The answer is a /56 subnet size. This is correct because a /48 prefix provides 8 bits for subnetting, and 2^8 equals 256 subnets, which comfortably covers the requirement of up to 250 subnets while minimizing waste—using a /55 would give only 128 subnets (too few), and a /57 would give 512 subnets (wasteful over-allocation). On the CompTIA Network+ N10-009 exam, this question tests your understanding of IPv6 subnetting math and the concept of “subnet bits” derived from the prefix length; a common trap is to confuse the number of subnets with the number of hosts per subnet, so remember that in IPv6, subnet size is about the number of subnets, not host capacity. A quick memory tip: think “/48 to /56 is 8 bits, 2^8 = 256, just enough for 250—no waste.”
N10-009 Networking Concepts 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. 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 new IPv6 addressing scheme. The company has been assigned a /48 prefix and needs to support up to 250 subnets. Which subnet size should be used to minimize waste while meeting 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.
Why wrong: A /52 prefix uses 4 bits for subnetting (48+4=52), providing only 16 subnets (2^4). This is insufficient for 250 subnets.
B
/56
A /56 prefix uses 8 bits for subnetting (48+8=56), providing 256 subnets (2^8). This meets the requirement of 250 subnets with minimal waste (6 unused subnets).
C
/64
Why wrong: A /64 prefix uses 16 bits for subnetting (48+16=64), providing 65,536 subnets. While it works, it wastes many subnet IDs and is not minimal for 250 subnets. Also, /64 is typically used for end-user subnets, not as a subnetting strategy from a /48.
D
/60
Why wrong: A /60 prefix uses 12 bits for subnetting (48+12=60), providing 4,096 subnets. This exceeds the requirement significantly and wastes more than a /56 would.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
/56
A /56 subnet provides 256 subnets (2^(56-48) = 2^8 = 256), which meets the requirement of up to 250 subnets with minimal waste. A /48 prefix is the site-level allocation, and using a /56 subnet mask leaves 8 bits for subnetting, offering exactly the needed capacity without over-allocating address space.
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.
✗
/52
Why it's wrong here
A /52 prefix uses 4 bits for subnetting (48+4=52), providing only 16 subnets (2^4). This is insufficient for 250 subnets.
✓
/56
Why this is correct
A /56 prefix uses 8 bits for subnetting (48+8=56), providing 256 subnets (2^8). This meets the requirement of 250 subnets with minimal waste (6 unused subnets).
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.
✗
/64
Why it's wrong here
A /64 prefix uses 16 bits for subnetting (48+16=64), providing 65,536 subnets. While it works, it wastes many subnet IDs and is not minimal for 250 subnets. Also, /64 is typically used for end-user subnets, not as a subnetting strategy from a /48.
✗
/60
Why it's wrong here
A /60 prefix uses 12 bits for subnetting (48+12=60), providing 4,096 subnets. This exceeds the requirement significantly and wastes more than a /56 would.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that /64 is the only valid subnet size in IPv6, but the question asks for subnet size to minimize waste for subnets, not for SLAAC, so candidates incorrectly choose /64 without considering the requirement for only 250 subnets.
Detailed technical explanation
How to think about this question
In IPv6, subnetting is performed by borrowing bits from the interface ID portion of the address, but the /64 boundary is critical for SLAAC (Stateless Address Autoconfiguration) as per RFC 4862. Using a /56 for site-level subnets is common in enterprise designs, as it balances granularity with simplicity, and many ISPs assign /56 prefixes to residential customers. The /48 prefix is typically the smallest allocation from a Regional Internet Registry (RIR) for a site, allowing flexible subnetting within the organization.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Networking Concepts — This question tests Networking Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: /56 — A /56 subnet provides 256 subnets (2^(56-48) = 2^8 = 256), which meets the requirement of up to 250 subnets with minimal waste. A /48 prefix is the site-level allocation, and using a /56 subnet mask leaves 8 bits for subnetting, offering exactly the needed capacity without over-allocating address space.
What should I do if I get this N10-009 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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