- A
255.255.255.240 (/28)
Why wrong: /28 provides 14 usable hosts, which is insufficient for 25 devices.
- B
255.255.255.224 (/27)
/27 provides 28 usable hosts, which meets the requirement with minimal waste.
- C
255.255.255.192 (/26)
Why wrong: /26 provides 62 usable hosts, which is more than needed but not the minimum.
- D
255.255.255.128 (/25)
Why wrong: /25 provides 126 usable hosts, far exceeding the need and not the minimal subnet.
Question 104 of 520
N10-009 /27 subnet mask Practice Question
This N10-009 practice question tests your understanding of networking concepts. 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. A key principle to apply: /27 subnet mask. 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 assign IP addresses to a new subnet that will support exactly 25 devices. Which subnet mask would provide the minimum number of usable host addresses while still accommodating the requirement?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
255.255.255.224 (/27)
Option B (255.255.255.224, /27) provides 32 total addresses per subnet, with 30 usable host addresses (2^(32-27)-2 = 30). This is the smallest subnet that can accommodate exactly 25 devices, as /28 yields only 14 usable hosts and /26 yields 62, which is excessive.
Key principle: /27 subnet mask
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
255.255.255.240 (/28)
Why it's wrong here
/28 provides 14 usable hosts, which is insufficient for 25 devices.
When this WOULD be correct
A /28 subnet would be correct if the requirement was to support exactly 14 devices or fewer, such as a small branch office with 10 workstations and a printer.
- ✓
255.255.255.224 (/27)
Why this is correct
/27 provides 28 usable hosts, which meets the requirement with minimal waste.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
/27 subnet mask
- ✗
255.255.255.192 (/26)
Why it's wrong here
/26 provides 62 usable hosts, which is more than needed but not the minimum.
When this WOULD be correct
This option would be correct if the requirement was to support exactly 62 devices, or if the question specified a subnet that must accommodate up to 60 hosts while leaving room for future expansion.
- ✗
255.255.255.128 (/25)
Why it's wrong here
/25 provides 126 usable hosts, far exceeding the need and not the minimal subnet.
When this WOULD be correct
This subnet mask would be correct in a scenario requiring at least 100 usable host addresses, such as a subnet for a medium-sized office with 100 devices.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓255.255.255.224 (/27)Correct answer▾
Why this is correct
/27 provides 28 usable hosts, which meets the requirement with minimal waste.
✗255.255.255.240 (/28)Wrong answer — click to see why▾
Why this is wrong here
A /28 subnet provides only 14 usable host addresses (2^(32-28)-2), which is insufficient for 25 devices.
★ When this WOULD be the correct answer
A /28 subnet would be correct if the requirement was to support exactly 14 devices or fewer, such as a small branch office with 10 workstations and a printer.
Why candidates choose this
Candidates may mistakenly think that 16 total addresses (2^(32-28)) are all usable, forgetting the network and broadcast addresses, or they may misapply the 'minus 2' rule.
✗255.255.255.192 (/26)Wrong answer — click to see why▾
Why this is wrong here
The /26 subnet mask provides 62 usable addresses, which far exceeds the requirement of 25 devices. The question asks for the minimum number of usable host addresses, so /27 with 30 usable addresses is the correct choice.
★ When this WOULD be the correct answer
This option would be correct if the requirement was to support exactly 62 devices, or if the question specified a subnet that must accommodate up to 60 hosts while leaving room for future expansion.
Why candidates choose this
Candidates may mistakenly think that a larger subnet (more hosts) is safer or easier to manage, or they may miscalculate the number of usable hosts for /26 as 30 instead of 62.
✗255.255.255.128 (/25)Wrong answer — click to see why▾
Why this is wrong here
A /25 subnet provides 126 usable host addresses, which far exceeds the requirement of 25 devices, making it inefficient and not the minimum.
★ When this WOULD be the correct answer
This subnet mask would be correct in a scenario requiring at least 100 usable host addresses, such as a subnet for a medium-sized office with 100 devices.
Why candidates choose this
Candidates may mistakenly think a larger subnet is safer or may not calculate the exact number of usable hosts, assuming more is better without considering efficiency.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The N10-009 exam often tests the common misconception that the number of usable hosts equals 2^(host bits) without subtracting the network and broadcast addresses, leading candidates to incorrectly choose a /28 mask thinking 16 addresses are enough for 25 devices.
Detailed technical explanation
How to think about this question
The subnet mask determines the boundary between the network and host portions of an IPv4 address. For a /27 prefix, the host portion is 5 bits, yielding 2^5 = 32 total addresses, with the first address reserved as the network ID and the last as the broadcast address. In real-world scenarios, using the smallest sufficient subnet conserves IP address space, which is critical in VLSM (Variable Length Subnet Mask) designs within a larger address block.
KKey Concepts to Remember
- /27 subnet mask
- Usable host calculation
- /28 subnet mask
- Subnet mask selection
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
/27 subnet mask
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review /27 subnet mask, then practise related N10-009 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this N10-009 question test?
Networking Concepts — This question tests Networking Concepts — /27 subnet mask.
What is the correct answer to this question?
The correct answer is: 255.255.255.224 (/27) — Option B (255.255.255.224, /27) provides 32 total addresses per subnet, with 30 usable host addresses (2^(32-27)-2 = 30). This is the smallest subnet that can accommodate exactly 25 devices, as /28 yields only 14 usable hosts and /26 yields 62, which is excessive.
What should I do if I get this N10-009 question wrong?
Review /27 subnet mask, then practise related N10-009 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
/27 subnet mask
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Last reviewed: Jun 11, 2026
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