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How to fix error message “loopback error detected on 3850 Switches”

How to fix error message “loopback error detected on 3850 Switches when you plug in an ethernet cable, this most likely happens when it is a circuit that is provided by the internet carrier and the cable is going to the modem

when the ethernet cable is plugged in – the switch starts negotiating and sends keepalive messages – the message is looped backed to the switch and the switch puts the port in the err-disable mode

The workaround to disable keepalive is as follows

  1. Log in to the switch
  2. “config t” to go the config mode
  3. use the interface command to go to the interface config mode “interface gig 0/1” and type “no keepalive”

This should do the trick and always check your interface settings to see how it is negotiated

 

 

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