I have a bunch of 3560 POE switches in my network. The individual ports are configured with voice vlans and data vlans. We had a user plug a cheap microswitch (netgear, linksys, etc.) into the back of the phone, and then their PC, printer, etc. into that. The phone is connected to the switch.
They had a loose cable that was plugged into something else earlier and thought that needed to be plugged in. This created a switching loop in the microswitch. Well, it brought that whole LAN segment down due to the broadcast/traffic storm loop.
What can I do to prevent this in the future. As the microswitch is not participating in STP, and neither is the phone?
switchport access vlan XX
switchport mode access
switchport voice vlan YY
mls qos trust dscp