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Exam CWNA-108 topic 1 question 20 discussion

Actual exam question from CWNP's CWNA-108
Question #: 20
Topic #: 1
[All CWNA-108 Questions]

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.
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Suggested Answer: A 🗳️


Chosen Answer:
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Highly Voted 1 year, 2 months ago
I think A is correct. If multiple APs operate on the same channel, multiple APs will reply.
upvoted 5 times
Most Recent 5 months, 3 weeks ago
Explanation: Probe Request are sent to the broadcast DA address (ff:ff:ff:ff:ff:ff). Once a Probe sent, STA starts a ProbeTimer countdown & wait for answers. At the end of the timer, STA process the answer it has received. If no answers received, STA moves to next channel & repeats the discovery process. STA sending Probe Request may specify the SSID they looking (called directed probe request). Then only IBSS STA or AP support that SSID will answer. The SSID value can also be set to 0 (ie SSID field is present, but empty). This is called Wildcard SSID or Null Probe Request. Null probe request: A probe request without the SSID information. A client station that is looking for any SSID sends a probe request with the SSID field set to null. If a null probe request is sent, all APs that hear the request should reply by sending a probe response.
upvoted 2 times
11 months, 3 weeks ago
B is correct!
upvoted 1 times
1 year, 3 months ago
Selected Answer: B
should be B, because you can only send a probe on 1 channel, so only 1 AP may reply.
upvoted 2 times
4 months ago
You can have way more than one AP on a channel within Rx distance of the STA who will respond.
upvoted 1 times
Community vote distribution
A (35%)
C (25%)
B (20%)
Most Voted
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