##### Which of the following can be the subnet mask?

The directed broadcast address of a subnet is given as 204.99.88.31

which of the following can be the subnet mask??

a) 255.255.255.224

b)255.255.255.240

c)255.255.255.248

d) b&c

which of the following can be the subnet mask??

a) 255.255.255.224

b)255.255.255.240

c)255.255.255.248

d) b&c

@pritam sir help me in this

Answer would be

d) b & cI want you to give it a try with the following hint:

I suggest you to solve it by your own.

sir can u pls elaborate ans seems diffrent

since, all 1s in the host id part represents direct broadcast.

so, for getting subnet mask we make 0 as1 and 1 as 0 in host part and all 1s in network part so we get 255.255.255.224 as subnet mask .

You can verify it , by ANDing 255.255.255.224 with 204.99.88.31 then we will get 204.99.88.0 which is subnet id and belongs to class C.

Directed Broadcast address is 204.99.88.31

if we write in binary it would be 11001100.01100011.01011000.00011111

The only hint we have about broadcast address is it has all ones in the host part.

Now host part can be last bit or last 2 bits or last 3 bits or last 4 bits or last 5 bits

Case1: Assume that last 4 bits as host part

Now make network part as all ones and host part as zeroes to get subnet mask

255.255.255.240

Case 2: Assume that last 3 bits as host part

Now make network part as all ones and host part as zeroes to get subnet mask

255.255.255.248

Case 3: If you do like above then subnet mask will be

255.255.255. 252

Case 4: if you do like above then subnet mask is

255.255.255.254

case 5: if you take last 5 one's as host part and then ANDing it with 255.255.255.224 then we will get subnet id as 204.99.88.0 but note that 204.99.88.0 is the network id of class C. so this is invalid

hence Option D is the answer

first subnet id is always network id , so how can you say that it can't be the subnet mask.

@pritam sir plz verify now