The correct answer is that a Layer 2 switch uses MAC addresses to make forwarding decisions. This is because it operates at the Data Link layer (Layer 2) of the OSI model, where it examines the destination MAC address in each incoming Ethernet frame and consults its MAC address table to determine the exact port for forwarding, enabling efficient local area network communication without inspecting IP addresses. On the CompTIA Network+ N10-009 exam, this characteristic is frequently tested to distinguish Layer 2 switches from routers (which use IP addresses) and hubs (which flood all ports). A common trap is confusing a switch’s forwarding method with a router’s routing table, so remember that switches build MAC address tables dynamically by learning source addresses. Memory tip: “Layer 2 looks at the MAC, not the IP stack.”
N10-009 Networking Concepts Practice Question
This N10-009 practice question tests your understanding of networking concepts. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which of the following is a characteristic of a Layer 2 network switch?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Uses MAC addresses to make forwarding decisions
A Layer 2 network switch operates at the Data Link layer of the OSI model and uses MAC addresses to make forwarding decisions. It examines the destination MAC address in an Ethernet frame and consults its MAC address table to determine the appropriate port to forward the frame, enabling efficient local area network communication.
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.
✗
Makes forwarding decisions based on IP addresses
Why it's wrong here
IP address forwarding is a Layer 3 function performed by routers and Layer 3 switches.
✓
Uses MAC addresses to make forwarding decisions
Why this is correct
Layer 2 switches use MAC address tables to forward frames to the correct port based on the destination MAC address.
Related concept
Read the scenario before looking for a memorised answer.
✗
Can route traffic between different VLANs without a router
Why it's wrong here
Routing between VLANs requires Layer 3 functionality. A pure Layer 2 switch cannot perform inter-VLAN routing.
✗
Provides Network Address Translation (NAT)
Why it's wrong here
NAT is a Layer 3 function typically performed by routers or firewalls.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between Layer 2 and Layer 3 functionality, and the trap here is that candidates may confuse a switch's ability to segment VLANs with the ability to route between them, forgetting that routing requires a Layer 3 device or process.
Detailed technical explanation
How to think about this question
Under the hood, a Layer 2 switch builds its MAC address table by learning the source MAC addresses of incoming frames on each port, associating them with the port number. When a frame arrives with an unknown destination MAC, the switch floods the frame out all ports except the ingress port, a process known as unknown unicast flooding. In a real-world scenario, this behavior can cause issues in large networks with asymmetric routing or when MAC address tables overflow, leading to excessive flooding and potential performance degradation.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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: Uses MAC addresses to make forwarding decisions — A Layer 2 network switch operates at the Data Link layer of the OSI model and uses MAC addresses to make forwarding decisions. It examines the destination MAC address in an Ethernet frame and consults its MAC address table to determine the appropriate port to forward the frame, enabling efficient local area network communication.
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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