how to check / find out the root cause of Link down on SFP Fiber Link

[Paul11]

How to check / find out the root cause of Link down on SFP Fiber Link

Fiber cable error ? SFP module error ? Why was the Link down?

The link is sharing port. LACP L2 (1:21 and 2:21)
Now the link is up and running.
I didn't see any collisions/congestion/anomalyrxerrors/txerrors on the port

Link State: Active, 1Gbps, full-duplex and AUTO

following is the log

09/25/2015 11:31:22.76 Slot-1: Add port 1:21 to aggregator09/25/2015 11:31:22.72 Slot-1: Port 1:21 link UP at speed 1 Gbps and full-duplex
09/25/2015 11:31:22.15 Slot-1: Remove port 1:21 from aggregator
09/25/2015 11:31:22.14 Slot-1: Port 1:21 is Down, remove from aggregator 1:21
09/25/2015 11:31:22.14 Slot-1: Port 1:21 link down

Appreciate your help.

Regards,
Paul

[Paul11]

Thanks Stephane,

It only happen about 14sec link flap up/down about 4 times within 14sec.
Now the link is up and running. yes i understand that it's not enough info and difficult to find out the root cause. link flap may be because of Physical layer issue.

Thanks for your time.

-Paul

[Stephane_Grosj1]

The command given by Marco will add a delay to help resolve false flapping detection. It shouldn't be used everytime, everywhere. In your case, if it flapped only once, that can be due to the other side, or something in the path (you have LX so I'm assuming there can be other active devices in-between). There's too little information to help find the root cause.

Is it happening a lot / often?

[Curtis_Parish1]

Have you tried looping back the fiber to test the SFP+ modules and the fiber path?

[Paul11]

Hi Curtis,

thanks for your suggestion. actually i didn't aware that portion. It really help me to troubleshoot the error. since link flap error are mostly from Physical Layer issue Bad Cable, ...

Thanks 😄