Tonight I had to install a used 3550 we recently picked up to power some of our Polycom conference phones we have in the office. To my chagrin, when I plugged the phones in, they started to boot then powered off, powered up again then back down. Why is nothing ever easy!?!? They just continuously flapped whenever they were powered by the 3550. Plug them into the wall and they worked fine. I suspected it was related to the power settings on the port of the switch but I have never dealt with POE settings in the past, they always just worked. Like most things in IOS, it’s a simple fix once you know what’s going on.
A little Googling and I found this link.
Adding this line fixed the issue 100%. I assume that phone does some kind of reset during the boot process that causes to the Cisco to drop the voltage of the POE supply. The phone reboots and the cycle repeats. This is from the Cisco docs: “For certain IEEE Power Devices that require multiple reloads during initialization, you can set a delay shutdown time to configure the switch to continue providing power during initialization.”
Of course, if you have different equipment you may need to play with the delay values a little.
This is a GRRREAT post! You saved my neck.