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

Products

• VMware vSphere ESXi

Issue/Introduction

• An ESXi host may automatically disable a physical Network Interface Card (NIC) if it detects frequent link status changes (flapping). This behavior is an intentional protective mechanism designed to prevent network instability and unnecessary link failover events.
• This article provides steps to check or modify the Net.LinkFlappingThreshold parameter, which controls the sensitivity of this protection mechanism.

Cause

 

The Net.LinkFlappingThreshold advanced system parameter defines the maximum number of link-down events allowed per minute before the ESXi host considers the link unstable.

• Default Value: 60 (events per minute)

• Deactivate: Setting the value to 0 disables the protection mechanism.

Note: Changes to this parameter take effect immediately; a reboot is not required.

Resolution

To modify the Net.LinkFlappingThreshold parameter, use either the vSphere Client or the ESXi command line.

Caution: It is best practice to maintain the default value (60) in most environments. Only modify this value if specific environmental conditions or troubleshooting requirements necessitate a change.

 

Method 1: vSphere Client

1. Log in to the vSphere Client.

2. Navigate to the ESXi host in the inventory.

3. Select the Configure tab.

4. Under System, select Advanced System Settings.

5. Click Edit.
   
   

6. Search for Net.LinkFlappingThreshold.

7. Update the value as required (e.g., 120 to increase the threshold, or 0 to disable).

8. Click OK to save.

 

Method 2: ESXi Command Line (ESXCLI)

1. Connect to the ESXi host via SSH or console.

2. To check the current value, run the following command:

   esxcli system settings advanced list -o /Net/LinkFlappingThreshold
   

   Example Output:

   Path: /Net/LinkFlappingThreshold
   Type: integer
   Int Value: 60
   Default Int Value: 60
   Min Value: 0
   Max Value: 65535
   Description: Max number of link down events per minute before considering a link unstable (0 to deactivate)
   

3. To update the value (for example, to set it to 120), run:

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

4. To reset the parameter to its default value, run:

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

Additional Information

For more details on why a physical NIC may be brought down due to flapping, see A physical NIC may be brought down due to frequent link status flapping.