We change a CPE router connected to a switch 2950 to a new CPE router. But after the change on teh switch we have :
Jun 9 14:10:35.091: %ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on FastEthernet0/5.
Jun 9 14:10:35.091: %PM-4-ERR_DISABLE: loopback error detected on Fa0/5, putting Fa0/5 in err-disable state
Jun 9 14:10:36.091: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down
Jun 9 14:10:37.099: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to down
when I put back the hold router still same issue.
I can bring up the interface with no keepalive, but still issue with the loop
If I change manually the mac address then the interafce came up, but still not passing any traffic