nielit 2018 q52

Question

Given a mask, M=255.255.255.248. How many subnet bits are required for given mask M?

(A) 2 (B) 3 (C) 4 (D)5

Answer 1

255.255.255.248 show N.N.N.H means 3 Network Oct and 1 Host Oct.

So we only need to check last oct. for subnet and host.

Here CIDR = 8+8+8+5=29 i.e. there are 29 no. of 1 in the subnet mask but in the last oct there is five 1

last oct is 11111000 so it represent 5 subnet bits and 3 host bits 

No. of Host = 2^no. of host bit i.e. 2^3=8 

So 8 hosts per subnet 

and no. of subnet=2^(8*no. of host oct)/no. of host per oct  = 2^8/8=2^5=32

So no. of subnet bits=5

Correct Answer is option (D) i.e. 5

Answer 2

there are 5 subnet bits

24 network bits

3 host bits