CCNA Network Infrastructure and Connectivity Practice Question
A host uses subnet mask 255.255.255.224. How many total addresses exist in each subnet block?
⚠ Common exam trap
Be careful to distinguish between total addresses and usable addresses. Many candidates automatically think of usable addresses when subnetting.
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
✓
32
The subnet mask 255.255.255.224 (/27) has 5 host bits, so each subnet has 2^5 = 32 total addresses. Option A (16) results from confusing /27 with /28 (4 host bits = 16). Option D (64) results from confusing /27 with /26 (6 host bits = 64). Option C (30) is the number of usable host addresses (32 - 2 = 30), not the total addresses asked for in the question.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
16
Why it's wrong here
An answer of 16 total addresses would correspond to a /28 prefix (255.255.255.240), which uses 4 host bits. Since the given /27 mask has 5 host bits, it doubles the address space to 32. Confusing the two prefix lengths leads to this incorrect total.
When this WOULD be correct
If the question specified a subnet mask of 255.255.255.240 instead, which corresponds to 28 subnet bits, then the total number of addresses would be 16. This would make option A the correct answer in that context.
- ✓
32
Why this is correct
The subnet mask 255.255.255.224 has 27 network bits, denoted as /27. The total number of addresses in a subnet is calculated as 2^(32-27) = 2^5 = 32. This total includes both the network address and the broadcast address, so the full address block size is 32 addresses.
- ✗
30
Why it's wrong here
The value 30 represents the usable host count for a /27 subnet, not the total address count. From the 32 total addresses in the block, the network address and the broadcast address are reserved, leaving exactly 30 assignable host addresses. The question asks for the total, so 30 is too small.
When this WOULD be correct
If the question asked for the number of usable addresses in a subnet with a mask of 255.255.255.224, option C would be correct, as there are 30 usable addresses after accounting for the network and broadcast addresses.
- ✗
64
Why it's wrong here
A total of 64 addresses corresponds to a /26 subnet mask (255.255.255.192), which has 6 host bits. The /27 prefix uses an additional network bit, reducing the host bits to 5 and therefore cutting the address space in half to 32. Thus, 64 is twice the correct total.
When this WOULD be correct
In a different question, if the subnet mask were 255.255.255.192, which allows for 64 addresses per subnet, option D would be correct. The question would need to specify that subnet mask to align with this answer.
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.
✓32Correct answer▾
Why this is correct
The subnet mask 255.255.255.224 has 27 network bits, denoted as /27. The total number of addresses in a subnet is calculated as 2^(32-27) = 2^5 = 32. This total includes both the network address and the broadcast address, so the full address block size is 32 addresses.
✗16Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because a subnet mask of 255.255.255.224 allows for 32 total addresses per subnet block, not 16. The calculation is based on the formula 2^(32 - subnet bits), where 224 corresponds to 27 subnet bits, yielding 32 addresses.
★ When this WOULD be the correct answer
If the question specified a subnet mask of 255.255.255.240 instead, which corresponds to 28 subnet bits, then the total number of addresses would be 16. This would make option A the correct answer in that context.
Why candidates choose this
Candidates may choose this option due to confusion between the number of usable addresses and total addresses, mistakenly recalling that 16 is a common subnet size for smaller networks.
✗30Wrong answer — click to see why▾
Why this is wrong here
Option C is incorrect because a subnet mask of 255.255.255.224 provides 32 total addresses per subnet block, not 30. The calculation is based on the formula 2^(32 - subnet bits), where 224 corresponds to 27 bits for the network.
★ When this WOULD be the correct answer
If the question asked for the number of usable addresses in a subnet with a mask of 255.255.255.224, option C would be correct, as there are 30 usable addresses after accounting for the network and broadcast addresses.
Why candidates choose this
Candidates may choose this option due to confusion between total addresses and usable addresses, leading them to mistakenly calculate the usable addresses instead of the total available in the subnet.
✗64Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because a subnet mask of 255.255.255.224 provides 32 total addresses per subnet block, not 64. The calculation is based on the formula 2^(32 - subnet bits), where 224 corresponds to 3 bits for hosts.
★ When this WOULD be the correct answer
In a different question, if the subnet mask were 255.255.255.192, which allows for 64 addresses per subnet, option D would be correct. The question would need to specify that subnet mask to align with this answer.
Why candidates choose this
Candidates may choose this option due to confusion between the number of usable addresses and total addresses, or they might mistakenly associate larger subnet masks with larger address counts without proper calculation.
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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Troubleshoot: DHCP Not Assigning Addresses
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
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 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.