Issue:
Link failure - Ethernet link continously goes down/up

Solution:
Error Recovery:
In certain configurations, and under specific conditions where the media converter brings down a link to convey status, there is potential for a deadlock. Recovery is achieved by momentarily restoring the link to see if the original failure has been resolved. If it has not, the link will be forced down again, however if the original problem has been resolved, the link will be restored.

If the Fiber Link goes down the Ethernet Link will go into Error Recovery mode (unless Smart Link Passthrough is disabled). The recovery retry mechanism enables the copper and fiber ports based on timers in order to initiate recovery of the ports with the local and remote devices. This retry mechanism uses progressively longer timeouts starting from 3 seconds with a 2 second interval between retries, until a maximum timeout of 24 seconds has been reached ( staying at that interval until the link is successfully re-established )

Note: this may cause some switches to disable the port: ie Cisco logs
Link-flap error
Link flap means that the interface continually goes up and down. The interface is put into the error disabled state if it flaps more than five times in 10 seconds.