The answer is the Physical layer, Layer 1 of the OSI model. This is the correct starting point for physical cable troubleshooting because the Physical layer governs the raw transmission of bits over the physical medium, defining the electrical, mechanical, and procedural specifications for copper or fiber optic cabling. When a network administrator suspects a cabling issue, they must begin here to check for faults like broken pins, signal degradation, improper termination, or distance limitations before moving up the stack. On the CompTIA Network+ N10-009 exam, this question tests your ability to map real-world symptoms to the correct OSI layer, often appearing in scenario-based questions where you must identify the first step in a structured troubleshooting methodology. A common trap is jumping to Layer 2 or 3 when the problem is purely physical, so remember: if you can touch it or see the cable, start at Layer 1. Keep the mnemonic “Please Do Not Throw Sausage Pizza Away” in mind—Physical is the first layer for a reason.
N10-009 Networking Concepts Practice Question
This N10-009 practice question tests your understanding of networking concepts. 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 and suspects the problem is related to the physical cabling. At which layer of the OSI model should the administrator begin their investigation?
Why wrong: The Transport layer is responsible for end-to-end communication and segmentation, not physical cabling.
B
Data Link layer
Why wrong: The Data Link layer handles framing and MAC addressing, but not the physical medium itself.
C
Physical layer
The Physical layer defines the electrical, mechanical, and procedural interface to the transmission medium, making it the correct layer for cabling issues.
D
Network layer
Why wrong: The Network layer handles logical addressing and routing, not physical connections.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Physical layer
The Physical layer (Layer 1) is the correct starting point because the administrator suspects the problem is related to physical cabling. The Physical layer defines the electrical, mechanical, and procedural specifications for transmitting raw bits over a physical medium, such as copper or fiber optic cables. Troubleshooting at this layer involves checking for cable faults, signal degradation, or improper termination before moving up the OSI stack.
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.
✗
Transport layer
Why it's wrong here
The Transport layer is responsible for end-to-end communication and segmentation, not physical cabling.
✗
Data Link layer
Why it's wrong here
The Data Link layer handles framing and MAC addressing, but not the physical medium itself.
✓
Physical layer
Why this is correct
The Physical layer defines the electrical, mechanical, and procedural interface to the transmission medium, making it the correct layer for cabling issues.
Related concept
Read the scenario before looking for a memorised answer.
✗
Network layer
Why it's wrong here
The Network layer handles logical addressing and routing, not physical connections.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often jump to the Data Link layer (Layer 2) because they associate 'connectivity issues' with MAC addresses or switching, forgetting that physical cabling faults must be ruled out first at Layer 1.
Detailed technical explanation
How to think about this question
At the Physical layer, issues like excessive attenuation, crosstalk, or impedance mismatches can cause bit errors that manifest as link flaps or CRC errors at Layer 2. Tools like a time-domain reflectometer (TDR) or cable tester are used to identify breaks, shorts, or length violations in copper cabling. In real-world scenarios, a miswired T568A/T568B termination can cause a link to fail at 1 Gbps but work at 100 Mbps, a subtle behavior that requires Layer 1 inspection.
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 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Networking Concepts — This question tests Networking Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Physical layer — The Physical layer (Layer 1) is the correct starting point because the administrator suspects the problem is related to physical cabling. The Physical layer defines the electrical, mechanical, and procedural specifications for transmitting raw bits over a physical medium, such as copper or fiber optic cables. Troubleshooting at this layer involves checking for cable faults, signal degradation, or improper termination before moving up the OSI stack.
What should I do if I get this N10-009 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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