This 200-301 practice question tests your understanding of network infrastructure and connectivity. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: subnetting divides an IPv4 network into smaller segments by using a prefix length that determines the number of host bits available.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A subnet must support 30 usable IPv4 host addresses. Which prefix is the smallest that meets the requirement?
/28
Why wrong: This is wrong because a /28 provides only 14 usable host addresses.
/27
This is correct because a /27 provides 30 usable host addresses.
/26
Why wrong: This is wrong because /26 works but is larger than necessary.
/25
Why wrong: This is wrong because /25 is much larger than required.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
/27
A /27 is the smallest valid prefix. In plain language, a /27 provides 32 total addresses, and after subtracting the network and broadcast addresses, 30 usable host addresses remain. A /28 would be too small because it provides only 14 usable hosts. This is a classic minimum-prefix question because it checks whether you can work backward from a host requirement and choose the smallest subnet that fits without over-allocating more space than necessary.
Key principle: Subnetting divides an IPv4 network into smaller segments by using a prefix length that determines the number of host bits available.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
/28
Why it's wrong here
This is wrong because a /28 provides only 14 usable host addresses.
When this WOULD be correct
If the question specified a requirement for 14 usable IPv4 host addresses instead of 30, then a /28 subnet would be the correct answer, as it meets that specific need.
/27
Why this is correct
This is correct because a /27 provides 30 usable host addresses.
Related concept
Subnetting divides an IPv4 network into smaller segments by using a prefix length that determines the number of host bits available.
/26
Why it's wrong here
This is wrong because /26 works but is larger than necessary.
When this WOULD be correct
If the exam question required a subnet that supports at least 62 usable addresses, then /26 would be the correct answer, as it provides the necessary capacity while still being a valid subnet size.
/25
Why it's wrong here
This is wrong because /25 is much larger than required.
When this WOULD be correct
If the exam question specified a requirement for a subnet that supports up to 126 usable addresses, then /25 would be the correct choice, as it would provide sufficient capacity for that scenario.
Option-by-option analysis
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.
Why this is correct
This is correct because a /27 provides 30 usable host addresses.
Why this is wrong here
A /28 subnet provides only 14 usable host addresses (16 total minus 2 for network and broadcast), which is insufficient for the requirement of 30 usable addresses.
★ When this WOULD be the correct answer
If the question specified a requirement for 14 usable IPv4 host addresses instead of 30, then a /28 subnet would be the correct answer, as it meets that specific need.
Why candidates choose this
Candidates may choose /28 due to a misunderstanding of subnetting calculations, mistakenly believing that a smaller subnet can still accommodate more hosts than it actually can.
Why this is wrong here
Option C: /26 provides 62 usable addresses, which exceeds the requirement of 30 usable addresses. Therefore, it is not the smallest prefix that meets the specified need.
★ When this WOULD be the correct answer
If the exam question required a subnet that supports at least 62 usable addresses, then /26 would be the correct answer, as it provides the necessary capacity while still being a valid subnet size.
Why candidates choose this
Candidates may choose /26 due to a misunderstanding of subnetting, mistakenly believing that a larger subnet is always acceptable without considering the requirement for the smallest prefix.
Why this is wrong here
Option D: /25 provides 126 usable addresses, which exceeds the requirement of 30 usable addresses. Therefore, it is not the smallest prefix that meets the specified need.
★ When this WOULD be the correct answer
If the exam question specified a requirement for a subnet that supports up to 126 usable addresses, then /25 would be the correct choice, as it would provide sufficient capacity for that scenario.
Why candidates choose this
Candidates may choose /25 due to a misunderstanding of subnetting, thinking that a larger subnet is always acceptable, or they might miscalculate the number of usable addresses needed for the given requirement.
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?”
Common exam traps
A frequent exam trap is choosing a /28 prefix because it appears to be the closest to supporting 30 hosts. However, a /28 subnet only provides 16 total addresses, of which 14 are usable for hosts after excluding the network and broadcast addresses. This mistake arises from confusing total addresses with usable hosts or failing to subtract the reserved addresses. Selecting a /28 leads to insufficient host capacity, causing network issues or exam failure. Always remember that usable hosts equal total addresses minus two, which is critical when calculating subnet sizes for CCNA questions.
Detailed technical explanation
Subnetting is a fundamental concept in IPv4 networking that divides a larger network into smaller, manageable subnetworks. Each subnet is identified by a network prefix, which determines the number of available host addresses. The prefix length, expressed as a slash followed by a number (e.g., /27), indicates how many bits are used for the network portion of the address, with the remaining bits available for host addressing. To determine the smallest subnet prefix that supports a specific number of usable hosts, you must calculate the total number of addresses needed, including network and broadcast addresses, which are not assignable to hosts. For 30 usable hosts, you need at least 32 total addresses (30 hosts + 1 network + 1 broadcast). A /27 prefix provides exactly 32 addresses (2^(32-27) = 32), making it the smallest subnet that meets the requirement. Prefixes longer than /27 (like /28) provide fewer addresses, while shorter prefixes (like /26 or /25) provide more than necessary. A common exam trap is confusing total addresses with usable host addresses. Candidates often select a /28 because it seems close to the required number, but it only provides 14 usable hosts, which is insufficient. Understanding the difference between total and usable addresses and correctly applying subnetting formulas is crucial for Cisco CCNA exam success and practical network design.
Key takeaway
Subnetting divides an IPv4 network into smaller segments by using a prefix length that determines the number of host bits available.
Real-world example
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Review subnetting divides an IPv4 network into smaller segments by using a prefix length that determines the number of host bits available., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Subnetting divides an IPv4 network into smaller segments by using a prefix length that determines the number of host bits available..
The correct answer is: /27 — A /27 is the smallest valid prefix. In plain language, a /27 provides 32 total addresses, and after subtracting the network and broadcast addresses, 30 usable host addresses remain. A /28 would be too small because it provides only 14 usable hosts. This is a classic minimum-prefix question because it checks whether you can work backward from a host requirement and choose the smallest subnet that fits without over-allocating more space than necessary.
Review subnetting divides an IPv4 network into smaller segments by using a prefix length that determines the number of host bits available., then practise related 200-301 questions on the same topic to reinforce the concept.
Subnetting divides an IPv4 network into smaller segments by using a prefix length that determines the number of host bits available.
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Last reviewed: May 17, 2026
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