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WAN Questions

November 24th, 2018 Go to comments

If you are not sure about WAN, please read our WAN tutorial.

Question 1


An example of the output of the “show interface serial …” command is shown below. We can see the line “Encapsulation HDLC”.


Question 2


PPP supports both synchronous (like analog phone lines) and asynchronous circuits (such as ISDN or digital links). With synchronous circuits we need to use clock rate.

Note: Serial links can be synchronous or asynchronous. Asynchronous connections used to be only available on low-speed (<2MB) serial interfaces, but now, there are the new HWICs (High-Speed WAN Interface Cards) which also support asynchronous mode. To learn more about them please visit http://www.cisco.com/en/US/prod/collateral/modules/ps5949/ps6182/prod_qas0900aecd80274424.html.

Question 3


The advantages of leased lines include:
+ Simplicity: Point-to-point communication links require minimal expertise to install and maintain.
+ Quality: Point-to-point communication links usually offer high service quality, if they have adequate bandwidth. The dedicated capacity removes latency or jitter between the endpoints.
+ Availability: Constant availability is essential for some applications, such as e-commerce. Point-to-point communication links provide permanent, dedicated capacity, which is required for VoIP or Video over IP.

The disadvantages of leased lines include:
+ Cost: Point-to-point links are generally the most expensive type of WAN access. The cost of leased line solutions can become significant when they are used to connect many sites over increasing distances. In addition, each endpoint requires an interface on the router, which increases equipment costs.
+ Limited flexibility: WAN traffic is often variable, and leased lines have a fixed capacity, so that the bandwidth of the line seldom matches the need exactly (therefore answer D is not correct). Any change to the leased line generally requires a site visit by ISP personnel to adjust capacity.

(Reference: Connecting Networks Companion Guide Book published by Cisco Networking Academy – Page 54)

Question 4

Question 5


The idea behind a WAN is to be able to connect two DTE networks together through a DCE network. The network’s DCE device (includes CSU/DSU) provides clocking to the DTE-connected interface (the router’s serial interface).


A modem modulates outgoing digital signals from a computer or other digital device to analog signals for a conventional copper twisted pair telephone line and demodulates the incoming analog signal and converts it to a digital signal for the digital device. A CSU/DSU is used between two digital lines -> A & D are correct but B & C are not correct.

For more explanation of answer D, in telephony the local loop (also referred to as a subscriber line) is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the carrier or telecommunications service provider’s network. Therefore a modem terminates an analog local loop is correct.


Question 6


Below is an example of the output of this command:


The “show controllers serial …” command tells us about the type of the cable (in the case V.35 DTE cable) and the status of the physical layer of the interface. In above output we learn that there is an cable attached on S0/0 interface. If no cable is found we will see the line “No DTE cable” instead.

Question 7


Nowadays all serial links are full-duplex (as serial interfaces have separate Rx & Tx pins) so maybe this question wants to ask about how to check the speed of the serial link. The “show interface” command gives us information about this. An example of this command is shown below:


In this output the speed of S0/0 interface is 1544 Kbits.

Question 8


Full-mesh is a network topology in which there is a direct link between all pairs of nodes. Below is an example of full-mesh topology.


Question 9

Question 10


A newer fiber-optic media development for long-range communications is called dense wavelength-division multiplexing (DWDM). DWDM multiplies the amount of bandwidth that a single strand of fiber can support.

DWDM circuits are used in all modern submarine communications cable systems and other long-haul circuits.

Specifically, DWDM:

+ Enables bidirectional communications over one strand of fiber -> Answer A is correct
+ Assigns incoming optical signals to specific wavelengths of light (i.e., frequencies)
+ Each channel is capable of carrying a 10-Gbps multiplexed signal -> Answer E is not correct
+ Can multiplex more than 80 different channels of data (i.e., wavelengths) onto a single fiber -> Answer C is not correct
+ Can amplify these wavelengths to boost the signal strength
+ Supports SONET and SDH standards

Reference: http://www.ciscopress.com/articles/article.asp?p=2202411&seqNum=6

Question 11

Question 12


In a dual-homed setup, the router in a company is still connected to the outside networks via only one ISP, but with two routers or two connections. When one of the dual-homed connection fails, traffic can still flow via other connection so it can tolerate the loss of a network link.


Note: Below is an example of Single Homed setup:


Comments (30) Comments
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  1. Ppetro
    February 6th, 2017

    Q3 answers should be B & C

    From Cisco website:
    The advantages of leased lines include
    Simplicity: Point-to-point communication links require minimal expertise to install and maintain.

    Quality: Point-to-point communication links usually offer high service quality, if they have adequate bandwidth. The dedicated capacity removes latency or jitter between the endpoints.

  2. 9tut
    February 7th, 2017

    @Ppetro: Thanks for your detection. We have just updated that question.

  3. lagarto
    February 8th, 2017

    i cannot see the questions

  4. JLopesn
    February 8th, 2017

    could someone add link for these questions? I am not a premium user but I want be ready for the test.

  5. lagarto
    February 8th, 2017

    hi f, the link not working can you send to my mail?

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    February 13th, 2017

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  7. buddy
    February 20th, 2017

    can someone explain question 4?

  8. CCNAer
    February 21st, 2017

    @Buddy the routers are on separate class C subnets, The Atlanta Router is known to have correct config therefore Brevard router should be in network

  9. Anonymous
    February 24th, 2017

    Here and in the associated quizzes several questions don’t say how many answers to choose.

  10. Rainbow
    February 27th, 2017

    Do u pass CCNA Exam?

  11. Aar@123
    March 10th, 2017

    Are the dumps available on 9tut valid??

    March 14th, 2017

    hi people if any one has the time could you please explain Q5 of the wan questions in more depth finding it a bit difficult to understand

  13. GRC
    March 21st, 2017

    Anyone with latest link for the dumps. Qns on the site dont show up

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    March 21st, 2017

    where found Questions, Im found only Explanation

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    March 24th, 2017


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  16. Powerade
    March 29th, 2017

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    April 6th, 2017

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    April 7th, 2017

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  19. poulsociety
    April 14th, 2017

    http*:*//jipime*.*co*.*tz/ {Remove the * to View the Latest Questions for CCNA 200-125}

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    April 17th, 2017

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    May 4th, 2017

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    May 13th, 2017

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  23. rajput……..
    May 14th, 2017

    if someone explain q4 ?

  24. adobong manok
    May 22nd, 2017

    WTF i can’t see the questions

  25. CC
    May 26th, 2017

    @ rajput

    For Q4, they’re telling you that the Atlanta router configs are okay, the only problem is with Brevard. When you look at the show interface input, you’ll see that Brevard serial interface has an ip while Atlanta serial interface has an ip of The interfaces need to be in the same subnet for the serial link to work, but they aren’t (11.0-11.255 vs. 10.0-10.255), so the problem would be:

    (e) an incorrect IP address

  26. Anonymous
    May 29th, 2017

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    June 7th, 2017

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  28. Jeanscyther
    June 10th, 2017

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  29. LadyAggy
    June 13th, 2017

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  30. jennyjfoy
    June 14th, 2017

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