Introduction
This document describes the reasons why a Fibre Channel (FC) port on a Multilayer Director Switch (MDS) or Nexus FC capable switch is brought down due to "Error disabled - bit error rate too high".
A detailed description of Error Disabled states can be found here:
Troubleshooting FC Ports
Verify
Step 1. Use the show interface command to verify that the switch detected a problem and disabled the port.
Verify the ErrDisable State Using the CLI:
show interface
fc3/1 is down (Error disabled - bit error rate too high)
Step 2. Use the show interface fcX/Y transceiver detail command to view information about the signal levels on the Small Form-Factor Pluggable (SFP) transceiver.
If the port is currently down, you may have to bring it up first:
switch# config ; interface fc3/1 ; no shut ; sh interface fc3/1 transceiver detail
fc3/1 sfp is present
Name is CISCO-AVAGO
Manufacturer's part number is SFBR-5780APZ-CS2
Revision is G2.3
Serial number is AGD16348ETR
Cisco part number is 10-2418-01
Cisco pid is DS-SFP-FC8G-SW
FC Transmitter type is short wave laser w/o OFC (SN)
FC Transmitter supports short distance link length
Transmission medium is multimode laser with 62.5 um aperture (M6)
Supported speeds are - Min speed: 2000 Mb/s, Max speed: 8000 Mb/s
Nominal bit rate is 8500 Mb/s
Link length supported for 50/125um OM2 fiber is 50 m
Link length supported for 62.5/125um fiber is 21 m
Link length supported for 50/125um OM3 fiber is 150 m
Cisco extended id is unknown (0x0)
No tx fault, no rx loss, in sync state, diagnostic monitoring type is 0x68
SFP Diagnostics Information:
----------------------------------------------------------------------------
Alarms Warnings
High Low High Low
----------------------------------------------------------------------------
Temperature 27.73 C 75.00 C -5.00 C 70.00 C 0.00 C
Voltage 3.30 V 3.63 V 2.97 V 3.46 V 3.13 V
Current 6.14 mA 10.50 mA 2.00 mA 10.50 mA 2.00 mA
Tx Power -2.52 dBm 1.70 dBm -14.00 dBm -1.30 dBm -10.00 dBm
Rx Power -2.81 dBm 3.00 dBm -17.30 dBm 0.00 dBm -13.30 dBm
Transmit Fault Count = 0
----------------------------------------------------------------------------
Note: ++ high-alarm; + high-warning; -- low-alarm; - low-warning
switch#
Above indicates signal levels are within specification.
Troubleshoot
A description of Error Disabled states can be found here:
Bit Error Threshold
Bit Error Thresholds
The Bit Error Rate (BER) threshold is used by a switch to detect an increased error rate before performance degradation seriously affects traffic.
Bit errors occur because of these reasons:
- Faulty or bad cable.
- Faulty or bad GBIC or SFP.
- GBIC or SFP is specified to operate at 1 Gbps but is used at 2 Gbps.
- GBIC or SFP is specified to operate at 2 Gbps but is used at 4 Gbps.
- Short haul cable is used for long haul or long haul cable is used for short haul.
- Momentary sync loss.
- Loose cable connection at one or both ends.
- Improper GBIC or SFP connection at one or both ends.
A BER threshold is detected when 15 error bursts occur in a 5-minute period. By default, the switch disables the interface when the threshold is reached. Use the shutdown and no shutdown command sequence to re-enable the interface.
Rule out faulty physical equipment by replacing cable/s, GBICs/SFPs and also by pass patch-panel a step at a time.
You can configure the switch to not disable an interface when the threshold is crossed. By default, the threshold disables the interface.
no switchport ignore bit-errors
Note: It is not advisable to leave above setting on indefinitely, rather to be used during troubleshooting sessions.
Note: Regardless of the setting of the switchport ignore bit-errors command, a switch generates a syslog message when the BER threshold is exceeded.
The creditmon process also monitors bit errors.
show process creditmon credit-loss-event-history
For the N5K and N6K, the command is
show platform software fcpc event-history errors
Event:E_DEBUG, length:102, at 571407 usecs after Tue Jan 5 05:33:02 2016
[102] CREDITMON_EVENT_ERR_COUNT, if_index 1105000: cur=0x2acfd01e76de prev=0x2acfd01e76dd ocurances=3
Once the problem hardware has been identified and addressed, a no shutdown of the interface may be required to bring the port up and the bit errors should not be seen thereafter.
Caveats
Be aware of these 2 defects that disables the port/s when 15 bursts of bit errors occur within 5 hours instead of 5 minutes.
It's still a physical layer issue and needs to be addressed.
FC interface disabled due to 'bit error rate too high' when rate is low
Nexus: Cisco BugID CSCux76712
MDS: Cisco BugID CSCuo56792
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