N10-009 Network Implementation Practice Question
A network engineer is designing a subnet for a department that requires exactly 50 usable host addresses. Which subnet mask provides the minimum number of usable host addresses while still accommodating the requirement?
⚠ Common exam trap
CompTIA often tests the confusion between total addresses and usable addresses, where candidates mistakenly think a /27 (32 total addresses) can support 50 hosts, or they forget to subtract the network and broadcast addresses from the total.
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
✓
/26
A /26 subnet mask (255.255.255.192) provides 2^(32-26) = 64 total addresses, of which 62 are usable (subtracting network and broadcast addresses). This is the smallest subnet that meets the requirement of exactly 50 usable hosts, as /27 yields only 30 usable addresses and /28 yields only 14, while /25 provides 126 usable addresses, which is more than necessary.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
/26
Why this is correct
A /26 CIDR mask allocates 26 bits for the network portion, leaving 6 bits for host addresses. This configuration provides 2^6 = 64 total IP addresses. After reserving one for the network address and one for the broadcast address, 62 usable host addresses remain, which is the smallest subnet size capable of accommodating exactly 50 required hosts without significant waste.
- ✗
/27
Why it's wrong here
A /27 CIDR mask dedicates 27 bits to the network, leaving only 5 bits for host addresses. Consequently, this subnet provides 2^5 = 32 total IP addresses. Subtracting the network and broadcast addresses leaves only 30 usable host addresses, rendering this subnet insufficient to support the department's requirement for 50 hosts.
When this WOULD be correct
This option would be correct if the question required exactly 30 usable host addresses, such as for a small department or a point-to-point link with additional devices.
- ✗
/28
Why it's wrong here
A /28 CIDR mask designates 28 bits for the network, leaving only 4 bits for host addresses. This results in 2^4 = 16 total IP addresses within the subnet. With two addresses reserved for the network and broadcast, only 14 usable host addresses are available, which is far too few to meet the requirement of 50 hosts.
When this WOULD be correct
A /28 subnet would be correct for a department requiring exactly 14 usable host addresses, such as a small lab or management network with limited devices.
- ✗
/25
Why it's wrong here
A /25 CIDR mask utilizes 25 bits for the network, leaving 7 bits available for host addresses. This configuration yields 2^7 = 128 total IP addresses. After accounting for the network and broadcast addresses, 126 usable host addresses are provided, which, while sufficient for 50 hosts, is not the most efficient choice as it allocates significantly more addresses than necessary and is not the minimum required size.
When this WOULD be correct
A /25 subnet would be correct if the department required exactly 100 usable host addresses, as it provides 126 usable addresses, which is the smallest subnet that can accommodate 100 hosts.
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.
✓/26Correct answer▾
Why this is correct
A /26 CIDR mask allocates 26 bits for the network portion, leaving 6 bits for host addresses. This configuration provides 2^6 = 64 total IP addresses. After reserving one for the network address and one for the broadcast address, 62 usable host addresses remain, which is the smallest subnet size capable of accommodating exactly 50 required hosts without significant waste.
✗/27Wrong answer — click to see why▾
Why this is wrong here
A /27 subnet provides 2^(32-27)-2 = 30 usable host addresses, which is insufficient for the requirement of 50 usable hosts.
★ When this WOULD be the correct answer
This option would be correct if the question required exactly 30 usable host addresses, such as for a small department or a point-to-point link with additional devices.
Why candidates choose this
Candidates may mistakenly calculate the number of hosts as 2^(32-27) = 32 without subtracting the network and broadcast addresses, or they may confuse /27 with /26.
✗/28Wrong answer — click to see why▾
Why this is wrong here
A /28 subnet provides only 14 usable host addresses (2^(32-28)-2 = 14), which is insufficient for the required 50 usable hosts.
★ When this WOULD be the correct answer
A /28 subnet would be correct for a department requiring exactly 14 usable host addresses, such as a small lab or management network with limited devices.
Why candidates choose this
Candidates may mistakenly think /28 provides 16 usable addresses (ignoring network and broadcast addresses) or miscalculate the number of hosts needed.
✗/25Wrong answer — click to see why▾
Why this is wrong here
A /25 subnet provides 126 usable host addresses, which far exceeds the requirement of 50. The question asks for the minimum number of usable addresses while still accommodating the requirement, so /26 (62 usable) is the correct choice, not /25.
★ When this WOULD be the correct answer
A /25 subnet would be correct if the department required exactly 100 usable host addresses, as it provides 126 usable addresses, which is the smallest subnet that can accommodate 100 hosts.
Why candidates choose this
Candidates may mistakenly think that a larger subnet (more hosts) is always better, or they may miscalculate the number of usable hosts for /25 (e.g., thinking it provides 128 usable addresses) and assume it fits the requirement without considering the 'minimum' constraint.
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?”
Visual reference
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Related to this question
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Physical Network Infrastructure
Key term
Subnet mask
A subnet mask is a 32-bit number that helps a computer or network device determine which part of an IP address identifies the network and which part identifies the host device on that network.
Key term
Usable hosts
Usable hosts are the IP addresses in a subnet that can actually be assigned to devices like computers, printers, or servers, excluding the network and broadcast addresses.
About these practice questions
Courseiva writes every N10-009 question from scratch — 464 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
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.