During installation of vCloud Director you must supply installation ID from range 1-63. Its purpose is very similar to vCenter Server ID, it is used for generation of unique MAC addresses for VMs running in the vCloud Director instance. The MAC address format is 00:50:56:ID:xx:xx. vCloud Director overrides MAC vCenter Server assignments.
Obviously on the same layer 2 network MAC addresses must always be unique so when using L2 VPN or similar network extension mechanisms a care should be given that each vCloud Director instance participating in such network extension has a different installation ID to guarantee non-overlapping MAC addresses of deployed VMs.
Until vCloud Director 9.5 it was not possible to change its installation ID. The reason was, that during the installation vCloud Director actually generates all possible MAC addresses in its database, so that table would have to be regenerated with the ID change.
This can now be accomplished with cell-management-tool mac-address-management CLI command that takes care of the MAC address table regeneration and also informs how many MAC addresses still exist that are based on the old ID. Those existing VMs will keep its old MAC unless it is manually reset/regenerated from vCloud Director UI or via vCloud API.
The CMT command can either regenerate MAC addresses with a specific ID that can differ from the installation ID (option –regenerate-with-seed), or you can change the installation ID in the database first (GSS alert!) and just use –regenerate option.
The pgAdmin screenshot below shows the ID location in the vCloud DB. For production setups this should be done with help from GSS.
Finally, here is a screenshot showing the –show-seed option listing the actual MAC usage based on the seed IDs.
Tom Fojta's Blog 