Symptom

Loopback error occurs when keepalive packet is looped back to the uplink port.The following error is detected on ten GigabitEthernet SFP ports with fiber SFP: ETHCNTR-3-LOOP_BACK_DETECTED & PM-4-ERR_DISABLE loopback error.

Conditions

By default, the loopback and keepalives should be disabled on fiber and cooper uplink ports. This issue impacts Catalyst 2960X and 6800IA platforms.

Workaround

Workaround 1: (Preferred, but not persistent on reload) On the physical port, first configure keepalives and then remove keepalives by entering the no keepalives command. When you follow the same configuration on the port-channel interface, it continues to send loop packets. Sw-Server4(config-if)# keepalive 10 Sw-Server4(config-if)# no keepalive Workaround2: Write an Embedded Event Manager (EEM) script to flap the configuration after reload. Workaround 3: If the port continues to detect ERR_DISABLE loopback error, Disable the loopback detection for all ports and enable UDLD to detect any unidirectional issues. Sw-Server4(config)# no errdisable detect cause loopback Interface X/Y Sw-Server4(config-if)# udld port Sw-Server4#show errdisable detect ErrDisable Reason Detection Mode ----------------- --------- ---- loopback Disabled

Further Problem Description