The answer is a misconfigured subnet mask. This is the most likely cause because the subnet mask determines which IP addresses a device considers local versus remote. When the subnet mask is incorrect, the laptop may see the file server as being on a different network, so it sends traffic for the server to the default gateway (the router) instead of directly to the local network. Since the router can forward traffic to the internet, web access works, but the file server’s response never comes back locally. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of network segmentation and IP addressing—specifically how a subnet mask mismatch isolates a device from local resources while leaving internet access intact. A common trap is assuming the issue is with the file server or DNS, but the key clue is that other devices work fine. Memory tip: think of the subnet mask as a fence—if it’s the wrong height, you can still see the road (internet) but can’t reach your neighbor (local shares).
220-1201 Network Troubleshooting Practice Question
This 220-1201 practice question tests your understanding of network troubleshooting. 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 customer reports that their laptop can connect to the internet via Wi-Fi but cannot access any network shares on the local file server. Other devices on the same network can access the shares. What is the most likely cause?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The laptop has a misconfigured subnet mask.
This scenario tests understanding of network segmentation and IP addressing. The laptop can reach the internet (default gateway works) but not local resources, indicating a subnet mask or VLAN mismatch. The most common cause is an incorrect subnet mask, which prevents the laptop from recognizing the file server as local.
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.
✗
The file server is powered off.
Why it's wrong here
Incorrect because other devices can access the shares, so the server is on.
✓
The laptop has a misconfigured subnet mask.
Why this is correct
Correct. A wrong subnet mask can allow internet access but block local LAN communication.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
✗
The Wi-Fi router is overloaded.
Why it's wrong here
Incorrect because other devices work fine, and internet access works.
✗
The laptop's firewall is blocking all traffic.
Why it's wrong here
Incorrect because internet access works; a full block would prevent all connectivity.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 220-1201 question in full detail.
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 220-1201 questions on switching, trunking, and access-port configuration.
Network Troubleshooting — This question tests Network Troubleshooting — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The laptop has a misconfigured subnet mask. — This scenario tests understanding of network segmentation and IP addressing. The laptop can reach the internet (default gateway works) but not local resources, indicating a subnet mask or VLAN mismatch. The most common cause is an incorrect subnet mask, which prevents the laptop from recognizing the file server as local.
What should I do if I get this 220-1201 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 220-1201 questions on switching, trunking, and access-port configuration.
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?
Access ports place end devices into a single VLAN.
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