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Question 1,283 of 1,052
hardmultiple choiceObjective-mapped
CCNA Practice Question: A network technician is troubleshooting a…
This 200-301 practice question tests your understanding of 200-301 exam topics. 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
SW1# show interfaces gigabitethernet 0/1
GigabitEthernet0/1 is up, line protocol is up
Hardware is Gigabit Ethernet, address is aaaa.bbbb.cccc (bia aaaa.bbbb.cccc)
Description: Link to SW2
Internet address is 10.10.10.1/30
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)
Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
input flow-control is off, output flow-control is unsupported
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 2000 bits/sec, 2 packets/sec
5 minute output rate 1000 bits/sec, 1 packets/sec
12345 packets input, 1234567 bytes
Received 1234 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 56789 multicast, 0 pause input
0 input packets with dribble condition detected
23456 packets output, 2345678 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 outA network technician is troubleshooting a connectivity issue between two directly connected switches, SW1 and SW2. Hosts on VLAN 10 connected to SW1 can ping each other but cannot ping the default gateway or any host on VLAN 10 connected to SW2. The interface on SW1 is up/up, but the interface on SW2 is up/down. Based on the output from SW1, what is the most likely cause of the problem?
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 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
✓
Ensure both switches are configured for the same duplex setting, preferably by enabling autonegotiation on both interfaces.
The root cause is a duplex mismatch. SW1's interface is configured for full-duplex, but the interface on SW2 is likely set to half-duplex due to a failed autonegotiation (possibly because SW2 has a hardcoded speed/duplex setting). This mismatch causes collisions and line protocol issues on the half-duplex side (SW2), resulting in the interface being up/down. The fix is to configure both ends to use the same duplex setting, preferably by enabling autonegotiation on both sides. The other options are incorrect: increasing MTU would not resolve a duplex mismatch; the interface is up/up on SW1, so a cable fault is unlikely; and while late collisions can indicate a duplex mismatch, the show interface output does not show late collisions (0 late collision), so that is not the direct evidence.
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.
- ✗
Configure the interface on SW2 to use a different MTU value.
Why it's wrong here
The MTU setting does not affect duplex negotiation or line protocol state. A mismatch in MTU would cause fragmentation issues, not an interface being up/down.
- ✓
Ensure both switches are configured for the same duplex setting, preferably by enabling autonegotiation on both interfaces.
Why this is correct
The output from SW1 shows the interface is full-duplex, but SW2's interface is up/down. This is a classic symptom of a duplex mismatch, where one side is full and the other half-duplex. Configuring both ends to the same duplex (or enabling autonegotiation) will resolve the issue.
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.
- ✗
Replace the Ethernet cable connecting SW1 and SW2.
Why it's wrong here
A faulty cable would typically cause both sides to show down/down or intermittent flaps, not a consistent up/up on one side and up/down on the other.
- ✗
Check for late collisions on the interface and increase the collision window size.
Why it's wrong here
Late collisions can be a symptom of a duplex mismatch, but the show output indicates 0 late collisions. Increasing collision window size is not a standard fix and would not address the underlying configuration mismatch.
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.
✓Ensure both switches are configured for the same duplex setting, preferably by enabling autonegotiation on both interfaces.Correct answer▾
Why this is correct
The output from SW1 shows the interface is full-duplex, but SW2's interface is up/down. This is a classic symptom of a duplex mismatch, where one side is full and the other half-duplex. Configuring both ends to the same duplex (or enabling autonegotiation) will resolve the issue.
✗Configure the interface on SW2 to use a different MTU value.Wrong answer — click to see why▾
Why this is wrong here
Changing MTU will not fix the duplex mismatch causing the interface to be up/down.
✗Replace the Ethernet cable connecting SW1 and SW2.Wrong answer — click to see why▾
Why this is wrong here
Cable issues usually affect both interfaces similarly, not causing a duplex mismatch scenario.
✗Check for late collisions on the interface and increase the collision window size.Wrong answer — click to see why▾
Why this is wrong here
The absence of late collisions in the output suggests this is not the immediate issue, and adjusting collision windows is not a recommended solution.
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: 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.
Trap categories for this question
Command / output trap
A faulty cable would typically cause both sides to show down/down or intermittent flaps, not a consistent up/up on one side and up/down on the other.
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 200-301 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Access ports place end devices into a single VLAN.
What is the correct answer to this question?
The correct answer is: Ensure both switches are configured for the same duplex setting, preferably by enabling autonegotiation on both interfaces. — The root cause is a duplex mismatch. SW1's interface is configured for full-duplex, but the interface on SW2 is likely set to half-duplex due to a failed autonegotiation (possibly because SW2 has a hardcoded speed/duplex setting). This mismatch causes collisions and line protocol issues on the half-duplex side (SW2), resulting in the interface being up/down. The fix is to configure both ends to use the same duplex setting, preferably by enabling autonegotiation on both sides. The other options are incorrect: increasing MTU would not resolve a duplex mismatch; the interface is up/up on SW1, so a cable fault is unlikely; and while late collisions can indicate a duplex mismatch, the show interface output does not show late collisions (0 late collision), so that is not the direct evidence.
What should I do if I get this 200-301 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 200-301 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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