Hi everyone,
We’ve recently seen a POE problem with some of our multi-gig 3850 stacks (WS-C3850-12X48U).
The symptom is after a power disturbance of some kind, even if the stack doesn’t completely lose power, POE is no longer given to the access points, causing a wireless outage. The rest of the switch stack is performing normally. The fix is to completely unplug/power down the switch, and fire it up again. That seems to work. Soft reloads and other less drastic measures don’t.
Cisco’s website has the below. TAC has only suggested RMA’ing the switch. Our SE says he hasn’t found any internal Cisco docs of a problem with the 3850’s.
We haven’t seen this kind of behavior on our widely deployed 3750X stacks, which the 3850’s are replacing, in the same locations with the same power. That has us wondering if it’s a 3850 issue of some kind.
Not all of our WS-C3850-12X48U’s are showing this problem. Just more than we saw with the 3750X’s. It has us concerned about our plans to widely deploy them.
Anyone else seeing this?
From Cisco's website:
AC Power and PoE Problems
Various disturbances on the AC power line (mains) can cause unusual PoE problems. The power supplies in various switches and powered devices sometimes have unique reactions to AC input disturbances. Problems caused by AC disruptions are usually temporary or one-time occurrences. For example, a specific switch or powered device might reboot due to an AC power problem, while other switches or powered devices might exhibit a greater immunity to the problem.
This is a typical occurrence during lightning storms or AC power maintenance. In a worst-case situation, a PoE power supply might appear to shut down (no PoE output voltage to any port). It is possible the Ethernet functions in the switch appear normal, and only the PoE functions are disrupted or degraded, or the switch might power-down completely in response to the AC disturbance. Powered devices might exhibit unusual behavior.
In such cases, power cycle the switch (unplug the switch, wait at least 3 seconds, then plug it back in). This ensures a total system reset and should restore normal operation.
When several or all PoE ports in a switch cannot provide power to powered devices, and entering the shut and no shut interface configuration commands does not clear the problem, verify that a power cycle restores the switch to normal operation. If it does, suspect an AC power disturbance as the source of the problem.
Sometimes an AC power disturbance can be so brief that it is missed by site personnel but detected by the switch or other electronic systems. If this happens frequently on multiple switches, carefully determine the stability and reliability of AC power. If it often occurs on only one switch, and other switches in the same location do not exhibit the symptom, contact Cisco TAC for guidance.
