This 200-901 practice question tests your understanding of network fundamentals. 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. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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 company uses a /24 subnet for its office LAN. The network must accommodate 30 hosts per VLAN. Which subnet mask would be most efficient for each VLAN while minimizing wasted IP addresses?
255.255.255.224
This is /27, provides 30 usable hosts, exactly meeting the requirement.
255.255.255.240
Why wrong: This is /28, provides 14 usable hosts, insufficient.
255.255.255.0
Why wrong: This is /24, provides 254 hosts, not efficient for 30 hosts.
255.255.255.128
Why wrong: This is /25, provides 126 usable hosts, too large.
255.255.255.192
Why wrong: This is /26, provides 62 usable hosts, wastes addresses.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
255.255.255.224
A /27 subnet mask (255.255.255.224) provides 32 total addresses per subnet, with 30 usable host addresses (2^5 - 2 = 30). This exactly meets the requirement of 30 hosts per VLAN without wasting IP addresses, as any larger subnet would leave unused addresses.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
255.255.255.224
Why this is correct
This is /27, provides 30 usable hosts, exactly meeting the requirement.
Related concept
Read the scenario before looking for a memorised answer.
255.255.255.240
Why it's wrong here
This is /28, provides 14 usable hosts, insufficient.
255.255.255.0
Why it's wrong here
This is /24, provides 254 hosts, not efficient for 30 hosts.
255.255.255.128
Why it's wrong here
This is /25, provides 126 usable hosts, too large.
255.255.255.192
Why it's wrong here
This is /26, provides 62 usable hosts, wastes addresses.
Common exam traps
Cisco often tests the misconception that the subnet mask must match the exact number of hosts without accounting for the network and broadcast addresses, leading candidates to choose a mask that provides exactly 30 total addresses (like /27) but forget that 2 addresses are reserved.
Detailed technical explanation
Subnetting uses the formula 2^(32 - prefix_length) - 2 to calculate usable hosts. For a /27, the prefix length is 27, giving 2^5 - 2 = 30 usable addresses. In real-world scenarios, VLANs often require precise host counts to conserve IP space in larger networks, and using a /27 allows for multiple VLANs within a /24 (8 subnets of 32 addresses each).
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
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FAQ
Network Fundamentals — This question tests Network Fundamentals — Read the scenario before looking for a memorised answer..
The correct answer is: 255.255.255.224 — A /27 subnet mask (255.255.255.224) provides 32 total addresses per subnet, with 30 usable host addresses (2^5 - 2 = 30). This exactly meets the requirement of 30 hosts per VLAN without wasting IP addresses, as any larger subnet would leave unused addresses.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This 200-901 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 200-901 exam.
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