Dark_Fiber

Dark fiber can ruin your day in the place of work, or on the lab, if you are stuck with non-Cisco branded SFP Transceivers that are the correct model number, but not the correct make (Cisco) for the switch without this hidden service.

The Cisco SFP Compatibility matrix can be found here, which I did NOT use while impulsively shopping for cheap lab accessories on eBay, and ended up with an incompatible SFP Transceiver.

When the switch booted up, this output was in the initial boot sequence:

SW1#sh log

(…)
%PLATFORM_PM-6-MODULE_ERRDISABLE: The inserted SFP module with interface name Gi1/0/1 is not supported

%PM-4-ERR_DISABLE: gbic-invalid error detected on Gi1/0/1, putting Gi1/0/1 in err-disable state

And this is the interface state:

SW1#sh int gi1/0/1
GigabitEthernet1/0/1 is administratively down, line protocol is down (err-disabled)

To remedy this, I issued the following commands hidden commands, meaning they will not show up in IOS help, and are unsupported by TAC if in use:

  • service unsupported-transceiver
  • no errdisable detect cause gbic-invalid

As seen here on SW1:

SW1(config)#service unsupported-transceiver ?
% Unrecognized command    <— IOS Help does not recognize it as a valid command

SW1(config)#service unsupported-transceiver
Warning: When Cisco determines that a fault or defect can be traced to

the use of third-party transceivers installed by a customer or reseller,

then, at Cisco’s discretion, Cisco may withhold support under warranty or

a Cisco support program. In the course of providing support for a Cisco

networking product Cisco may require that the end user install Cisco

transceivers if Cisco determines that removing third-party parts will

assist Cisco in diagnosing the cause of a support issue.

SW1(config)#

As seen it won’t even recognize it once entered with a “?” at the end, but once entered it gave the whole lecture about the use of 3rd party Transceivers Voiding Support / Warranty for the switch.

The command to prevent the err-disable state:

SW1(config)#no errdisable detect cause gbic-invalid ?
<cr>

SW1(config)#no errdisable detect cause gbic-invalid
SW1(config)#

This kicks out no error, and is recognized by Cisco IOS help.

Upon rebooting the switch:

Dark_Fiber2

STP even kicked in to put one of the interfaces into Blocking mode on SW2 🙂

This is not CCNP SWITCH related for the exam, but good to know for home labs or if a local SFP Transceiver needs to be sourced for work, until a Cisco replacement can be obtained.

I have actual Cisco SFP Transceivers plugged into my lab so it won’t create any glitches or bugs during studies:

SW1#sh inv
NAME: “1”, DESCR: “WS-C3750V2-24PS”
PID: WS-C3750V2-24PS-S , VID: V08 , SN: FDO1640X1W8

NAME: “GigabitEthernet1/0/1”, DESCR: “1000BaseSX SFP”
PID: Unspecified , VID: , SN: AGM120716QD

NAME: “GigabitEthernet1/0/2”, DESCR: “1000BaseSX SFP”
PID: Unspecified , VID: , SN: AGM124915FX

One thing to keep in mind, the model # must match from the Compatibility Matrix for this to work, these commands only allow different manufacturers with the same Transceiver specs to work on a Cisco Catalyst switch.

I found this and wanted to post it on here for later reference if ever needed, and for anyone in countries where Cisco Transceivers may not be inexpensive and readily available for home labs or work.