The option to retain the MAC address is a check box in the migration wizard. It is only visible for replication-based migration.

By default, “Retain MAC” is enabled if the source virtual machine is in a stretched network, and disabled when the network is not stretched. If you do not retain the MAC address, the virtual machine obtains a new address when the migration is done. The decision to retain a MAC address or acquire a new one can impact the migration process and the post-migration network traffic flow.

You might retain the MAC address for one of the following reasons:

Licenses based on the MAC address: Some software pairs the license to the MAC address of the VM. Changing the MAC address of a virtual machine invalidates the license.

Linux NIC order: In Linux, if you change the MAC address on a virtual machine, the NIC Ethernet device number might change after a reboot. A device number change can alter the NIC presentation order within the operating system, breaking applications or scripts that depend on NIC order.

Less downtime if the network is stretched: If the virtual machine is migrated over a stretched network, enabling “Retain MAC” minimizes downtime because the network does not have to learn a new MAC address.

The check box is on the “Select destination network” page:

When you are using the bidirectional migration wizard to go from vSphere to vCloud® Air™. See From vSphere to vCloud Air.

When you run the migration wizard from the context menu. See Migrate a Selected Virtual Machine from an On-Premises vCenter to the Cloud.

When you migrate from vCloud® Air™ to vSphere, the check box is on the “Select virtual machine(s)” page. See From vCloud Air to vSphere.