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Cisco 3650 err-disabled loopback error

Posted on 2015-01-23
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Last Modified: 2015-01-23
Hi all

i am new at a job trying to work on a cisco issue. from showing port status i found below

FastEthernet0/6 is down, line protocol is down (err-disabled)
  Hardware is Fast Ethernet, address is 001c.f9a4.ba08 (bia 001c.f9a4.ba08)
  Description: xxx Internet access
  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Auto-duplex, Auto-speed, media type is 10/100BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 02:45:22, output 02:45:20, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     94431258 packets input, 74960012744 bytes, 0 no buffer
     Received 17641379 broadcasts (15741759 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 15741759 multicast, 0 pause input
     0 input packets with dribble condition detected
     77517461 packets output, 28293274573 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

I then googled err disable and found below after running in the console

Port      Name               Status       Reason               Err-disabled Vlan                         s
Fa0/6     xxx Inter err-disabled loopback

Can you please advice what i need to do to resolve the issue? I am training on cisco so not expert at it but using this experience to learn as well

Please advice

thanks in advance for your help
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Question by:Sundeep V
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by:Otto_N
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This error is caused when the Rx and Tx pair of a specific port get linked to each other (i.e. the port gets looped).  The default action on a Cisco switch is to put the port in err-disable state, and create a log entry.  Even after the loop is removed, the port will remain in the err-disable state until you clear the port (I find it easiest to "shut" and " no shut" the port).

I'll try to get you some additional documentation on this condition...
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by:Sundeep V
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Awesome, many thanks for that, will have read. I did shut down and no shutdown and this seemed to have done the trick

Is there anything i need to do to avoid this happening again ?
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by:Otto_N
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Other than keeping your cables straight (I assume that is not always in your control), you can configure "errdisable recovery" (it is treated very near the end of the link provided) on the switch, which will attempt to recover err-disabled ports after a timer has expired (usually 300 seconds / 5 minutes).
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