[VMC on AWS] MAC Address is Duplicated When Cloning Virtual Machine After Bulk Migration from On-Premises to VMC

Products

• VMware HCX
• VMware Cloud on AWS

Issue/Introduction

After performing a bulk migration of virtual machines (VMs) from an on-premises environment to VMware Cloud (VMC) on AWS, some users have encountered an issue where cloning these migrated VMs results in duplicated MAC addresses. This duplication can lead to network conflicts, causing connectivity problems within the virtual environment.

Environment

VMware HCX

Cause

The duplication of MAC addresses occurs due to specific settings applied during the bulk migration process. Here's a detailed breakdown of the factors contributing to this issue:

On-Premises VM Configuration

• Automatic MAC Address Assignment
  • On-premises VMs are typically configured to assign MAC addresses automatically. This ensures that each VM receives a unique MAC address, preventing duplication.

Bulk Migration Settings via vSphere Client (HCX Plug-in)

• Retain MAC Option Enabled
  • When initiating a bulk migration using the on-premises vSphere Client with the HCX plug-in, the Retain MAC option is enabled by default. This setting preserves the original MAC addresses of the VMs during migration.

Post-Migration VM Configuration on VMC

• • Manual MAC Address Setting
    • Due to the Retain MAC option, migrated VMs on VMC have their MAC address settings switched from Automatic to Manual. As a result, when these VMs are cloned, the cloning process duplicates the existing (manual) MAC addresses instead of generating new ones.

Resolution

To prevent MAC address duplication when cloning VMs post-migration, follow the appropriate steps based on whether the VMs are already migrated to VMC or still reside on-premises.

1. For Migrated Virtual Machines on VMC

Change MAC Address Setting from Manual to Automatic

• Step 1: Power Off the VM
  • Before making changes to the MAC address settings, ensure that the VM is powered off to avoid any disruptions.
• Step 2: Access VM Settings
  • Navigate to the settings of the affected VM within the VMC environment.
• Step 3: Modify Network Adapter Settings
  • Locate the network adapter settings and change the MAC address option from Manual to Automatic. This allows VMware to assign a unique MAC address during the cloning process.
• Step 4: Power On the VM
  • After making the changes, power the VM back on to apply the new settings.

2. For Virtual Machines Not Yet Migrated on On-Premises

Disable the "Retain MAC" Option During Bulk Migration

• Step 1: Access HCX Plug-in Settings
  • Open the on-premises vSphere Client and navigate to the HCX plug-in used for migration.
• Step 2: Locate Extended Options
  • Within the migration settings, find the Extended Options section.
• Step 3: Uncheck Retain MAC
  • Ensure that the Retain MAC option is unchecked. This will allow the migration process to generate new MAC addresses for the VMs in the VMC environment, preventing duplication when cloned.
• Step 4: Proceed with Migration
  • Continue with the bulk migration process as usual.