Subnetting

Question

An organization has a class C network and wishes to from subnet for 32 departments. The subnet mask would be:-

• A. $255.255.255.248$
• B. $255.255.255.252$ 

Answer 1

I guess it should be A. As it is a class C network we have 24 bits for the network Id part . Now we are left with 8 bits. As we want subnets for 32 networks so we have to reserve 5 bits for the subnet Id part . So for subnet mask we have  all 1's in place of NID and SID and rest all 0's. So we get: 1111 1111:1111 1111:1111 1111:1111 1000=255:255:255:248

Comments

But why not B?

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for b : for the last octet we will get 1111 1100 that means only 2^6=64 subnets and we require only 32 subnets..

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The requirement is just according to the present scenario, it may be the case that organization will require more in future.

I think in the question along with subnet they should also ask no of hosts in each subnet then it would be more clear.

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ya.. It would have been more clear then but if it is not specified I guess we have to do it according to the present scenario

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I think in the question along with subnet they should also ask no of hosts in each subnet then it would be more clear.

yes, we can prefer b also as subnet mask, due to our requirement is 32 subnets and it gives us 64 subnets, which satisfies us... but there is a better option which will give exactly 32 subnets, then it is preferrable !

Answer 2

Ans is A