CCNA Network Infrastructure and Connectivity Practice Question
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 outA 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?
⚠ Common exam trap
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.
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
✓
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.
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
A faulty Ethernet cable typically manifests as a Layer 1 problem, causing link flapping or 'down/down' status, and would generate an increasing count of CRC errors, runts, giants, or late collisions in the interface output. Here, the physical link is up (Layer 1 is operational), and the scenario explicitly reports no such input errors, making a cabling fault unlikely. Duplex mismatch-related line protocol failures occur even when the cable is perfectly good, because the two endpoints are using different CSMA/CD parameters. Since the interface is up and the remote side is also up/up, the issue lies in Layer 2 negotiation rather than physical cabling.
- ✓
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.
- ✗
Issue the 'shutdown' and 'no shutdown' commands on the interface to recover from err-disabled state.
Why it's wrong here
The 'shutdown'/'no shutdown' sequence is used to recover an interface from the 'err-disabled' state, which is triggered by security violations such as port security or a storm-control threshold. In this scenario, the interface status is 'up, line protocol is down,' not 'err-disabled,' so the interface is not error-disabled and the command sequence would have no effect on the line protocol state. A duplex mismatch, which is the actual cause, does not place the interface into an error-disabled state; it simply prevents proper Layer 2 framing. Therefore, issuing these commands would not resolve the underlying configuration mismatch.
- ✗
Check the VLAN configuration on SwitchA because the interface is administratively down.
Why it's wrong here
The interface output in the scenario shows 'up, line protocol is down,' not 'administratively down.' An administratively down interface is explicitly disabled with the 'shutdown' command and displays a line status of 'administratively down,' which blocks all communication at Layer 1. A VLAN misconfiguration would not change the line protocol state to down on a physical interface that is up; at most, it would affect traffic forwarding or cause a trunking mismatch, but the physical and data-link layers would still appear operational. Since the interface is not administratively down, checking VLAN configuration is not the correct next step.
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?”
Visual reference
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Related to this question
Learn chapter
ARP — Address Resolution Protocol
Key term
Duplex mismatch
A duplex mismatch occurs when two connected network devices are configured with different duplex settings (one half-duplex, one full-duplex), leading to poor performance and data errors.
Key term
Cyclic Redundancy Check
A Cyclic Redundancy Check (CRC) is an error-detecting code used to verify that data transmitted over a network or stored on a device has not been corrupted.
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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.