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CCNA – Subnetting

April 21st, 2015 Go to comments

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

Question 1

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

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

Explanation

First we should observe the answers, they are all 192.168.252.x so they are in class C with a default subnet mask of 255.255.255.0. We need three web servers (three hosts) in a subnet so we need 3 bits 0 (using the formula 23 – 2 = 6 > 5 hosts) so the last octet of our subnet mask should be 1111 1000 -> 248.

Question 4

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

Question 6

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

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

Question 9

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

Explanation

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

-> A is correct.

Comments (20) Comments
Comment pages
1 5 6 7 1778
  1. Tanis
    July 22nd, 2016

    Question 3
    Explanation:
    … We need three web servers (three hosts) in a subnet so we need 3 bits 0 (using the formula 23 – 2 = 6 > 5 hosts) so the last octet of our subnet mask should be 1111 1000 -> 248.

    6 > 5 hm, we need just 3 hosts, so I would calculate with 3 and not 5.

  2. Mike
    July 22nd, 2016

    Yeah I cant see the questions either….

  3. Subnet
    August 1st, 2016

    Hi
    In an interview i got a questio that 170.16.8.0/12
    Determine network id , fhid, lhid and broadcast.
    Please answer this

  4. Cisco2016
    August 4th, 2016

    Address: 172.16.8.0 10101100.0001 0000.00001000.00000000
    Netmask: 255.240.0.0 = 12 11111111.1111 0000.00000000.00000000
    Wildcard: 0.15.255.255 00000000.0000 1111.11111111.11111111
    =>
    Network: 172.16.0.0/12 10101100.0001 0000.00000000.00000000 (Class B)
    Broadcast: 172.31.255.255 10101100.0001 1111.11111111.11111111
    HostMin: 172.16.0.1 10101100.0001 0000.00000000.00000001
    HostMax: 172.31.255.254 10101100.0001 1111.11111111.11111110
    Hosts/Net: 1048574

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    August 27th, 2016

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    September 20th, 2016

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    September 21st, 2016

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    October 24th, 2016

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  11. Sakraan01
    November 7th, 2016

    I did not see the questions , just only show the explanations of the questions.. So what is the problem??? why the questions are not shown????

  12. Lo Sing
    November 11th, 2016

    Passed the CCNA Finally! I had to take the CCNA twice, as I failed on my first attempt. However for my second, I used the e8ay dump to study the update that happened for the CCNA and passed the exam finally :D All Questions came from the dump. The e8ay dump has a total of 142 questions (58 + 84 updated questions) and the 4 variations of the ACL sims.

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  13. Love TRUMPS hate
    November 14th, 2016

    I have passed the CCNA! I thank this community and also “Lo Sing” providing the e8ay link to a valid dump for the recent update to the CCNA. Altogether 142 questions after the recent update from 10/22. Good luck to others! Onto my CCNP Route!

  14. Anonymous
    December 1st, 2016

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    December 10th, 2016

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    December 18th, 2016

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    December 31st, 2016

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  18. ali
    January 10th, 2017

    can any one explain Q10 plz coz the explanation provided is not enough.

  19. Anonymous
    January 27th, 2017

    does anybody knows the official certi guide for CCNP RnS which can be downloaded form net??

  20. Ricky
    May 13th, 2017

    Need help#
    Suppose You have a big company of 63 hosts per network. You are the System Administrator of your company. You have to plan the addressing scheme. Your are given IP 172.72.157.253 And your Dept. (Engtneering) uses Subnet N 399.
    Q. What will be the Subnet bit?

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