Cisco: Unsupported Transceivers

One of the most infuriating things with enterprise gear – other products included – is vendor lock in.
I understand when there’s a ligament reason, but it’s exceptionally rare. Now there’s a long list of reasons vendors choose to do so – good or bad, but I’ll save my ramblings for another time.

Cisco – kindly – does allow you do use unsupported transceivers. You just need to acknowledge the fact it may cause issues, and is not officially supported. Which in turn also means you acknowledge that Cisco TAC will not help you resolve an issue either, if you have to contact support, they won’t t help you while you’re running an unsupported configuration. They may ask you to reproduce any issues with Cisco optics installed in order to proceed with support cases.

Configuration Mode

Fist we need to enable privileged execution mode with the command “enable” or “en” for shorthand in the terminal. Then, to execute the commands bellow, we need to be in the “configuration terminal” which can be typed exactly or as “conf t” for short. Once you enter privileged execution mode, you will see a ‘#’ after the host name (ie. “Switch-13>” becomes “Switch-13#”).

NOTE: You use the command “exit” to exit the configuration terminal, and don’t forget to commit the configuration to NVRAM as I’ve shown below. You only need to exit and commit one time if you enter both commands.

Allow Unsupported Transceivers

Switch-13(config)#service unsupported-transceiver
Switch-13(config)#exit
Switch-13(config)#write memory

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.

This tells the switch to allow 3rd party (non-Cisco-certified) SFPs instead of rejecting them purely because they’re not on Cisco’s approved list. Translation – Any random optic will be accepted no matter what.

Reverting: no service unsupported-transceiver

Prevent Interface Error

Switch-13(config)#no errdisable detect cause gbic-invalid

No output after entering the command is exactly what you want and how we know it’s recognized as a valid command.

This doesn’t actually “allow” 3rd party transceivers directly, it tells the switch to not set the state of the transceiver / port to “errdisable” solely based on the transceiver’s manufacturer. Translation – If I think the optic is invalid, do I shut the port down? (Other shit than the vendor can make a transceiver actually invalid / incompatible).

Reverting: errdisable detect cause gbic-invalid

Comparison

Thank you to ChatGPT for differentiating the nuance of why you would use both commands as they both seem to cover almost exactly the same thing.

Neither set: third-party optic often triggers unsupported/invalid → may end up err-disabled

Only service unsupported-transceiver: works when vendor policy is the only blocker; fails if the optic still trips gbic-invalid → err-disable

Only no errdisable detect cause gbic-invalid: stops errdisable, but the optic may still be refused / not come up because you never enabled third-party support

Both: best chance to bring up third-party optics on platforms/versions where gbic-invalid errdisable happens

Conclusion

That should wrap it up! If your switch / Cisco device still continues to hate you, you may have to persuade it with something… larger.. and heavier..

I hope you found this helpful and as always, reach out if you need a hand.