N10-009 /29 subnet mask Practice Question
A network technician is assigned a subnet mask of 255.255.255.248. How many usable host addresses are available in this subnet?
⚠ Common exam trap
The N10-009 exam often tests the distinction between total addresses and usable host addresses, trapping candidates who forget to subtract the two reserved addresses (network and broadcast) 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
✓
A) 6
The subnet mask 255.255.255.248 corresponds to a /29 prefix length, which provides 2^(32-29) = 8 total addresses. Subtracting the network address and broadcast address leaves 8 - 2 = 6 usable host addresses.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A) 6
Why this is correct
Correct. /29 gives 8 total addresses minus 2 = 6 usable hosts.
- ✗
B) 8
Why it's wrong here
Incorrect. 8 is the total number of addresses in the subnet, but two are reserved for network and broadcast.
When this WOULD be correct
This option would be correct if the question asked for the total number of addresses in the subnet (including network and broadcast), or if the subnet mask were 255.255.255.240 (/28) which provides 14 usable hosts.
- ✗
C) 14
Why it's wrong here
Incorrect. 14 usable hosts correspond to a /28 subnet (255.255.255.240), not /29.
When this WOULD be correct
If the subnet mask were 255.255.255.240 (/28), the number of usable host addresses would be 14. This is a common question variation.
- ✗
D) 30
Why it's wrong here
Incorrect. 30 usable hosts correspond to a /27 subnet (255.255.255.224), not /29.
When this WOULD be correct
This would be correct for a subnet mask of 255.255.255.224 (/27), which provides 2^(32-27)=32 total addresses and 30 usable 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.
✓A) 6Correct answer▾
Why this is correct
Correct. /29 gives 8 total addresses minus 2 = 6 usable hosts.
✗B) 8Wrong answer — click to see why▾
Why this is wrong here
The subnet mask 255.255.255.248 corresponds to a /29 prefix, which provides 2^(32-29) = 8 total addresses. Subtracting 2 for network and broadcast addresses leaves 6 usable hosts, not 8.
★ When this WOULD be the correct answer
This option would be correct if the question asked for the total number of addresses in the subnet (including network and broadcast), or if the subnet mask were 255.255.255.240 (/28) which provides 14 usable hosts.
Why candidates choose this
Candidates often forget to subtract the network and broadcast addresses, mistakenly counting all 8 addresses as usable.
✗C) 14Wrong answer — click to see why▾
Why this is wrong here
A /28 subnet (255.255.255.240) provides 14 usable hosts, but the given mask is /29 (255.255.255.248), which has only 6 usable hosts.
★ When this WOULD be the correct answer
If the subnet mask were 255.255.255.240 (/28), the number of usable host addresses would be 14. This is a common question variation.
Why candidates choose this
Candidates may misremember the host formula or confuse /29 with /28, especially under time pressure.
✗D) 30Wrong answer — click to see why▾
Why this is wrong here
A subnet mask of 255.255.255.248 corresponds to a /29 prefix, which provides 2^(32-29)=8 total addresses. Subtracting the network and broadcast addresses leaves 6 usable hosts, not 30.
★ When this WOULD be the correct answer
This would be correct for a subnet mask of 255.255.255.224 (/27), which provides 2^(32-27)=32 total addresses and 30 usable hosts.
Why candidates choose this
Candidates may mistakenly apply the formula for a /27 subnet (30 hosts) or confuse the mask with 255.255.255.224, a common subnet mask for larger networks.
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
Learn chapter
IPv6 Addressing and Address Types
Key term
Network address
A network address is a unique identifier that allows devices to find and communicate with each other on a computer network.
Key term
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
About these practice questions
Courseiva writes every N10-009 question from scratch — 472 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 →
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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.