CCNA Network Infrastructure and Connectivity Practice Question
A subnet uses the mask 255.255.255.224. How many usable host addresses does it provide?
⚠ Common exam trap
Remember to subtract the network and broadcast addresses from the total count of addresses in a subnet.
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
✓
30
A mask of 255.255.255.224 corresponds to a /27 prefix. In plain language, that leaves 5 host bits available in the address, which creates 32 total addresses in each subnet. Two of those are reserved: one for the network address and one for the broadcast address. That leaves 30 usable host addresses. This is a classic subnetting question because it tests whether you can move from mask to prefix idea to host count without getting lost. Many learners remember the block size but forget to subtract the network and broadcast entries. The correct answer comes from that full logic chain: /27 means 32 total, and therefore 30 usable.
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 it's wrong here
The value 14 would imply 16 total addresses in the subnet, because 2^4 - 2 = 14 usable hosts. That requires exactly 4 host bits, which corresponds to a /28 mask (255.255.255.240). The /27 mask in the question has one additional host bit, so it generates roughly double that number of usable addresses, not 14.
When this WOULD be correct
This option would be correct in a scenario where the question specifies a subnet mask of 255.255.255.240, which allows for 14 usable host addresses. In this case, the calculation would be 2^(4) - 2 = 14.
- ✓
30
Why this is correct
The subnet mask 255.255.255.224 equates to a /27 prefix, which leaves only 3 bits for host addressing in the final octet. With 5 host bits total, the block contains 2^5 = 32 addresses. Subtracting the network and broadcast addresses yields exactly 32 - 2 = 30 usable host addresses.
- ✗
62
Why it's wrong here
A total of 62 usable hosts would come from a block of 64 addresses, which requires 6 host bits because 2^6 = 64. That scenario matches a /26 mask (255.255.255.192), not the /27 mask given here. Since the question's mask provides only 5 host bits, it cannot support 64 addresses in the subnet.
When this WOULD be correct
If the question asked about a subnet mask of 255.255.255.192 instead, which provides 62 usable addresses, then option C would be the correct answer. In this case, the calculation would be 2^(32-26) - 2 = 62 usable addresses.
- ✗
126
Why it's wrong here
To get 126 usable hosts, you would need a subnet with 128 total addresses, since 2^7 - 2 = 126. That necessitates 7 host bits, which is the hallmark of a /25 mask (255.255.255.128). The specified /27 mask carries only 5 host bits, so its address capacity is far smaller than what would produce 126 usable hosts.
When this WOULD be correct
If the question asked how many usable addresses are in a subnet with a mask of 255.255.255.0, which allows for 256 total addresses minus 2 for the network and broadcast addresses, then option D would be correct as it would provide 254 usable addresses.
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.
✓30Correct answer▾
Why this is correct
The subnet mask 255.255.255.224 equates to a /27 prefix, which leaves only 3 bits for host addressing in the final octet. With 5 host bits total, the block contains 2^5 = 32 addresses. Subtracting the network and broadcast addresses yields exactly 32 - 2 = 30 usable host addresses.
✗14Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because a subnet mask of 255.255.255.224 provides 30 usable host addresses, not 14. The calculation is based on the formula 2^(number of host bits) - 2, where the number of host bits is 5 for this subnet mask.
★ When this WOULD be the correct answer
This option would be correct in a scenario where the question specifies a subnet mask of 255.255.255.240, which allows for 14 usable host addresses. In this case, the calculation would be 2^(4) - 2 = 14.
Why candidates choose this
Candidates may choose this option due to confusion between different subnet masks and their corresponding usable addresses, particularly if they miscalculate or misremember the formula for determining usable hosts.
✗62Wrong 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, of which 30 are usable after subtracting the network and broadcast addresses. The calculation is 2^(32-27) - 2 = 30 usable addresses.
★ When this WOULD be the correct answer
If the question asked about a subnet mask of 255.255.255.192 instead, which provides 62 usable addresses, then option C would be the correct answer. In this case, the calculation would be 2^(32-26) - 2 = 62 usable addresses.
Why candidates choose this
Candidates may choose this option due to confusion between subnet sizes and their corresponding usable addresses, especially if they have recently studied larger subnets and misapplied the calculations.
✗126Wrong answer — click to see why▾
Why this is wrong here
Option D is incorrect because a subnet mask of 255.255.255.224 allows for 30 usable host addresses, not 126. The calculation is based on the formula 2^(32 - subnet bits) - 2, where the subnet bits for this mask is 27.
★ When this WOULD be the correct answer
If the question asked how many usable addresses are in a subnet with a mask of 255.255.255.0, which allows for 256 total addresses minus 2 for the network and broadcast addresses, then option D would be correct as it would provide 254 usable addresses.
Why candidates choose this
Candidates may choose this option due to confusion with larger subnet sizes, mistakenly associating the number 126 with a common subnet size, or miscalculating the usable hosts based on a misunderstanding of subnetting principles.
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?”
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Key term
CAN
A CAN (Controller Area Network) is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other without a host computer.
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.