The correct subnet mask is 255.255.224.0. This is because to create 8 subnets from a /16 network, you must borrow 3 host bits for subnetting, as 2³ equals 8. Borrowing those 3 bits extends the network prefix from /16 to /19, which in dotted decimal is 255.255.224.0. Each of these /19 subnets then provides 2¹³ minus 2, or 8190 usable hosts, easily satisfying the requirement of at least 1000 hosts per subnet. On the CompTIA A+ Core 1 220-1201 exam, this type of question tests your ability to apply subnetting fundamentals under real-world constraints—specifically, balancing the number of subnets against host capacity. A common trap is to stop at the subnet count without verifying the host count, or to mistakenly use a /24 mask which would only yield 254 hosts per subnet. A helpful memory tip: remember that borrowing 3 bits from a /16 gives you a /19, and the magic number for the third octet is 32 (256 minus 224), so your subnets increment by 32 in that octet.
220-1101 IP Addressing Practice Question
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 company has a network with the IP range 172.16.0.0/16. They need to create 8 separate subnets for different departments, each with at least 1000 usable hosts. What subnet mask should be used?
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.
Why wrong: This is a /20 subnet mask, which would provide 16 subnets (2^4) but only 4094 usable hosts per subnet, which is sufficient but not the most efficient for exactly 8 subnets.
B
255.255.224.0
A /19 mask (255.255.224.0) provides 8 subnets (2^3) with 8190 usable hosts each, meeting both requirements.
C
255.255.248.0
Why wrong: This is a /21 subnet mask, which would provide 32 subnets (2^5) but only 2046 usable hosts per subnet, which is enough but not the best fit for exactly 8 subnets.
D
255.255.192.0
Why wrong: This is a /18 subnet mask, which would provide 4 subnets (2^2), not enough to create 8 separate subnets.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
255.255.224.0
To create 8 subnets from a /16 network, you need to borrow 3 bits (2^3=8 subnets). This gives a /19 subnet mask (255.255.224.0), which provides 8190 usable hosts per subnet (2^13-2), meeting the requirement of at least 1000 hosts.
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.
✗
255.255.240.0
Why it's wrong here
This is a /20 subnet mask, which would provide 16 subnets (2^4) but only 4094 usable hosts per subnet, which is sufficient but not the most efficient for exactly 8 subnets.
✓
255.255.224.0
Why this is correct
A /19 mask (255.255.224.0) provides 8 subnets (2^3) with 8190 usable hosts each, meeting both requirements.
Clue confirmation
The clue word "least" in the question point toward this answer.
This is a /21 subnet mask, which would provide 32 subnets (2^5) but only 2046 usable hosts per subnet, which is enough but not the best fit for exactly 8 subnets.
✗
255.255.192.0
Why it's wrong here
This is a /18 subnet mask, which would provide 4 subnets (2^2), not enough to create 8 separate subnets.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 220-1201 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
IP Addressing — This question tests IP Addressing — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: 255.255.224.0 — To create 8 subnets from a /16 network, you need to borrow 3 bits (2^3=8 subnets). This gives a /19 subnet mask (255.255.224.0), which provides 8190 usable hosts per subnet (2^13-2), meeting the requirement of at least 1000 hosts.
What should I do if I get this 220-1201 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 220-1201 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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