary. For example, 0x0A is hexadecimal for 10 in decimal or 00001010 in binary. The other options are not valid prefixes for hexadecimal values.References:
CWAP-404 Study Guide, Chapter 2: Protocol Analysis, page 35
CWAP-404 Objectives, Section 2.2: Analyze field values
質問 # 38
Using a portable analyzer you perform a packet capture next to a client STA and you can see that the STA is associated to a BSS. You observe the STA sending packets to the AP and the AP sending packets to the STA.
Less than 2% of all packets are retransmissions. You move to capture packets by the AP and, while the retry rate is still less than 2%, you now only see unidirectional traffic from the AP to the client. How do you explain this behavior?
- A. The portable analyzer has a lower receive sensitivity than the AP and while it can't capture the packets from the client STA, the AP can receive them OK
- B. The portable analyzer is too close to the AP causing CCI, blinding the AP to the clients packets
- C. The STA is transmitting data using more spatial streams than the potable analyzer can support
- D. There is a transmit power mismatch between the client and the AP and while the client can hear the APs traffic, the AP cannot hear the client
正解：A
解説：
Explanation
Receive sensitivity is the minimum signal level that a receiver can detect and decode. Different devices may have different receive sensitivity levels depending on their hardware specifications and antenna configurations.
In this scenario, the portable analyzer has a lower receive sensitivity than the AP, meaning that it requires a stronger signal to capture the packets from the client STA. The AP, on the other hand, has a higher receive sensitivity and can receive the packets from the client STA even if they have a weaker signal. This explains why the portable analyzer can only see unidirectional traffic from the AP to the client when capturing near the AP5 References:
CWAP-403 Study Guide, Chapter 4: PHY Layer Analysis, page 121
CWAP-403 Objectives, Section 4.3: Analyze PHY layer metrics
質問 # 39
Which one of the following portions of information is communicated by bits in the PHY Header?
- A. Signal strength
- B. Data rate
- C. SNR
- D. Noise
正解：B
解説：
Explanation
One of the information that is communicated by bits in the PHY header is data rate. Data rate is the speed at which data is transmitted or received over the wireless medium. Data rate depends on factors such as modulation, coding, channel width, spatial streams, and guard interval. Data rate is indicated by bits in different fields of the PHY header, depending on the type of PPDU (e.g., OFDM, HT, VHT, HE). The receiver uses these bits to determine how to decode and demodulate the rest of the PPDU. The other options are not correct, as they are not communicated by bits in the PHY header. SNR (Signal-to-Noise Ratio), noise, and signal strengthare measured by the receiver based on its own capabilities and environment. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 4: 802.11 Physical Layer, page 101-105
質問 # 40
What is the function of 802.11 Management frames?
- A. Manage the flow of data
- B. Communicate configuration changes between WLAN controller and APs
- C. Manage the BSS
- D. Prioritize network administration traffic
正解：C
解説：
Explanation
The function of 802.11 management frames is to manage the BSS. A BSS (Basic Service Set) is a group of STAs (stations) that share a common SSID (Service Set Identifier) and communicate with each other through an AP (access point) or directly in an ad hoc mode. Management frames are one of the three types of 802.11 frames, along with control and data frames. Management frames are used to establish, maintain, and terminate associations between STAs and APs, as well as to advertise and discover BSSs, exchange security information, report errors, and perform other management functions. The other options are not correct, as they are not functions of 802.11 management frames. Prioritizing network administration traffic, communicating configuration changes between WLAN controller and APs, and managing the flow of data are functions of other types of frames or protocols. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 5: 802.11 MAC Sublayer, page 120-121
質問 # 41
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