- A
The default gateway is missing.
Why wrong: Even with a gateway, they are on different subnets; but the gateway could route, but the question asks most likely reason. Actually, both could be true, but the subnet mismatch is the root cause.
- B
The subnet mask is incorrect; they are on different subnets.
192.168.1.10 is in subnet 0, 192.168.1.200 is in subnet 128.
- C
The ARP cache is corrupted.
Why wrong: ARP is needed for same subnet; they are on different subnets.
- D
The hosts are using different DNS servers.
Why wrong: DNS is not involved in local communication.
Question 32 of 1,000
200-901 Network Fundamentals Practice Question
This 200-901 practice question tests your understanding of network fundamentals. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 network administrator notices that a host with IP 192.168.1.10/25 cannot communicate with a host at 192.168.1.200/25. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
✓
The subnet mask is incorrect; they are on different subnets.
With a /25 mask (255.255.255.128), the network is divided into two subnets: 192.168.1.0-127 and 192.168.1.128-255. The two hosts are in different subnets and require a router to communicate.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The default gateway is missing.
Why it's wrong here
Even with a gateway, they are on different subnets; but the gateway could route, but the question asks most likely reason. Actually, both could be true, but the subnet mismatch is the root cause.
- ✓
The subnet mask is incorrect; they are on different subnets.
Why this is correct
192.168.1.10 is in subnet 0, 192.168.1.200 is in subnet 128.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
The ARP cache is corrupted.
Why it's wrong here
ARP is needed for same subnet; they are on different subnets.
- ✗
The hosts are using different DNS servers.
Why it's wrong here
DNS is not involved in local communication.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-901 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this 200-901 question test?
Network Fundamentals — This question tests Network Fundamentals — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The subnet mask is incorrect; they are on different subnets. — With a /25 mask (255.255.255.128), the network is divided into two subnets: 192.168.1.0-127 and 192.168.1.128-255. The two hosts are in different subnets and require a router to communicate.
What should I do if I get this 200-901 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-901 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Last reviewed: Jul 4, 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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