Static mac address in Esxi 5.5 “conflicts with VMware reserved MACs”

By | 29/03/2015

Virtual MAC address assignments are based on Microsoft’s organizationally unique identifier (OUI) registration with the Institute for Electrical and Electronic Engineers (IEEE). An OUI is a unique MAC address prefix assigned that is assigned to all NIC vendors, both physical and virtual.

VMware Organizationally Unique Identifier (OUI) allocation uses the default OUI 00:50:56 as the first three bytes of the MAC address generated for each virtual network. The MAC address-generation algorithm produces the rest of the MAC address. The algorithm guarantees unique MAC addresses within a virtual machine and attempts to provide unique MAC addresses across virtual machines.

The VMware Universally Unique Identifier (UUID) generates MAC addresses that are checked for conflicts. The generated MAC addresses are created by using three parts: the VMware OUI, the SMBIOS UUID for the physical ESXi machine, and a hash based on the name of the entity that the MAC address is being generated for. All MAC addresses that have been assigned to network adapters of running and suspended virtual machines on a given physical machine are tracked.

So if you are trying to use some other Mac Address (of range 00:0c:29) for your VM other than dynamically generated by VMware, then at the time of VM startup you will get error as shown below:


In Esxi 5.5 new policies have been added where the statically assigned MAC addresses can only be in the range 00:50:56:xx:xx:xx series, If you try to change it to something else and then power on the guest machine, you may see above error.


This issue can be resolved by changing the value of parameter “ethernetX.checkMACAddress = “false””

Note: Replace X with ethernet number for e.g ethernet1

Following is an sample of working .vmx file for static mac address.

ethernet0.networkName = "LAN"
ethernet0.addressType = "static"
ethernet0.present = "TRUE"
ethernet0.checkMACAddress = "false"
ethernet0.address = "00:0C:29:xx:xx:xx"

Hope this post is informational to you. Hit like and share it on social media if you find it useful. Happy learning!!!

Category: VMware

About Alex Hunt

Hi All I am Manish Jha. I am currently working in OVH US as Operations Support Engineer (vCloud Air Operations). I have around 7 Years of IT experience and have exposure on VMware vSphere, vCloud Director,vSphere Replication, vRealize Automation, NSX and RHEL. If you find any post informational to you please press like and share it across social media and leave your comments if you want to discuss further on any post. Disclaimer: All the information on this website is published in good faith and for general information purpose only. I don’t make any warranties about the completeness, reliability and accuracy of this information. Any action you take upon the information you find on this blog is strictly at your own risk. The Views and opinions published on this blog are my own and not the opinions of my employer or any of the vendors of the product discussed.

2 thoughts on “Static mac address in Esxi 5.5 “conflicts with VMware reserved MACs”

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    1. Alex Hunt Post author

      Hi There,

      Thanks for reaching out. Sorry to say bud that I want to manage my blog by my own.