Virtual machine MAC address conflicts
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 vCenter instance ID to generate MAC addresses and UUIDs for virtual machines. If two vCenter Server systems have the same vCenter instance ID, they might generate identical MAC addresses for virtual machines. This can cause conflicts if the virtual machines are on the same network, leading to packet loss and other problems.