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255.255.255.224

which of the following can be DBA of subnet.

a)201.55.66.15

b)201.55.66.31

c)201.55.66.63

d)all

Option B
Hey why not C? Isn't both B and C right?

The first 27 bits belong to the network here .Free bits are last 5 bits which are Host id bits. To get DBA we need to make the host bits all 1's .

Here host bits are 5 . so make allo of them as 1. This gives 11111=31
But doesn't the subnet mask the network in subnets ..in this case into 201.55.66.0 - 31 and 201.55.66.32 - 63 and so on...... ?
As u said to get 63 we need  --111111 but here the first 3 bits are fixed . you cannot do anything on the first 3 bits .So we can only use the remaining 5 bits
What I mean is if a subnet mask 255.255.255.224 is applied on 201.55.66.0, it means that the ip address can be subnetted into groups of 32 ip's (2^5)
In this case 201.55.66.0/27 will have 201.55.66.31 has DBA
In the case of 201.55.66.32/27, 201.55.66.63 will be the DBA

Correct me if I'm wrong
yes , u r correct . It was my mistake . Thank you Bro :)