- A
Check physical connectivity (cables, link lights, interface status).
The bottom-up OSI approach starts at Layer 1 (physical). Checking physical connectivity ensures the cable is plugged in, link lights are on, and the interface is up/up, which is the foundation for all higher-layer communication.
- B
Verify DNS resolution (nslookup, DNS server reachability).
This step belongs to Layer 7 (application) and is too high in the OSI model for a bottom-up approach. Starting with DNS skips lower-layer checks that could be the root cause.
- C
Check IP configuration (IP address, subnet mask, default gateway).
This step corresponds to Layer 3 (network). While important, it should come after verifying Layer 1 and Layer 2 in a bottom-up approach.
- D
Verify MAC address table and VLAN configuration on the switch.
This step belongs to Layer 2 (data link). In a bottom-up approach, it should come after Layer 1 but before Layer 3. Placing it after Layer 3 violates the order.
CCNA Network Infrastructure and Connectivity Practice Question
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.
Drag and drop the following troubleshooting steps into the correct order to diagnose a client connectivity issue using the OSI bottom-up method. The client cannot access a web server by its FQDN.
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
Check physical connectivity (cables, link lights, interface status).
The bottom-up OSI approach starts with Layer 1 (physical) – step A; then Layer 2 (data link) – step D; then Layer 3 (network) – step C; and finally Layer 7 (application) – step B. This methodical progression isolates the issue layer by layer, ensuring all dependencies are checked systematically.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Check physical connectivity (cables, link lights, interface status).
Why this is correct
The bottom-up OSI approach starts at Layer 1 (physical). Checking physical connectivity ensures the cable is plugged in, link lights are on, and the interface is up/up, which is the foundation for all higher-layer communication.
Related concept
Access ports place end devices into a single VLAN.
- ✓
Verify DNS resolution (nslookup, DNS server reachability).
- ✓
Check IP configuration (IP address, subnet mask, default gateway).
Why this is correct
This step corresponds to Layer 3 (network). While important, it should come after verifying Layer 1 and Layer 2 in a bottom-up approach.
Related concept
Access ports place end devices into a single VLAN.
- ✓
Verify MAC address table and VLAN configuration on the switch.
Why this is correct
This step belongs to Layer 2 (data link). In a bottom-up approach, it should come after Layer 1 but before Layer 3. Placing it after Layer 3 violates the order.
Related concept
Access ports place end devices into a single VLAN.
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
- Access ports place end devices into a single VLAN.
- Trunk ports carry multiple VLANs between switches.
- Allowed VLAN lists decide which VLANs can cross a trunk.
- Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
- Use show vlan brief to verify access VLANs.
- Use show interfaces trunk to verify trunk state and allowed VLANs.
- Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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.
What to study next
Got this wrong? Here's your next step.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
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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 — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: Check physical connectivity (cables, link lights, interface status). — The bottom-up OSI approach starts with Layer 1 (physical) – step A; then Layer 2 (data link) – step D; then Layer 3 (network) – step C; and finally Layer 7 (application) – step B. This methodical progression isolates the issue layer by layer, ensuring all dependencies are checked systematically.
What should I do if I get this 200-301 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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Last reviewed: Jun 6, 2026
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