- A
Physical Layer (Layer 1)
Why wrong: The Physical Layer deals with the transmission of raw bits over a physical medium, not with IP addressing.
- B
Data Link Layer (Layer 2)
Why wrong: 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.
- C
Network Layer (Layer 3)
The Network Layer is responsible for logical addressing (IP addresses) and routing. Incorrect IP addresses indicate a problem at this layer.
- D
Transport Layer (Layer 4)
Why wrong: The Transport Layer handles end-to-end communication, segmentation, and port numbers, not IP addresses.
Question 1,256 of 1,819
Layer 3 Troubleshooting: Incorrect Source and Destination IPs
This 200-301 practice question tests your understanding of network infrastructure and connectivity. 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.
Quick Answer
The answer is the Network Layer (Layer 3), as it is solely responsible for logical IP addressing and routing decisions between different subnets. When captured frames show correct MAC addresses but incorrect source and destination IPs, the problem is clearly in how the IP headers are constructed or assigned, not in the data-link layer’s physical delivery. On the CCNA 200-301 v2 exam, this scenario tests your ability to isolate OSI layer faults—a common trap is blaming Layer 2 because MAC addresses look fine, but the real issue lies in misconfigured IP settings, subnet masks, or default gateways on the source host. Remember the memory tip: “MACs move locally, IPs route globally”—if the IPs are wrong, the network layer is where you must look.
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 Network Layer (Layer 3) is responsible for logical addressing (IP addresses) and routing packets between different subnets. Since the captured frames have correct MAC addresses (Layer 2) but incorrect source and destination IP addresses, the issue lies in how the IP headers are being constructed or assigned, which is a Layer 3 function. This could be caused by misconfigured IP addresses, subnet masks, or default gateways on the source host.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
Read the scenario before looking for a memorised answer.
- ✗
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: answer the scenario, not the keyword
Cisco often tests the distinction between MAC addresses (Layer 2) and IP addresses (Layer 3) in troubleshooting scenarios, and the trap here is that candidates might incorrectly blame the Data Link Layer because they see 'frames' and 'MAC addresses' in the question, without recognizing that the IP address error points to the Network Layer.
Detailed technical explanation
How to think about this question
When a host sends a packet to a different subnet, it must use its own IP address as the source and the destination host's IP address (or the default gateway's IP for routing) as the destination. If the IP addresses are incorrect, the packet may be dropped by routers or delivered to the wrong host; this is often due to misconfiguration in the host's network stack (e.g., static IP assignment errors or DHCP lease issues). In practice, tools like `ipconfig` (Windows) or `ip addr` (Linux) can verify the assigned IP addresses, and a packet capture (e.g., Wireshark) can confirm whether the IP headers match the expected values.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Network Layer (Layer 3) — The Network Layer (Layer 3) is responsible for logical addressing (IP addresses) and routing packets between different subnets. Since the captured frames have correct MAC addresses (Layer 2) but incorrect source and destination IP addresses, the issue lies in how the IP headers are being constructed or assigned, which is a Layer 3 function. This could be caused by misconfigured IP addresses, subnet masks, or default gateways on the source host.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 11, 2026
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