CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. 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.
Exhibit
R1#show interfaces GigabitEthernet0/1
GigabitEthernet0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 00aa.bbcc.1122
Description: Uplink to Distribution Switch
MTU 1500 bytes, BW 100000 Kbit, DLY 10 usec, reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
Last input never, output 00:00:01, output hang never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 12450
Queueing strategy: fifo
Output queue: 40/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 10000000 bits/sec, 2500 packets/sec
12345 packets input, 1234567 bytes, 0 no buffer
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
9876 packets output, 1234567890 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
Total output drops: 12450
Refer to the exhibit. A network engineer notices packet loss and sluggish application performance on a branch-office uplink. While troubleshooting, the engineer executes the show interfaces GigabitEthernet0/1 command on the router. Based on the output, what is the most likely cause of the performance 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.
R1#show interfaces GigabitEthernet0/1
GigabitEthernet0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 00aa.bbcc.1122
Description: Uplink to Distribution Switch
MTU 1500 bytes, BW 100000 Kbit, DLY 10 usec, reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
Last input never, output 00:00:01, output hang never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 12450
Queueing strategy: fifo
Output queue: 40/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 10000000 bits/sec, 2500 packets/sec
12345 packets input, 1234567 bytes, 0 no buffer
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
9876 packets output, 1234567890 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
Total output drops: 12450
A
The interface is experiencing excessive collisions due to a duplex mismatch.
Why wrong: The output shows the interface operating in full-duplex mode and 0 output collisions, ruling out a duplex mismatch or collision-related drops.
B
An upstream device is sending traffic at a rate higher than this interface can transmit, causing the output queue to overflow.
The output queue is maxed (40/40) and output drops are very high (12450). The 5-minute output rate of 10 Mbps is far below the interface bandwidth of 100 Mbps, yet the queue is overflowing, which indicates microbursts from a faster upstream link overwhelming the slower interface. This is the classic signature of a speed mismatch.
C
The interface is receiving corrupted frames, indicated by the zero input errors on the interface.
Why wrong: Zero input errors, CRC, and frame counters actually indicate no corrupted frames are being received. This statement contradicts the output.
D
The output queue is full because its size is too small, and increasing the queue depth will resolve the packet loss.
Why wrong: While the default output queue size (40) is filled, simply increasing the queue depth would not fix the root cause of a speed mismatch. It would only delay the inevitable drops and introduce additional latency (bufferbloat).
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An upstream device is sending traffic at a rate higher than this interface can transmit, causing the output queue to overflow.
The exhibit shows 12,450 output drops and an output queue that is completely full (40/40). The interface is up, operating at 100 Mb/s full-duplex, and shows zero input errors or CRC errors, ruling out physical layer corruption. The high output drops with a maxed-out output queue typically indicate that an upstream device is transmitting at a rate that exceeds the interface’s egress capacity, causing tail drops. This is a classic symptom of a speed mismatch where, for example, a distribution switch is forwarding traffic at 1 Gbps toward a 100 Mbps uplink.
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.
✗
The interface is experiencing excessive collisions due to a duplex mismatch.
Why it's wrong here
The output shows the interface operating in full-duplex mode and 0 output collisions, ruling out a duplex mismatch or collision-related drops.
✓
An upstream device is sending traffic at a rate higher than this interface can transmit, causing the output queue to overflow.
Why this is correct
The output queue is maxed (40/40) and output drops are very high (12450). The 5-minute output rate of 10 Mbps is far below the interface bandwidth of 100 Mbps, yet the queue is overflowing, which indicates microbursts from a faster upstream link overwhelming the slower interface. This is the classic signature of a speed mismatch.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The interface is receiving corrupted frames, indicated by the zero input errors on the interface.
Why it's wrong here
Zero input errors, CRC, and frame counters actually indicate no corrupted frames are being received. This statement contradicts the output.
✗
The output queue is full because its size is too small, and increasing the queue depth will resolve the packet loss.
Why it's wrong here
While the default output queue size (40) is filled, simply increasing the queue depth would not fix the root cause of a speed mismatch. It would only delay the inevitable drops and introduce additional latency (bufferbloat).
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓An upstream device is sending traffic at a rate higher than this interface can transmit, causing the output queue to overflow.Correct answer▾
Why this is correct
The output queue is maxed (40/40) and output drops are very high (12450). The 5-minute output rate of 10 Mbps is far below the interface bandwidth of 100 Mbps, yet the queue is overflowing, which indicates microbursts from a faster upstream link overwhelming the slower interface. This is the classic signature of a speed mismatch.
✗The interface is experiencing excessive collisions due to a duplex mismatch.Wrong answer — click to see why▾
Why this is wrong here
Candidates sometimes associate packet loss with duplex mismatches, but a duplex mismatch would also show collisions and typically input errors, both of which are zero here.
✗The interface is receiving corrupted frames, indicated by the zero input errors on the interface.Wrong answer — click to see why▾
Why this is wrong here
Zero input errors means no physical-layer receiving problems; the candidate may misinterpret the absence of errors as a sign of some other problem, which is logically incorrect.
✗The output queue is full because its size is too small, and increasing the queue depth will resolve the packet loss.Wrong answer — click to see why▾
Why this is wrong here
Increasing the queue size is a common workaround that masks the real problem, but the underlying mismatch in forwarding rates remains. CCNA candidates may incorrectly focus on the queue size rather than the relationship between the 100 Mb/s interface speed and a faster upstream sender.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
The output shows the interface operating in full-duplex mode and 0 output collisions, ruling out a duplex mismatch or collision-related drops.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Identify which 200-301 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Switching and Network Access — This question tests Switching and Network Access — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: An upstream device is sending traffic at a rate higher than this interface can transmit, causing the output queue to overflow. — The exhibit shows 12,450 output drops and an output queue that is completely full (40/40). The interface is up, operating at 100 Mb/s full-duplex, and shows zero input errors or CRC errors, ruling out physical layer corruption. The high output drops with a maxed-out output queue typically indicate that an upstream device is transmitting at a rate that exceeds the interface’s egress capacity, causing tail drops. This is a classic symptom of a speed mismatch where, for example, a distribution switch is forwarding traffic at 1 Gbps toward a 100 Mbps uplink.
What should I do if I get this 200-301 question wrong?
Identify which 200-301 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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