Core issue
A Catalyst switch generates LINK-4-ERROR error messages after configuration changes. This message means that excessive errors have occurred on the interface specified by [char] and occurs due to duplex mismatch between both ends of the link.
These errors could also result when cabling distance has been exceeded, or a bad cable has been used. Cabling distance for 100BaseTX connections is exceeded when the distance between the port and the attached device exceeds100 meters, or if the switch is attached to a repeater and the total distance between the two end stations exceeds the 100BaseT cabling guidelines.
Resolution
If LINK-4-ERROR error messages are received, check for duplex mismatch between both ends of the link. You can see the port speed and duplex by issuing the show interfaces status command.
The recommended policy is to always configure both link partners in the same way. So both sides of a link should have auto-negotiation on, or both sides should have it off. The switches that run Cisco IOS Software (as opposed to Catalyst OS (CatOS)) default to having auto-negotiation for speed and duplex set to On. To hard code the speed and duplex on a switch running Cisco IOS Software (turning off auto-negotiation), issue the speed and duplex commands underneath the specific interface.
If the issue is due to bad cables then swap the cables or it is best to reduce the cable length to within the recommended distances.
Note: This error message is not seen on Catalyst 2950, 2970 and Catalyst 3550 switches even though the switches faces duplex mismatch or issues with the cable connected to the interface.
Port LED status
Blinking amber
Error message
%LINK-4-ERROR
