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 user reports that they can ping the IP address of the default gateway but cannot ping a server on a different subnet. The administrator checks the ARP table on the user's PC and sees an incomplete entry for the server's IP. 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 PC is not configured with a default gateway.
The user can ping the default gateway, confirming that the PC has local connectivity and a correctly configured IP address and subnet mask. However, the incomplete ARP entry for the server's IP indicates that the PC cannot resolve the server's MAC address, which is required to send frames to a different subnet. Without a default gateway configured, the PC will not send ARP requests for remote hosts to the router; instead, it will attempt to ARP for the server directly, which fails because the server is on a different broadcast domain.
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.
✗
There is an IP address conflict on the network.
Why it's wrong here
IP conflict would cause intermittent issues.
✗
Spanning Tree Protocol is blocking the port on the switch.
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between Layer 2 (ARP) and Layer 3 (routing) failures, and the trap here is that candidates assume a firewall or STP is blocking traffic, when the real issue is the PC's lack of a default gateway preventing it from even attempting to reach the remote subnet via ARP for the router.
Detailed technical explanation
How to think about this question
When a host needs to send a packet to a different subnet, it must forward the frame to the default gateway's MAC address. The ARP table entry for the remote server remains incomplete because the PC never sends an ARP request for the server; instead, it should ARP for the gateway. In Windows, you can verify the default gateway with `ipconfig` and the ARP cache with `arp -a`; an incomplete entry (e.g., with no MAC address) for a remote IP strongly suggests the host is not using the gateway for off-subnet traffic.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Fundamentals — This question tests Network Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The PC is not configured with a default gateway. — The user can ping the default gateway, confirming that the PC has local connectivity and a correctly configured IP address and subnet mask. However, the incomplete ARP entry for the server's IP indicates that the PC cannot resolve the server's MAC address, which is required to send frames to a different subnet. Without a default gateway configured, the PC will not send ARP requests for remote hosts to the router; instead, it will attempt to ARP for the server directly, which fails because the server is on a different broadcast domain.
What should I do if I get this 200-901 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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Question Discussion
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