200-901 Network Fundamentals Practice Question
A network administrator needs to assign IP addresses to devices on a subnet with a /25 prefix. How many usable host addresses are available?
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
✓
126
A /25 subnet has 7 bits for hosts (32-25=7), giving 2^7 = 128 total addresses, minus 2 (network and broadcast) = 126 usable hosts.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
254
Why it's wrong here
A /25 leaves 7 host bits, giving 128 addresses minus 2 reserved for network and broadcast, so 126 usable hosts, not 254. It is tempting because 254 is the familiar answer for a /24, and would be correct if the prefix were /24 rather than /25.
- ✓
126
Why this is correct
A /25 prefix leaves 7 host bits (32 − 25), giving 2⁷ = 128 total addresses. Subtracting the network and broadcast addresses yields 126 usable host addresses, satisfying the subnet's requirement. This matches the standard formula 2^h − 2, where h is the number of host bits available.
- ✗
64
Why it's wrong here
A /25 leaves 7 host bits, yielding 128 addresses and 126 usable hosts, so 64 understates the subnet. It is tempting because 64 is the usable count for a /26, and would be correct if the prefix were /26 instead of /25.
- ✗
128
Why it's wrong here
A /25 contains 128 total addresses, but two are reserved for the network and broadcast addresses, leaving 126 usable hosts. It is tempting because 128 is the block size, and would be correct if the question asked for total addresses rather than usable host addresses.
Visual reference
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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.