N10-009 Networking Concepts Practice Question
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?
⚠ Common exam trap
The N10-009 exam 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.
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
✓
/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.
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
Selecting a /52 prefix for subnetting from a /48 global routing prefix allocates only 4 bits for subnet identification (52 - 48 = 4). This results in 2^4, or 16, available subnets. This quantity is significantly less than the required 250 subnets, rendering /52 an inadequate choice for the specified network design.
When this WOULD be correct
If the requirement were to support up to 16 subnets, a /52 would be the correct choice to minimize waste.
- ✓
/56
Why this is correct
A /48 global routing prefix is typically assigned to an organization. To create 250 subnets, additional bits beyond the /48 must be used for subnetting. A /56 prefix length means 8 bits are available for subnetting (56 - 48 = 8). This yields 2^8, or 256, possible subnets, which perfectly accommodates the requirement for 250 subnets with minimal address space waste.
- ✗
/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.
When this WOULD be correct
If the question required each subnet to support SLAAC (Stateless Address Autoconfiguration) or needed a standard subnet size for end-user networks, /64 is the correct choice because IPv6 standards mandate /64 for SLAAC.
- ✗
/60
Why it's wrong here
Utilizing a /60 prefix for subnetting from a /48 global routing prefix dedicates 12 bits for subnet identification (60 - 48 = 12). This provides 2^12, or 4,096, distinct subnets. While this technically satisfies the requirement for 250 subnets, it represents a substantial over-allocation and inefficient use of the available address space, making it a less optimal choice compared to a /56.
When this WOULD be correct
If the requirement were to support up to 4000 subnets, a /60 would be correct because it provides 4096 subnets, meeting the need with minimal waste compared to larger subnet sizes like /64.
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.
✓/56Correct answer▾
Why this is correct
A /48 global routing prefix is typically assigned to an organization. To create 250 subnets, additional bits beyond the /48 must be used for subnetting. A /56 prefix length means 8 bits are available for subnetting (56 - 48 = 8). This yields 2^8, or 256, possible subnets, which perfectly accommodates the requirement for 250 subnets with minimal address space waste.
✗/52Wrong answer — click to see why▾
Why this is wrong here
A /52 prefix provides 16 subnets (2^(52-48)=16), which is insufficient for the requirement of up to 250 subnets.
★ When this WOULD be the correct answer
If the requirement were to support up to 16 subnets, a /52 would be the correct choice to minimize waste.
Why candidates choose this
Candidates may mistakenly think that a /52 offers more subnets than a /56 because it has a larger subnet portion, but they forget that the number of subnets is 2^(subnet bits), and /52 gives only 16 subnets, far fewer than needed.
✗/64Wrong answer — click to see why▾
Why this is wrong here
A /64 subnet provides 2^64 addresses per subnet, which is far more than needed for 250 subnets. Using /64 would waste a huge number of addresses and does not minimize waste given the /48 prefix.
★ When this WOULD be the correct answer
If the question required each subnet to support SLAAC (Stateless Address Autoconfiguration) or needed a standard subnet size for end-user networks, /64 is the correct choice because IPv6 standards mandate /64 for SLAAC.
Why candidates choose this
Candidates often default to /64 because it is the most common IPv6 subnet size and is required for SLAAC, forgetting that the question emphasizes minimizing waste for a specific number of subnets.
✗/60Wrong answer — click to see why▾
Why this is wrong here
A /60 subnet provides only 2^(60-48)=4096 subnets, which is far more than the required 250, but it wastes more addresses than a /56 (which gives 256 subnets). The question asks to minimize waste, so /56 is optimal.
★ When this WOULD be the correct answer
If the requirement were to support up to 4000 subnets, a /60 would be correct because it provides 4096 subnets, meeting the need with minimal waste compared to larger subnet sizes like /64.
Why candidates choose this
Candidates may think a larger subnet prefix (like /60) is more efficient because it provides more subnets, but they overlook that the requirement is only 250 subnets, so a /56 wastes fewer addresses overall.
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?”
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Related to this question
Learn chapter
Network Virtualization and VXLAN
Key term
IPv6
IPv6 is the most recent version of the Internet Protocol, designed to replace IPv4 by providing a vastly larger number of unique addresses and improved network features.
Key term
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.