ESXi VMNIC Order Changed After Upgrade or Reboot

Products

• VMware vSphere ESXi

Issue/Introduction

After rebooting or upgrading your ESXi host you notice that the VMNIC#/MAC address correlation has changed. 

 

Example - Pre-Upgrade/Reboot:

• VMNIC1 - 1A:1B:1C:1D:1E:1F
• VMNIC2 - 2A:2B:2C:2D:2E:2F
• VMNIC3 - 3A:3B:3C:3D:3E:3F
• VMNIC4 - 4A:4B:4C:4D:4E:4F

Example - Post-Upgrade/Reboot:

• VMNIC1 - 2A:2B:2C:2D:2E:2F
• VMNIC2 - 4A:4B:4C:4D:4E:4F
• VMNIC3 - 3A:3B:3C:3D:3E:3F
• VMNIC4 - 1A:1B:1C:1D:1E:1F

 

NOTE: Just like in the example above, the VMNIC# change can effect some VMNICs, but can also effect all VMNICs depending on the causes.

Environment

VMware ESXi

Cause

Starting in ESXi 5.5, the device alias assignment function was made a part of a newly designed device manager, and the device alias assignment upgraded as described in this document. This was done because in ESXi releases earlier to 5.5, there was little documentation of the assignment of aliases to physical (or logical) devices. Additionally, device assignments made by specialized programs (esxcfg-init and later jumpstart plug-in) were difficult to correlate with case markings, and difficult to predict for a new machine before ESXi installation. Finally, the assignments could change across reboots when other devices were added or removed from the system.

Resolution

There is no direct way from ESXi to change back the VMNIC#/MAC Address correlation due to how the VMNIC# alias is created. For more information, please see How VMware ESXi determines the order in which names are assigned to devices