Home > New CCNA – Subnetting

New CCNA – Subnetting

September 27th, 2013 Go to comments

Note: If you are not sure about Subnetting, please read our Subnetting Tutorial – Subnetting Made Easy.

Question 1

Refer to the exhibit. Which subnet mask will place all hosts on Network B in the same subnet with the least amount of wasted addresses?

subnetting_wan.jpg

A. 255.255.255.0
B. 255.255.254.0
C. 255.255.252.0
D. 255.255.248.0

 

Answer: B

Explanation

310 hosts < 512 = 29 -> We need a subnet mask of 9 bits 0 -> 1111 1111.1111 1111.1111 1110.0000 0000 -> 255.255.254.0

Question 2

Refer to the exhibit. All of the routers in the network are configured with the ip subnet-zero command. Which network addresses should be used for Link A and Network A? (Choose two)

Subnetting_divide_hosts.jpg

A. Network A – 172.16.3.48/26
B. Network A – 172.16.3.128/25
C. Network A – 172.16.3.192/26
D. Link A – 172.16.3.0/30
E. Link A – 172.16.3.40/30
F. Link A – 172.16.3.112/30

 

Answer: B D

Explanation

Network A needs 120 hosts < 128 = 27 -> Need a subnet mask of 7 bit 0s -> “/25″.

Because the ip subnet-zero command is used, network 172.16.3.0/30 can be used.

Answer E “Link A – 172.16.3.40/30″ is not correct because this subnet belongs to MARKETING subnet (172.16.3.32/27).
Answer F “Link A – 172.16.3.112/30″ is not correct because this subnet belongs to ADMIN subnet (172.16.3.96/27).

Question 3

You have been asked to come up with a subnet mask that will allow all three web servers to be on the same network while providing the maximum number of subnets. Which network address and subnet mask meet this requirement?

A. 192.168.252.0 255.255.255.252
B. 192.168.252.8 255.255.255.248
C. 192.168.252.8 255.255.255.252
D. 192.168.252.16 255.255.255.240
E. 192.168.252.16 255.255.255.252

 

Answer: B

Question 4

Which subnet mask would be appropriate for a network address range to be subnetted for up to eight LANs, with each LAN containing 5 to 26 hosts?

A. 0.0.0.240
B. 255.255.255.252
C. 255.255.255.0
D. 255.255.255.224
E. 255.255.255.240

 

Answer: D

Explanation

A is not correct because it is a wildcard mask (not subnet mask).

This question is a bit unclear but we can suppose we have to begin with default subnet mask and “subnet” it. And the default subnet mask here should be class C: 255.255.255.0

For answer B: 252 = 1111 1100 -> with this subnet mask we can subnet up to 26 = 64 subnets but only 22 – 2 = 2 hosts per subnet -> B is not correct.

C is not correct because it is the default subnet mask of class C and that means we don’t “subnet” it.

For answer E: 240 = 1111 0000 -> There are 24 = 16 subnets but only 24 – 2 = 14 hosts per subnet < 26 hosts -> E does not satisfy the second requirement (of 26 hosts per subnet).

For answer D: 224 = 1110 0000 -> There are 23 = 8 subnets and 25 – 2 = 30 hosts > 26 hosts -> This is the correct answer.

Note: The number “5″ in ” with each LAN containing 5 to 26 hosts” is just used to trick you and it does not have any effect on our answer.

Question 5

An administrator must assign static IP addresses to the servers in a network. For network 192.168.20.24/29, the router is assigned the first usable host address while the sales server is given the last usable host address. Which of the following should be entered into the IP properties box for the sales server?

A. IP address: 192.168.20.14
Subnet Mask: 255.255.255.248
Default Gateway: 192.168.20.9

B. IP address: 192.168.20.254
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.20.1

C. IP address: 192.168.20.30
Subnet Mask: 255.255.255.248
Default Gateway: 192.168.20.25

D. IP address: 192.168.20.30
Subnet Mask: 255.255.255.240
Default Gateway: 192.168.20.17

E. IP address: 192.168.20.30
Subnet Mask: 255.255.255.240
Default Gateway: 192.168.20.25

 

Answer: C

Question 6

Refer to the exhibit. In this VLSM addressing scheme, what summary address would be sent from router A?

VLSM_summary.jpg

A. 172.16.0.0/16
B. 172.16.0.0/20
C. 172.16.0.0/24
D. 172.32.0.0/16
E. 172.32.0.0/17
F. 172.64.0.0/16

 

Answer: A

Explanation

Router A receives 3 subnets: 172.16.64.0/18, 172.16.32.0/24 and 172.16.128.0/18.

All these 3 subnets have the same form of 172.16.x.x so our summarized subnet must be also in that form -> Only A, B or C is correct.

The smallest subnet mask of these 3 subnets is /18 so our summarized subnet must also have its subnet mask equal or smaller than /18.

-> Only answer A has these 2 conditions -> A is correct.

Question 7

You are working in a data center environment and are assigned the address range 10.188.31.0/23. You are asked to develop an IP addressing plan to allow the maximum number of subnets with as many as 30 hosts each.Which IP address range meets these requirements?

A. 10.188.31.0/27
B. 10.188.31.0/26
C. 10.188.31.0/29
D. 10.188.31.0/28
E. 10.188.31.0/25

 

Answer: A

Explanation

Each subnet has 30 hosts < 32 = 25 so we need a subnet mask which has at least 5 bit 0s -> /27. Also the question requires the maximum number of subnets (which minimum the number of hosts-per-subnet) so /27 is the best choice -> A is correct.

Question 8

Which two benefits are provided by using a hierarchical addressing network addressing scheme? (Choose two)

A. reduces routing table entries
B. auto-negotiation of media rates
C. efficient utilization of MAC addresses
D. dedicated communications between devices
E. ease of management and troubleshooting

 

Answer: A E

Question 9

The network administrator is asked to configure 113 point-to-point links. Which IP addressing scheme best defines the address range and subnet mask that meet the requirement and waste the fewest subnet and host addresses?

A. 10.10.0.0/18 subnetted with mask 255.255.255.252
B. 10.10.0.0/25 subnetted with mask 255.255.255.252
C. 10.10.0.0/24 subnetted with mask 255.255.255.252
D. 10.10.0.0/23 subnetted with mask 255.255.255.252
E. 10.10.0.0/16 subnetted with mask 255.255.255.252

 

Answer: D

Explanation

We need 113 point-to-point links which equal to 113 sub-networks < 128 so we need to borrow 7 bits (because 2^7 = 128).

The network used for point-to-point connection should be /30.
So our initial network should be 30 – 7 = 23.

So 10.10.0.0/23 is the correct answer.

You can understand it more clearly when writing it in binary form:

/23 = 1111 1111.1111 1110.0000 0000
/30 = 1111 1111.1111 1111.1111 1100 (borrow 7 bits)

Question 10

Given an IP address 172.16.28.252 with a subnet mask of 255.255.240.0, what is the correct network address?

A. 172.16.16.0
B. 172.16.24.0
C. 172.16.0.0
D. 172.16.28.0

 

Answer: A

Explanation

Increment: 16 (of the third octet)
Network address: 172.16.16.0

-> A is correct.

Comments (208) Comments
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  1. goodlucktoall
    September 27th, 2013

    Question 2 was in today’s exam.

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    September 29th, 2013

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  3. Wazif
    October 18th, 2013

    Can someone explain No.6?

  4. Yefry
    October 18th, 2013

    @Wazif
    If you translate the three networks in binary you’ll note that the addresses match only up to the second octet. So you would have:

    10101100.00010000.100000000.0 (128 subnet)
    10101100.00010000.010000000.0 (64 subnet)
    10101100.00010000.001000000.0 (32 subnet)
    10101100.00010000.000000000.0 (All bits that not match are 0. Result: summarized subnet is 172.16.0.0/16)

  5. Fezzy
    October 20th, 2013

    This Q9 is not clear to me.

  6. Imtiaz
    October 20th, 2013

    Thanks Yefry for the answer Q.6
    But /16 notation giving me bit confusion can you explain it please

    What i can see from last line of your answer is
    10101100.00010000.00000000.0 i can’t see 16 bit’s are on. though i can see 16 bits are off.

  7. Yefry
    October 20th, 2013

    @Imtiaz
    As you can see from the binary addresses, matches until the bit 16. Also, you’ve answered yourself: if you can see 16 bits off, so you should see 16 bits on too (32-16=16). Note: /16 are representing subnet mask bits!

  8. Yefry
    October 20th, 2013

    @Fezzy
    For each point-point network you have /30 subnet mask, so 4 ip addreess. As you need 113 subnet, so simply do these operations:

    113×4= 452 (total ip you need)
    2^9= 512 (you need to take 9 borrow bits from subnet mask)
    11111111.11111111.11111110.00000000 (total bits 32 – borrow bit 9 = 23 bits)
    So you can deduce that you need a subnet mask /23.

  9. Ramya
    October 22nd, 2013

    Could someone plz explain ques 10? Thanks

  10. Imtiaz
    October 22nd, 2013

    Thanks Yefry

  11. cinemaxik
    October 24th, 2013

    Q3. Why B?

  12. winshlaw
    October 24th, 2013

    @cinemaxik
    From the question,the main area of interest is ‘maximum number of sub-nets’ we only need to secure three bits for the three servers.therefore our subnet mask will be all ones with only three bits reserved for three servers,the rest of the bits will be 1s so that we can have the maximum number of sub-nets.This will yield:
    111111.11111111.11111000/29 subnet mask or 255.255.255.248.
    To find the network address,we need to find the increment,which is obtained by looking at what value corresponds to the least significant bit,which is 8 looking at our
    111111.11111111.11111000/29 subnet mask or 255.255.255.248.
    Ans.B meets both these conditions.

  13. winshlaw
    October 24th, 2013

    I left out two bits in the first octet,please add them so it has eight bits in total(not 6 bits)

  14. Omar
    October 24th, 2013

    Cinermaxik the answer is B because it requires 3 host. Host = 2^3 – 2 = 8-2 = 6 by using 3 bits for host network have 5 Bit for the computation of the mask.

    Mascara=8+8+8+5=/29 o 255.255.255.248

  15. Omar
    October 24th, 2013

    Could someone explain ques 10? Thanks

  16. Ranvir
    October 27th, 2013

    @Omar – answer toac q 10
    172.16.28.252 with a subnet mask of 255.255.240.0

    In such case, you need to see the subnet mask..which is 255.255.240.0, so it means we have to work on 3rd octet. 240 means – a block size of 16 network…. so networks will be in this range :

    1st network – 172.16.16.0 2nd network – 172.16.32.0 and so on.. it means this IP – 172.16.28.252 lies in network 172.16.16.0 which is your answer…

    hope its clear to you..

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    October 28th, 2013

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  18. Goryn
    November 14th, 2013

    Hello.
    why in Q4 answer is 255.255.255.224?

    we need to define the subnet mask of the lan which:
    to be subnetted for up to eight LANs, with each LAN containing 5 to 26 hosts.
    This mean that that we need 3 bits (2^3=8) for subnets and 5 bits (2^5=32>26) for hosts.
    Thus we need 3+5=8 bits for parent subnet. (255.255.255.0)
    Or i’m wrong?

  19. EFOWEL
    November 18th, 2013

    can someone here explain question 4? im really confuse about it!

  20. EFOWEL
    November 18th, 2013

    i got confuse about it too, coz i choose (E:255.255.255.240) which makes 16 networks and 16 host, but the question states that UP TO EIGHT lans and 5-26host, if i choose (C:255.255.255.224) it makes 8 networks BUT 32 HOST! which also conflicts the 5-26 HOST LIMITS!

  21. ebemusty
    November 18th, 2013

    @efowl ,, dere is no conflict ,,, Slash 28 , will only give u 16 host and 16 networks , , bt d questn requires 8netwoks and 5-26host , since slash 27 will give u 8networks and 32 honest , dis is more closer , u choose slash 27 (255.255.255.224)

  22. viru
    November 20th, 2013

    i think for ques 7 it should be /28 and not /27 can anyone pls explain ?

  23. avtech
    November 21st, 2013

    /28 would only leave 4 bits for hosts the would be only up to 14 hosts per subnet, the questions asks for as many as 30, so you need 5 bits for hosts which would allow exactly up to 30 hosts per subnet. you need a /27 to leave 5 host bits

  24. Anonymous
    November 22nd, 2013

    Somebody explain Q-6 using total host and no of bits used. Is it 256+512+512 and nearest round up is 2048?

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  26. Aman
    December 3rd, 2013

    please any one can help me in question 5 i don’t understand

  27. aNONYMOUS
    December 4th, 2013

    Can someone explain why the answer is not D for question 3.

  28. papashango
    December 6th, 2013

    @aNONYMOUS,
    Q3 For the 3 servers to be in the same network it means that you need 3 valid host addresses, 252 will give 2 valid addresses and 248 will give 14 addresses, 240 will give 30 valid addresses but will give less number of networks compare to 248 as demanded by the question.

  29. Adnan W
    December 6th, 2013

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  30. Rosemary
    December 11th, 2013

    @Anonymous I fail to download help please ma exam is this week

  31. joyel
    December 25th, 2013

    Q3 the 3 networks 192.168.252.0 / 252.8 / 252.16 only falls in the same network when the mask is 255.255.255.248
    Magic number is 8 and the subnet address will be multiples of 8. (this is how is figured the answer. don’t whether it is correct)

  32. SDoeblah
    December 28th, 2013

    I am so grateful to all you guys who are sharing these worthy experience and knowledge with us. I Think I can see real clearly now on subnetting. And many thanks and appreciation the the staff of 9tut…..

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  35. Jas…
    January 9th, 2014

    Any one pls explain q5?

  36. Surya Kanth
    January 12th, 2014

    Jas,, Expln to q5 is for /29 select the subnet 248 in the last octet. and then look for range where the given ip address falls into. As they asked the sales server to be the last one, it is .30 as .31 will be the broadcast address.

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  39. jas
    January 21st, 2014

    thk u surya…

  40. Sabry
    January 29th, 2014

    Q9 was in today’s exam.

  41. lochinvar_2001
    February 6th, 2014

    Thank you Yefry

  42. Nadeesha
    February 10th, 2014

    Plz anyone can help me on question 8? I can’t understand meaning of answers.

  43. Valentine
    February 11th, 2014

    Using any IP address class B subnet according to the following requirement 60, 100, 120.

    (a) what is the new subnet mask?
    (b) How many usable IP can be found in a subnet and what is the host size per subnets.
    (c) write out the first 10 IP blocks.
    (d) How many subnets are derivable by this.

    Please help me with this questions.

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    February 12th, 2014

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  45. Hossam
    February 13th, 2014

    Q7 i think the answer is D not A , am i right ?

  46. harish
    February 16th, 2014

    Plz. I didnt get Q9. Help me frndzzzzzzzzzzzzzzzz

  47. Benjamin
    February 19th, 2014

    Q7

    10.188.31.0/23 cannot exist

    10.188.31.0 would fall in the net 10.188.30.0/23 as the 2nd /24 in the net

  48. kijaga from tz
    February 20th, 2014

    Hello guys kindly assist , I don’t understand this question

    The network 172.25.0.0 has been divided into eight equal subnets. Which of the following IP addresses can be assigned to hosts in the third subnet if the ip subnet-zero command is configured on the router? (Choose three)

    A – 172.25.78.243
    B – 172.25.98.16
    C – 172.25.72.0
    D – 172.25.94.255
    E – 172.25.96.17
    F. 172.25.100.16

    Answer: A C D

    Explanation

    If the “ip subnet-zero” command is configured then the first subnet is 172.25.0.0. Otherwise the first subnet will be 172.25.32.0 (we will learn how to get 32 below).

    The question stated that the network 172.25.0.0 is divided into eight equal subnets therefore the increment is 256 / 8 = 32 and its corresponding subnet mask is /19 (1111 1111.1111 1111.1110 0000).

    First subnet: 172.25.0.0/19
    Second subnet: 172.25.32.0/19
    Third subnet: 172.25.64.0/19
    4th subnet: 172.25.96.0/19
    5th subnet: 172.25.128.0/19
    6th subnet: 172.25.160.0/19
    7th subnet: 172.25.192.0/19
    8th subnet: 172.25.224.0/19

    In fact, we only need to specify the third subnet as the question requested. The third subnet ranges from 172.25.64.0/19 to 172.25.95.255/19 so A C D are the correct answers.

  49. @ kijaga from tz
    February 25th, 2014

    HI kijaga from tz

    Question clearly states that we need to assign Ip address from third sub-network which is
    172.25.64.0/19
    so valid hosts in this subnet would be
    from 172.25.64.1 to 172.25.95.255

    only A, C and D ip addresses fall in this range so these would be the correct answer other are from different subnetworks.

    Hope this helps…

  50. Toshky
    February 26th, 2014

    Q9 where did the /30 come from?? Not mentioned anywhere on the question. Is that a given for point to point links??

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