Odd Cisco PoE Switch Reset

By V.H. Scarpacci ·
This is an odd situation to me. Eight months ago a user disconnected their VoIP deskset from the switch at the wall drop. This caused 'all of the phones to reset'. I thought this was impossible, but spent a couple of hours trying to duplicate this. No luck.

Today I got a call( via cell phone) that all of the VoIP phones on a different subnet just reset. At the same time I received a notification from the network monitor that a wireless access (also PoE) was offline. I found that someone had unplugged the WAP from the drop.

Is it possible that unplugging a device from a PoE switch can reset the switch causing all of the devices on that switch to reset?

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It should not work that way

by robo_dev In reply to Odd Cisco PoE Switch Rese ...


there are some instances where the phones would switch to a secondary call manager host, so I would look carefully to make sure that somehow the phones think the primary CM is offline, and are all dropping to connect to a secondary CM.

With respect to POE, if this issue was isolated to one switch I would wonder if it's power supply was going bad, but if POE is actually dropping on more than one, that sounds like one of those weird and wonderful Cisco bugs to me....

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As stated above this shouldn't be happening

by OH Smeg Moderator In reply to Odd Cisco PoE Switch Rese ...

The other thing I would check is the quality of the Mains in the building.

I've seen cases where some very dirty Mains has screwed things so badly that some really screwy things happen.

So if this is happening to more than 1 switch I would also check the Mains for a lot of Noise and maybe install Filters to see if that helps stop this happening.


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power anomalies, PoE power supply anomalies

by wfairley In reply to Odd Cisco PoE Switch Rese ...

I have observed where the power supplied to a building from the street was not within specs and thus minor power fluctuations could cause sensitive power supplies to experience "brown out" conditions. I recommend getting a specialist to monitor the building power for a 24-48 hour period to observe for anomalies. For your "sensitive" phones (executives, doctors, etc.) I recommend installing the phone power supply, if you are seeing consistent failures. Also follow this policy for the WAP's and other network access devices that have demonstrated a pattern of spontaneous power resets. In parallel, I also recommend setting up primary and secondary DHCP and DNS servers, as these services are critical, and if a series of phones lose network connectivity to the soft switch, they will appear to be resetting as a result of power anomalies when in fact their DHCP lease times might be expiring within a few seconds of each other. Redundant DHCP/DNS servers will also heal any other network anomalies your users are experiencing as well.


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