220-1101 Networking Practice Question
A technician configures a new managed switch in a small network. After connecting the switch to the existing switch via a single Ethernet cable, the link LED on the uplink port is solid amber. Devices on the new switch cannot communicate with devices on the existing network. The existing network has no loops and uses a single switch. Which of the following is the MOST likely cause?
⚠ Common exam trap
CompTIA often tests the misconception that a solid amber LED always indicates a physical or cabling issue, when in fact it is a deliberate STP blocking state that prevents loops and must be resolved by verifying STP configuration or enabling PortFast on edge ports.
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
✓
Spanning Tree Protocol (STP) is blocking the uplink port
The solid amber link LED on the uplink port indicates that the port is administratively up but being blocked by Spanning Tree Protocol (STP). When a new switch is connected to an existing network, STP transitions the port through listening and learning states before forwarding, but if a loop is detected or the port remains in a blocking state, the amber LED confirms STP is preventing traffic. Since the existing network has no loops, STP is likely blocking the port due to a misconfiguration or because it is still in the process of convergence, which prevents communication between devices on the new switch and the existing network.
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 new switch has an IP address conflict
Why it's wrong here
An IP address conflict is a Layer 3 addressing problem that occurs at the IP protocol level, whereas the port LED on a switch is a Layer 1 physical-layer indicator reflecting the presence of a valid electrical or optical link. Even with duplicate IP addresses assigned to the new switch and another device, the link between the two switches would still come up normally because Ethernet framing and carrier detection operate independently of IP addressing. This issue would cause connectivity, routing, or DHCP problems for hosts, but it would not alter the physical link status or produce a solid amber LED on the switch port.
When this WOULD be correct
In a scenario where a technician configures a new switch and it cannot be managed remotely or pings fail, but link LEDs are green and other devices communicate fine, an IP address conflict with the management IP would be the likely cause.
- ✗
The new switch is in a different VLAN
Why it's wrong here
If the new switch were configured with a different untagged VLAN ID from the existing switch, traffic might not pass. However, by default, most switches have all ports in VLAN 1. A different VLAN configuration is possible but less common than STP blocking.
When this WOULD be correct
This would be correct in a scenario where a new switch is connected to an existing network and devices on the new switch cannot communicate with devices on the existing network, but the link LED is green and the existing switch has multiple VLANs configured. The new switch's ports might be in a different VLAN than the existing network's default VLAN, requiring trunk configuration or VLAN reassignment.
- ✓
Spanning Tree Protocol (STP) is blocking the uplink port
Why this is correct
STP is designed to prevent loops. When a new switch is added, STP may block the uplink port temporarily or permanently if it detects a topology that could cause loops. Solid amber LED is a typical indication of a port in STP blocking state.
- ✗
The cable connecting the switches is faulty
Why it's wrong here
A faulty or damaged cable would typically manifest as a loss of link or intermittent connectivity, which the switch's port LED would indicate as either completely off or blinking. A steady solid amber light on a managed switch port generally represents a protocol-level state or administrative condition, such as STP blocking, not a physical-layer issue. While a bad cable could cause electrical signaling anomalies, it would not consistently produce the deterministic solid amber output associated with STP's loop-prevention logic.
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 220-1101 exam frequently reuses these exact scenarios with slightly different constraints.
✓Spanning Tree Protocol (STP) is blocking the uplink portCorrect answer▾
Why this is correct
STP is designed to prevent loops. When a new switch is added, STP may block the uplink port temporarily or permanently if it detects a topology that could cause loops. Solid amber LED is a typical indication of a port in STP blocking state.
✗The new switch has an IP address conflictWrong answer — click to see why▾
Why this is wrong here
An IP address conflict would not cause a solid amber link LED; that LED indicates a physical or Layer 1/2 issue. Also, devices on the new switch cannot communicate with the existing network, but the amber LED suggests a port blocking issue, not an IP conflict.
★ When this WOULD be the correct answer
In a scenario where a technician configures a new switch and it cannot be managed remotely or pings fail, but link LEDs are green and other devices communicate fine, an IP address conflict with the management IP would be the likely cause.
Why candidates choose this
Candidates may confuse IP configuration issues with connectivity problems, especially when the symptom is 'cannot communicate,' which can be caused by IP conflicts in some contexts.
✗The new switch is in a different VLANWrong answer — click to see why▾
Why this is wrong here
A different VLAN assignment would prevent communication between switches only if the ports are not configured as trunk ports or if VLAN mismatches exist, but the question does not mention VLAN configuration; the solid amber LED indicates STP blocking, not a VLAN issue.
★ When this WOULD be the correct answer
This would be correct in a scenario where a new switch is connected to an existing network and devices on the new switch cannot communicate with devices on the existing network, but the link LED is green and the existing switch has multiple VLANs configured. The new switch's ports might be in a different VLAN than the existing network's default VLAN, requiring trunk configuration or VLAN reassignment.
Why candidates choose this
Candidates may confuse VLAN misconfiguration with STP blocking because both can cause connectivity loss, and they might overlook the diagnostic clue of the solid amber LED, which specifically indicates STP port state.
Analysis generated from the official 220-1101blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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