Network issues with virtual machine traffic when there is more than one vCenter on the same physical network infrastructure

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

• Intermittent disruptions on traffic to/from the virtual machines.
• Packet capture would show the traffic leaving the esxi host successfully . 
• There is more than one vCenter deployed within the same Physical network infrastructure . 
• MAC/ARP tables on the upstream switches/routers would show incorrect MAC - IP/interface mapping.
• Both vCenters have same vCenter server instance ID.

Environment

• VMware vSphere ESXi 6.x
• VMware vSphere ESXi 7.x
• VMware vSphere ESXi 8.x
• VMware vCenter Server 6.x
• VMware vCenter Server 7.x
• VMware vCenter Server 8.x

Cause

With two separate vCenter Servers in place, a potential exists to create duplicate MAC addresses for the virtual machines. This is expected behavior for two vCenter Servers, however if these two environments are connected to the same Physical Switch, there will be a conflict.

 

Each vCenter Server system has a vCenter Server instance ID. This ID is a number between 0 and 63 that is randomly generated at installation time, but can be reconfigured after installation. vCenter Server uses the instance ID to generate MAC addresses and UUIDs for virtual machines. If two vCenter Server systems have the same vCenter Server instance ID, they might generate identical MAC addresses (duplicate MAC address) for virtual machines. This can cause conflicts if the virtual machines are on the same network, leading to packet loss and other problems.

Resolution

There are three ways of resolving this:

1. Ensure that the two vCenter Servers and their inventory are connected to separate networks/physical switches.
2. Ensure that the two vCenter Servers do not share the same instance ID.
3. Choose to use a single vCenter Server and create separate datacenters for each vCenter environment.

Change the vCenter Server instance ID using the vSphere Client:

   

• Required privilege: GlobalSettings
• In the vSphere Client, navigate to the vCenter Server instance.
• Select the Configure tab.
• Under Settings, select General.
• Click Edit.
• In the Edit vCenter Server Settings dialog box, select Runtime Settings.
• In vCenter Server unique ID, enter a unique ID.
  • You can change this value to a number from 0 through 63 to identify each vCenter Server system running in a common environment. By default, an ID value is generated randomly.
    
    
• Reboot vCenter Server

 

Additional Information

You can change the vCenter Server ID, managed address, and name. You might need to make changes if you run multiple vCenter Server systems in the same environment.