• Troubleshooting Error-disabled Interface States

 
 
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Overview

Interfaces will transition into an error-disabled state due to reasons like excessive link-flaps or speed mismatch. A link-flap happens when there is a high number of flaps in a short time-frame due to a low light level or inconsistency in the incoming Rx optical signal or due to a faulty cable in the path. If the Arista switch observes more than 5 flaps within a 10-sec interval, Arista’s default behavior is to put the port in an error-disabled state. This prevents port(s) from going into a wedged state because of excessive flapping, thereby eliminating instability on the network.

Steps to Check

Let us take a look at how to verify state and take corrective action once all issues are resolved.

1. To check the default setting we can use the following command:

switch#sh errdisable flap-values
ErrDisable Reason  Flaps    Time
=================  =====    ====
link-flap          5        10.0


 2. To check the reason the port(s) have gone into errdisabled state, we look at the below output:


switch#show interfaces status errdisabled
Port        Name                      Status            Reason
---------- -------------------------- ----------------- ---------------------
Et23                                  errdisabled       link-flap
Et24                                  errdisabled       link-flap
Et33 Link-DCA-R1C20SW3B-E             errdisabled       speed-misconfigured
Et34 Link-DCA-R1C20SW3B-E             errdisabled       speed-misconfigured
Et35 Link-DCA-R1C20SW3A-E             errdisabled       speed-misconfigured
Et36 Link-DCA-R1C20SW3A-E             errdisabled       speed-misconfigured   


3. Now that we have identified the symptom, let’s restore the port.

a. A general rule of thumb when the reason cited is “link-flap” is to check the underlying cables/connections in the path ensuring proper Tx/Rx power for the optical ports. Once the L1 path is inspected and cleaned, we can bounce the port(s) by simply using the “shut/no shut” command and check to see the link has stabilized and is back in a connected state.
b. Alternatively, to keep the port in Link-Up and to prevent the port from going into an err-disabled state due to marginal optical light levels, we can also perform the below command
after we determine the cause of flap in step2

Switch(conf-if-Etx/y)#errdisable recovery cause?     <<List of options
..
..
link-flap                  Enable the link-flap cause
no-internal-vlan           Enable the no-internal-vlan cause
portchannelguard           Enable the portchannelguard cause
portsec                    Enable the portsec cause
speed-misconfigured        Enable the speed-misconfigured cause
xcvr-misconfigured         Enable the xcvr-misconfigured cause
xcvr-overheat              Enable the xcvr-overheat cause
xcvr-power-unsupported     Enable the xcvr-power-unsupported cause
xcvr-unsupported           Enable the xcvr-unsupported cause


4. Another common reason for port(s) transitioning to an errdisabled state is due to speed mismatch. This is also dependent on port speed combinations on various platforms. Please refer to our datasheet: https://www.arista.com/en/products/platforms

For example, note the 7050X3/Trident3 platform below:

 The high-density SFP ports can be configured in groups of 4 (1-4, 5-8….) to run either at 25G or a mix of 10G/1G speeds. Where ethernet 1,5,9 and so on are master interfaces in the quad group. The speed on slave interfaces must be compatible with the master interface or they will go into an errdisable state.

Datasheet and TOI :Trident3 Platform on 7050SX3-48YC12 and Hardware speed group TOI

Additional Resources

For a fiber cleaning guide based on the type of optic, please refer to the literature in the technical resources section:
https://www.arista.com/en/products/transceivers-cables

 

If the issue is still seen after following the above steps, please collect the below outputs and reach out to Arista TAC support by sending an email at support@arista.com.

CLI commands:

show tech-support | gzip > /mnt/flash/show-tech-$HOSTNAME-$(date +%m_%d.%H%M).log.gz
show agent log | gzip > /mnt/flash/show-agentlog-$HOSTNAME-$(date +%m_%d.%H%M).log.gz
bash sudo tar -cvf - /var/log/qt/ > /mnt/flash/qt-logs-$HOSTNAME-$(date +%m_%d.%H%M).tar.gz
show agent qtrace | gzip >/mnt/flash/show-agentqt-$HOSTNAME-$(date +%m_%d.%H%M).log.gz
show logging system | gzip >/mnt/flash/show-logsys-$HOSTNAME-$(date +%m_%d.%H%M).log.gz
bash sudo tar -cvf - /mnt/flash/schedule/tech-support/* > /mnt/flash/history-tech-$HOSTNAME-$(date +%m_%d.%H%M).tar

 

 


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