A loopback error occurs when the keepalive packet is looped back to the port that sent the keepalive. The switch sends keepalives out all the interfaces by default. A device can loop the packets back to the source interface, which usually occurs because there is a logical loop in the network that the spanning tree has not blocked. The source interface receives the keepalive packet that it sent out, and the switch disables the interface (errdisable). This message occurs because the keepalive packet is looped back to the port that sent the keepalive:
%PM-4-ERR_DISABLE: loopback error detected on Gi4/1, putting Gi4/1 in
Keepalives are sent on all interfaces by default in Cisco IOS Software Release 12.1EA-based software. In Cisco IOS Software Release 12.2SE-based software and later, keepalives are not sent by default on fiber and uplink interfaces. For more information, refer to Cisco bug ID CSCea46385 ( registered customers only) .
The suggested workaround is to disable keepalives and upgrade to Cisco IOS Software Release 12.2SE or later.
hi, in aiddition to great suggestions from all, you need to investigate a bit fruther on whay type or switc/hub you are connecting to your fe5/0/0, and the systems connecting into that hub.
error-disable mechanish was design to provide protection to your network, the last thing you want to have is problems in your network such as bridging loops that may render your network useless. Before desabling these types of protection please read Mohammed's provided link which covers all angles to help you troubleshoot this problem.
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