switch port blinking green and amber then returns to blink green

[MustafaRagheb06718]

Hi ...

I have 3750G 12S and one of its ports is a trunk port connected to another cisco switch, this port works properly with no issues.

But every few minutes it starts to blink green and amber (slowly) for 3-7 seconds and returns to blink green as normal (I didn't notice any problems in both states). It is the only port in the switch that does that.

what could it be ?

[Leo Laohoo · Accepted solution]

Either duplex mismatch or line errors.

Post the complete output (minus IP address &/or description) to the following commands: 

sh version
sh interface <PORT> controll

[marce1000]

 - Also look at the logs when this happens, preferably use a syslog server as a log-collector, which simplifies the task for 'overviewing' the problem at   longer time frame(s).

 M.