CWAP-404のPDFで合格させるスゴ問題集でCWAP-404最新のリアル試験問題
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質問 # 70
What does the value of the Listen Interval field in an Association Request frame indicate?
- A. How long a STA performing active scanning will listen for Probe Responses before changing channels
- B. How long a STA waits for an Ack before retransmitting the frame
- C. How often a STA will go off channel to look for other BSSs
- D. How often a STA in power save mode wakes up to listen to Beacon frames
正解：D
解説：
Explanation
The value of the Listen Interval field in an Association Request frame indicates how often a STA in power save mode wakes up to listen to Beacon frames. The Listen Interval is expressed in units of Beacon Intervals (typically 100 TU or 102.4 ms). For example, if the Listen Interval is set to 10, it means that the STA will wake up every 10 Beacon Intervals (or about 1 second) to check for buffered frames at the AP. The Listen Interval is used by the AP to determine how long it can hold frames for a STA in power save mode before discarding them . References: CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 6: MAC Sublayer Frame Exchanges, page 197; CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 6: MAC Sublayer Frame Exchanges, page 198.
質問 # 71
An RTS frame should be acknowledged by which frame?
- A. Ack
- B. Block Ack
- C. CTS
- D. RTS-Ack
正解：C
解説：
Explanation
An RTS (Request to Send) frame should be acknowledged by a CTS (Clear to Send) frame. An RTS and CTS frame are types of control frames that are used to implement a virtual carrier sense mechanism called RTS/CTS. RTS/CTS is a technique that helps 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, followed by an ACK (Acknowledgement) frame from the receiver. The other options are not correct, as they are not used to acknowledge an RTS frame. An ACK frame is used to acknowledge a data frame, not an RTS frame. An RTS-Ack frame does not exist, as there is no such type of control frame in 802.11. A Block Ack (BA) frame is used to acknowledge multiple data frames in a single frame, not an RTS frame. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 6: 802.11 Frame Exchanges, page 166-167
質問 # 72
In the analyzer trace shown, the TBTT is nominally 102.5 milliseconds.
Why does the Beacon transmission interval vary?
- A. The access point must arbitrate to gain access to the RF medium in order to transmit a Beacon.
- B. This trace shows an HT network where HR/DSSS nodes are active on the network. The access point is changing slot times from short to long as needed.
- C. Beacon frames vary in size, and therefore some take slightly longer to send than others.
- D. The DCF Interframe space (DIFS) is nominally 50 µs, but typically varies by as much as 10 µs, which causes delays in Beacons.
正解：A
質問 # 73
How is the length of an AIFS is calculated?
- A. SIFS * Slot Time + AIFSN
- B. AIFSN * Slot Time + SIFS
- C. SIFS + AIFS * Time Unit
- D. DIFS + SIFS + AIFSN
正解：B
解説：
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.
質問 # 74
How does a VoIP Phone, using WMM Power Save, request data frames buffered at the AP?
- A. The VoIP phone transmits a trigger frame, which is a QoS Null frame or a QoS Data frame
- B. The VoIP phone transmits a PS-Poll frame
- C. The VoIP phone The VoIP transmits a WMM Action frame
- D. The VoIP phone sets the More Data bit in the MAC Header to 1
正解：A
解説：
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 for different 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.
質問 # 75
What should the To DS and From DS flags be to set to in an Association Response frame?
- A. To DS = 0, From DS = 0
- B. To DS = 0, From DS = 1
- C. To DS = 1, From DS = 1
- D. To DS = 1, From DS = 0
正解：B
解説：
The To DS and From DS flags should be set to 0 in an Association Response frame. An Association Response frame is a type of management frame that is transmitted by an AP to accept or reject an association request from a STA. The To DS (To Distribution System) and From DS (From Distribution System) flags are two bits in the Frame Control field of the MAC header that indicate whether a frame is destined for or originated from the DS (Distribution System), which is a system that connects multiple BSSs together. The To DS and From DS flags can have four possible combinations: 00, 01, 10, or 11. For an Association Response frame, which is sent from an AP to a STA within a BSS, both flags should be set to 0.
質問 # 76
Which one of the following is required for Wi-Fi integration in laptop-based Spectrum Analyzer software in addition to the spectrum analysis adapter?
- A. SNMP read credentials to the WLAN controller or APs
- B. A directional antenna
- C. A firmware upgrade for the spectrum analysis adapter
- D. An 802.11 wireless adaptor
正解：D
解説：
Explanation
An 802.11 wireless adaptor is required for Wi-Fi integration in laptop-based spectrum analyzer software in addition to the spectrum analysis adapter. The spectrum analysis adapter is a hardware device that captures the RF signals in the wireless environment and sends them to the spectrum analyzer software for analysis and display. The 802.11 wireless adapter is a hardware device that connects the laptop to the wireless network and allows the spectrum analyzer software to correlate the RF data with the Wi-Fi data, such as SSID, channel, and BSSID. This enables the spectrum analyzer software to provide more context and insight into the spectrum activity and its impact on the Wi-Fi network. A firmware upgrade for the spectrum analysis adapter is not required for Wi-Fi integration, but it may be needed to fix bugs or add features to the device. A directional antenna is an antenna that focuses the RF energy in a specific direction and has a high gain and a narrow beamwidth. A directional antenna can be used with a spectrum analysis adapter to pinpoint the location or source of interference or noise in the wireless environment, but it is not required for Wi-Fi integration. SNMP read credentials to the WLAN controller or APs are not required for Wi-Fi integration, but they may be useful for obtaining additional information about the wireless network configuration and performance from the network devices.References:
CWAP-404 Study Guide, Chapter 4: Spectrum Analysis and Troubleshooting, page 123 CWAP-404 Objectives, Section 4.2: Integrate Wi-Fi data with spectrum analysis data CWAP-404 Study Guide, Chapter 4: Spectrum Analysis and Troubleshooting, page 131
質問 # 77
What is the difference between a Data frame and a QoS-Data frame?
- A. QoS Data frames include a QoS information element
- B. QoS Data frames include a DSCP control field
- C. QoS Data frames include a QoS control field
- D. QoS Data frames include an 802.1Q VLAN tag
正解：C
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 # 78
Given: Your network consists of HT and ERP access points, and you are implementing VoWiFi with support for U-APSD.
When an ERP handset operating in WMM Power Save mode with a ReceiveDTIMs parameter of TRUE receives a Beacon containing a DTIM indicating queued broadcast traffic, what task is the handset required to perform?
- A. The handset must send a PS-Poll frame to the access point for every broadcast frame it receives with the More Data bit set to one.
- B. The handset must broadcast a CTS-to-Self frame indicating the station's need to control the medium long enough to receive all of the broadcast frames.
- C. The handset is to remain awake to receive the broadcast frame(s) following the Beacon that contains the DTIM.
- D. The handset must arbitrate for the medium and immediately issue an RTS directed to the access point with the NAV set to a value of 32,768.
正解：C
質問 # 79
A new firmware has been released for the AP model you use in your WLAN.
You have more than 120 of these APs installed.
What is a good reason for applying a firmware update on an enterprise AP?
- A. Enable the short guard interval
- B. Enable new security features and patch vulnerabilities
- C. Disable lower data rates
- D. Enable 4x4:4 spatial streams on a 3x3:3 AP
正解：B
質問 # 80
An RST frame should be acknowledged by which frame?
- A. Ack
- B. Block Ack
- C. CTS
- D. RTS-Ack
正解：C
解説：
An RTS (Request to Send) frame should be acknowledged by a CTS (Clear to Send) frame. An RTS and CTS frame are types of control frames that are used to implement a virtual carrier sense mechanism called RTS/CTS. RTS/CTS is a technique that helps 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, followed by an ACK (Acknowledgement) frame from the receiver. The other options are not correct, as they are not used to acknowledge an RTS frame. An ACK frame is used to acknowledge a data frame, not an RTS frame. An RTS-Ack frame does not exist, as there is no such type of control frame in 802.11. A Block Ack (BA) frame is used to acknowledge multiple data frames in a single frame, not an RTS frame.
質問 # 81
Many access points support IEEE 802.1Q VLAN tagging. When analyzing a WLAN system using IEEE 802.1Q tags, where can the VLAN tag number be seen?
- A. In the Ethernet header on the wired port of the access point
- B. In the Beacon Management frame's Capabilities fixed field
- C. In the Sequence Control field of the MSDU
- D. In the PLCP header's Service field
- E. In the Frame Control field of the MPDU header
正解：A
質問 # 82
You are repairing a misconfiguration in WMM settings on an AP.
The aCWmin and aCWmax values were all changed.
What is the default aCWmax for AC_BK?
- A. 0
- B. 1
- C. 2
- D. 3
正解：B
質問 # 83
What is the Extended IFS used in 802.11 contention?
- A. When the lower data rates are used and you want the fastest medium access times
- B. When a frame reception begins but the received frame is incomplete or corrupted based on the FCS
- C. When 802.11ac must coexist with 802.11n
- D. When the higher data rates are used and you want the fastest medium access times
正解：C
質問 # 84
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 BSSISs 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 customers APs are misbehaving and a technical support case should be open with the vendor
- B. 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
- C. The CCI from the APs on the floor 4 is the problem and you need to ask the tenant below to turn down their AP's Tx power
- D. The customer should replace all their Bluetooth wireless mice as they are stopping the users on floor 5 from connecting to the wireless network
正解：B
解説：
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 below.
質問 # 85
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