Troubleshooting a bad cable

Cause
Bad cables can cause the stack port to flap or go down completely. If there are an excessive number of port flaps, the port is disabled and the following log message appears: 
W 10/06:00 23:23:16 03260 chassis: ST4–CMDR: Stack port 1 disabled due to excessive errors. Check cable. To reenable use 'stacking member 4 stack-port 1 enable'.
Action
  1. When this occurs, the show stacking stack-ports command shows the port with a status of “Disabled”.

    Viewing a disabled stack port 

    switch(config)# show stacking stack-ports 

Member Stacking      Port State Peer Member Peer Port
------ ------------- --------   ----------- -----------
1      1             Up         2            2        
1      2             Down       0            0        
2      1             Up         3            2        
2      2             Up         1            1        
3      1             Up         4            2        
3      2             Up         2            1        
4      1             Disabled   0            0        
4      2             Up         3            1        
5      1             Down       0            0        
5      2             Up         4            1     
   
switch(config)#

  2. The following example shows member 3, port 2, which should be connected to member 4, port 1. The ports are down because the cable is bad or disconnected.

    Viewing that two ports are down due to a bad connection 

    switch# show stacking stack-ports 

Member Stacking Port State    Peer Member Peer Port
------ ------------- -------- ----------- ---------
1      1             Up       2           2        
1      2             Down     0           0        
2      1             Up       3           2        
2      2             Up       1           1        
3      1             Down     0           0        
3      2             Up       2           1        
4      1             Up       5           2        
4      2             Down     0           0        
5      1             Down     0           0        
5      2             Up       4           1
  3. The solution in both cases is to ensure that the cable is firmly connected at both ends. If the problem continues, replace the cable. It is possible that there could be a problem with the stack port itself. In this case, validation of this issue requires the installation of a known good cable to see if that cable also fails.

    The port state is not UP until both ends of the cable are connected and the cable has been validated as a genuine cable.

    To view the statistics on the physical port, execute the show tech command in member-context 4. The following examples show the types of information displayed.

    Viewing show tech output 

    Port Number : 1 State : Available
Last Event  : Available Start Req : 1
NE Present  : 1 HPID Good : 1
HPID Fails  : 0 FE Present : 1
Rem Dev Rdy : 1
ESSI Link   : 1 ESSI Good : 1
ESSI Fails  : 0 ESSI TX En : 1
ICL Good    : 1 ICL Enabled : 1
30 Stack Management for 2930M
LP Local RDY: 1 LP Rem RDY : 1
LP DONE     : 1 ICL FailCnt : 0 (10 second interval)
ICL FailCnt : 0 (10 minute interval)
NE Presence HW : 1
FE Presence HW : 1
Rem Dev Rdy HW : 1
Local Dev Rdy HW : 1
Asserted NE Presence HW : 1
Asserted FE Presence HW : 1
Asserted Rem Dev Rdy HW : 1
Phy Frame Errors : 0
Invalid Status Errors      : 0
Invalid Packet Type Errors : 0
Incomplete Packet Errors   : 0
Checksum Errors            : 0
ESSI Flow Out This Port (HW) : 0x2

    Viewing trace information for a port 

    Trace for Port 1
[ 0] [Info ] Start Request Received (Empty) [0]
[ 1] [Info ] Waiting for Stack Module Good (Empty) [0]
[ 2] [Info ] Stack Module Good Received (Empty) [0]
[ 3] [Info ] Cable Insertion Detected (Empty) [1]
[ 4] [Info ] Re-enable NE Present Int [487]
[ 5] [Info ] Starting Cable HPID Validation (Inserted) [488]
[ 6] [Info ] Skipping Cable HPID Validation (Inserted) [488]
[ 7] [Info ] Far End Insertion Detected (Valid) [988]
[ 8] [Info ] Polling for ESSI phy link up (Valid) [988]
[ 9] [Info ] ESSI Link Up [9988]
[10] [Info ] ESSI Link Good (Valid) [9988]
[11] [Info ] ESSI Linked at 9988 ms [9988]
[12] [Info ] Remote Device Ready Detected (Valid) [10898]
[13] [Info ] ICL Change Request Enable (Cable Ready) [10898]
[14] [Info ] Detected Remote Ready Drop. (Cable Ready) [12651]
[15] [Info ] ICL Good. Behind. Partner ready. (Cable Ready) [12988]
[16] [Info ] ICL GOOD received at 2091 ms [12988]
[17] [Info ] Partner LP ready. (Cable Ready) [13980]
[18] [Info ] Set Device Ready. (Cable Ready) [13987]
[19] [Info ] ESSI Link Verified [13988]
[20] [Info ] ESSI Able to Transmit (Cable Ready)