101 · Question #573

101 Question #573: Real Exam Question with Answer & Explanation

The correct answer is D: 2. A Class C address has 8 host bits, and creating 64 subnets requires borrowing 6 of those bits, leaving only 2 host bits for 2 usable host addresses per subnet.

Question

An administrator is given the IP Address of 192.168.100.124 and needs 64 subnets. How many hosts per network are allowed?

Options

Explanation

A Class C address has 8 host bits, and creating 64 subnets requires borrowing 6 of those bits, leaving only 2 host bits for 2 usable host addresses per subnet.

Common mistakes.

A. Achieving 4 usable hosts is not derivable from the remaining bits in this calculation; the closest valid value requires 3 host bits (2^3 - 2 = 6 hosts), which leaves only 5 subnet bits supporting a maximum of 32 subnets rather than 64.
B. Allocating enough host bits to support 8 usable hosts would consume at least 4 host bits, leaving fewer than 6 subnet bits and making 64 subnets impossible from a Class C address space.
C. 6 usable hosts requires 3 host bits (2^3 - 2 = 6), leaving only 5 subnet bits that support at most 32 subnets, which is half the required 64.

Concept tested. IPv4 subnetting with required number of subnets

Reference. https://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13788-3.html

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