Allow Virtual machines with duplicate MAC address on vSphere 5.5

In a migration project to VMware vSphere 5.5 I bumped into duplicate MAC address issue (I found out after some investigation).

Some info on the setup.

There are ESXi hosts that we are migrating from 5.0 to 5.5. Some VM’s where 2 VM’s (VM1 and VM2) share the same MAC address (production and test machine).

On ESXi 5.0 these 2 VM’s can run together on the same ESXi host.

I want to move the VM’s to an already upgraded ESXi 5.5 host, the first VM (VM1 moves without any problems. ) For the second VM (VM2) I get following error during vMotion. Same error happens when I cold migrate the VM2 to the same host (ESXi 5.5) as VM1 and try to power VM2 on.

 

 

 

 

 

 

 

 

 

After some Google research I came across following blog

http://jasonnash.com/2008/08/30/disabling-mac-address-checking-in-vmware/

And adding the advanced setting to VM2 fixed the problem.