We recently found a problem with a stacking cable. After resolving this issue, we decided it would be a good idea to monitor the StackWise ports on our 3750s.
Looking through the MIB, I found the cswRingRedundant object (188.8.131.52.184.108.40.206.500.1.1.3.0). It is available on our current IOS version 12.2(25)SEE2. On many of our switches, all of the StackWise ports are up and running (per IOS sh switch stack-port and per SNMP), but cswRingRedundant still returns 2 (false).
Any suggestions? This results on switches where there are definitely multiple switches in the stack (I'm not looking at a single-switch stack). We have our switches connected as per a Cisco recommended setup, whereby SW port 1 connects to SW port 2 of the next switch, then SW port 1 on that switch to SW port 2 on the next, etc., until the last switch, where SW port 1 connects to SW port 2 on the first switch.