The answer is a duplex mismatch between the switch port and the workstation. This is the most likely cause because a duplex mismatch forces one side to operate in half-duplex, which relies on CSMA/CD and collision detection, while the other side runs in full-duplex and transmits without listening. The half-duplex end interprets the full-duplex transmissions as collisions, triggering late collisions and CRC errors that degrade performance and cause intermittent connectivity, even though the interface status shows up/up. On the CCNA 200-301 v2 exam, this scenario tests your understanding of Ethernet autonegotiation failures and the hidden nature of duplex mismatches—the port appears operational, but error counters reveal the truth. A common trap is assuming a speed mismatch, but speed mismatches usually cause the link to drop, while duplex mismatches keep the link up but broken. Remember the memory tip: “Full sends, half defends—collisions never end.”
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. 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
Switch# show interfaces gigabitEthernet 0/1
GigabitEthernet0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 0011.2233.4455 (bia 0011.2233.4455)
Description: Workstation port
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Auto-duplex, Auto-speed, 100Mb/s, Half-duplex
input flow-control is off, output flow-control is off
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 12000 bits/sec, 15 packets/sec
5 minute output rate 8000 bits/sec, 10 packets/sec
123456 packets input, 98765432 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
98765 packets output, 87654321 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out
A network administrator notices that a workstation connected to a Cisco switch port cannot communicate with other devices on the same VLAN. The switch port is up/up, but the workstation reports slow performance and intermittent connectivity. What is the most likely cause of this 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.
Switch# show interfaces gigabitEthernet 0/1
GigabitEthernet0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 0011.2233.4455 (bia 0011.2233.4455)
Description: Workstation port
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Auto-duplex, Auto-speed, 100Mb/s, Half-duplex
input flow-control is off, output flow-control is off
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 12000 bits/sec, 15 packets/sec
5 minute output rate 8000 bits/sec, 10 packets/sec
123456 packets input, 98765432 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
98765 packets output, 87654321 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out
A
Replace the faulty Ethernet cable between the switch and the workstation.
Why wrong: Cable issues typically cause input errors, CRC errors, or interface resets, none of which are present in the output.
B
A duplex mismatch between the switch port and the workstation.
Duplex mismatch causes one side to transmit simultaneously while the other waits, leading to collisions, errors, and degraded throughput, consistent with the described symptoms.
C
Assign the switch port to the correct VLAN.
Why wrong: There is no evidence of VLAN misconfiguration in the output; the port is up/up and passing traffic.
D
Disable spanning-tree on the port to prevent frequent topology changes.
Why wrong: Spanning-tree issues would manifest as port flapping or err-disabled states, not slow performance with a stable up/up state.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A duplex mismatch between the switch port and the workstation.
A duplex mismatch occurs when one end of the link is set to full-duplex and the other to half-duplex. The half-duplex end detects collisions and the full-duplex end does not, causing late collisions, CRC errors, and retransmissions. This results in slow performance and intermittent connectivity even though the port is operationally up.
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.
✗
Replace the faulty Ethernet cable between the switch and the workstation.
Why it's wrong here
Cable issues typically cause input errors, CRC errors, or interface resets, none of which are present in the output.
✓
A duplex mismatch between the switch port and the workstation.
Why this is correct
Duplex mismatch causes one side to transmit simultaneously while the other waits, leading to collisions, errors, and degraded throughput, consistent with the described symptoms.
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.
✗
Assign the switch port to the correct VLAN.
Why it's wrong here
There is no evidence of VLAN misconfiguration in the output; the port is up/up and passing traffic.
✗
Disable spanning-tree on the port to prevent frequent topology changes.
Why it's wrong here
Spanning-tree issues would manifest as port flapping or err-disabled states, not slow performance with a stable up/up state.
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.
✓A duplex mismatch between the switch port and the workstation.Correct answer▾
Why this is correct
Duplex mismatch causes one side to transmit simultaneously while the other waits, leading to collisions, errors, and degraded throughput, consistent with the described symptoms.
✗Replace the faulty Ethernet cable between the switch and the workstation.Wrong answer — click to see why▾
Why this is wrong here
No cable-related errors are shown.
✗Assign the switch port to the correct VLAN.Wrong answer — click to see why▾
Why this is wrong here
VLAN issues would typically prevent communication entirely or show input errors from misconfigured trunking.
✗Disable spanning-tree on the port to prevent frequent topology changes.Wrong answer — click to see why▾
Why this is wrong here
The port is stable and not flapping.
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
Cisco often tests the concept that a link being up/up does not guarantee error-free communication, and candidates mistakenly focus on VLAN or cable issues instead of recognizing duplex mismatch as the cause of slow performance and intermittent connectivity.
Trap categories for this question
Command / output trap
Cable issues typically cause input errors, CRC errors, or interface resets, none of which are present in the output.
Detailed technical explanation
How to think about this question
Duplex mismatch occurs when one device operates in full-duplex (simultaneous send/receive) and the other in half-duplex (one direction at a time), causing the half-duplex device to detect collisions when the full-duplex device transmits while receiving. This leads to excessive frame errors (e.g., runts, CRC errors) visible in 'show interfaces' output, and the switch may increment the 'collisions' or 'late collisions' counter. In real-world scenarios, this often happens when a switch port is hardcoded to full-duplex but the workstation uses auto-negotiation, which defaults to half-duplex if negotiation fails.
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 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 200-301 question in full detail.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A duplex mismatch between the switch port and the workstation. — A duplex mismatch occurs when one end of the link is set to full-duplex and the other to half-duplex. The half-duplex end detects collisions and the full-duplex end does not, causing late collisions, CRC errors, and retransmissions. This results in slow performance and intermittent connectivity even though the port is operationally up.
What should I do if I get this 200-301 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are connected to the console of R1. The network administrator reports that hosts in VLAN 10 cannot reach the server at 192.168.1.100. R1 is the default gateway for VLAN 10 via subinterface G0/0.10. The link between R1 and the switch SW1 appears to be up, but pings fail. Your task is to identify and resolve the issue.
hard
A.Check the interface status on R1's G0/0.10 subinterface; it may be administratively down.
B.Verify that the VLAN 10 SVI on SW1 has an IP address in the correct subnet.
✓ C.Check the duplex and speed settings on the physical interface G0/0 of R1 and the corresponding switchport on SW1; they may be mismatched.
D.Ensure that the native VLAN on the trunk between R1 and SW1 is VLAN 1.
Why C: The link between R1 and SW1 had mismatched duplex/speed settings because auto-negotiation failed, causing excessive CRC errors and packet loss. Manually setting both sides to 100/full resolves the issue.
Variation 2. A network administrator notices that file transfers to a server are extremely slow, and on the switch interface connecting to the server, the output of 'show interfaces' indicates a high number of runts and CRC errors, but no collisions. Which of the following is the most likely cause?
hard
A.The cable connecting the server to the switch is faulty.
✓ B.The switch port is configured for full-duplex, but the server's NIC is set to half-duplex.
C.The switch port speed is set to 100 Mbps, but the server NIC is set to 10 Mbps.
D.The server's NIC driver is outdated, causing packet loss.
Why B: The combination of runts (frames smaller than 64 bytes) and CRC errors with zero collisions is a classic symptom of a duplex mismatch. When one side operates at full-duplex and the other at half-duplex, the half-duplex side will detect collisions and invoke its backoff algorithm, causing the full-duplex side to receive truncated frames (runts) and frames with invalid FCS (CRC errors). The switch interface statistics show no collisions because the switch port is full-duplex and does not detect collisions, while the server's half-duplex NIC is causing the corruption.
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