This 200-901 practice question tests your understanding of network fundamentals. 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. A PC with IP address 192.168.1.10/24 cannot ping a server at 192.168.1.20/24. Both are on the same VLAN and connected to the same switch. What is the most likely cause of the issue?
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 server has a firewall blocking ICMP echo requests.
Since both devices are on the same subnet, a firewall on either device blocking ICMP is a common cause. Incorrect subnet mask would cause them to be on different subnets, but they have /24, so that is correct. ARP cache issue could be resolved, but not most likely. Default gateway is not needed for same subnet communication.
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 ARP cache on the PC needs to be cleared.
Why it's wrong here
ARP cache can be cleared, but it is not the most likely cause of persistent failure.
✗
The subnet mask on the PC is incorrect.
Why it's wrong here
The /24 mask is correct for the given IP range.
✗
The switch port is in the wrong VLAN.
Why it's wrong here
Both are on the same VLAN as stated, so this is not the issue.
✓
The server has a firewall blocking ICMP echo requests.
Why this is correct
A firewall can block ping, which is a common troubleshooting scenario.
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 default gateway is misconfigured on the PC.
Why it's wrong here
Default gateway is not required for communication within the same subnet.
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 200-901 questions on switching, trunking, and access-port configuration.
Network Fundamentals — This question tests Network Fundamentals — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The server has a firewall blocking ICMP echo requests. — Since both devices are on the same subnet, a firewall on either device blocking ICMP is a common cause. Incorrect subnet mask would cause them to be on different subnets, but they have /24, so that is correct. ARP cache issue could be resolved, but not most likely. Default gateway is not needed for same subnet communication.
What should I do if I get this 200-901 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 200-901 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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