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Enthusiast
Enthusiast

Static MAC address not starting with 00:50:56?

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Hi,

I have a quick question before I go to bed (so I have no time for some test).

I have just found this article about static MAC address: VMware KB: Setting a static MAC address for a virtual NIC

The article said that "VMware uses a different OUI for manually generated addresses: 00:50:56."  But can I reuse the automatically generated MAC address which starts with 00:0c:29 (and of course make sure ESXi won't use the same MAC address for another VM)?

Thanks

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Virtuoso
Virtuoso

Hi..

Both are actually automatically generated... 00:00c:29 is generated by the ESXi host itself when not joined to a vCenter instance. 00:50:56 is generated by vCenter if the ESXi host is joined to such.

But can I reuse the automatically generated MAC address which starts with 00:0c:29 (and of course make sure ESXi won't use the same MAC address for another VM)?

Yes..

/Rubeck

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User Moderator
User Moderator

Hey,

this KB is only valid until ESX 2.5

Is this really the version you are using?

The valid guide for ESXi 5.5 can be found here: http://pubs.vmware.com/vsphere-55/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-552-networ...

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Virtuoso
Virtuoso

Hi..

Both are actually automatically generated... 00:00c:29 is generated by the ESXi host itself when not joined to a vCenter instance. 00:50:56 is generated by vCenter if the ESXi host is joined to such.

But can I reuse the automatically generated MAC address which starts with 00:0c:29 (and of course make sure ESXi won't use the same MAC address for another VM)?

Yes..

/Rubeck

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Expert
Expert

Hi,

the KB you have posted is quite obsolete ... but I will try to depict some facts:

- When you are creating VMs through vCenter autogenerated MAC address for the VM is based on vCenter ID. ... respectively last three octets are based on vCenter unique ID.

- When you are creating VMs through ESXi host :

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.

In addition to your questions ... below is a list of all registered OUIs in IEEE by VMware, Inc. :

1) 00:50:56 - auto generated MAC by vCenter server

2) 00:05:69 - probably auto-generated MAC on legacy ESX hosts

3) 00:0C:29 - auto generated MAC on ESXi hosts and products like VMware Workstation

4) 00:1C:14 - reserved prefix for some future products ?!

Q: But can I reuse the automatically generated MAC address which starts with 00:0c:29 (and of course make sure ESXi won't use the same MAC address for another VM)?

A: Autogenerated MAC addresses assigned by ESXi host/vCenter are checked for possible conflicts on creation ... but static MAC addresses which you set doesn't

    i.e. if you manually configure two identical MAC on two VMs nothing will stop you because you are the arbiter.

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

As an alternative you can switch from default VMware OUI to range- or prefixed-based MAC address allocation by changing the vCenter server Advanced Settings:

For detailed steps and explanation see this part of documentation:

Change to or Adjust Range- or Prefixed-Based Allocations in the vSphere Web Client

... but go for it only in extreme cases and double check if your new range isn't in conflict with already registered OUIs:

https://standards.ieee.org/develop/regauth/oui/oui.txt

_________________________________________________________________________________________ If you found this or any other answer helpful, please consider to award points. (use Correct or Helpful buttons) Regards, P.
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Enthusiast
Enthusiast

Tim Scheppeit wrote:

Hey,

this KB is only valid until ESX 2.5

Is this really the version you are using?

No, not at all!  I'm using 5.5 :smileylaugh:  A proof that I needed the sleep badly :smileygrin:

The valid guide for ESXi 5.5 can be found here: http://pubs.vmware.com/vsphere-55/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-552-networ...

Thanks

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