How to Re-Enable Errdisabled Ports Manually or Automatically
Once we know the cause of the errdisabled port, we can take steps to resolve the problem and reactivate the port. There are two ways to re-enable errdisabled ports: manually or automatically.
How to Re-Enable Errdisabled Ports Manually
The way to manually re-enable errdisabled ports is to use the shutdown command and no shutdown in interface configuration mode. This command forcibly deactivates and reactivates the port, removing the errdisabled state from that port. The following is an example of using this command:
Switch# configure terminal
Switch(config)# interface gigabitethernet 1/0/1
Switch(config-if)# shutdown
Switch(config-if)# no shutdown
Switch(config-if)# end
The above command will re-enable the Gi1/0/1 port which was errdisabled due to link flapping. However, note that this method is only temporary because the port can revert to errdisabled if the error condition still exists or recurs. Therefore, before manually re-enabling an errdisabled port, we must make sure that the problem that caused the errdisabled port is resolved or prevented.
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How to Re-Enable Errdisabled Ports Automatically
The way to re-enable errdisabled ports automatically is to use the errdisable recovery feature on the switch. This feature will allow the switch to re-enable errdisabled ports automatically after a certain time, without the need for manual intervention. This feature can save time and effort in resolving errdisabled ports, especially if there are many ports affected.
To enable the errdisable recovery feature, we must use the commands errdisable recovery cause and errdisable recovery interval in global configuration mode. The errdisable recovery cause command will specify what error conditions this feature can handle, while the errdisable recovery interval command will specify the timeout in seconds before the switch reactivates the errdisabled port. The following is an example of using this command:
Switch# configure terminal
Switch(config)# errdisable recovery cause link-flap
Switch(config)# errdisable recovery cause bpduguard
Switch(config)# errdisable recovery cause psecure-violation
Switch(config)# errdisable recovery cause udld
Switch(config)# errdisable recovery cause channel-misconfig
Switch(config)# errdisable recovery interval 300
Switch(config)# end
The above command will enable errdisable recovery for the five most common error conditions, namely link flapping, STP violation, Port Security violation, UDLD violation, and EtherChannel misconfiguration. In addition, the command will also set a timeout of 300 seconds (5 minutes) before the switch re-enables the errdisabled port.
By using the errdisable recovery feature, we can reduce the negative impact of errdisabled ports and speed up network recovery. However, note that this feature is also only temporary, as the port may revert to errdisabled if the error condition persists or recurs. Therefore, this feature should be used as an emergency solution, not as a permanent solution.
How to Prevent Errdisabled Ports by Using the Errdisable Detect and Errdisable Flap Features
In addition to re-enabling errdisabled ports, we can also prevent errdisabled ports by using the errdisable detect and errdisable flap features on the switch. These features will help us identify and isolate ports that have the potential to cause errors, thereby reducing the risk of errdisabled ports.
How to Prevent Errdisabled Ports by Using the Errdisable Detect Feature
The errdisable detect feature is a feature that will detect error conditions that can cause the port to become errdisabled and give a warning to us. This feature can help us find out which ports are problematic and what causes them, so we can take precautions before they become errdisabled.
To enable the errdisable detect feature, we must use the command errdisable detect cause in global configuration mode. This command will determine what error conditions this feature can detect. The following is an example of using this command:
Switch# configure terminal
Switch(config)# errdisable detect cause link-flap
Switch(config)# errdisable detect cause bpduguard
Switch(config)# errdisable detect cause psecure-violation
Switch(config)# errdisable detect cause udld
Switch(config)# errdisable detect cause channel-misconfig
Switch(config)# end
The above command will enable errdisable detection for five of the most common error conditions, namely link flapping, STP violation, Port Security violation, UDLD violation, and EtherChannel misconfiguration.
After the errdisable detect feature is enabled, the switch will send a warning message to the console or syslog if any port encounters the specified error condition. The following is an example of a warning message generated by this feature:
%PM-4-ERR_DISABLE: link-flap error detected on Gi1/0/1, putting Gi1/0/1 in err-disable state
%PM-4-ERR_DISABLE: bpduguard error detected on Gi1/0/2, putting Gi1/0/2 in err-disable state
%PM-4-ERR_DISABLE: psecure-violation error detected on Gi1/0/3, putting Gi1/0/3 in err-disable state
%PM-4-ERR_DISABLE: udld error detected on Gi1/0/4, putting Gi1/0/4 in err-disable state
%PM-4-ERR_DISABLE: channel-misconfig (STP) error detected on Gi1/0/5, putting Gi1/0/5 in err-disable state
By using the errdisable detect feature, we can find out which ports have the potential to cause errors and take precautions before they become errdisabled.
How to Prevent Errdisabled Ports by Using the Errdisable Flap Feature
The errdisable flap feature is a feature that will isolate ports that repeatedly become errdisabled due to the same error conditions. This feature can help us avoid network interference caused by unstable ports and reduce the burden of switches in reactivating errdisabled ports.
To enable the errdisable flap feature, we must use the command errdisable flap setting in global configuration mode. This command determines the maximum number of errdisabled ports that can be handled by a switch at one time and the time interval in seconds between two ports that are the same errdisabled. The following is an example of using this command:
Switch# configure terminal
Switch(config)# errdisable flap setting 10 60
Switch(config)# end
The above command will enable the errdisable flap feature by setting the maximum number of errdisabled ports that a switch can handle at 10 and the time interval between two ports that are errdisabled the same at 60 seconds.
After the errdisable flap feature is enabled, the switch will isolate ports that repeatedly become errdisabled due to the same error conditions in the specified time interval. Isolated ports will not be re-enabled by the switch, even if the errdisable recovery feature is enabled. Isolated ports can only be manually re-enabled by using the shutdown and no shutdown commands. The following is an example of a message generated by this feature:
%PM-4-ERR_RECOVER: Attempting to recover from link-flap err-disable state on Gi1/0/1
%PM-4-ERR_DISABLE: link-flap error detected on
%PM-4-ERR_DISABLE: link-flap error detected on Gi1/0/1, putting Gi1/0/1 in err-disable state
%PM-4-ERR_DISABLE: Too many link-flap error detected on Gi1/0/1, putting Gi1/0/1 in permanent err-disable state
From the above message, we can see that the Gi1/0/1 port became errdisabled due to link flapping and then isolated by the switch due to too much link flapping occurring within 60 seconds.
By using the errdisable flap feature, we can avoid network interference caused by unstable ports and reduce the burden of switches in reactivating errdisabled ports.