Question 159 of 1,020

IP Addressing →hardMultiple ChoiceObjective-mapped

Which Subnet Mask for 50 Hosts Using VLSM?

This 220-1201 practice question tests your understanding of ip addressing. 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 is designing a subnet scheme for a company with three departments: Sales (50 devices), HR (20 devices), and IT (10 devices). The company uses the 10.0.0.0/24 network. To minimize waste, the engineer decides to use variable-length subnet masking (VLSM). Which of the following subnet masks should be assigned to the Sales department?

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.

A
255.255.255.128
Why wrong: Incorrect. A /25 provides 126 usable addresses, which is more than needed and wastes addresses.
B
255.255.255.192
Correct. A /26 provides 62 usable addresses, enough for 50 devices with minimal waste.
C
255.255.255.224
Why wrong: Incorrect. A /27 provides only 30 usable addresses, which is insufficient for 50 devices.
D
255.255.255.240
Why wrong: Incorrect. A /28 provides only 14 usable addresses, far too few for Sales.

Full breakdown with real-world context →

Quick Answer

The answer is 255.255.255.192, which is a /26 subnet mask. This is the correct VLSM subnet mask for 50 devices because it provides 62 usable host addresses, the smallest power of two that accommodates the required 50 hosts without excessive waste. In variable-length subnet masking, you always allocate the largest subnet first, so the Sales department’s need for 50 devices dictates a /26 prefix, while smaller subnets like /27 (30 usable hosts) or /28 (14 usable hosts) would fall short. On the CompTIA A+ Core 1 220-1201 exam, this question tests your ability to apply VLSM to minimize IP waste in a real-world scenario, often appearing as part of a multi-department subnetting problem. A common trap is forgetting to subtract the network and broadcast addresses when counting usable hosts, or assuming a /25 (126 hosts) is needed, which wastes addresses. For a quick memory tip, remember that a /26 gives you 64 total addresses minus 2 for network and broadcast, leaving exactly 62—plenty for 50 devices, and the “6” in /26 can remind you of the 6 bits for hosts (2^6 = 64).

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

✓

255.255.255.192

The Sales department requires 50 hosts. A /26 subnet mask (255.255.255.192) provides 62 usable addresses (2^(32-26)-2 = 62), which is the smallest subnet that can accommodate 50 devices without waste. VLSM allows using this mask within the 10.0.0.0/24 network, leaving room for other subnets.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
255.255.255.128
Why it's wrong here
Incorrect. A /25 provides 126 usable addresses, which is more than needed and wastes addresses.
✓
255.255.255.192
Why this is correct
Correct. A /26 provides 62 usable addresses, enough for 50 devices with minimal waste.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
255.255.255.224
Why it's wrong here
Incorrect. A /27 provides only 30 usable addresses, which is insufficient for 50 devices.
✗
255.255.255.240
Why it's wrong here
Incorrect. A /28 provides only 14 usable addresses, far too few for Sales.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the candidate's ability to calculate the exact number of usable hosts per subnet (2^(32-prefix)-2) and match it to the requirement, tricking those who forget to subtract the network and broadcast addresses or who round up to the nearest power of two without considering the -2.

Detailed technical explanation

How to think about this question

VLSM relies on borrowing bits from the host portion to create subnets of varying sizes. For a /24 network, a /26 mask borrows 2 bits, creating 4 subnets (2^2) each with 62 usable hosts. In practice, network engineers must also account for future growth; if Sales might expand beyond 62 devices, a /25 mask (126 hosts) would be chosen instead, but the question explicitly minimizes waste.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

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

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 220-1201 question test?

IP Addressing — This question tests IP Addressing — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: 255.255.255.192 — The Sales department requires 50 hosts. A /26 subnet mask (255.255.255.192) provides 62 usable addresses (2^(32-26)-2 = 62), which is the smallest subnet that can accommodate 50 devices without waste. VLSM allows using this mask within the 10.0.0.0/24 network, leaving room for other subnets.

What should I do if I get this 220-1201 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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?

Read the scenario before looking for a memorised answer.

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