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Traffic Flow and AP

Here you will find answers to Traffic Flow and AP QuestionsAccording to the IEEE 802.11 standard

Question 1

What two statements about beacon frames used by access points are true? (Choose two)

A. contains SSIDs if this feature is enabled
B. provides vendor proprietary information
C. is another name for an associated request
D. sent in response to a probe frame
E. includes ATIM window information for power save operations

 

Answer: A B

Explanation

Prior to authentication/association, devices must identify any access-points that are within range. Two methods of scanning are available; namely, passive and active. In passive scanning mode, a device monitors each channel for beacon frames that are broadcast by the access-points in the vicinity.

A beacon frame is a management frame in IEEE 802.11-based wireless LANs. It contains all the information about the network. Beacon frames are transmitted periodically to announce the presence of a wireless LAN network and are transmitted by the Access Point (AP). A beacon frame includes timestamp, beacon interval, its capabilities, SSIDs, supported rates,  TIM (Traffic Indication Map) and some configuration and security information to the client devices. Some of them are standard; other are vendor proprietary. Below shows a beacon frame with “Cisco Proprietary” parameters from the Cisco AP:

Cisco_Beacon_Frame.jpg

(Note: beacon interval is the time interval between two consecutive beacon frames)

Question 2

In general, what is the difference in transmit power between an AP operating at Tx Power Level 1 and the same AP operating at Tx Power Level 3?

A. 2 dB
B. 3 dB
C. 6 dB
D. 11 dB
E. 17 dB

 

Answer: C

Explanation

In Tx Power Level term, a level of “1” represents the highest power level available in the country for which this AP is configured. A level of “2” is 50 percent of this maximum, a level of “3” is 25 percent of this maximum, a level of “4” is 12.5 percent, and so on. Each level is half the power strength of the previous level.

Therefore, the difference between Tx Power Level 1 and Level 3 is calculated (in dB) as follows:

Difference (dB) = 10* log(25%) = -6 dB but we just need its amplitude-> C is correct.

Question 3

Which interface is considered a dynamic interface?

A. the virtual interface
B. the AP manager interface
C. the LAG interface
D. the management interface
E. the service port interface
F. a WLAN client data interface

 

Answer: F

Explanation

Each interface performs specific roles within the unified wireless environment. The static interfaces perform system roles, while the dynamic interfaces are user-defined, and provide client connectivity. Therefore a WLAN client data interface is considered a dynamic interface.

Question 4

An indoor 1240 AP is booting and has obtained an IP address using DHCP. The AP has confirmed prior controller IP addresses from a previously joined mobility group stored in NVRAM. What is the next step the AP performs?

A. DHCP option 43.
B. DNS resolution of CISCO-LWAPP-CONTROLLER.localdomain.
C. Layer 2 LWAPP discovery broadcast.
D. Layer 3 LWAPP discovery broadcast.
E. Ping each Cisco WLC to verify its current status.
F. Select a Cisco WLC based on its position in the configured join selection sequence.

 

Answer: A

Explanation

In a controller-based architecture, access points are dependent on a wireless controller to provide the software image, configuration, and centralized control and optionally data forwarding functions. Therefore, it is necessary for the access point to find a list of available controllers with which it can associate. Below is the process of finding as many controllers as possible in order to choose the best candidate to join after the AP has an IP address:

1 – LWAPP discovery broadcast on local subnet. This is a broadcast that is sent at Layer 2.
2 – OTAP
3 – Locally stored WLC IPs
4 – DHCP Option 43
5 – DNS Discovery.

DHCP protocol has become more and more popular over the time, hard and software vendors have started using the DHCP protocol to distribute all kinds of configuration options for their network devices or for their software. Now the problem is that the number of official options is limited and the process to get a new option recognized is difficult. For this reason, a new mechanism was introduced to make it easier for vendors to distribute their own proprietary information without clashing with other vendors and without having to register new options each time they decide the need them. This is achieved through the DHCP option 43 (Vendor Specific Information). Now the DHCP server has a private table of DHCP options which is kept separately for each vendor. Each vendor is identified by a vendor string. Now when a DHCP client asks for vendor specific options it makes a request with option 43 using the vendor string and a list of requested vendor specific options.

The information provided by DHCP option 43 is presumably interpreted by vendor-specific code on the clients and servers. The definition of this information is vendor specific. The vendor is indicated in the vendor class identifier option. Servers not equipped to interpret the vendor-specific information sent by a client MUST ignore it (although it may be reported). Clients which do not receive desired vendor-specific information SHOULD make an attempt to operate without it, although they may do so (and announce they are doing so) in a degraded mode.

Question 5

Which AP to Wireless LAN Controller discovery process requires a previous association of the AP with a Cisco WLC?

A. AP priming
B. defining a master controller
C. DHCP Option 6
D. DHCP Option 43
E. over-the-air provisioning

 

Answer: A

Explanation

AP priming happens after an AP is associated with at least one controller. The AP then gets a list of other controllers that it can associate with from the one it is already associated with. These other controllers are part of a mobility group. This information then gets stored in NVRAM and can be used if the AP reboots. To contact these controllers, the AP sends a broadcast to the primary controller and all the other controllers in the group.

Question 6

Which of the following methods is NOT used to access an AP in autonomous mode?

A. Browse
B. Telnet
C. Auxiliary
D. Console

 

Answer: C

Explanation

Well, there is no clear explanation why we can’t access an AP in auxiliary mode. You can access an autonomous AP in four ways:
* Console to it using a console cable and the console port.
* Telnet into it if it has an IP address.
* Browse to it with a web browser if it has an IP address.
* SSH into it if configured (preferred over Telnet).

(Reference: CCNA Wireless Official Exam Certification Guide)

Comments (27) Comments
  1. Adrian
    August 7th, 2011

    Hi
    i had a wireless network with different vendors, if the probe are diferents the interoperability can be achieved ?

  2. mister x
    October 29th, 2011

    1. D. sent in response to a probe frame

    why this is wrong? If we send probe request, then AP will send probe response to us! (a beacon)

  3. mister x
    November 1st, 2011

    4. A – wrong

    the answer is D , L3 broadcast

  4. rv
    November 14th, 2011

    hi,so in the #4 what is the correct answer?thanks

  5. bidy
    November 15th, 2011

    hi i think correct answer is C Layer 2……..

  6. Dovinant
    November 21st, 2011

    Question 4
    I guess the answer A is wrong. “The AP has confirmed prior controller IP addresses from a previously joined mobility group stored in NVRAM” Therefore the AP already has controller IP addresses. So the next step “Select a Cisco WLC based on its position in the configured join selection sequence” and right answer is F.

  7. Dovinant
    November 24th, 2011

    Ok, perhaps I was wrong. AP uses the hunting process and discovery algorithm to find as many controllers as possible. So the AP uses DHCP option 43 to obtain controller IP addresses.

  8. Hosam
    January 1st, 2012

    Q4: I think the AP already obtained an IP address, why the answer is A????

    D. Layer 3 LWAPP discovery broadcast. << looks the correct one to me.

  9. Hosam
    January 1st, 2012

    “The AP has confirmed prior controller IP addresses from a previously joined mobility group stored in NVRAM.” It already have the controller’s IP address in the memory, it doesn’t need to do DHCP option 43. All it needs to do is to try to communicate with one of these controllers and see which one is alive and continue down that path.

  10. wifi1
    January 27th, 2012

    Do we know what the correct answer is for number 4???? i think D

  11. RJ
    March 12th, 2012

    Q. 4 answer is D here is the link from CCO

    http://www.cisco.com/en/US/products/ps6366/products_tech_note09186a00808f8599.shtml#backinfo

    Question is the state in 2c and state 2D is

    d. A Layer 3 broadcast on the subnet

  12. DJM
    April 6th, 2012

    @RJ:
    the link you mentioned, lists DIFFERENT CHOICES to get a list of management interfaces, but they are not “in order”: the statement 2D is not the 4th step.
    The LAP sends discovery requests to controllers through the various discovery algorithms and builds a controller list. Essentially, the LAP learns as many management interface addresses for the controller list as possible via:

    DHCP option 43 (good for global companies where offices and controllers are on different continents)

    DNS entry for cisco-capwap-controller (good for local businesses – can also be used to find where brand new APs join)

    Note: If you use CAPWAP, make sure that there is a DNS entry for cisco-capwap-controller.

    Management IP addresses of controllers the LAP remembers previously

    A Layer 3 broadcast on the subnet

    Over the air provisioning

    Statically configured information

  13. DJM
    April 6th, 2012

    the CCNA Wireless book, page 197, explain this situation in method 3: the AP gets a list of controllers, all part of the same mobility group, and it stores in its NVRAM. To contact those controllers after a reboot, the AP sends a broadcast to the primary controller and all the other controllers in the group.

    to me, it seems that in Q4 the AP already has “controller IP addresses”: however, I don’t understand if the question means “ip addresses af a list of controllerS” or “different IP addresses of a single controller” (which doesn’t make sense if we are talking about Layer 3 LWAPP discovery…)

    :(

  14. CCNA
    April 8th, 2012

    hi can some one explain me how Q.2 works because I can understand the Level 1 means? how they calculate the values.?

  15. CCNA
    April 8th, 2012

    Correction : I cant understand

  16. Leo
    April 11th, 2012

    Anyone knows the corrected answer?

  17. Gunti
    May 2nd, 2012

    @CCNA
    on the WLC 1 is the max power you can chose – each step “up” decrease the power to a half so when you chose 2 then you have 3db, when you chose 3 then you have 6db and so on…
    Remember that + 3db doubles the power and – 3db decrease the power to a half
    example: If 1 = 1W then 2 = 0,5W, 3=0,25W…

  18. Brian
    May 9th, 2012

    Question 4: Layer 3 broadcast is incorrect. The AP will send a unicast LWAPP Discovery Request to the WLC. This can be a DHCP Option 43 IP address offer.

  19. fassolo
    July 19th, 2012

    Q4: According to this docu the correct answer should be ‘C’ -> http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a00806c9e51.shtml#topic1

  20. CCNAW learner
    November 7th, 2012

    why do you guys that advertise yourself use this forum to advertise? do you ever think if I need a service of the kind I will ever come to you. I won’t because you are abusing, idea the efforts and time taken by inteligent individuals who sacrifice there times and skills to put this things together.

    Please stop this act!

  21. AlanTheAussie
    February 6th, 2013

    Q4 from Cisco’s web doc, from this D should be correct.
    3.If the LAP was registered to a WLC in a previous deployment, the LAP maintains the list of WLC IP addresses locally in NVRAM. The stored WLC IP addresses include all of the WLCs that are in previously joined WLC “mobility groups”. This is the discovery process:

    a.LAPs send a unicast Layer 3 LWAPP discovery request to each of the WLC IP addresses that the LAP has in its NVRAM.

    b.WLCs that receive the LWAPP discovery message reply with a unicast LWAPP discovery response message to the LAP.

  22. AlanTheAussie
    March 7th, 2013

    Also Q5 answers Q4 – L3 BC

  23. CiscoKID
    December 4th, 2013

    Can we prepare for 640-722 exam using 640-721 guide. As I understand it 640-722 guide will only be available next month.

  24. Royce
    May 1st, 2014

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    I read the 640-722 quick reference guide twice and also watched the CBT nugget series on CCNA wireless. Going through these questions is a great way to identify your weaknesses and then study up, but if your planning to go into the exam using this as a dump your going to fail.

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    August 4th, 2014

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    August 12th, 2014

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  27. FELY N
    October 2nd, 2014

    what about the process of communication between the client , WLC and AP