CCNA Network Infrastructure and Connectivity Practice Question
Exhibit
Switch# show interfaces gigabitEthernet 0/1
GigabitEthernet0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 0011.2233.4455 (bia 0011.2233.4455)
Description: Workstation port
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)
Auto-duplex, Auto-speed, 100Mb/s, Half-duplex
input flow-control is off, output flow-control is off
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 12000 bits/sec, 15 packets/sec
5 minute output rate 8000 bits/sec, 10 packets/sec
123456 packets input, 98765432 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
98765 packets output, 87654321 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 administrator notices that a workstation connected to a Cisco switch port cannot communicate with other devices on the same VLAN. The switch port is up/up, but the workstation reports slow performance and intermittent connectivity. What is the most likely cause of this issue?
⚠ Common exam trap
Cisco often tests the concept that a link being up/up does not guarantee error-free communication, and candidates mistakenly focus on VLAN or cable issues instead of recognizing duplex mismatch as the cause of slow performance and intermittent connectivity.
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
✓
A duplex mismatch between the switch port and the workstation.
A duplex mismatch occurs when one end of the link is set to full-duplex and the other to half-duplex. The half-duplex end detects collisions and the full-duplex end does not, causing late collisions, CRC errors, and retransmissions. This results in slow performance and intermittent connectivity even though the port is operationally up.
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 faulty Ethernet cable between the switch and the workstation.
Why it's wrong here
Replacing the Ethernet cable is unlikely to resolve the issue because physical-layer faults such as a damaged cable typically produce observable error counters on the interface—for example, CRC errors, runts, giants, or interface resets. The described output does not report any of these increments, and the interface remains up/up; instead, the symptoms align with a logical Layer 1/2 configuration problem. A duplex mismatch does not generate CRC errors but causes late collisions and excessive deferrals, which are not corrected by swapping the cable.
- ✓
A duplex mismatch between the switch port and the workstation.
Why this is correct
A duplex mismatch between the switch port and the workstation is the correct cause because it creates a half-duplex device that performs CSMA/CD while the full-duplex peer transmits without sensing the medium. When both devices transmit simultaneously, the half-duplex side detects a late collision and backs off, while the full-duplex side is unaware and does not retransmit, causing dropped frames, high latency, and degraded throughput. The switch output would likely show a high number of late collisions or a significant rate of alignment errors, even though the link remains up/up, matching the symptom of a slow but stable connection.
- ✗
Assign the switch port to the correct VLAN.
Why it's wrong here
Assigning the switch port to the correct VLAN is not a valid fix because VLAN misconfiguration typically produces a total loss of connectivity rather than a gradual performance degradation—the workstation would fail to reach its default gateway or other subnets, and DHCP would likely fail. The interface in question is up/up and passing traffic, which indicates the port is already in an operational VLAN and layer 2 forwarding is working. Without evidence of unreachable peers or a VLAN membership mismatch in the output, this option does not address the observed symptom.
- ✗
Disable spanning-tree on the port to prevent frequent topology changes.
Why it's wrong here
Disabling spanning-tree on the port is incorrect because Spanning Tree Protocol (STP) itself does not cause slow throughput when the port is stable in the forwarding state. STP issues manifest as port flapping, listening/learning transitions, or err-disabled states, none of which appear in a show interface output that reports up/up. Frequent topology changes would be reflected in incrementing Topology Change Notification (TCN) counters, not in a persistent slow performance, so disabling STP would be both unnecessary and potentially harmful by enabling forwarding loops.
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.
✓A duplex mismatch between the switch port and the workstation.Correct answer▾
Why this is correct
A duplex mismatch between the switch port and the workstation is the correct cause because it creates a half-duplex device that performs CSMA/CD while the full-duplex peer transmits without sensing the medium. When both devices transmit simultaneously, the half-duplex side detects a late collision and backs off, while the full-duplex side is unaware and does not retransmit, causing dropped frames, high latency, and degraded throughput. The switch output would likely show a high number of late collisions or a significant rate of alignment errors, even though the link remains up/up, matching the symptom of a slow but stable connection.
✗Replace the faulty Ethernet cable between the switch and the workstation.Wrong answer — click to see why▾
Why this is wrong here
No cable-related errors are shown.
✗Assign the switch port to the correct VLAN.Wrong answer — click to see why▾
Why this is wrong here
VLAN issues would typically prevent communication entirely or show input errors from misconfigured trunking.
✗Disable spanning-tree on the port to prevent frequent topology changes.Wrong answer — click to see why▾
Why this is wrong here
The port is stable and not flapping.
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
Go deeper
Related to this question
Learn chapter
Network Topology Types
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.
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.