The answer is to configure both interfaces with the same duplex and speed settings, either both auto or both manually set to full-duplex and 1000 Mbps. This is correct because a speed mismatch between directly connected Cisco switches causes the interface to show up/down—Layer 1 is active, but the line protocol fails to establish, whereas a duplex mismatch typically leaves both interfaces up/up while generating CRC errors. On the CCNA 200-301 v2 exam, this scenario tests your ability to distinguish between speed and duplex mismatch symptoms during troubleshooting, a common trap where candidates assume duplex is the culprit when the interface state is up/down. Remember the key indicator: speed mismatch breaks the line protocol, duplex mismatch corrupts frames. For a quick memory tip, think “speed stops the protocol, duplex drops the packets.”
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
SwitchA# show interfaces GigabitEthernet0/1
GigabitEthernet0/1 is up, line protocol is down
Hardware is Gigabit Ethernet, address is aabb.cc00.0101 (bia aabb.cc00.0101)
Description: Link to SwitchB Gi0/1
Internet address is 192.168.10.1/24
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 never, 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 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 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
0 packets output, 0 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 technician is troubleshooting connectivity between two directly connected Cisco switches. Hosts on VLAN 10 connected to SwitchA cannot ping the default gateway on SwitchB. The interface on SwitchB shows up/up, but the interface on SwitchA shows up/down. The technician examines the interface configuration and status on SwitchA. 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.
SwitchA# show interfaces GigabitEthernet0/1
GigabitEthernet0/1 is up, line protocol is down
Hardware is Gigabit Ethernet, address is aabb.cc00.0101 (bia aabb.cc00.0101)
Description: Link to SwitchB Gi0/1
Internet address is 192.168.10.1/24
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 never, 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 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 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
0 packets output, 0 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 Ethernet cable because it is faulty.
Why wrong: No cable errors are reported (no CRC, runts, giants, or collisions), so the cable is likely not the issue.
B
Configure both interfaces with the same duplex and speed settings, either both auto or both manually set to full-duplex and 1000 Mbps.
The line protocol being down with up/up on the remote suggests a duplex mismatch, which can occur when one side is manually set and the other is auto-negotiating. Setting both sides consistently resolves the issue.
C
Issue the 'shutdown' and 'no shutdown' commands on the interface to recover from err-disabled state.
Why wrong: The interface is not in err-disabled state; it shows 'up, line protocol is down'.
D
Check the VLAN configuration on SwitchA because the interface is administratively down.
Why wrong: The interface status is 'up', not 'administratively down', so the VLAN configuration is not the primary issue.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure both interfaces with the same duplex and speed settings, either both auto or both manually set to full-duplex and 1000 Mbps.
The interface on SwitchA shows up/down, meaning Layer 1 is active but the line protocol is down. This is commonly caused by a speed mismatch between the two ends. A duplex mismatch, in contrast, typically results in both interfaces showing up/up with CRC errors. Therefore, the most likely cause is that the speed settings differ—for example, one interface is set to auto-negotiate while the other is hard-coded to a specific speed. Configuring both interfaces with identical speed and duplex settings, either both auto or both manually configured, resolves the issue.
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 Ethernet cable because it is faulty.
Why it's wrong here
No cable errors are reported (no CRC, runts, giants, or collisions), so the cable is likely not the issue.
✓
Configure both interfaces with the same duplex and speed settings, either both auto or both manually set to full-duplex and 1000 Mbps.
Why this is correct
The line protocol being down with up/up on the remote suggests a duplex mismatch, which can occur when one side is manually set and the other is auto-negotiating. Setting both sides consistently resolves the issue.
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.
✗
Issue the 'shutdown' and 'no shutdown' commands on the interface to recover from err-disabled state.
Why it's wrong here
The interface is not in err-disabled state; it shows 'up, line protocol is down'.
✗
Check the VLAN configuration on SwitchA because the interface is administratively down.
Why it's wrong here
The interface status is 'up', not 'administratively down', so the VLAN configuration is not the primary issue.
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.
✓Configure both interfaces with the same duplex and speed settings, either both auto or both manually set to full-duplex and 1000 Mbps.Correct answer▾
Why this is correct
The line protocol being down with up/up on the remote suggests a duplex mismatch, which can occur when one side is manually set and the other is auto-negotiating. Setting both sides consistently resolves the issue.
✗Replace the Ethernet cable because it is faulty.Wrong answer — click to see why▾
Why this is wrong here
The interface status shows 'up, line protocol is down', which indicates a Layer 2 issue, not a physical cable fault. Additionally, no CRC, runts, giants, or collisions are reported, so the cable is likely not faulty.
Why candidates choose this
Students often assume that any connectivity problem is due to a bad cable, especially when the interface is up/down. However, the absence of physical layer errors suggests the cable is fine.
✗Issue the 'shutdown' and 'no shutdown' commands on the interface to recover from err-disabled state.Wrong answer — click to see why▾
Why this is wrong here
The interface status is 'up, line protocol is down', not 'err-disabled'. The err-disabled state would show 'err-disabled' in the interface status, and a shutdown/no shutdown would be appropriate only for err-disabled recovery.
Why candidates choose this
Students may confuse the 'up/down' state with an err-disabled state, as both can cause connectivity loss. However, err-disabled is a specific condition triggered by port security or other violations.
✗Check the VLAN configuration on SwitchA because the interface is administratively down.Wrong answer — click to see why▾
Why this is wrong here
The interface status is 'up', not 'administratively down'. An administratively down interface would show 'administratively down, line protocol is down'. VLAN configuration issues typically cause the interface to be up/up but unable to forward traffic, not up/down.
Why candidates choose this
Students might think VLAN misconfiguration can cause the interface to go down, but VLAN issues usually affect Layer 3 connectivity, not the line protocol state of a trunk or access port.
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
The trap is that up/down is often misinterpreted as a faulty cable or an err-disabled state, but it actually points to a speed mismatch or auto-negotiation failure, not a duplex mismatch.
Trap categories for this question
Command / output trap
The interface is not in err-disabled state; it shows 'up, line protocol is down'.
Detailed technical explanation
How to think about this question
When two Ethernet interfaces negotiate speed and duplex, they use the IEEE 802.3 auto-negotiation protocol, which exchanges Fast Link Pulses (FLPs). If one side is manually set to full-duplex and the other is set to auto-negotiate, the auto side may detect the carrier but default to half-duplex due to the lack of FLPs, causing a duplex mismatch. This mismatch leads to late collisions and frame errors on the half-duplex side, resulting in the interface showing up/down. In real-world scenarios, this often occurs after a switch replacement or when a technician hard-codes settings without verifying the peer.
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: Configure both interfaces with the same duplex and speed settings, either both auto or both manually set to full-duplex and 1000 Mbps. — The interface on SwitchA shows up/down, meaning Layer 1 is active but the line protocol is down. This is commonly caused by a speed mismatch between the two ends. A duplex mismatch, in contrast, typically results in both interfaces showing up/up with CRC errors. Therefore, the most likely cause is that the speed settings differ—for example, one interface is set to auto-negotiate while the other is hard-coded to a specific speed. Configuring both interfaces with identical speed and duplex settings, either both auto or both manually configured, resolves the issue.
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.
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