I have 2960 switch that is connected to 2 3560 switches for redundancy through the GE ports on the 2960. 2 days ago, I started getting loopback detected errors which disabled the ports and effectly took down the switch. I got the following response from the output interpreter when I plugged in my log messages:
%ETHCNTR-3-LOOP_BACK_DETECTED: Interface [chars]: [chars]
Explanation: The problem occurs because the keepalive packet is looped back to
the port that sent the keepalive. Keepalives are sent on the Catalyst switches
in order to prevent loops in the network. Keepalives are enabled by default on
all interfaces. You see this problem on the device that detects and breaks the
loop, but not on the device that causes the loop.
My question is this. Is the loopback caused by the fact that the switch is connected to 2 different switches (I thought that's what STP was for) or is this just between the two individual ports on the two switches?