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27 votes
27 votes

An organization has a class $B$ network and wishes to form subnets for $64$ departments. The subnet mask would be:

  1. $255.255.0.0$

  2. $255.255.64.0$

  3. $255.255.128.0$

  4. $255.255.252.0$

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5 Answers

Best answer
46 votes
46 votes

D is correct answer.

To form subnet for $64$ departments we need $6$ continuous bit and the value of  11111100 = 252.

Organization has class $B$ network so subnet mask would be 255.255.252.0

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9 votes
9 votes

In class B network

16 bit network id and 16 bits are for host id part.

Here we want 64 subnets so we have to borrow 6 bits from host id part.

Subnet mask will be all 1 in network id and subnet id part.

255.255.252.0

Option d is correct

5 votes
5 votes

D is correct answer.

In class B the network bits are 16 and host bits are 16. In subnetting the bits are borrowed from Host portion and as given " wishes to form subnets"  directs that 2^6 means 6 continuous 1's. We don't need to subtract 2 here as we wish to form subnets, therefore instead of Net ID and DBA of network we will use them for Zero subnet and DBA Subnet.

2 votes
2 votes

subnets for 64 departments

means 

you need 6 bits for subnets

here by 6 bits we mean with 6 unique bits we can have 64 sub networks

classB

16 bits NID rest 16 bits host ID

first 6 bits of the third octet will be used

mask

11111111.11111111.11111100.00000000

255.255.252.0

Answer:

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