N10-009 Question 329
Single answerBasic networking device commands: show mac-address-table, show route, show interface, show config, show arp, show vlan, show powerA network technician is troubleshooting why a newly installed PoE security camera is not coming online after being connected to an access switch. The switch port shows a physical link light, but the camera is not receiving network connectivity or power. The technician wants to verify whether the switch is actually providing power on the port before investigating VLAN or Layer 2 forwarding issues. Which command should the technician use first?
- A
show power
- B
show vlan
- C
show mac-address-table
- D
show arp
Show answer and explanation
Correct answer: A
Explanation
In a real troubleshooting workflow, technicians start with the most immediate dependency. A PoE camera must first receive electrical power before it can participate in VLAN forwarding, MAC learning, or IP communication. Therefore, checking switch power delivery with show power is the best first step. After confirming power, the technician could move on to commands such as show interface to confirm link state and errors, show vlan to verify the access VLAN, and show mac-address-table to see whether the switch is learning the camera's MAC address. This follows standard layered troubleshooting practice used across enterprise networks and aligns with common switch operating procedures documented by major vendors.
- A. Correct.
Correct. The technician's first task is to confirm whether the switch is delivering Power over Ethernet to the camera. The show power command is used on supported switches to display PoE status, power allocation, and available power budget. Since the problem statement specifically mentions uncertainty about whether the device is receiving power, this is the most direct and efficient command to use first.
- B. Incorrect.
Incorrect. The show vlan command helps verify VLAN membership and whether the switch port is assigned to the expected VLAN. That is useful for troubleshooting connectivity after power has been confirmed, but it does not directly verify whether the camera is receiving PoE.
- C. Incorrect.
Incorrect. The show mac-address-table command displays learned MAC addresses and the switch ports associated with them. This helps determine whether the switch is seeing Layer 2 traffic from the camera. However, if the camera is not powering on, there may be no MAC address learned at all, so this is not the best first step when PoE delivery is in question.
- D. Incorrect.
Incorrect. The show arp command displays IP-to-MAC address mappings in the ARP table, typically on routers or Layer 3 devices. This would only be useful after the device is powered on, connected, and attempting IP communication. It does not confirm PoE status and is therefore not the best initial command.