Two simple unmanaged switches have died in the same cabinet in two years, one at 18 months and one just today at six months.
Both times we gradually experienced increasing intermittent verified connectivity failures for all equipment (two linux boxes and a Debit/credit terminal) except the uplink (port 1) and the fourth item, a cisco phone connected to the switch via a PoE injector in port 2. Connectivity would eventually return with or without power cycling the switch. At the onset of symptoms power cycling reestablishes connectivity, but eventually it does not.
Link lights remain on and flickering regardless of interrupted connectivity. Interrupted connectivity initially occurs on a port-by-port basis but ends up affecting all ports except the PoE-phone port. Earlier today I, in an attitude of stupefied mystification sat there and plugged each item into port 2 previously inhabited by the PoE-phone and watched it work just perfectly while not working in ports 3/4/5.
The deceased are a D-Link DSS-5+ and a DES-105G. The switches took wall power, but all else, including the PoE injector, are powered through a UPS.
It sure looks like the PoE injector is somehow frying the switches, but 1) does that make any sense, and 2) what's the reasonable workaround?
Attentions to my little mystery much appreciated!