CCNA Switching and Network Access Practice Question
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?
⚠ Common exam trap
Cisco often tests the distinction between output drops (congestion) and input errors (physical layer issues), and the trap here is that candidates may misinterpret 'output drops' as a sign of duplex mismatch or assume that increasing queue depth is a fix, when the real issue is a speed mismatch between incoming and outgoing traffic.
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
✓
An upstream device is sending traffic at a rate higher than this interface can transmit, causing the output queue to overflow.
The interface shows a high number of output drops, indicating that the output queue is experiencing congestion and packets are being dropped because the router cannot transmit traffic as fast as it is being received from the upstream device. This causes packet loss and sluggish performance.
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 interface is operating in full-duplex mode, where collisions cannot occur due to separate transmit and receive pairs. The output counters show 0 collisions, directly contradicting the claim. Additionally, a duplex mismatch typically manifests as late collisions on the half-duplex side and framing/alignment errors on the full-duplex side, none of which are present here. The real issue is output queue overflow from a speed mismatch, not 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.
- ✗
The interface is receiving corrupted frames, indicated by the zero input errors on the interface.
Why it's wrong here
This option misinterprets the counter values. Zero input errors, CRC errors, and frame errors actually prove that the interface is not receiving corrupted frames; these counters would be nonzero if corruption were occurring. The question's output shows the problem is on the transmit side, with the output queue at capacity and a high output drop count. Corrupted inbound frames would appear as input errors and cause the interface to discard them, not produce output queue drops.
- ✗
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?”
Go deeper
Related to this question
Learn chapter
Troubleshoot: ACL Blocking Legitimate Traffic
Key term
Router
A router is a networking device that connects different networks together and directs data traffic between them by choosing the best path for data to travel.
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
About these practice questions
One of 1,450 original 200-301 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.