Dedicated MAC address per IP address

[stephan2024]

How can I configure a dedicated MAC address per IP address in OPNsense? The UI allows me to configure a single interface per VLAN only. Also, looks like there is no support for MACVLAN or any other helpful solution.

The use case: When having a business contract with more than one public static IPv4 address, my ISP (Vodafone, ex Unitymedia, Internet over cable) provides an AVM Fritz!Box that remains under its control and cannot be replaced by a more suitable router. The Fritz!box requires a fixed MAC/IP assignment for forwarding traffic to the public IP addresses of connected devices.

When running OPNsense as a Virtual Machine, I can simply add more virtual network interfaces, each connected to the same VLAN. So, I added five NICs for five public IP addresses, each having a unique MAC address. When using physical hardware, this workaround is obviously not feasible.

Are there any solutions or workarounds available?