6.0.1

Table Of Contents
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If the vCenter Server instance generates the MAC addresses of virtual machines according to the default
allocation, VMware OUI, change the vCenter Server instance ID or use another allocation method to
resolve conflicts.
NOTE Changing the vCenter Server instance ID or switching to a different allocation scheme does not
resolve MAC address conflicts in existing virtual machines. Only virtual machines created or network
adapters added after the change receive addresses according to the new scheme.
For information about MAC address allocation schemes and setup, see the vSphere Networking
documentation.
Solution Description
Change the vCenter Server ID
You can keep using the VMware OUI allocation scheme if your
deployment contains a small number of vCenter Server instances.
According to this scheme, a MAC address has the following format:
00:50:56:XX:YY:ZZ
where 00:50:56 represents the VMware OUI, XX is calculated as (80 +
vCenter Server ID), and YY:ZZ is a random number.
To change the vCenter Server ID, configure the vCenter Server unique ID
option in the Runtime Settings section from the General settings of the
vCenter Server instance and restart it.
The VMware OUI allocation works with up to 64 vCenter Server instances
and is suitable for small scale deployments.
Switch to prefix-based allocation
You can use a custom OUI. For example, for a 02:12:34 locally
administered address range, MAC addresses have the form
02:12:34:XX:YY:ZZ. You can use the fourth octet XX to distribute the
OUI address space between the vCenter Server instances. This structure
results in 255 address clusters, each cluster managed by a vCenter Server
instance, and in about 65000 MAC addresses per vCenter Server. For
example, 02:12:34:01:YY:ZZ for vCenter Server A, 02:12:34:02:YY:ZZ
for vCenter Server B, and so on.
Prefix-based allocation is suitable for deployments of a larger scale.
For globally unique MAC addresses, the OUI must be registered in IEEE.
a Configure MAC address allocation.
b Apply the new MAC address allocation scheme to an existing virtual machine in its Virtual
Hardware settings.
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Power off a virtual machine, configure the adapter to use a manual MAC address, revert to
automatic MAC address allocation, and power on the virtual machine.
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If the virtual machine is in production and you cannot power it off for configuration, after you
change the vCenter Server ID or the address allocation scheme, re-create the network adapter
in conflict with enabled automatic MAC address assignment. In the guest operating system,
set the same static IP address to the re-added adapter as before.
Chapter 8 Troubleshooting Networking
VMware, Inc. 79