CCNA Network Infrastructure and Connectivity Practice Question
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?
⚠ Common exam trap
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.
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.
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 defines the electrical, mechanical, and procedural specifications for transmitting raw bit streams over a physical medium. Problems at this layer typically manifest as signal degradation, cabling faults, or carrier loss, not as logical addressing errors. Because the issue involves incorrect IP addresses, which are logical identifiers, the Physical Layer cannot be the source of the problem.
- ✗
Data Link Layer (Layer 2)
Why it's wrong here
The Data Link Layer provides node-to-node delivery by framing packets and using MAC addresses for local network communication. The scenario explicitly states that the MAC addresses are correct, so frame delivery and addressing at this layer are functioning properly. Incorrect IP addresses are a Layer 3 concern, not a Layer 2 issue, since IP addressing is not part of the Data Link Layer's responsibilities.
- ✓
Network Layer (Layer 3)
Why this is correct
The Network Layer is responsible for logical addressing, routing, and forwarding packets based on IP addresses. When an IP address is incorrect, the host cannot participate in proper network communication, and routers cannot make accurate forwarding decisions. Because the problem directly involves IP addresses, the Network Layer is the most likely layer where the fault exists.
- ✗
Transport Layer (Layer 4)
Why it's wrong here
The Transport Layer manages end-to-end communication between applications, handling segmentation, flow control, and port numbers via TCP or UDP. It does not assign or configure IP addresses; that function belongs exclusively to the Network Layer. Therefore, an issue with incorrect IP addresses cannot be caused by the Transport Layer, as its duties do not encompass logical addressing.
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, routing, and forwarding packets based on IP addresses. When an IP address is incorrect, the host cannot participate in proper network communication, and routers cannot make accurate forwarding decisions. Because the problem directly involves IP addresses, the Network Layer is the most likely layer where the fault exists.
✗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?”
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 |
Go deeper
Related to this question
Learn chapter
The OSI Model
Key term
OSI model
The OSI model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers, from physical hardware to application software.
Key term
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.