N10-009 Networking Concepts Practice Question
A network administrator is configuring IP addresses for a new subnet. The network address is 192.168.1.0 with a subnet mask of 255.255.255.240. How many usable host addresses are available on this subnet?
⚠ Common exam trap
The trap here is that candidates often forget to subtract the network and broadcast addresses, selecting the total number of addresses (16) instead of the usable host count (14).
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
✓
14
The subnet mask 255.255.255.240 (or /28) provides 16 total addresses per subnet. The network address (192.168.1.0) and the broadcast address (192.168.1.15) are reserved, leaving 16 - 2 = 14 usable host addresses. This is calculated as 2^(32-28) - 2 = 2^4 - 2 = 16 - 2 = 14.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
14
Why this is correct
A /28 subnet mask (255.255.255.240) designates 4 bits for the host portion of the IP address (32 total bits - 28 network bits = 4 host bits). This allows for 2^4 = 16 total IP addresses within the subnet. However, two addresses are reserved: one for the network address itself and one for the broadcast address. Subtracting these two reserved addresses leaves 14 usable IP addresses for hosts and other network devices.
- ✗
16
Why it's wrong here
While a /28 subnet indeed encompasses 16 total IP addresses, this count represents the entire address range from the network address to the broadcast address, inclusive. The first address in this range is always reserved as the network identifier, and the last address is reserved as the broadcast address for that specific subnet. Therefore, 16 is the gross number of addresses, not the number available for assignment to individual hosts.
When this WOULD be correct
If the question asked for the total number of addresses in the subnet (including network and broadcast), then 16 would be correct. For example: 'How many IP addresses are in a subnet with mask 255.255.255.240?'
- ✗
30
Why it's wrong here
To accommodate 30 usable host addresses, a subnet would need to provide 32 total addresses (30 usable + 2 reserved). This quantity of addresses is achieved with a /27 CIDR prefix, which allocates 5 bits for the host portion (2^5 = 32 total addresses). A /28 subnet, by contrast, only provides 16 total addresses, making 30 an impossible number of usable hosts for that specific subnet size.
When this WOULD be correct
This option would be correct if the subnet mask were 255.255.255.224 (/27), which provides 32 total addresses and 30 usable hosts. For example, a question asking for usable hosts on 192.168.1.0/27 would have answer 30.
- ✗
62
Why it's wrong here
An address count of 62 usable hosts would require a subnet mask that provides 64 total addresses (62 usable + 2 reserved). This corresponds to a /26 CIDR prefix, which leaves 6 host bits (2^6 = 64 total addresses). A /28 subnet is significantly smaller, providing only 16 total addresses, making 62 an incorrect value for usable hosts in this context.
When this WOULD be correct
If the subnet mask were 255.255.255.192 (/26) instead of 255.255.255.240, the network would have 64 total addresses, yielding 62 usable hosts. This would be the correct answer for a question with that mask.
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.
✓14Correct answer▾
Why this is correct
A /28 subnet mask (255.255.255.240) designates 4 bits for the host portion of the IP address (32 total bits - 28 network bits = 4 host bits). This allows for 2^4 = 16 total IP addresses within the subnet. However, two addresses are reserved: one for the network address itself and one for the broadcast address. Subtracting these two reserved addresses leaves 14 usable IP addresses for hosts and other network devices.
✗16Wrong answer — click to see why▾
Why this is wrong here
The subnet mask 255.255.255.240 (/28) provides 16 total addresses per subnet, but the network address and broadcast address are reserved, leaving only 14 usable host addresses.
★ When this WOULD be the correct answer
If the question asked for the total number of addresses in the subnet (including network and broadcast), then 16 would be correct. For example: 'How many IP addresses are in a subnet with mask 255.255.255.240?'
Why candidates choose this
Candidates often forget to subtract the network and broadcast addresses, mistakenly counting all 16 addresses as usable.
✗30Wrong answer — click to see why▾
Why this is wrong here
A /28 subnet (255.255.255.240) provides 16 total addresses, but the network and broadcast addresses are reserved, leaving 14 usable hosts. Option C (30) corresponds to a /27 subnet (255.255.255.224), not /28.
★ When this WOULD be the correct answer
This option would be correct if the subnet mask were 255.255.255.224 (/27), which provides 32 total addresses and 30 usable hosts. For example, a question asking for usable hosts on 192.168.1.0/27 would have answer 30.
Why candidates choose this
Candidates often confuse the number of total addresses (32) with usable addresses, forgetting to subtract 2 for network and broadcast. They may also misapply the formula 2^(32 - prefix) - 2, mistakenly using 2^5 = 32 instead of 2^4 = 16.
✗62Wrong answer — click to see why▾
Why this is wrong here
A /28 subnet (255.255.255.240) provides 16 total addresses, but 2 are reserved for network and broadcast, leaving 14 usable. Option D (62) corresponds to a /26 subnet (255.255.255.192), which is not the mask in this question.
★ When this WOULD be the correct answer
If the subnet mask were 255.255.255.192 (/26) instead of 255.255.255.240, the network would have 64 total addresses, yielding 62 usable hosts. This would be the correct answer for a question with that mask.
Why candidates choose this
Candidates may mistakenly calculate 2^(32-26) = 64 and forget to subtract 2, or confuse the mask with a /26, which is a common subnet size.
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
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.
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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.