- The MAC addresses of virtual machines on the same broadcast domain or IP subnet are in conflict, or vCenter Server generates a duplicate MAC address for a newly created virtual machine. A virtual machine powers on and functions properly, but shares a MAC address with another virtual machine. This situation might cause packet loss and other.
- Quick tip today on a static MAC address assignement, How to set a static MAC address in VMware Environment? Or rather what to look after when having alarms showing VM MAC conflict. MAC address “Spoofing” if you prefer, is well known. Sometimes you may need to “mess” with MAC address.
- May 04, 2017 Note: The use of parts of the console operating system's IP address as part of the MAC address is an attempt to generate MAC addresses that are unique across different ESX Server machines. However, there is no guarantee that different ESX machines with physical network adapters that share a subnet always generate mutually exclusive MAC addresses.
- The MAC addresses of virtual machines on the same broadcast domain or IP subnet are in conflict, or vCenter Server generates a duplicate MAC address for a newly created virtual machine. A virtual machine powers on and functions properly, but shares a MAC address with another virtual machine.
When you create a VM on VMware ESXi, each network interface of the VM is assigned a dynamically generated MAC address. If you want to change this default behavior and assign a static MAC address to your VM, here is how to do it.
A few days ago I was P2V’ing some servers for a customer. The servers had application license bound to the MAC address of the NIC adapter so I had to change the auto-generated MAC address to a static one.
Follow these steps to change the MAC address from auto-generated to static.
- First, remove the VM from the vCenter Server inventory.
- Open the datastore containing the VM and download the .vmx file. Optionally, make a back-up copy of this file for safe keeping.
- Open the .vmx file (I use Notepad++) and modify the following entries:
- Change the ethernet0.addressType to static:ethernet0.addressType = “static”
- Add the following line: ethernet0.checkMACAddress = “FALSE”
- Change the ethernet0.generatedAddress line to: ethernet0.Address = “<00:AA:BB:CC:DD:EE>”(enter the old MAC address here)
- You should end up with something similar to this:
- Next, save the .vmx file and upload it back to the datastore. Overwrite the existing file.
- Add the VM back to the vCenter Server inventory and power on the VM.
- Done ?
You can verify the MAC address in the Windows VM by typing: C:>ipconfig /all from the command prompt.
Cheers!
– Marek.Z
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?
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.
Generate Mac Address
4th Octet of MAC = (128+ vCenter Instance ID) Convert it to Hexadecimal
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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.
Generate Manual Mac Address Vmware 7
![Vmware download for mac Vmware download for mac](/uploads/1/2/5/2/125295891/283497616.gif)
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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