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I have been asked by many VMware Administrators about how MAC addresses are assigned to Virtual Machine?. We all aware that first 3 octets will be 00:50:56. The first three parts never change. This is the VMware Organizational Unique Identifier (OUI). How do other 3 octets are generated?. This may be the biggest question in our mind? Let’s discuss How MAC addresses are assigned to VMware Virtual Machines by the vCenter server. This post only applies to the VM MAC generation, in which ESXi host is managed by vCenter Server. ESXi host which is not managed by the vCenter server will have the different mechanism to generate the MAC address for Virtual Machine.
How vCenter Assigns Virtual MAC Address to VMware Virtual Machine?
Because ESXi virtual machines do not support arbitrary MAC addresses, you must use the example format. Choose a unique value for XX:YY:ZZ among your hard-coded addresses to avoid conflicts between the automatically assigned MAC addresses and the manually assigned ones. This post only applies to the VM MAC generation, in which ESXi host is managed by vCenter Server. ESXi host which is not managed by the vCenter server will have the different mechanism to generate the MAC address for Virtual Machine. How vCenter Assigns Virtual MAC Address to VMware Virtual Machine? As we aware that, First 3 Octects will be 00. On ESXi hosts 5.1 and later, you can use prefix-based allocation to specify an OUI other than the default one 00:50:56 by VMware, or to introduce Locally Administered MAC Addresses (LAA) for a larger address space. Range-Based MAC Address Allocation On ESXi hosts 5.1 and later you can use range-based allocation to include or exclude ranges of. Maintaining and Changing the MAC Address of a Virtual Machine When a virtual machine is powered on, VMware Workstation automatically assigns each of its virtual network adapters an Ethernet MAC address. MAC stands for media access control. A MAC address is the unique address assigned to each Ethernet network device. However, the range of free address provided by the VMware OUI is restricted. Assign a Static MAC Address by Using the vSphere Web Client You can assign static MAC addresses to the virtual NIC of a powered off virtual machine by using the vSphere Web Client. Assign a Static MAC Address in the Virtual Machine Configuration File.
As we aware that, First 3 Octects will be 00:50:56. This is the VMware Organizational Unique Identifier (OUI). How does 4th octet of VM MAC address are calculated? Let’s begin the Calculation.
4th Octet of MAC = (128+ vCenter Instance ID) Convert it to Hexadecimal
To get the vCenter Server Instance ID -> Login to vSphere Client ->Administration -> vCenter Server Settings -> Runtime Settings. Note down the vCenter Server Unique ID. My vCenter Server Unique ID is 24.
How to Calculate 4th Octet of the VM MAC Address?
The automatically generated MAC address has the fourth octet is equal to 128 + the vCenter instance ID converted to hexadecimal.
4th Octet of MAC = (128+ vCenter Instance ID) Convert it to Hexadecimal
= 128+24 = 152
4th Octet of VM MAC = 98 (Conversion of 152 to Hexadecimal)
I have confirmed the Same from the few of Virtual Machine MAC Address. 4 octet is assigned as “98”.
The last two bytes are assigned in the mechanism so that each MAC address is assigned would be unique. I hope this is informative for you. Thanks for Reading!!!. Be Social and share it on social media, if you feel worth sharing it.
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I think we are all familiar with the manual MAC address issue - some software depends on the MAC for licensing, and in VMware you need to stick to a certain range of Ethernet addresses if you want to be able to manually put in your own MAC address.
Somehow I think that should have been written in big, bold letters before I started virtualizing a couple of years ago. I'm pretty sure it wasn't mentioned in the class, either. I have several apps that generate their license based on a server's MAC. And yes, now I have to change virtual NICs on several VMs from either Flexible or E1000 to VMXNET2.
Currently running vSphere 4.1, ESX build 320092 across the board.
Since I didn't plan ahead far enough to manually put in those MAC addresses, now I have no choice but to find some way to keep them until the vendors can regen the licensences.
So, here's the procedure I'm using to keep the MAC address:
1) Write down the old MAC
2) Replace Flexible NIC with VMXNET2
3) Unregister the VM
4) Edit the .vmx file and replace the automatically assigned MAC address with the old MAC address
- this is how I get around the GUI
5) Re-register the VM with the host
6) Boot up
So far it has worked for me just fine on two test servers. The question is: Will this cause any problems down the road?
Esxi Manual Mac Address Ranger
I am currently running a 'vanilla' network setup - no distributed vSwitches. However I do plan on putting that in place later this year, and that's where I'm not sure it my little procedure will come up to surprise me at that point.