This 200-901 practice question tests your understanding of network fundamentals. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network engineer needs to create a new subnet that can support at least 50 usable host addresses for a development environment. Which TWO subnet masks would meet this requirement? (Choose two.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
255.255.255.128 (/25)
Subnet masks /25 and /26 provide 126 and 62 usable host addresses respectively, both exceeding the requirement of 50. /27 provides only 30 usable addresses, /28 provides 14, and /29 provides 6, all insufficient.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
255.255.255.224 (/27)
Why it's wrong here
Incorrect. /27 provides only 30 usable host addresses, which is insufficient for 50 hosts.
✓
255.255.255.128 (/25)
Why this is correct
Correct. /25 provides 2^(32-25)-2 = 126 usable host addresses, which is more than 50.
Clue confirmation
The clue word "least" in the question point toward this answer.
Incorrect. /29 provides only 6 usable host addresses, insufficient.
✗
255.255.255.240 (/28)
Why it's wrong here
Incorrect. /28 provides only 14 usable host addresses, far below the requirement.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-901 subnetting questions on CIDR, address ranges, and subnet selection.
Network Fundamentals — This question tests Network Fundamentals — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: 255.255.255.128 (/25) — Subnet masks /25 and /26 provide 126 and 62 usable host addresses respectively, both exceeding the requirement of 50. /27 provides only 30 usable addresses, /28 provides 14, and /29 provides 6, all insufficient.
What should I do if I get this 200-901 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-901 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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