Dealing with an err-disabled port

A port on a Cisco switch may be put into an err-disabled state, which will drop any connections through the switch that are using that port. After logging into the switch you can see if a port is in the err-disabled state by issuing the show interface status command.
Swtch1>show interface status

Port      Name               Status       Vlan       Duplex  Speed Type
Fa0/1                        err-disabled 1            auto   auto 10/100BaseTX
Fa0/2                        notconnect   1            auto   auto 10/100BaseTX
Fa0/3                        notconnect   1            auto   auto 10/100BaseTX
Fa0/4                        notconnect   1            auto   auto 10/100BaseTX
Fa0/5                        notconnect   1            auto   auto 10/100BaseTX
Fa0/6                        notconnect   1            auto   auto 10/100BaseTX
Fa0/7                        notconnect   1            auto   auto 10/100BaseTX
Fa0/8                        notconnect   1            auto   auto 10/100BaseTX
Fa0/9                        notconnect   1            auto   auto 10/100BaseTX
Fa0/10                       connected    1          a-full  a-100 10/100BaseTX
Fa0/11                       notconnect   1            auto   auto 10/100BaseTX
Fa0/12                       connected    1          a-full  a-100 10/100BaseTX
Fa0/13                       notconnect   1            auto   auto 10/100BaseTX
Fa0/14                       notconnect   1            auto   auto 10/100BaseTX
Fa0/15                       notconnect   1            auto   auto 10/100BaseTX
Fa0/16                       connected    1          a-half   a-10 10/100BaseTX
Fa0/17                       notconnect   1            auto   auto 10/100BaseTX
Fa0/18                       connected    1          a-full  a-100 10/100BaseTX
Fa0/19                       connected    1          a-full  a-100 10/100BaseTX
Fa0/20                       notconnect   1            auto   auto 10/100BaseTX
Fa0/21                       notconnect   1            auto   auto 10/100BaseTX
 --More--
Port      Name               Status       Vlan       Duplex  Speed Type
Fa0/22                       notconnect   1            auto   auto 10/100BaseTX
Fa0/23                       notconnect   1            auto   auto 10/100BaseTX
Fa0/24                       notconnect   1            auto   auto 10/100BaseTX

In this case port 1, i.e., Fast Ethernet 0/1, is in the err-disabled state. You can see further information the port using the show interface port_designator command, e.g., show interface fa0/1.

Swtch1>show interface fa0/1
FastEthernet0/1 is down, line protocol is down (err-disabled)
  Hardware is Fast Ethernet, address is 0009.e897.d281 (bia 0009.e897.d281)
  MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
     reliability 255/255, txload 3/255, rxload 28/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Auto-duplex, Auto-speed, media type is 100BaseTX
  input flow-control is unsupported output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:05:22, 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 148000 bits/sec, 59 packets/sec
     3922390118 packets input, 2836932384 bytes, 0 no buffer
     Received 173810 broadcasts (0 multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     2946274033 packets output, 3308865164 bytes, 0 underruns
     1816 output errors, 219858312 collisions, 4 interface resets
     0 babbles, 0 late collision, 549016730 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out
Swtch1>

To bring the port back up, you can take the following steps:

  1. Enter the enable enable command and then provide the enable secret.
    Swtch1>enable
    Password:
    Swtch1#
  2. Enter the configure command and hit Enter to accept the default value of terminal when prompted to configure from terminal, memory, or network.
    Swtch1#configure
    Configuring from terminal, memory, or network [terminal]?
    Enter configuration commands, one per line.  End with CNTL/Z.

    Or you can just enter configure t to skip the prompt.

  3. Enter interface followed by the port designator.
    Swtch1(config)#interface fa0/1
  4. Then enter the shutdown command followed by no shutdown.
    Swtch1(config-if)#shutdown
    Swtch1(config-if)#no shutdown
  5. Then enter exit twice
    Swtch1(config-if)#exit
    Swtch1(config)#exit

If you then enter the show interface command for that particular port, you will see it is up.

Hoggle#show interface fa0/1
FastEthernet0/1 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 0009.e897.d281 (bia 0009.e897.d281)
  MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Half-duplex, 10Mb/s, media type is 100BaseTX
  input flow-control is unsupported output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:00, 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
     3922390145 packets input, 2935343150 bytes, 0 no buffer
     Received 173837 broadcasts (0 multicast)
     0 runts, 0 giants, 0 throttles
     2 input errors, 0 CRC, 2 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     2946317008 packets output, 3313196356 bytes, 0 underruns
     1831 output errors, 219862940 collisions, 10 interface resets
     0 babbles, 0 late collision, 549025392 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

If you have not addressed the underlying problem that caused the port to be placed in an err-disabled status, though, the problem is likely to reoccur.

In this particular case I found that shortly after I issued the no shutdown command the port would go back into the err-disabled state. The status for the port was showing a lot of collisions. At Errdisable Port State Recovery on the Cisco IOS Platforms, Cisco lists excessive collisons as being one of the reasons a port will go into the err-disabled state.

This feature was first implemented to handle special collision situations in which the switch detected excessive or late collisions on a port. Excessive collisions occur when a frame is dropped because the switch encounters 16 collisions in a row. Late collisions occur after every device on the wire should have recognized that the wire was in use.

Only half-duplex configurations should experience collisions.

A port duplex misconfiguration is a common cause of the errors because of failures to negotiate the speed and duplex properly between two directly connected devices (for example, a NIC that connects to a switch). Only half-duplex connections should ever have collisions in a LAN. Because of the carrier sense multiple access (CSMA) nature of Ethernet, collisions are normal for half duplex, as long as the collisions do not exceed a small percentage of traffic.

When I checked the port's status I saw that it was showing a-half for the duplex seeting and a-10 for the speed setting.

Swtch1#show interface fa0/1 status

Port      Name               Status       Vlan       Duplex  Speed Type
Fa0/1                        connected    1          a-half   a-10 10/100BaseTX

That meant that the duplex and speed settings were being autonegotiated to 10 Mbs half-duplex. I thought the settings should have been 100 Mbs full-duplex. However, after it went into the err-disabled state, I would see the following.

Swtch1>show interface fa0/1 status

Port      Name               Status       Vlan       Duplex  Speed Type
Fa0/1                        err-disabled 1            auto   auto 10/100BaseTX

To resolve that problem, I configured the port so the speed was set to 100 Mbs and the duplex to full duplex.

Swtch1>enable
Password:
Swtch1#configure
Configuring from terminal, memory, or network [terminal]?
Enter configuration commands, one per line.  End with CNTL/Z.
Swtch1(config)#interface fa0/1
Swtch1(config-if)#speed 100
Swtch1(config-if)#duplex full
Swtch1(config-if)#shutdown
Swtch1(config-if)#no shutdown
Swtch1(config-if)#exit
Swtch1(config)#exit
Swtch1#show interface fa0/1 status

Port      Name               Status       Vlan       Duplex  Speed Type
Fa0/1                        notconnect   1            full    100 10/100Base

But, after seeing the status listed as notconnect, I realized the device to which it connected was only capable of supporting the 10 Mbs speed, so I reset the port speed and then saved the configuration changes.

Swtch1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Swtch1(config)#exit
Swtch1#show interface fa0/1 status

Port      Name               Status       Vlan       Duplex  Speed Type
Fa0/1                        notconnect   1            full    100 10/100BaseTX
Swtch1#enable
Swtch1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Swtch1(config)#interface fa0/1
Swtch1(config-if)#speed 10
Swtch1(config-if)#shutdown
Swtch1(config-if)#no shutdown
Swtch1(config-if)#exit
Swtch1(config)#exit
Swtch1#show interface fa0/1 status

Port      Name               Status       Vlan       Duplex  Speed Type
Fa0/1                        connected    1            full     10 10/100BaseTX
Hoggle#write
Building configuration...
[OK]

That resolved the problem; I did not see a reoccurence of the problem.

If you have enabled errdisable recovery, you can determine the reason for the errdisable status if you issue the show errdisable recovery command.

For this switch, when I checked the settings, I found that errdisable recovery was disabled.

Swtch1#show errdisable recovery
ErrDisable Reason    Timer Status
-----------------    --------------
udld                 Disabled
bpduguard            Disabled
security-violatio    Disabled
channel-misconfig    Disabled
vmps                 Disabled
pagp-flap            Disabled
dtp-flap             Disabled
link-flap            Disabled
psecure-violation    Disabled
gbic-invalid         Disabled
dhcp-rate-limit      Disabled
unicast-flood        Disabled
loopback             Disabled

Timer interval: 300 seconds

Interfaces that will be enabled at the next timeout:

The errdisable recovery command allows you to choose the type of errors that automatically reenable the ports after a specified amount of time. See Errdisable Port State Recovery on the Cisco IOS Platforms for further information.

References:

  1. Errdisable Port State Recovery on the Cisco IOS Platforms
    Cisco
  2. Troubleshooting Switch Port and Interface Problems
    Cisco

 

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Created: Tuesday March 22, 2011