Slow File Transfers: Duplex Mismatch from Manual Setting
A technician is troubleshooting a workstation that experiences slow file transfers and occasional timeouts on the local network. The workstation is connected to a managed switch via a Cat5e cable. The technician checks the switch port configuration and finds it is set to 'auto-negotiate'. The workstation's network adapter properties show it is manually configured to '100 Mbps Full Duplex'. Other workstations on the same switch do not experience these issues. Which of the following is the MOST likely cause of the problem?
Quick Answer
The answer is a duplex mismatch caused by the manual configuration on the workstation. When the network adapter is manually set to 100 Mbps Full Duplex but the switch port remains on auto-negotiate, the switch detects the speed via link pulses but cannot determine the duplex setting, defaulting to half-duplex. This forces the workstation to transmit while the switch is receiving, causing collisions that manifest as slow file transfers and timeouts. On the CompTIA A+ Core 1 220-1101 exam, this scenario tests your understanding that auto-negotiation requires both sides to be set to auto; a manual setting breaks the negotiation, and the switch falls back to half-duplex. A common trap is assuming both sides will match if the speed matches, but duplex is negotiated independently. Remember the mnemonic: "Manual breaks the handshake, half-duplex is the mistake."
⚠ Common exam trap
CompTIA often tests the misconception that manually setting speed and duplex on both sides is always better, but the trap here is that a manual full-duplex setting on one side with auto-negotiation on the other causes a half-duplex fallback, not a full-duplex connection.
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
✓
The switch port is negotiating to half-duplex because the workstation is manually set to full duplex.
The workstation's NIC is manually set to 100 Mbps Full Duplex, while the switch port is set to auto-negotiate. During auto-negotiation, if one side is manually configured, the other side will detect the speed via link pulses but cannot determine the duplex setting, defaulting to half-duplex. This duplex mismatch causes collisions, leading to slow file transfers and timeouts, while other workstations using auto-negotiation on both sides operate correctly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The Cat5e cable is damaged or too long.
Why it's wrong here
A damaged or excessively long cable could cause errors and slowdowns, but the specific symptom of a duplex mismatch (due to manual configuration) is a more direct cause. Other workstations work fine on the same switch, suggesting the cable is not likely the issue.
- ✓
The switch port is negotiating to half-duplex because the workstation is manually set to full duplex.
Why this is correct
When one side is manually set to a specific duplex (100 Full), the auto-negotiating side may detect the link but fail to negotiate duplex properly and default to half-duplex. This results in a duplex mismatch that causes collisions, CRC errors, and poor performance. Changing the workstation NIC to auto-negotiate would resolve the issue.
- ✗
The switch port is faulty and needs to be replaced.
Why it's wrong here
A faulty switch port would likely affect all traffic on that port equally, but the symptom is specific to this workstation's configuration. Other devices work fine on the same switch, so the port is likely functional.
- ✗
The workstation's NIC driver is outdated or corrupt.
Why it's wrong here
While outdated drivers can cause performance issues, the fact that the NIC is manually set to a specific speed/duplex and the switch is on auto makes a duplex mismatch the most likely cause. Updating the driver alone may not fix the mismatch unless the configuration is also changed.
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Same concept, more angles
2 more ways this is tested on 220-1101
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A user reports that their workstation experiences intermittent network drops and slow speeds. The technician checks the switch port status and notices a high number of late collisions. The workstation's network adapter is set to auto-negotiate. The switch port is also set to auto-negotiate but the technician observes that the link has negotiated at 100 Mbps half-duplex. Which of the following is the MOST likely cause of this issue?
medium- A.Faulty Ethernet cable causing excessive crosstalk
- ✓ B.Duplex mismatch between the workstation NIC and the switch port
- C.Incorrect VLAN assignment on the switch port
- D.IP address conflict on the network
Why B: Late collisions are a classic symptom of a duplex mismatch. In this scenario, the switch port has negotiated to 100 Mbps half-duplex, which means the switch is operating at half-duplex. If the workstation NIC is actually operating at full-duplex—possibly due to a failed auto-negotiation process or a driver-level forced setting—the mismatch causes the switch to detect late collisions. The full-duplex workstation does not perform carrier sensing, so the half-duplex switch can transmit at the same time and later receive a collision, which it registers as a late collision because it occurs after the collision window.
Variation 2. A user reports that their workstation experiences intermittent network drops and slow performance. The technician checks the switch port statistics and observes a high number of late collisions and CRC errors. The workstation's NIC is set to auto-negotiate, and the switch port is manually configured for 100 Mbps full duplex. Which two of the following are the MOST likely causes of this problem? (Select TWO).
hard- A.Incorrect IP configuration
- ✓ B.Duplex mismatch
- ✓ C.Faulty Ethernet cable
- D.Broadcast storm
Why B: A duplex mismatch occurs when one side is set to full duplex and the other to half duplex. In this scenario, the switch port is manually configured for 100 Mbps full duplex, but the workstation's NIC is set to auto-negotiate. Auto-negotiation on the NIC will fail to detect the manually configured switch port, causing the NIC to fall back to half duplex. This mismatch leads to late collisions (because the half-duplex side waits for a clear channel while the full-duplex side transmits without listening) and CRC errors (from corrupted frames due to collisions). Additionally, a faulty Ethernet cable can cause CRC errors and intermittent network drops due to signal degradation or interference; in some cases, damaged cabling can also lead to late collisions if the signal is reflected or delayed.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA 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 220-1101 exam.