Link down on block

Today one of my fibre links to a particular school block went down. Nagios was screaming away bloody murder, emailing me constantly every 15 minutes. The link light on the connection was a steady orange

I went up to the switch rack and checked both ends. The SFP convertor looked alright and there was no physical damage to the connecting fibre link, nor to the RJ45 cables connecting both access and distribution switches. The switches' SNMP readout looked fine with no other errors whatsoever.

The problem had to be software and not hardware.

I rechecked the system logs and noticed that the port and the line conditions were down. This was confirmed by issuing the command "sh port GiX/X status".

I performed a "shutdown" and "no shutdown" on the port and the link went up immediately.