N10-009 Question 307
Single answerHardware issues: Power over Ethernet (PoE) (Power budget exceeded, Incorrect standard), Transceivers (Mismatch, Signal strength)A network administrator replaces several office phones with new video-enabled VoIP phones and also installs two new 802.11ax wireless access points. All devices are connected to the same 24-port access switch. After the change, some phones boot normally, but two access points repeatedly power cycle and never fully come online. The switch log shows "PoE power denied" on those ports. The administrator verifies that the Ethernet cabling is good and link lights are present. Which action is the BEST next step to restore service?
- A
Replace the SFP transceivers on the switch uplink because low optical signal strength can prevent PoE delivery to edge devices
- B
Configure the affected switch ports to half duplex so the access points draw less power during initialization
- C
Check the switch's total PoE budget and either reduce the connected PoE load or move the access points to a switch that supports higher available PoE power
- D
Change the access point ports from 802.3at to 802.3af because 802.3af provides more compatible power negotiation for newer devices
Show answer and explanation
Correct answer: C
Explanation
This scenario points to a PoE power budget problem, not a cabling or transceiver issue. The key evidence is that the switch log reports "PoE power denied" and the affected devices power cycle rather than simply losing network connectivity. In practice, PoE troubleshooting should include checking both the per-port power requirement and the switch's total available PoE budget. Modern devices such as video phones and 802.11ax access points often require more power than older devices, especially if they support additional radios, USB peripherals, or enhanced features. According to IEEE PoE standards, 802.3af provides up to 15.4W at the port, while 802.3at provides up to 30W at the port; some devices may also require 802.3bt for higher power classes. Vendor switch documentation typically provides commands or dashboards to review allocated and remaining PoE wattage, which is a best practice when adding or upgrading powered devices.
- A. Incorrect.
This is incorrect. SFP transceivers and optical signal strength affect uplink connectivity, not whether the switch can supply electrical power over copper access ports. A transceiver mismatch or poor optical receive power could cause packet loss or a down uplink, but it would not produce a "PoE power denied" message on specific access ports.
- B. Incorrect.
This is incorrect. Duplex settings affect Ethernet traffic behavior, collisions, and performance on compatible links, not the amount of PoE wattage delivered to a powered device. An access point that is power cycling due to insufficient PoE will not be fixed by changing duplex.
- C. Correct.
This is correct. The log message specifically indicates the switch refused power because available PoE capacity was exceeded. Adding higher-draw video phones and Wi-Fi 6 access points can exhaust the switch's total PoE budget even when cabling and link status look normal. The best next step is to verify the switch's remaining PoE capacity and reduce load, redistribute devices, or use hardware with a larger power budget or higher PoE capability.
- D. Incorrect.
This is incorrect. 802.3at delivers more power than 802.3af, not less. If the access points require more than 15.4W at the port, forcing 802.3af would likely worsen the issue or leave features disabled. This option reflects a common misconception about PoE standards and compatibility.