CCNA Network Infrastructure and Connectivity Practice Question
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. What is the most likely cause of the problem?
⚠ Common exam trap
Cisco often tests the distinction between up/down (Layer 1 issue like duplex mismatch) and down/down (cable or power issue) to trap candidates who assume any interface problem is a bad cable.
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 interface on SW2 is up/down, which typically indicates a Layer 1 issue such as a duplex mismatch. Duplex mismatch occurs when one switch is manually set to full duplex and the other to half duplex or auto-negotiation fails, causing the side expecting full duplex to report up/down due to excessive errors. Option A is incorrect because MTU mismatch would cause connectivity issues but not an up/down interface state. Option C is incorrect because a faulty cable would likely cause both interfaces to be down/down, not up/down. Option D is incorrect because late collisions are a symptom of duplex mismatch, not a separate cause; increasing collision window size is not a standard troubleshooting step. The correct solution is to ensure both switches use the same duplex setting, preferably via autonegotiation (IEEE 802.3u).
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
Altering the MTU value on SW2 would affect Layer 3 packet handling (e.g., fragmentation thresholds) and would not change the physical or data-link layer state of an Ethernet interface. The line protocol status (up/down) is determined by Layer 1/2 factors such as carrier detection, duplex negotiation, and keepalive messaging; an MTU mismatch might cause large-frame drops or performance issues but would not force an interface to show down. In fact, even if an MTU mismatch were present, the interface would remain in an up/up state, so this command cannot resolve the reported symptom.
- ✓
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.
- ✗
Replace the Ethernet cable connecting SW1 and SW2.
Why it's wrong here
A defective Ethernet cable would typically produce a loss of link on both switches simultaneously, resulting in both interfaces displaying down/down, or cause intermittent flapping on both ends if the fault is marginal. Here, SW1's interface is operational (full-duplex) while SW2 shows up/down, which is a one-sided condition that a physical cable fault does not create. A cable problem cannot selectively disable one side while leaving the other fully functional, so replacing the cable is irrelevant to correcting a duplex mismatch.
- ✗
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?”
Visual reference
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Related to this question
Learn chapter
ICMP and Ping
Key term
Default gateway
A default gateway is a network device, typically a router, that acts as the exit point for traffic from a local network to other networks, including the internet.
Key term
VLAN
A VLAN (Virtual Local Area Network) is a logical grouping of network devices that behave as if they are on the same physical network segment, regardless of their actual physical location.
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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.