Question

You have a network that needs 29 subnets while maximizing the number of host addresses available on each subnet. How many bits must you borrow from the host field to provide the correct subnet mask?

(a) 2

(b) 3

(c) 4

(d) 5

I had been asked this question during a job interview.

Question is taken from Designing Subnet Masks topic in section TCP/IP Protocol Suite of Computer Network

Answer 1

Correct answer is (d) 5

The explanation is: A 240 mask is 4 subnet bits and provides 16 subnets, each with 14 hosts. We need more subnets, so let’s add subnet bits. One more subnet bit would be a 248 mask. This provides 5 subnet bits (32 subnets) with 3 host bits (6 hosts per subnet). This is the best answer.