sfp-no light

[bluesea2010]

Hi all,

I noticed something odd with a fiber SFP module. When it's plugged in, there's no light visible from the transmitter. But if I unplug it and then plug it back in, the light appears.

To compare, I checked another working SFP — the TX light is visible immediately, and the RX/TX power levels look normal.

Why does this happen? Could it be a faulty SFP, an initialization issue, or maybe something with the port?

Appreciate any insights!

[Kasun Bandara]

@bluesea2010 hi what is the model of SFP and switch ?

[Mark Elsen]

  - @bluesea2010   Difficult to tell ; you are not mentioning any switch model or software version.
                               Make sure to use a compatible SFP : Cisco Optics-to-Device Compatibility Matrix
                               Check SFP details according to :       show sfp defails on (SMB) switches

                               + Check logs on the switch after you plug the SFP in and also when you unplug it and then plug it back in

  M.

[bluesea2010]

The link was flapping, so the logs only reflect that behavior—aside from the 'changed state to down' messages

[pieterh]

As other members have posted, the logs are very important here.

But just guessing I think the port has been err-disabled because of the flapping. That's where there was no light.

Then after changing the SFP, err-disabled recovery has re-enabled the port again, and there where light!

[M02@rt37]

Hello @bluesea2010 

Do you have check any logs ?

[Leo Laohoo]

Look at the Tx/Rx power and for interface-level line errors. 

The link could be failing.