Contents

Introduction

Verify

Troubleshoot

Bit Error Thresholds

Caveats

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