Subnetting Question

kianm

Hi guys, please help me verify these 2 questions and answers.

Q: You are a senior network engineer at X Pty Ltd. Your boss, Mr.
Martin, asks you to create a subnet with room for 12 IPs for some new managers.
Mr. Martin promises that there will never be more than 12 managers, and he asks
you to make sure that you conserve IP address space by providing the minimum
number of possible host IPs on the subnet. What subnet mask will best meet
these requirements?
P A. 255.255.255.12
P B. 255.255.255.0
P C. 255.255.240.0
P D. 255.255.255.240
P E. 255.255.255.224

Article says answer is D. I got answer as E by reserving 6 host bits (14 hosts) in the 4th octet (11100000) = 255.255.255.224

Q: Your boss, Duncan, does not seem to be able to grasp subnetting. He comes
out of a management meeting and quietly asks you to help him with a subnetting
issue. He needs to divide the Class B address space the company uses into six
subnets for the various buildings in the plant, while keeping the subnets as large
as possible to allow for future growth. What is the best subnet mask to use in this
scenario?
P A. 255.255.0.0
P B. 255.255.248.0
P C. 255.255.224.0
P D. 255.255.240.0
P E. 255.255.255.224

Article says answer is C. I got D as answer by reserving 4 network bits in the 3rd octet (8 subnets being closest) thus 11111111. 11111111. 11110000. 00000000 255.255.240.0

Please help and point out where i'm getting it wrong or otherwise. I ended up doubting the article's answers but i might be totally wrong so please help me see the light. Thanks

clarson

q1) answer is d you need four host bits, 2^4 = 16 then minus two for 14.
E has 5 host bits for 32 -2 or 30 hosts.

clarson

q2) the answer is c you only need 3 network bits. 2 raised to the thrid power is 8. you have 4 network bits or 2 raised to the forth power which is 16.

kianm

I see where i went wrong, i misplaced the bit positions and shifted the values of the powers of 2 in both scenarios. Very silly of me (brain f@rt), thanks bud

tntech55

I need help with this type of subnetting question, I am studying for my CCENT but this type question really stumps me. Any help or suggestions I would greatly appreciate. Thanks.

Jon_Cisco

tntech55 wrote: »

I need help with this type of subnetting question, I am studying for my CCENT but this type question really stumps me. Any help or suggestions I would greatly appreciate. Thanks.

You might want to start with your ideas. Not many people will answer a question until you have at least tried.