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Table Of Contents
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The virtual machine configuration file does not contain the MAC address and information about the
MAC address allocation type.
MAC Address Format
The host generates MAC addresses that consists of the VMware OUI 00:0C:29 and the last three octets
in hexadecimal format of the virtual machine UUID. The virtual machine UUID is based on a hash
calculated by using the UUID of the ESXi physical machine and the path to the configuration file (.vmx) of
the virtual machine.
Preventing MAC Address Conflicts
All MAC addresses that have been assigned to network adapters of running and suspended virtual
machines on a given physical machine are tracked for conflicts.
If you import a virtual machine with a host-generated MAC address from one vCenter Server to another,
select the I Copied It option when you power on the virtual machine to regenerate the address and avoid
potential conflicts in the target vCenter Server or between the vCenter Server systems.
Setting a Static MAC Address to a Virtual Machine
In most network deployments, generated MAC addresses are a good approach. However, you might
need to set a static MAC address for a virtual machine adapter with unique value.
The following cases show when you might set a static MAC address:
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Virtual machine adapters on different physical hosts share the same subnet and are assigned the
same MAC address, causing a conflict.
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Ensure that a virtual machine adapter always has the same MAC address.
By default, VMware uses the Organizationally Unique Identifier (OUI) 00:50:56 for manually generated
addresses, but all unique manually generated addresses are supported.
Note Make sure that no other non-VMware devices use addresses assigned to VMware components.
For example, you might have physical servers in the same subnet, which use 11:11:11:11:11:11,
22:22:22:22:22:22 as static MAC addresses. The physical servers do not belong to the vCenter Server
inventory, and vCenter Server is not able to check for address collision.
VMware OUI in Static MAC Addresses
By default, static MAC addresses have the VMware Organizationally Unique Identifier (OUI) as the prefix.
However, the range of free address provided by the VMware OUI is restricted.
If you decide to use the VMware OUI, part of the range is reserved for use by vCenter Server, host
physical NICs, virtual NICs, and for future use.
vSphere Networking
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