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Question 971 of 1,052
hardmultiple choiceObjective-mapped
CCNA Practice Question: Is troubleshooting intermittent connectivity on…
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
Switch#show interfaces gigabitEthernet 1/0/24
GigabitEthernet1/0/24 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is aabb.cc01.1824 (bia aabb.cc01.1824)
Description: Server-01
Internet address is 192.168.1.10/24
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/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 00:02:34
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, 12 packets/sec
5 minute output rate 8000 bits/sec, 8 packets/sec
12345 packets input, 1234567 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
12345 packets output, 1234567 bytes, 0 underruns
0 output errors, 0 collisions, 0 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
Switch#show controllers gigabitEthernet 1/0/24
Interface GigabitEthernet1/0/24
Hardware is Gigabit Ethernet
Media Type: 10/100/1000BaseTX
PHY: Marvell 88E1111
MASTER: internal
Auto-negotiation: enabled
Link Partner Capabilities: 10/100/1000BaseT, Full-duplex
Local Capabilities: 10/100/1000BaseT, Full-duplex
Advertised Capabilities: 10/100/1000BaseT, Full-duplex
Operational: 1000BaseT, Full-duplex
Flow Control: off (both sides)
MDIX: off (crossover cable not detected)
Cable length: 100 meters
Speed: 1000 Mb/s
Duplex: Full
Errors:
CRC errors: 0
Alignment errors: 0
Symbol errors: 0
False carrier: 0
Runts: 0
Giants: 0
Transceiver: internal
DTE status: up
Loopback: none
Last link flapped: 00:00:05 agoA network engineer is troubleshooting intermittent connectivity on an access switch port connected to a server. The output of 'show interfaces gigabitEthernet 1/0/24' shows an increasing number of runts and giants, but no CRC errors. The 'show interfaces status' command indicates the port is in 'err-disabled' state every few hours and must be manually re-enabled. 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.
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
✓
Faulty cable or connector causing physical layer errors
The exhibit shows zero runts and giants in the 'show interfaces' and 'show controllers' output, but the problem description states the counters are increasing. This discrepancy indicates the counters were cleared recently (last clearing 2 minutes ago). The port flaps every few hours, causing the server to re-negotiate. The 'show controllers' output shows cable length of 100 meters (maximum for 1000BaseT) and MDIX is off, suggesting a potential cable issue like a faulty or marginal cable that causes intermittent errors. The increasing runts and giants (frames shorter/longer than allowed) point to physical layer problems such as excessive noise or signal degradation, not duplex mismatch or VLAN mismatch. The absence of CRC errors suggests the errors are not due to collisions or late collisions, but rather physical layer issues like a bad cable or connector. The port flapping and err-disabled state further support a hardware fault.
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.
- ✗
Duplex mismatch between the switch port and the server NIC
Why it's wrong here
Duplex mismatch typically causes CRC errors and late collisions, not runts and giants. The 'show controllers' shows both sides are Full-duplex, so duplex mismatch is unlikely.
- ✓
Faulty cable or connector causing physical layer errors
Why this is correct
Runts and giants without CRC errors often indicate physical layer issues like a bad cable, connector, or excessive noise. The cable length at maximum (100 meters) and MDIX off suggest potential signal degradation, leading to intermittent flapping and err-disabled state.
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.
- ✗
Incorrect VLAN configuration on the switch port
Why it's wrong here
VLAN mismatch causes connectivity issues but does not produce runts or giants. It would result in packets being dropped at Layer 2, not physical layer errors.
- ✗
Speed mismatch between the switch port and the server NIC
Why it's wrong here
Speed mismatch would cause the port to not come up or to flap with errors like CRC errors. The 'show controllers' shows both sides are operating at 1000 Mb/s Full-duplex, so speed mismatch is not present.
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.
✓Faulty cable or connector causing physical layer errorsCorrect answer▾
Why this is correct
Runts and giants without CRC errors often indicate physical layer issues like a bad cable, connector, or excessive noise. The cable length at maximum (100 meters) and MDIX off suggest potential signal degradation, leading to intermittent flapping and err-disabled state.
✗Duplex mismatch between the switch port and the server NICWrong answer — click to see why▾
Why this is wrong here
Duplex mismatch would cause CRC errors and late collisions, which are not present in the exhibit.
✗Incorrect VLAN configuration on the switch portWrong answer — click to see why▾
Why this is wrong here
VLAN mismatch does not cause runts or giants; it causes Layer 2 issues like no connectivity.
✗Speed mismatch between the switch port and the server NICWrong answer — click to see why▾
Why this is wrong here
Speed mismatch would prevent the link from coming up or cause CRC errors, but the link is up at 1000 Mb/s.
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
Duplex mismatch typically causes CRC errors and late collisions, not runts and giants. The 'show controllers' shows both sides are Full-duplex, so duplex mismatch is unlikely.
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: Faulty cable or connector causing physical layer errors — The exhibit shows zero runts and giants in the 'show interfaces' and 'show controllers' output, but the problem description states the counters are increasing. This discrepancy indicates the counters were cleared recently (last clearing 2 minutes ago). The port flaps every few hours, causing the server to re-negotiate. The 'show controllers' output shows cable length of 100 meters (maximum for 1000BaseT) and MDIX is off, suggesting a potential cable issue like a faulty or marginal cable that causes intermittent errors. The increasing runts and giants (frames shorter/longer than allowed) point to physical layer problems such as excessive noise or signal degradation, not duplex mismatch or VLAN mismatch. The absence of CRC errors suggests the errors are not due to collisions or late collisions, but rather physical layer issues like a bad cable or connector. The port flapping and err-disabled state further support a hardware fault.
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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