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CCNA Practice Question: A network administrator is troubleshooting a…
This 200-301 practice question tests your understanding of 200-301 exam topics. 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 is troubleshooting a connectivity issue between two hosts on different subnets. The administrator captures packets on the source host and notices that the frames contain the correct source and destination MAC addresses but the encapsulated packets have incorrect source and destination IP addresses. According to the OSI model, which layer is most likely responsible for this issue?
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
✓
Network Layer (Layer 3)
The IP addresses are part of the Network Layer (Layer 3) header. Since the MAC addresses (Data Link Layer) are correct but the IP addresses are wrong, the problem lies at Layer 3, the Network Layer.
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.
- ✗
Physical Layer (Layer 1)
Why it's wrong here
The Physical Layer deals with the transmission of raw bits over a physical medium, not with IP addressing.
- ✗
Data Link Layer (Layer 2)
Why it's wrong here
The Data Link Layer handles MAC addresses and framing. The problem statement says the MAC addresses are correct, so the issue is not at this layer.
- ✓
Network Layer (Layer 3)
Why this is correct
The Network Layer is responsible for logical addressing (IP addresses) and routing. Incorrect IP addresses indicate a problem at this layer.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
Transport Layer (Layer 4)
Why it's wrong here
The Transport Layer handles end-to-end communication, segmentation, and port numbers, not IP addresses.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Network Layer (Layer 3)Correct answer▾
Why this is correct
The Network Layer is responsible for logical addressing (IP addresses) and routing. Incorrect IP addresses indicate a problem at this layer.
✗Physical Layer (Layer 1)Wrong answer — click to see why▾
Why this is wrong here
The issue is with the IP addresses, which are not handled at Layer 1.
✗Data Link Layer (Layer 2)Wrong answer — click to see why▾
Why this is wrong here
The MAC addresses are correct, so the Data Link Layer is functioning properly.
✗Transport Layer (Layer 4)Wrong answer — click to see why▾
Why this is wrong here
IP addresses are not part of the Transport Layer header; they belong to the Network Layer.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this 200-301 question test?
CIDR notation defines the prefix length.
What is the correct answer to this question?
The correct answer is: Network Layer (Layer 3) — The IP addresses are part of the Network Layer (Layer 3) header. Since the MAC addresses (Data Link Layer) are correct but the IP addresses are wrong, the problem lies at Layer 3, the Network Layer.
What should I do if I get this 200-301 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 200-301 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.
About these practice questions
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