N10-009 Network Implementation Practice Question
A network technician installs a new 802.3at (PoE+) access point in a warehouse. The AP is connected via a 200-foot Cat5e cable to a switch that only supports 802.3af (PoE). The AP powers on but experiences intermittent connectivity drops. What is the most likely cause?
⚠ Common exam trap
The trap here is that candidates see the AP powers on and assume power is sufficient, overlooking that 802.3at devices can operate at reduced functionality on 802.3af but will fail under higher load, leading them to incorrectly blame cable length or RF interference instead of the power budget mismatch.
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 AP is not receiving enough power from the switch
The switch only supports 802.3af (PoE), which provides a maximum of 15.4 watts per port, while the 802.3at (PoE+) access point requires up to 25.5 watts to operate reliably. The AP powers on because it can negotiate 802.3af power, but under load (e.g., transmitting at higher power or using multiple radios), it draws more current than the switch can supply, causing voltage droop and intermittent resets or link drops. This is a classic power budget mismatch scenario.
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 cable length exceeds the maximum allowed for PoE
Why it's wrong here
Standard Ethernet specifications, including those for Power over Ethernet (PoE), dictate a maximum cable segment length of 100 meters (328 feet) for reliable data and power transmission. A cable length of 200 feet, which is approximately 61 meters, falls well within this established maximum. Consequently, the cable length is not a contributing factor to any power delivery issues or intermittent connectivity for the access point in this scenario.
When this WOULD be correct
A network technician connects a PoE device using a 150-meter Cat5e cable and the device fails to power on. The cable length exceeds the 100-meter limit for Ethernet, causing signal degradation and power loss.
- ✓
The AP is not receiving enough power from the switch
Why this is correct
An 802.3at PoE+ access point requires up to 30 watts of power at the port for full functionality. If connected to a switch that only supports 802.3af PoE, it will receive a maximum of 15.4 watts. This significant power deficit means the AP cannot operate reliably, leading to intermittent reboots, erratic behavior, or failure to fully initialize, directly causing intermittent connectivity issues.
- ✗
Duplex mismatch between the AP and the switch
Why it's wrong here
A duplex mismatch occurs when one device operates in full-duplex mode while the other operates in half-duplex, leading to severe packet collisions and retransmissions. This issue primarily manifests as drastically reduced data throughput, network errors, and very slow or intermittent data communication. However, a duplex mismatch specifically affects the data link layer communication and does not interfere with the physical layer's ability to deliver stable DC power over the Ethernet cable to the access point.
When this WOULD be correct
A network technician connects two switches with a crossover cable but one switch is set to half-duplex and the other to auto-negotiation, resulting in high error rates and intermittent connectivity. The most likely cause is duplex mismatch.
- ✗
Radio frequency interference from warehouse equipment
Why it's wrong here
Radio frequency interference from other warehouse equipment, such as motors or cordless phones, primarily impacts the wireless communication signals transmitted and received by the access point. While this could degrade wireless client connectivity or throughput, it does not affect the stable delivery of DC power through the wired Ethernet cable. Therefore, RF interference would not cause power-related intermittent connectivity for the AP itself.
When this WOULD be correct
A wireless AP experiences intermittent connectivity in a warehouse with heavy machinery. The AP is powered by a local power adapter, not PoE. The most likely cause is RF interference from equipment operating in the same frequency band (e.g., 2.4 GHz).
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 AP is not receiving enough power from the switchCorrect answer▾
Why this is correct
An 802.3at PoE+ access point requires up to 30 watts of power at the port for full functionality. If connected to a switch that only supports 802.3af PoE, it will receive a maximum of 15.4 watts. This significant power deficit means the AP cannot operate reliably, leading to intermittent reboots, erratic behavior, or failure to fully initialize, directly causing intermittent connectivity issues.
✗The cable length exceeds the maximum allowed for PoEWrong answer — click to see why▾
Why this is wrong here
The maximum cable length for Ethernet (including PoE) is 100 meters (328 feet), so a 200-foot cable is within the limit and not the cause of the issue.
★ When this WOULD be the correct answer
A network technician connects a PoE device using a 150-meter Cat5e cable and the device fails to power on. The cable length exceeds the 100-meter limit for Ethernet, causing signal degradation and power loss.
Why candidates choose this
Candidates may mistakenly believe that PoE has a shorter distance limit than standard Ethernet, or they confuse the 100-meter limit with a shorter PoE-specific limit.
✗Duplex mismatch between the AP and the switchWrong answer — click to see why▾
Why this is wrong here
Duplex mismatch typically causes symptoms like high error rates, collisions, or complete link failure, not intermittent connectivity drops specifically tied to power delivery. The AP powers on, indicating the link is established, and the issue is power-related due to PoE+ device on PoE switch.
★ When this WOULD be the correct answer
A network technician connects two switches with a crossover cable but one switch is set to half-duplex and the other to auto-negotiation, resulting in high error rates and intermittent connectivity. The most likely cause is duplex mismatch.
Why candidates choose this
Candidates may recall that duplex mismatch is a common cause of intermittent connectivity issues, but they overlook that the AP powers on, suggesting the link is functional, and the specific power difference (802.3af vs 802.3at) is the key clue.
✗Radio frequency interference from warehouse equipmentWrong answer — click to see why▾
Why this is wrong here
The AP powers on, indicating it receives some power, but intermittent drops are due to insufficient power (802.3af provides 15.4W vs. 802.3at's 30W). RF interference would cause consistent connectivity issues or packet loss, not intermittent drops tied to power negotiation.
★ When this WOULD be the correct answer
A wireless AP experiences intermittent connectivity in a warehouse with heavy machinery. The AP is powered by a local power adapter, not PoE. The most likely cause is RF interference from equipment operating in the same frequency band (e.g., 2.4 GHz).
Why candidates choose this
Candidates may assume warehouse environments have significant RF interference from machinery, and intermittent drops seem consistent with interference, overlooking the power mismatch as the root cause.
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
Physical Network Infrastructure
Key term
UTP
Unshielded Twisted Pair (UTP) is a copper cabling type with pairs of twisted wires and no shielding, used for Ethernet networks.
Key term
Unshielded Twisted Pair
Unshielded Twisted Pair (UTP) is a type of copper cabling used in Ethernet networks, where pairs of wires are twisted together to reduce electrical interference, without additional metallic shielding.
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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.