CCNA Practice Exam Test Sample – Question 91

You are working in a data center environment and are assigned the address range 10.188.31.0/23. You are asked to develop an IP addressing plan to allow the maximum number of subnets with as many as 30 hosts each. Which IP address range meets these requirements?

A. 10.188.31.0/26
B. 10.188.31.0/25
C. 10.188.31.0/28
D. 10.188.31.0/27
E. 10.188.31.0/29

Correct Answer: D
Section: IP addressing (IPv4 / IPv6)

Explanation:
Each subnet has 30 hosts < 32 = 25 so we need a subnet mask which has at least 5 bit 0s -> /27. Also the question requires the maximum number of subnets (which minimum the number of hosts-per-subnet) so /27 is the best choice.