IT Certification Practice Exams

CCNA 640-802 Exam Practice Questions
Host, and subnet calculation.

Q2. You have an IP of 156.233.42.56 with a subnet mask of 7 bits. How many hosts and subnets are possible?

A. 126 hosts and 510 subnets

B. 128 subnets and 512 hosts

C. 510 hosts and 126 subnets

D. 512 subnets and 128 hosts

Correct answer: C

Explanation:

Class B network has the form N.N.H.H, the default subnet mask is 16 bits long.

There is additional 7 bits to the default subnet mask. The total number of bits in subnet are 16+7 = 23.

This leaves us with 32-23 =9 bits for assigning to hosts.

7 bits of subnet mask corresponds to (2^7-2)=128-2 = 126 subnets.

9 bits belonging to host addresses correspond to (2^9-2)=512-2 = 510 hosts.