ESXi vmnic order doesn't match the Cisco vNIC order

Products

• VMware vSphere ESXi

Issue/Introduction

On Cisco UCS hardware running VMware ESXi (including version 9.0.2), you may observe the following behavior:

• The primary Management vNIC (intended to be vmnic0) is moved to the end of the vNIC order (e.g., vmnic7 or vmnic9) after installation or reboot.
• The order of vmnics does not match the desired order defined in the Cisco UCS Service Profile.
• This occurs primarily in new deployments or when the number of configured vNICs is greater than two.

 

Example:

S1-Mgmt_A is the first vNIC in the Cisco UCS configuration, but ESX is detecting it as vmnic9 as described in How VMware ESXi determines the order in which names are assigned to the devices

Cause

This behavior is typically caused by the Cisco UCS vNIC/vHBA Placement Policy being set to "Let System Perform Placement" (Auto).

When the placement is automatic, the PCIe bus addresses for virtual interfaces can shift during hardware discovery. Since VMware ESXi enumerates vmnics based on their position on the PCIe bus, any shift in these addresses results in a re-enumeration of the vmnic names (vmnic0, vmnic1, etc.). This is a known interaction detailed in Cisco Bug CSCuv34051.

In addition to configuring the placement policy, there was a Connection Policy that needed to be removed

 

 

Resolution

To ensure a consistent and predictable vmnic order, the hardware paths must be stabilized within the Cisco UCS configuration.

The steps below are provided for reference only. Please contact Cisco for additional information or assistance.

 

Step 1: Explicitly Define vNIC Placement

1. Log in to Cisco UCS Manager or Cisco Intersight.
2. Navigate to the Service Profile or Service Profile Template associated with the affected ESXi hosts.
3. Go to the Network tab and select Modify vNIC/vHBA Placement.
4. Modify the selection from Let System Perform Placement to Manually Place vNICs/vHBAs (or similar explicit placement option) if needed.
5. Assign the vNICs to specific virtual slots in the desired order (e.g., Management_A to Slot 1, Management_B to Slot 2).

Step 2: Remove any vNIC Template Connection Policies

 1. Remove any connection policies that may be configured on the vNIC template

In this scenario, usNIC was selected and needed to be removed

Working configuration with no policy configured

 

Step 3: Apply and Verify

1. Save the changes to the Service Profile and allow the host to reboot to apply the updated profile.
2. Log in to the ESXi shell and verify the mapping is correct

Additional Information

How VMware ESXi determines the order in which names are assigned to the devices

https://knowledge.broadcom.com/external/article/324534