6.0

MAC Address Management
MAC addresses are used in the Layer 2 (Data Link Layer) of the network protocol stack to transmit frames
to a recipient. In vSphere, vCenter Server generates MAC addresses for virtual machine adapters and
VMkernel adapters, or you can assign addresses manually.
Each network adapter manufacturer is assigned a unique three-byte prefix called an Organizationally
Unique Identifier (OUI), which it can use to generate unique MAC addresses.
VMware supports several address allocation mechanisms, each of them with a separate OUI:
n
Generated MAC addresses
n
Assigned by vCenter Server
n
Assigned by the ESXi host
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Manually set MAC addresses
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Generated for legacy virtual machines, but no longer used with ESXi
If you reconfigure the network adapter of a powered off virtual machine, for example by changing the
automatic MAC address allocation type, or setting a static MAC address, vCenter Server resolves any MAC
address conflict before the adapter reconfiguration takes effect.
Add or Adjust Range- or Prefixed-Based Allocations in the vSphere Client
If you use a range- or prefixed-based allocation, you can use the vSphere Client to adjust the parameters of
your allocation.
To change allocation schemes from VMware OUI to a range- or prefixed-based allocation, you must add a
key and default value to Advanced Settings. If you already added the key and default values, use Advanced
Settings to adjust the parameters for each key.
To change from a range- or prefixed-based allocation to the VMware OUI allocation, you cannot use the
vSphere Client. You must edit the vpxd.cfg file manually. VMware recommends changing allocation types
through the vSphere Client because editing files can introduce errors. For information about editing the
vpxd.cfg file, see the vSphere Networking publication.
CAUTION Prefix-based MAC address allocation is only supported invCenter Server 5.1 and 5.1 hosts. If you
add pre-5.1 hosts to vCenter Server 5.1 , and use anything other than VMware OUI prefix-based MAC
address allocation, virtual machines assigned non-VMware OUI prefixed MAC addresses fail to power on
their pre-5.1 hosts.
The prefix-based MAC address allocation schemes are not supported on pre-5.1 hosts because pre-5.1 hosts
explicitly validate if an assigned MAC address uses the VMware OUI 00:50:56 prefix. If the MAC address is
not prefixed with 00:50:56, the virtual machine pre-5.1 host fails to power on.
Prerequisites
Launch the vSphere Client and log in to a vCenter Server system.
Procedure
1 In the vSphere Client, select Administration > Server Settings.
2 Select Advanced Settings.
vSphere Administration with the vSphere Client
296 VMware, Inc.