The ESXi parameter "LinkFlappingThreshold" to adjust the link flap protection mechanism

Products

• VMware vSphere ESXi
• VMware vSphere ESXi 8.0

Issue/Introduction

When a physical NIC experiences frequent link status flapping, 
ESXi may turn off the physical NIC to avoid unnecessary link failover and network instability.
It's an ESXi link flap protection mechanism.

Refer the KB324499, A physical NIC may be brought down due to frequent link status flapping

Cause

This behavior could be adjusted by an ESXi advanced system parameter "Net.LinkFlappingThreshold". 

   Net.LinkFlappingThreshold 
It's the max number of link down events per minute before considering a link unstable.
The default value is 60.
If it's set to 0 ,the feature will be deactivate.

Notes:

If update, the new value will take effect immediately, no reboot is required.
This is an ESXi protection mechanism to avoid unnecessary link failover and network instability.
It's best practice to keep the default value in most of situation.

Resolution

How to check or modify the parameter.

1.From vCenter web client
In the vCenter inventory, select the host ,
On the right tab Configure  -> System -> Advanced System Settings 
Use "EDIT" button to update the value.

2.From the ESXi command line

Check current value
# esxcli system settings advanced list -o /Net/LinkFlappingThreshold
   Path: /Net/LinkFlappingThreshold
   Type: integer
   Int Value: 60
   Default Int Value: 60
   Min Value: 0
   Max Value: 65535
   String Value:
   Default String Value:
   Valid Characters:
   Description: Max number of link down events per minute before considering a link unstable (0 to deactivate)

Update the value, for example to set "120"

# esxcli system settings advanced set -i 120 -o /Net/LinkFlappingThreshold

Reset to default value

# esxcli system settings advanced set -d -o /Net/LinkFlappingThreshold

Additional Information

A physical NIC may be brought down due to frequent link status flapping
https://knowledge.broadcom.com/external/article/324499/