220-1101 Networking Practice Question
A technician is troubleshooting a workstation that is connected to a managed switch. The link lights on both the workstation and switch are illuminated, but the workstation cannot obtain an IP address from the DHCP server. The technician manually configures a static IP address (192.168.1.100, subnet mask 255.255.255.0, default gateway 192.168.1.1) on the workstation, but it still cannot ping the router (192.168.1.1). Other workstations on the same switch can ping the router successfully. Which of the following is the MOST likely cause of this issue?
⚠ Common exam trap
CompTIA often tests the misconception that link lights guarantee full Layer 2 functionality, when in fact a speed/duplex mismatch can break data transmission while keeping the physical link active.
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
✓
Speed/duplex mismatch between the switch port and the workstation NIC
The link lights are on, indicating Layer 1 connectivity, but the inability to obtain a DHCP lease or ping the gateway despite a correct static IP suggests a Layer 2 issue. A speed/duplex mismatch causes excessive frame errors and collisions, effectively breaking communication even though the physical link appears active. This is the most likely cause because other workstations on the same switch work fine, isolating the problem to the specific switch port or workstation NIC configuration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Duplicate IP address on the network
Why it's wrong here
A duplicate IP address would cause an address conflict warning, but other workstations on the same switch can communicate, and the static IP 192.168.1.100 is unlikely to be duplicated since the technician just configured it. More importantly, a duplicate IP would typically still allow some connectivity, but here there is no connectivity at all.
- ✓
Speed/duplex mismatch between the switch port and the workstation NIC
Why this is correct
A speed/duplex mismatch can cause the link to be up but with severe packet loss or complete communication failure, even though the link lights are on. This explains why the workstation cannot ping the router while other workstations on the same switch can.
- ✗
Incorrect subnet mask
Why it's wrong here
The subnet mask 255.255.255.0 is correct for the 192.168.1.0/24 network, and the workstation can ping other local devices? Actually, the problem states it cannot ping the router. If the subnet mask were incorrect, the workstation might still be able to ping local devices but not the gateway. However, the technician set the mask correctly.
- ✗
Damaged Ethernet cable
Why it's wrong here
A damaged cable would typically cause the link lights to be off or to blink intermittently. Since both link lights are solidly on, a damaged cable is unlikely. Moreover, other workstations on the same switch work fine, so the cable is probably not the issue.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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