Planning for 29 subnets: To create at least 29 subnets while maximizing host addresses per subnet, how many bits must be borrowed from the host field?
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A2
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B3
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C4
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D5
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E6
Answer
Correct Answer: 5
Explanation
Introduction / Context:Subnet-count planning uses powers of two. The number of subnet bits you borrow from the host field must be large enough so that 2^(borrowed_bits) meets or exceeds the number of required subnets.
Given Data / Assumptions:
- Required subnets: at least 29.
- Goal: maximize hosts per subnet (so borrow the minimum bits that satisfy subnet count).
Concept / Approach:Find the smallest n such that 2^n ≥ 29. The fewer bits we borrow, the more host bits remain, maximizing host capacity.
Step-by-Step Solution:
2^4 = 16 → not enough.2^5 = 32 → sufficient for 29.Therefore, borrow 5 bits to create at least 29 subnets and preserve as many host bits as possible.Verification / Alternative check:Check next lower value (4) fails; next higher (6) would reduce host space unnecessarily.
Why Other Options Are Wrong:
- 2/3/4: Provide 4, 8, or 16 subnets—insufficient.
- 6: Provides 64 subnets but reduces host counts more than needed.
Common Pitfalls:Forgetting that modern designs allow using all subnets (subnet-zero included); borrowing more bits than needed and needlessly shrinking host capacity.
Final Answer:5