200-901 Network Fundamentals Practice Question
A network engineer is designing a subnet that needs to support 30 usable hosts. Which subnet mask should be used?
⚠ Common exam trap
Cisco often tests the formula 2^n - 2 for usable hosts, and the trap here is that candidates may forget to subtract the network and broadcast addresses, or they may confuse the number of host bits with the subnet mask value (e.g., thinking /28 supports 16 usable hosts instead of 14).
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 (/27)
(255.255.255.224, /27) provides 5 host bits, yielding 2^5 = 32 total addresses per subnet. Subtracting the network and broadcast addresses leaves exactly 30 usable hosts, meeting the requirement precisely.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
255.255.255.240 (/28)
Why it's wrong here
A /28 yields 16 addresses, leaving 14 usable after network and broadcast, short of the 30 required. It tempts because /28 is the natural fit for a 14-host segment, and it is the correct mask when a subnet must support up to 14 usable hosts.
- ✗
255.255.255.0 (/24)
Why it's wrong here
A /24 mask yields 254 usable hosts, far exceeding the 30 required, wasting 224 addresses. It is tempting because /24 is the default classful boundary and common in small LANs, but a /27 (255.255.255.224) provides exactly 30 usable hosts.
- ✓
255.255.255.224 (/27)
Why this is correct
A /27 mask leaves five host bits, yielding 32 addresses minus network and broadcast, so exactly 30 usable hosts. It is the smallest subnet satisfying the stated requirement without waste, whereas /28 would provide only 14 usable addresses.
- ✗
255.255.255.192 (/26)
Why it's wrong here
A /26 mask yields 62 usable hosts, exceeding the 30 required and wasting 32 addresses. It is tempting because /26 is a common subnetting choice, but a /27 (255.255.255.224) provides exactly 30 usable hosts for this requirement.
Visual reference
About these practice questions
Courseiva writes every 200-901 question from scratch — 975 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
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.