Hey Guys, i Have a stack with 2 2960 switches, that connect to my core switch using one single CAT6 cable. On this stack, i have user PCs and IP Phones only. The cable connects port 1/0/24 on the stack to port 2/1 on my core switch. Lately, i have noticed that my stack keeps going down. The log on the core, just shows int 2/1 down, and then up. The log on the stack, shows
00511: Jun 6 12:33:17.138 BR: %STORM_CONTROL-3-FILTERED: A Broadcast storm detected on Gi1/0/24. A packet filter action has been applied on the interface.
000512: Jun 6 12:33:17.793 BR: %ETHCNTR-3-LOOP_BACK_DETECTED: Loop-back detected on GigabitEthernet1/0/24.
000513: Jun 6 12:33:17.793 BR: %PM-4-ERR_DISABLE: loopback error detected on Gi1/0/24, putting Gi1/0/24 in err-disable state
000514: Jun 6 12:33:18.516 BR: %DTP-5-NONTRUNKPORTON: Port Gi1/0/24 has become non-trunk
000515: Jun 6 12:33:18.910 BR: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/24, changed state to down
000516: Jun 6 12:33:20.016 BR: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/24, changed state to down
I dont understand what could be causing the switch to detect a loopback on its trunk uplink port. Usually, when there is a loop, span tree should block the port where the loop comes from. How can it be that it detects the loop on the uplink and err-disables it?
