Duplicate MAC Addresses of Virtual Machines on the Same Network
You encounter loss of packets and connectivity because virtual machines have duplicate MAC addresses generated by vCenter Server.
The MAC addresses of virtual machines on the same broadcast domain or IP subnet are in conflict, or vCenter Server generates a duplicate MAC address for a newly created virtual machine.
A virtual machine powers on and functions properly, but shares a MAC address with another virtual machine. This situation might cause packet loss and other problems.
Virtual machines might have duplicate MAC addresses due to several reasons.
Two vCenter Server instances with identical IDs generate overlapping MAC addresses for virtual machine network adapters.
Each vCenter Server instance has an ID 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 for the network adapters of the machine.
A virtual machine has been transferred from one vCenter Server instance to another in the same network, and a new virtual machine network adapter on the first vCenter Server receives the freed MAC address.
Change the MAC address of a virtual machine network adapter manually.
If you have an existing virtual machine with a conflicting MAC address, you must provide a unique MAC address in the Virtual Hardware settings.
Power off the virtual machine, configure the adapter to use a manual MAC address, and type the new address.
If you cannot power the virtual machine off for configuration, re-create the network adapter that is in conflict with enabled manual MAC address assignment and type the new address. In the guest operating system, set the same static IP address to the re-added adapter as before was mentioned.