Emulate a interface (Orange/DMZ) for ipfire without an adapter

Hello everybody,

on my old ipfire system i was able to add a third network interface by means of "USB-LAN-Adapter“. This interface is provided by the network “Orange” (DMZ) and there a VM is connected via bridge mode. On my new system I have only 2 interfaces but my “USB-LAN-Adapter” is currently occupied. How can I also provide / emulate such an interface (Orange/DMZ) for ipfire without such an adapter? Only VMs are connected to the DMZ interface.

Regards Paul