N10-009 Question 306
Select 3Hardware issues: Power over Ethernet (PoE) (Power budget exceeded, Incorrect standard), Transceivers (Mismatch, Signal strength)A network administrator replaces several office phones with new color-display VoIP phones and also adds two pan-tilt-zoom IP cameras to the same 24-port access switch. The switch provides PoE and has a total PoE budget of 185W. After the changes, some devices boot, then repeatedly power-cycle, while others never power on. On a different uplink, a newly installed fiber SFP shows link lights on both ends, but users report intermittent connectivity and high CRC errors. Which TWO issues most likely explain these symptoms?
- A
The switch PoE budget has been exceeded, causing the switch to deny or drop power to some powered devices
- B
The IP cameras require a higher PoE standard than the switch ports provide, causing insufficient power delivery even if total budget is available
- C
The fiber uplink problem is most likely caused by an incorrect VLAN assignment on the access switch
- D
The fiber transceivers are mismatched or have unsuitable optical characteristics, causing a marginal link despite link lights being present
- E
The phones are failing because PoE devices require Cat 6 cabling and will not function on Cat 5e
Show answer and explanation
Correct answers: A, B, D
Explanation
This scenario intentionally combines two common Network+ hardware troubleshooting domains: PoE power delivery and fiber transceiver health. For the PoE symptoms, the administrator should verify both the switch's total PoE budget and each port's supported IEEE PoE standard. According to IEEE PoE standards, 802.3af provides up to 15.4W at the port, 802.3at up to 30W, and newer 802.3bt levels provide more for higher-draw devices. In production networks, PTZ cameras frequently require more power than basic IP phones, so either budget exhaustion or an incorrect PoE standard can cause boot loops or failed startup. For the fiber uplink, a link light does not rule out a physical-layer problem. Best practice is to confirm that both ends use compatible transceivers with matching speed, wavelength, connector type, and supported fiber mode, and then validate optical levels and error counters. Vendor hardware documentation, switch PoE allocation tables, and transceiver compatibility matrices are the primary references administrators should consult when diagnosing these issues.
- A. Correct.
Correct. A PoE-capable switch has both per-port power limits and a total chassis power budget. When the total budget is exceeded, some powered devices may fail to start, repeatedly reboot, or be administratively denied power depending on the switch model and power allocation policy. This matches the symptom of multiple devices power-cycling or not powering on after additional PoE devices were added.
- B. Correct.
Correct. PoE compatibility depends on the IEEE standard supported by both the power sourcing equipment and the powered device. For example, a device that needs PoE+ (802.3at) or 802.3bt may not operate correctly on a port that only provides 802.3af power. PTZ cameras commonly draw more power than basic phones or fixed cameras, so an incorrect PoE standard is a realistic cause even when the switch still has some overall budget remaining.
- C. Incorrect.
Incorrect. A VLAN mismatch can cause connectivity or segmentation problems, but it does not explain powered devices repeatedly rebooting or failing to power on. It also does not typically produce a fiber link with physical link lights and CRC errors. CRC errors on a fiber uplink usually point to a Layer 1 issue such as transceiver mismatch, bad fiber, contamination, or signal problems rather than VLAN configuration.
- D. Correct.
Correct. Link lights only indicate that some optical signal is being detected; they do not guarantee a healthy or supported link. Intermittent connectivity with CRC errors is consistent with mismatched transceivers, wrong wavelength, unsupported optics, incorrect fiber type for the optic, excessive attenuation, or overpowered/underpowered optical signal. This is a classic transceiver or signal-strength issue.
- E. Incorrect.
Incorrect. PoE does not require Cat 6 specifically. Standard Ethernet cabling such as Cat 5e is commonly used for PoE within specification limits. While poor-quality or damaged cabling can affect PoE performance, the statement that PoE devices will not function on Cat 5e is false and reflects a common misconception.