=====Verify port status:
show int status
show interfaces Gi1/0/1 status
Cisco-2960X#sh int status Port Name Status Vlan Duplex Speed Type Gi1/0/1 HP_C7K err-disabled 20 auto auto 10/100/1000BaseTX Gi1/0/2 HP_C7K connected 20 a-full a-1000 10/100/1000BaseTX Gi1/0/3 HP_C7K notconnect 20 auto auto 10/100/1000BaseTX Gi1/0/4 HP_C7K notconnect 20 auto auto 10/100/1000BaseTX Gi1/0/5 HP_C7K connected 20 a-full a-1000 10/100/1000BaseTX Gi1/0/6 HP_C7K connected 20 a-full a-1000 10/100/1000BaseTX Gi1/0/7 HP_C7K notconnect 20 auto auto 10/100/1000BaseTX Gi1/0/8 HP_C7K connected 20 a-full a-1000 10/100/1000BaseTX Gi1/0/9 HP_C7K notconnect 20 auto auto 10/100/1000BaseTX Gi1/0/10 HP_C7K notconnect 20 auto auto 10/100/1000BaseTX
Cisco-2960X#show interfaces Gi1/0/1 status Port Name Status Vlan Duplex Speed Type Gi1/0/1 HP_C7K err-disabled 20 auto auto 10/100/1000BaseTX
=====Check to see if errdisable recovery is turned on
Cisco-2960X#show errdisable recovery ErrDisable Reason Timer Status ----------------- -------------- arp-inspection Disabled bpduguard Disabled channel-misconfig (STP) Disabled dhcp-rate-limit Disabled tp-flap Disabled gbic-invalid Disabled inline-power Disabled link-flap Disabled mac-limit Disabled loopback Disabled pagp-flap Disabled port-mode-failure Disabled pppoe-ia-rate-limit Disabled psecure-violation Disabled security-violation Disabled sfp-config-mismatch Disabled small-frame Disabled storm-control Disabled udld Disabled vmps Disabled psp Disabled dual-active-recovery Disabled evc-lite input mapping fa Disabled Recovery command: clear Disabled Timer interval: 300 seconds Interfaces that will be enabled at the next timeout:
=====To enable auto recovery:
I’m not recommending this because you should figure out WHY the port is going into an error disabled state and fix it. But if you just want the port to auto-recover from that state, you can set it.
For this example I’m using loopback.
errdisable recovery cause loopback errdisable recovery interval 30 [interval is in seconds]
So basically what the above is doing, when the port goes into a error-disabled state caused by loopback, recover from that state in 30 seconds. It’s just like you going in there and doing a shut/no shut on the port.
Verify it’s enabled:
Cisco-2960X#show errdisable recovery ErrDisable Reason Timer Status ----------------- -------------- arp-inspection Disabled bpduguard Disabled channel-misconfig (STP) Disabled dhcp-rate-limit Disabled dtp-flap Disabled gbic-invalid Disabled inline-power Disabled link-flap Disabled mac-limit Disabled loopback Enabled pagp-flap Disabled port-mode-failure Disabled pppoe-ia-rate-limit Disabled psecure-violation Disabled security-violation Disabled sfp-config-mismatch Disabled small-frame Disabled storm-control Disabled udld Disabled vmps Disabled psp Disabled dual-active-recovery Disabled evc-lite input mapping fa Disabled Recovery command: clear Disabled Timer interval: 30 seconds Interfaces that will be enabled at the next timeout:
=====Reasons why this happens:
There are various reasons for the interface to go into errdisable. The reason can be:
-Duplex mismatch
-Port channel misconfiguration
-BPDU guard violation
-UniDirectional Link Detection (UDLD) condition
-Late-collision detection
-Link-flap detection
-Security violation
-Port Aggregation Protocol (PAgP) flap
-Layer 2 Tunneling Protocol (L2TP) guard
-DHCP snooping rate-limit
-Incorrect GBIC / Small Form-Factor Pluggable (SFP) module or cable
-Address Resolution Protocol (ARP) inspection
-Inline power
=====To see why it happened:
1. show logging command
Cisco-2960X#sh logging May 2 14:01:17.223 Tampa: %ETHCNTR-3-LOOP_BACK_DETECTED: Loop-back detected on GigabitEthernet0/20. May 2 14:01:17.223 Tampa: %PM-4-ERR_DISABLE: loopback error detected on Gi0/2, putting Gi0/20 in err-disable state May 2 14:01:18.229 Tampa: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/20, changed state to down
2. If you have enabled errdisable recovery, you can determine the reason for the errdisable status if you issue the show errdisable recovery command. Here is an example:
Cisco-2960X#show errdisable recovery ErrDisable Reason Timer Status ----------------- -------------- udld Enabled bpduguard Enabled security-violatio Enabled channel-misconfig Enabled pagp-flap Enabled dtp-flap Enabled link-flap Enabled l2ptguard Enabled psecure-violation Enabled gbic-invalid Enabled dhcp-rate-limit Enabled mac-limit Enabled unicast-flood Enabled arp-inspection Enabled Timer interval: 300 seconds Interfaces that will be enabled at the next timeout: Interface Errdisable reason Time left(sec) --------- --------------------- -------------- Gi1/0/20 bpduguard 273