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質問 # 76
Which one of the following portions of information is communicated in the PHY Header?
- A. SNR
- B. Signal strength
- C. Noise
- D. Date rate
正解：D
解説：
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 strength are measured by the receiver based on its own capabilities and environment.
質問 # 77
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 # 78
You are creating a baseline configuration for a pool of 100 laptops related to Wi-Fi.
The laptops have dual- band 802.11ac adapters. They are configured for aggressive roaming.
What additional setting might you configure to ensure they access the WLAN on the channels with the least interference assuming the enterprise WLAN is well-designed?
- A. USB speed
- B. Band preference
- C. 802.11h
- D. Power management
正解：B
質問 # 79
You have received reports of performance problems in a BSS. One specific user is indicating that her downloads are taking a very long time compared to other users around her.
You want to determine if the AP is sending frames multiple times to get through to the user's computer.
Where should you monitor with the protocol analyzer to see retries from the AP in this scenario?
- A. Directly in the middle of the AP and client STA
- B. Very near the AP
- C. Capture from another AP in another BSS
- D. Very near the client STA
正解：B
質問 # 80
You have captured 802.11 traffic using an adapter that includes the radio tap header. You see several frames often called announcement frames in the capture.
What best describes these types of frames?
- A. They are meant to provide information to the network that may result in state changes, but they are not open for rejection
- B. They are used to allow a STA to awake from sleep and for no other reason
- C. They only include beacon and probe request frames
- D. They only include beacon and probe response frames
正解：D
質問 # 81
Which common feature of a Spectrum Analyzer would be the best to help you locate a non-802.11 interference source?
- A. Max hold
- B. Device finder
- C. Min hold
- D. Location filter
正解：B
解説：
Explanation
The device finder is a common feature of a spectrum analyzer that helps locate a non-802.11 interference source. The device finder uses a directional antenna to measure the signal strength of a specific frequency or signal source. By pointing the antenna in different directions, the device finder can indicate the direction and distance of the interference source. The device finder can also filter out other signals that are not related to the interference source. The other options are not correct, as they do not help locate a non-802.11 interference source. Max hold and min hold are features that show the maximum and minimum RF power levels over time,respectively. Location filter is a feature that filters out signals that are not from a specific location or area. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 3: Spectrum Analysis, page 77-78
質問 # 82
How is the length of an AIFS calculated?
- A. AIFSN * Slot Time + SIFS
- B. SIFS + AIFS * Time Unit
- C. SIFS * Slot Time + AIFSN
- D. DIFS + SIFS + AIFSN
正解：A
解説：
Explanation
The length of an AIFS (Arbitration Interframe Space) is calculated by multiplying the AIFSN (Arbitration Interframe Space Number) by the Slot Time and adding the SIFS (Short Interframe Space). An AIFS is a variable interframe space introduced by 802.11e to help prioritize medium access for different Access Categories (ACs). An AC is a logical queue that corresponds to a QoS (Quality of Service) level for different types of traffic. Each AC has a different AIFSN value, which determines how long it has to wait before attempting to access the medium. A lower AIFSN value means a higher priority and a shorter waiting time.
The Slot Time is a fixed value that depends on the PHY type and channel width. The SIFS is the shortest interframe space that is used for high-priority transmissions, such as ACKs or CTSs. The formula for calculating the AIFS length is: AIFS = AIFSN * Slot Time + SIFS. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 7: QoS Analysis, page 194-195
質問 # 83
You are troubleshooting throughput problems for a WLAN cell. The cell is provisioned with an
802.11ac dual-band AP. Users connected with both 5 GHz and 2.4 GHz connections are reporting performance problems. The AP settings are properly optimized. No interface issues have been detected (either co- channel interference or non-Wi-Fi interference) and the number of associated users is low.
What should you analyze to resolve the issue?
- A. The 2.4 GHz radio configuration
- B. The antennas used on the client devices
- C. the Ethernet uplink and the network infrastructure
- D. The 5 GHz radio configuration
正解：C
質問 # 84
You are analyzing a problem with a specific client adapter.
The vendor specifications sheet does not provide detailed information.
What tool can you use to provide the most detailed specification information in many such cases?
- A. Wi-Fi finder
- B. FCC ID Search
- C. WLAN controller
- D. Spectrum analyzer
正解：B
質問 # 85
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 three sub-fields and eight one-bit flags
- C. The Frame Control field is always set to 0
- D. The Frame Control field is used to communicate the duration value
正解：C
解説：
This field is simply used to indicate which protocol version of 802.11 is being used by the frame.
This is always set to "0"
Reference: https://mrncciew.com/2014/09/27/cwap-mac-header-frame-control/
質問 # 86
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 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
- 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 customer should replace all their Bluetooth wireless mice as they are stopping the users on floor 5 from connecting to the wireless network
- D. The customers APs are misbehaving and a technical support case should be open with the vendor
正解：A
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 # 87
What is the function of the PHY Preamble?
- A. To terminate a conversation between transmitter and receiver
- B. Allows the receiver to detect and synchronize with the signal
- C. Carries the NDP used in Transmit Beamforming and MU-MIMO
- D. To set the modulation method for the MPDU
正解：B
解説：
The function of the PHY preamble is to allow the receiver to detect and synchronize with the signal. The PHY preamble is a part of the PPDU that is transmitted before the PHY header and the PSDU. The PHY preamble consists of a series of training fields that help the receiver to adjust its parameters, such as frequency, timing, and gain, to match the incoming signal. The PHY preamble also helps the receiver to estimate the channel conditions and noise level.
質問 # 88
A PHY Header is added to the PSDU at which sub-layer?
- A. PHY
- B. LLC
- C. Network
- D. MAC
正解：A
解説：
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.
質問 # 89
Which statements accurately describe IEEE 802.11 EDCA collision handling in a WMM-compliant infrastructure WLAN? (Choose 2)
- A. Collisions between contending EDCAFs within a QoS STA are resolved within the QoS STA
- B. After frames collide within a QoS STA and the lower priority AC subsequently gains a TXOP, the retry bit in the MAC header must be set to 1 to indicate a retry.
- C. The WMM specification requires use of RTS/CTS as part of the EDCAF within each QoS STA to avoid internal collisions between ACs.
- D. When frames collide within a QoS STA, data frames from lower priority ACs behave (as it relates to contention) as if there were an external collision on the wireless medium.
- E. When a frame transmission on the wireless medium fails, the transmitter may not transmit another frame from any AC or to any destination until the frame experiencing a failure is successfully transmitted or the max retry count for that frame is reached.
正解：A、D
質問 # 90
Where, in a protocol analyzer, would you find an indication that a frame was transmitted as part of an A-MPDU?
- A. A-MPDU flag in the Frame Control Field
- B. A-MPDU flag in the QoS Control Field
- C. The Aggregation flag in the Radio Tap Header
- D. The HT Operation Element
正解：C
解説：
Explanation
In a protocol analyzer, you would find an indication that a frame was transmitted as part of an A-MPDU by looking at the Aggregation flag in the Radio Tap Header. The Radio Tap Header is a pseudo-header that is added by some wireless capture devices to provide additional information about the physical layer characteristics of a frame. The Aggregation flag is one of the fields in this header, and it indicates whether the frame belongs to an A-MPDU or not. If the flag is set to 1, it means that the frame is part of an A-MPDU; if it is set to 0, it means that the frame is not part of an A-MPDU . References: CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 9: PHY Layer Frame Formats andTechnologies, page 303; CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 9: PHY Layer Frame Formats and Technologies, page 304.
質問 # 91
When 802.11 standard compliant AES-CCMP security is being used with IPSec/ESP for layered security, what will a WLAN protocol analyzer see as the security mechanism in use when a user browses to an HTTPS secured web page?
- A. AES-CCMP
- B. IPSec/ESP
- C. SSLv3
- D. AES-CCMP, IPSec/ESP, AND SSLv3
- E. AES-CCMP and IPSec/ESP
正解：A
質問 # 92
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：
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.
質問 # 93
Which one of the following is an advantage of using display filters that is not an advantage of capture-time filters?
- A. Once created they are reusable for later captures
- B. They only hide the packets from view and the filtered packets can be enabled for view later
- C. Multiple of them can be applied simultaneously
- D. They allow for focused analysis on just the packets of interest
正解：B
解説：
Display filters are applied after the capture is completed and they only hide the packets from view. The filtered packets are still present in the capture file and can be enabled for view later by changing or removing the display filter. This is an advantage over capture-time filters, which discard the packets that do not match the filter criteria and cannot be recovered later.
質問 # 94
What is encrypted within the third message of the 4-Way Handshake?
- A. PMK
- B. PTK
- C. GTK
- D. GMK
正解：C
解説：
Explanation
The GTK (Group Temporal Key) is encrypted within the third message of the 4-Way Handshake. The 4-Way Handshake is a process that establishes a secure connection between a STA (station) and an AP (access point) using WPA2 (Wi-Fi Protected Access 2), which is a security protocol that uses AES-CCMP (Advanced Encryption Standard-Counter Mode CBC-MAC Protocol) as its encryption algorithm. The 4-Way Handshake consists of four messages that are exchanged between the STA and the AP. The first message is sent by the AP to the STA, containing the ANonce (Authenticator Nonce), which is a random number generated by the AP.
The second message is sent by the STA to the AP, containing the SNonce (Supplicant Nonce), which is a random number generated by the STA, and the MIC (Message Integrity Code), which is a value that verifies the integrity of the message. The third message is sent by the AP to the STA, containing the GTK, which is a key that is used to encrypt and decrypt multicast and broadcast data frames, and the MIC. The GTK is encrypted with the KEK (Key Encryption Key), which is derived from the PTK (Pairwise Temporal Key). The PTK is a key that is used to encrypt and decrypt unicast data frames, and it is derived from the PMK (Pairwise Master Key), the ANonce, and the SNonce. The fourth message is sent by the STA to the AP, containing only the MIC, to confirm the completion of the 4-Way Handshake. The other options are not correct, asthey are not encrypted within the third message of the 4-Way Handshake. The PMK is a key that is derived from a passphrase or obtained from an authentication server, and it is not transmitted in any message of the 4-Way Handshake. The PTK is a key that is derived from the PMK, the ANonce, and the SNonce, and it is not transmitted in any message of the 4-Way Handshake. The GMK (Group Master Key) is a key that is generated by the AP and used to derive the GTK, and it is not transmitted in any message of the 4-Way Handshake. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 8: Security Analysis, page 211-213
質問 # 95
You are explaining capacity planning to another engineer assisting you on a WLAN implementation project.
As part of the explanation, you provide the following formula:
C = B * log2(1 + S/N).
What does this formula define?
- A. Maximum signal strength of a channel
- B. Bandwidth capabilities of a channel
- C. The WEP encryption algorithm
- D. Minimum signal strength for a data rate
正解：B
質問 # 96
You are performing a multiple adapter channel aggregation capture to troubleshoot a VoIP roaming problem and would like to measure the roaming time from the last VoIP packet sent on the old AP's channel to the first VoIP packet sent on the new AP's channel. Which timing column in the packet view would measure this for you?
- A. Absolute
- B. Delta
- C. Relative
- D. Roaming
正解：B
解説：
Explanation
Delta is the timing column in the packet view that measures the time difference between two consecutive packets in a capture file. Delta can be used to measure the roaming time from the last VoIP packet sent on the old AP's channel to the first VoIP packet sent on the new AP's channel by selecting these two packets and looking at their delta values. The other timing columns are not suitable for this measurement because they do not show the time difference between two specific packets. Roaming is a column that shows whether a packet belongs to a roaming event or not. Relative is a column that shows the time elapsed since the beginning of the capture file. Absolute is a column that shows the date and time when a packet was captured5 References:
CWAP-404 Study Guide, Chapter 2: Protocol Analysis, page 57
CWAP-404 Objectives, Section 2.4: Analyze timing values
質問 # 97
What types of wireless systems are illustrated?
- A. An ERP IEEE 802.11 system using channel 6 and Bluetooth v1.2 discovery
- B. A Bluetooth v2.0 file transfer and a 40 MHz HT AP on channels 11, 7 (primary, secondary)
- C. An 802.11 HR/DSSS system using channel 2 and a digital FHSS phone
- D. A 2.4 GHz cordless phone on channel 14 and a wireless RFID reader
正解：A
質問 # 98
What is used to respond with an uplink transmission to an MU-RTS trigger frame in the 802.11ax PHY?
- A. HE MU PPDU
- B. VHT PPDU
- C. HE SU PPDU
- D. HE TB PPDU
正解：D
解説：
Explanation
An HE TB PPDU (High Efficiency Trigger-Based Packet Data Unit) is used to respond with an uplink transmission to an MU-RTS trigger frame in the 802.11ax PHY (Physical Layer). An MU-RTS trigger frame is a frame that initiates a multi-user transmission opportunity (MU-TXOP) by requesting multiple stations (STAs) to send clear-to-send (CTS) frames on different spatial streams or resource units (RUs). An HE TB PPDU is a frame that contains data from multiple STAs that have been allocated RUs by an MU-RTS trigger frame or another type of trigger frame. An HE SU PPDU (High Efficiency Single User Packet Data Unit) is a frame that contains data from a single STA using all available spatial streams or RUs. An HE MU PPDU (High Efficiency Multi User Packet Data Unit) is a frame that contains data from multiple STAs using different spatial streams or RUs without being triggered by another frame. A VHT PPDU (Very High Throughput Packet Data Unit) is a frame that uses the 802.11ac PHY and does not support multi-user transmissions.References:
CWAP-404 Study Guide, Chapter 3: 802.11 MAC Layer Frame Formats and Technologies, page 101 CWAP-404 Objectives, Section 3.4: Analyze multi-user transmissions CWAP-404 Study Guide, Chapter 3: 802.11 MAC Layer Frame Formats and Technologies, page 99
質問 # 99
Which statements are true regarding Beacons from an AP in an HT infrastructure BSS that is configured with multiple WLAN profiles? (Choose 3)
- A. The Beacon interval must be the same for all WLANs (SSIDs) supported by a single AP
- B. The Destination Address is always FF:FF:FF:FF:FF:FF.
- C. Beacons can be disabled for security purposes.
- D. All Beacons generated by APs contain a TIM information element.
- E. The BSSID and Source Address are always the same.
- F. The Receiver address and the BSSID are always the same.
- G. When the SSID is "hidden," the ESS subfield of the Capability Information field distinguishes one BSS from another.
正解：B、D、E
質問 # 100
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