N10-009 Networking Concepts Practice Question
A network switch is experiencing a high number of collisions on a specific port. The connected device is configured for half-duplex. Which of the following is the most likely cause?
⚠ Common exam trap
Watch out — candidates often assume collisions are always caused by cable length or physical issues, overlooking the duplex mismatch as the primary cause when one side is half-duplex and the other is full-duplex.
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 configured for full-duplex
When a switch port is configured for full-duplex but the connected device operates in half-duplex, a duplex mismatch occurs. The switch transmits without checking for collisions (as full-duplex does not use CSMA/CD), while the half-duplex device expects to sense the carrier before sending, leading to collisions on the port. This is the most common cause of excessive collisions on a single switch port.
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 switch port is configured for full-duplex
Why this is correct
When a switch port is configured for full-duplex, it transmits data without performing Carrier Sense Multiple Access with Collision Detection (CSMA/CD), assuming a dedicated transmit and receive path. If the connected device is operating in half-duplex, it will perform CSMA/CD, listening before transmitting. When the full-duplex switch transmits while the half-duplex device is also transmitting, the half-duplex device detects a collision, leading to a high number of reported collisions on the switch port due to this fundamental operational conflict.
- ✗
The cable length exceeds 100 meters
Why it's wrong here
Exceeding the maximum Ethernet cable length of 100 meters primarily leads to signal attenuation and increased propagation delay. This can result in corrupted frames or, more specifically, "late collisions" where a collision is detected after the first 64 bytes of a frame have been transmitted. While it indicates a physical layer issue, it typically manifests as late collisions rather than a general high collision count, and often causes link instability or complete failure before just high collisions.
When this WOULD be correct
A question about a network experiencing high error rates, late collisions, or intermittent connectivity on a link where the cable run is known to be near or beyond 100 meters for twisted-pair copper.
- ✗
The device is using an incorrect VLAN
Why it's wrong here
An incorrect Virtual Local Area Network (VLAN) assignment means the device is logically segmented into the wrong broadcast domain. This would prevent the device from communicating with intended resources or receiving IP addresses, leading to connectivity failures at Layer 3. However, VLANs operate at Layer 2 (data link layer) for logical segmentation and do not directly influence the physical layer (Layer 1) collision domain or the mechanics of collision detection.
When this WOULD be correct
A question about a device unable to communicate with other devices on the same network, but can communicate with some, and the network uses VLANs. The correct answer would be that the device is using an incorrect VLAN ID, causing it to be isolated from its intended broadcast domain.
- ✗
The switch port is configured for 1000BASE-T but the device only supports 100BASE-TX
Why it's wrong here
Speed mismatch would cause the link to negotiate down or fail, but not typically result in a high collision count. Most modern switches auto-negotiate speed and duplex, and mismatches usually prevent link from coming up.
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 N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓The switch port is configured for full-duplexCorrect answer▾
Why this is correct
When a switch port is configured for full-duplex, it transmits data without performing Carrier Sense Multiple Access with Collision Detection (CSMA/CD), assuming a dedicated transmit and receive path. If the connected device is operating in half-duplex, it will perform CSMA/CD, listening before transmitting. When the full-duplex switch transmits while the half-duplex device is also transmitting, the half-duplex device detects a collision, leading to a high number of reported collisions on the switch port due to this fundamental operational conflict.
✗The cable length exceeds 100 metersWrong answer — click to see why▾
Why this is wrong here
Excessive cable length causes attenuation and signal degradation, not collisions. Collisions are a Layer 2 issue related to duplex mismatch, not physical layer cabling limits.
★ When this WOULD be the correct answer
A question about a network experiencing high error rates, late collisions, or intermittent connectivity on a link where the cable run is known to be near or beyond 100 meters for twisted-pair copper.
Why candidates choose this
Candidates often associate cable length limits with general network problems and may incorrectly assume that exceeding 100 meters causes collisions, rather than understanding that collisions are a duplex mismatch symptom.
✗The device is using an incorrect VLANWrong answer — click to see why▾
Why this is wrong here
Incorrect VLAN assignment does not cause collisions; it prevents communication between devices in different VLANs or causes connectivity issues, but collisions are a layer 1/physical layer issue related to duplex mismatch or cabling.
★ When this WOULD be the correct answer
A question about a device unable to communicate with other devices on the same network, but can communicate with some, and the network uses VLANs. The correct answer would be that the device is using an incorrect VLAN ID, causing it to be isolated from its intended broadcast domain.
Why candidates choose this
Candidates may confuse VLAN misconfiguration with other network issues like collisions, or think that VLAN problems can cause frame collisions, but collisions are unrelated to logical segmentation.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
Related to this question
Learn chapter
Network Virtualization and VXLAN
Key term
CSMA/CD
Carrier Sense Multiple Access with Collision Detection is a network protocol used in Ethernet to manage data transmission and handle collisions when two devices send data at the same time.
Key term
IoT
IoT (Internet of Things) is a network of physical devices embedded with sensors and software to connect and exchange data over the internet.
About these practice questions
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 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 N10-009 exam.