CCNA Network Infrastructure and Connectivity Practice Question
A host uses the subnet mask 255.255.255.240. How many usable host addresses exist in each subnet?
⚠ Common exam trap
A frequent exam trap is selecting the total number of addresses in the subnet (16) instead of the usable host addresses (14). Candidates often forget to subtract the network and broadcast addresses, which are reserved and cannot be assigned to hosts. Another common mistake is confusing the /28 subnet mask with /27, which offers 30 usable hosts, leading to incorrect answers like 30. This confusion arises because both subnet masks are close in size but differ significantly in host capacity. Always remember that usable hosts equal total addresses minus two reserved addresses.
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 mask 255.255.255.240 corresponds to /28. In practical terms, that leaves 4 host bits, which gives 16 total addresses in each subnet. After subtracting the network and broadcast addresses, 14 usable hosts remain. This is a classic host-capacity calculation and a very common subnetting pattern on the exam.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
12
Why it's wrong here
Choosing 12 often results from incorrectly reserving more than two addresses. With a /28 mask, the block contains exactly 16 IPs; after setting aside the network ID and the directed broadcast, 14 remain. If you also deduct addresses for a default gateway or a 'reserved' value, you would get 12, but standard subnetting only excludes those two specific addresses. Thus 12 undercounts the true usable host capacity.
When this WOULD be correct
This option would be correct in a scenario where the question mistakenly asks for the total number of addresses in the subnet instead of usable addresses. For example, if the question stated, 'How many total addresses exist in a subnet with a mask of 255.255.255.240?' then 16 would be the correct answer.
- ✓
14
Why this is correct
A subnet mask of 255.255.255.240 is a /28 prefix, meaning 4 bits are available for host addresses. This yields 2^4 = 16 total IP addresses within the subnet. To determine usable host addresses, subtract the network address and the broadcast address, leaving 16 - 2 = 14 assignable addresses. So 14 is the correct number of usable hosts for a /28 network.
- ✗
16
Why it's wrong here
The number 16 represents the total size of the /28 address block, not the usable host count. Since 255.255.255.240 provides four host bits, 2^4 equals 16 total IP addresses, ranging from the network address to the broadcast address. However, the first and last addresses cannot be assigned to hosts, so the actual usable host count is 14. Confusing the total address block size with the assignable host capacity makes 16 an incorrect answer.
When this WOULD be correct
If the question asked about the total number of addresses in a subnet with a mask of 255.255.255.240, then the correct answer would be 16, as it counts all addresses including the network and broadcast addresses.
- ✗
30
Why it's wrong here
An answer of 30 would be accurate for a /27 subnet mask (255.255.255.224), which offers five host bits and therefore 32 total addresses with 30 usable. With the given mask of 255.255.255.240 (/28), there are only four host bits, producing a 16-address block and 14 usable hosts. Selecting 30 indicates you likely misread the subnet mask as /27 rather than /28, so it is incorrect for this question.
When this WOULD be correct
If the question specified a subnet mask of 255.255.255.252, which allows for 4 total addresses, then option D would be correct, as there would be 2 usable host addresses in that subnet.
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 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓14Correct answer▾
Why this is correct
A subnet mask of 255.255.255.240 is a /28 prefix, meaning 4 bits are available for host addresses. This yields 2^4 = 16 total IP addresses within the subnet. To determine usable host addresses, subtract the network address and the broadcast address, leaving 16 - 2 = 14 assignable addresses. So 14 is the correct number of usable hosts for a /28 network.
✗12Wrong answer — click to see why▾
Why this is wrong here
Option A is incorrect because the subnet mask 255.255.255.240 allows for 16 total addresses in each subnet, but only 14 of those are usable for hosts after accounting for the network and broadcast addresses.
★ When this WOULD be the correct answer
This option would be correct in a scenario where the question mistakenly asks for the total number of addresses in the subnet instead of usable addresses. For example, if the question stated, 'How many total addresses exist in a subnet with a mask of 255.255.255.240?' then 16 would be the correct answer.
Why candidates choose this
Candidates may choose this option due to confusion between total addresses and usable addresses, leading them to incorrectly calculate the usable host count without considering the network and broadcast addresses.
✗16Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because a subnet mask of 255.255.255.240 allows for 16 total IP addresses in each subnet, but only 14 of those are usable due to the network and broadcast addresses being reserved.
★ When this WOULD be the correct answer
If the question asked about the total number of addresses in a subnet with a mask of 255.255.255.240, then the correct answer would be 16, as it counts all addresses including the network and broadcast addresses.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of how to calculate usable addresses versus total addresses, leading them to mistakenly count all addresses in the subnet.
✗30Wrong answer — click to see why▾
Why this is wrong here
Option D is incorrect because the subnet mask 255.255.255.240 allows for 16 total addresses in each subnet, but only 14 of those are usable for hosts after accounting for the network and broadcast addresses.
★ When this WOULD be the correct answer
If the question specified a subnet mask of 255.255.255.252, which allows for 4 total addresses, then option D would be correct, as there would be 2 usable host addresses in that subnet.
Why candidates choose this
Candidates might choose option D because they miscalculate the total number of addresses without considering the reserved network and broadcast addresses, leading them to believe that all addresses are usable.
Analysis generated from the official 200-301blueprint 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
Subnetting and VLSM
Key term
Subnetting
Subnetting is the process of dividing a larger IP network into smaller, more manageable subnetworks (subnets) to improve performance, security, and efficient use of IP addresses.
Key term
Variable Length Subnet Mask
A Variable Length Subnet Mask (VLSM) allows network engineers to divide an IP address space into subnets of different sizes, using different subnet masks for each subnet to match the exact number of hosts needed.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco 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 200-301 exam.