220-1101 Hardware and Network Troubleshooting Practice Question
A technician is troubleshooting a workstation that has a solid link light on its NIC and on the switch port, but the workstation fails to obtain an IP address via DHCP. The technician manually assigns a static IP and can ping other devices, but experiences slow transfers and packet loss. Checking the switch's port statistics reveals a high number of CRC errors and runts. Which of the following is the MOST likely cause?
⚠ Common exam trap
The trap here is that candidates see a solid link light and assume Layer 1 is perfect, but duplex mismatch is a Layer 2 issue that still allows link detection while corrupting traffic, leading them to incorrectly blame the cable or VLAN.
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 NIC and the switch port.
A duplex mismatch causes the NIC and switch port to use different methods for collision detection (half-duplex vs. full-duplex). This leads to CRC errors and runts because frames are corrupted when both sides transmit simultaneously (collisions) or when the half-duplex side misinterprets full-duplex traffic. The solid link light and successful static IP ping confirm Layer 1 and basic Layer 3 connectivity, but the high error counts point directly to a Layer 2 duplex negotiation failure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A duplex mismatch between the NIC and the switch port.
Why this is correct
A duplex mismatch occurs when one side negotiates full duplex and the other operates at half duplex. On the half-duplex side, late collisions occur because the full-duplex side never defers, forcing the half-duplex NIC to retransmit and creating runt frames and FCS/CRC errors on the switch. The link remains lit because both sides still detect carrier signal at the physical layer, even though data corruption makes throughput abysmal.
- ✗
The cable is too long (exceeds 100 meters).
Why it's wrong here
Exceeding the 100-meter UTP specification increases attenuation and return loss, so electrical signals become too weak or distorted for reliable receiver clock recovery. The primary symptoms are link negotiation failures, intermittent link flaps, or an absent link LED—not a steady solid link with high CRC/runts. Even when link stays up, marginal timing jitter could cause occasional errors, but it would not produce a consistent stream of runts typical of a duplex mismatch.
- ✗
The switch port is in a different VLAN.
Why it's wrong here
A VLAN mismatch places the workstation and switch port in different broadcast domains, so the switch will not forward unicast/BPDU/DHCP frames to the workstation, causing "no network" symptoms. However, VLAN filtering occurs in the switch's forwarding engine after the frame is received and after FCS validation; it does not generate physical-layer CRC errors or runt frames. The port's error counters would remain clean, and the link would still be operational at layers 1 and 2.
- ✗
The workstation's NIC driver is corrupted.
Why it's wrong here
A corrupted NIC driver can prevent the OS from configuring the interface, which can cause Link-Local addresses or an unusable network stack, but the NIC hardware still performs frame generation, preamble insertion, and CRC computation independent of driver content. Switch-port CRC errors and runts are caused by signal integrity or duplex/collision problems on the wire, not by software in the host. If the driver were at fault, the workstation's own NIC statistics would more likely show transmit timeouts or no carrier, not the switch logging hundreds of runts.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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