Fix a Cisco 3750 with blinking PoE light

In this article I’ll discuss how to fix a Cisco 3750 24 Port power over Ethernet (PoE) switch with a rapidly blinking amber PoE light. Amber lights usually indicate something bad, so I consoled into the switch and did a “show power inline” to find out that several ports showed faulty PoE operation. Here’s how to resolve the issue…

Interface  Admin  Oper …
Fa1/0/1   auto   faulty …

I opened a TAC case & was instructed to fix the problem by simply rebooting the switch. The technician did note that in some cases rebooting the switch may not resolve the problem and in those rare cases the switch needed to be replaced completely–awesome.

When I did reboot the switch, I noticed that every switch daisy chained after the affected one also performed a reset thereby bouncing all clients attached to those switches temporarily. So if you’ve got a blinking PoE light on your switch, just reboot it, but make sure you do it early in the morning or late at night…especially if you’ve got lots of other switches in your stack.

5 Responses So Far... Leave a Reply:

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  2. TheMachineWhisperer says:

    This can also often be resolved without rebooting the switch. It ca be done by simply shutting down and restarting the interface affected.

    In your case:
    conf t
    int Fa1/0/1
    no shut

    Then confirm with the “show power inline” command from the enable mode. Obviously if a faulty device was the cause then you want to remove it first.