Your network design calls for 17 subnets supporting 35 hosts

Your network design calls for 17 subnets supporting 35 hosts each. Your company provides the 135.72.0.0 address space. Which subnet mask would you create to satisfy the requirement?

A. 255.255.252.0

B. 255.255.254.0

C. 255.255.248.0

D. 255.255.240.0

Solution

C is correct. Following the five steps to create a subnet mask, 255.255.248.0 is the correct choice. The Class B address space has a default mask of 255.255.0.0, and we need to borrow 5 bits to accomplish the task (2ⁿ greater than or equal to the number of subnets needed, and 2⁵ complies). Counting from left to right, starting with the 17th bit (due to the default mask), the line is drawn after the 21st bit. Setting all bits to 1 on the left of the line, we have 11111111.11111111.11111000.00000000, which equates to 255.255.248.0.

A, B, and D are incorrect. These choices do not comply with the scenario needs.