Recently we had an issue - Duplicate MAC detected when couple with a cloud Environment
to understand the issue we need to know How vCenter allocates MAC addresses.
EX - MAC address - 00:50:56:XX:YY:ZZ
where 00:50:56 represents the VMware OUI,
XX is calculated as (80 + vCenter Server ID in Hexadecimal),
and YY:ZZ is a random number.
Each vCenter Server instance has an ID between 0 and 63 that is randomly generated at installation time(This can be reconfigured after installation)
reference - https://docs.vmware.com/en/VMware-vSphere/6.5/com.vmware.vsphere.troubleshooting.doc/GUID-8D7D0126-8E8A-470F-A61E-4197EE32D08F.html
VMware KB - https://kb.vmware.com/s/article/1024025
in this case legacy VC
- DTEST1VC65 - vCenter ID 63
- DTEST2VC65 - vCenter ID 4
cloud VC
- vCenter ID
4 <==
The New VC
so both DTEST2VC65 and cloud vCenter was using 00:50:56:84:YY:ZZ and YY:ZZ is a random number
this was went UN-detected for a while and suddenly they having this issue .
in this case
- we change vCenter ID (which we need to restart the services to get updated when creating new VMs) on both Legacy and New VC, so no duplication in the future
- Generate a list of MAC using each vCenter - Powercli or RV tools
- removed all duplicated ones
hope this will useful when you are using a vcenter from a cloud provider connect to your legacy / on-prem VC.
