Sunday, October 20, 2019

PoE issue on Cisco 4500R+E w/ WS-X4748-RJ45V+E

I've got a weird issue that I'm wondering if anyone else has come across before. I've got some older PoE (Zebra MK500) devices that won't get power on the above switch. I've got other PoE devices (Cisco APs, MiTel Phones, MiTel DECT APs, etc) that all get PoE just fine, the issue seems specific to these Zebra devices. I'd say the issue is a problem on the MK500 and call it a day, however, my LinkRunner AT2000 won't test ports on these switches if I have the PoE test enabled. Which leads me back to suspecting the switch. The behavior of the LinkRunner with PoE tests enabled is that I get link for about 2 seconds, then it goes away for 5-10 seconds and repeats. As soon as I disable the PoE tests on the LinkRunner the port comes up as expected and I get the CDP info from the switch. We've tested these devices across numerous 4500s at this location with the same modules so I don't think it's bad hardware. We also have these devices running in a different location with the same hardware and software versions without issue. Unfortunately, no one at that other location has a LinkRunner so I can't test if that behavior is the same there or not. Interestingly enough, a LinkSprinter (the LinkRunners baby cousin) tests PoE without issue.

We also have some 3850 (MGig w/ UPOE) and 3560 switches at this location and the MK500 (and my Fluke) operate fine on those.

I'm at a loss as to what else might be wrong here. It's essentially a generic PoE configuration, we don't enable/disable poe on ports, no policing, etc. Has anyone seen PoE devices behave like this on these switches? Any ideas on where to go with it?



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