Swapping fibres in VSP SMLT to EXOS LAG = SMLT port down

[dabbler]

I have 2 VSPs, VSP1 and VSP2 that have SMLT fibre connections to EXOS switch stacks that use sharing.

I built a new EXOS switch stack to replace an existing one, created a new SMLT and all that worked fine. I then disconnected both fibres from the existing EXOS stack and connected both fibres from the new EXOS stack as I need to use the existing VSP SMLT ports.

The fibre on VSP2 works and provides connectivity but the fibre port on VSP1 is now down. Changing fibre cables, SFPs, rebooting the EXOS and VSP did not help.

Anyone know why moving both fibres on an SMLT connection to a new switch stack would cause this?

[RobertD1]

Sounds like a physical L1 problem if you are unable to go back to the original port. Don't see a reason for the port being down and is still admin enabled. Sometimes good to disable one side especially when changing stacking but you are not doing this here.. Check show pluggable basic to see transceiver recognised and show pluggable detail to see info on status of tx and rx signals (should be normal with no warnings for both). Did you get the tx and rx wrong way around when you moved the fibre cable maybe? Is your VIST up?

[dabbler]

VIST is UP ok.
I ran a show pluggable details and the port on VSP1 is showing

RxPower(dBm) -20.0 -19.0 -40.0 0.0 1.0 Low Alarm

I assume the -40 is because the VSP port is down and not transmitting anything

[RobertD1]

If you compare with a working port the low alarm should be 'normal' and a stronger signal, -40 is not normal. You could check with your phone to see if the fibre is receiving light? Make sure tx and rx cores are inserted correctly / right way around (sometimes have to swap them if using new fibre path). 

[dabbler]

I checked and there is no light being transmitted by the VSP port on either fibre core, I'm thinking because the port is down. I tried a shut/no shut, rebooted the EXOS switch stack, the VSP, replaced the SFPs and fibre but nothing made any difference.

[RobertD1]

Are you seeing light from the fibre?

Are you using new fibre for the new EXOS stack? 

Have you tried splitting the LC connector and changing the tx and rx around at one end?