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200-901 Practice Question: A company uses a /24 subnet for its office LAN
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?
⚠ Common exam trap
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.
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
✓
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.
Answer analysis
Option-by-option breakdown
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.