Interfaces Mac Address & external Switch issues

Freyja

Hi Everyone.

I have a Netgate 1100 with all ports connected to the same switch on different VLANs
On my old Netgear gs108t, everything was fine, but he died and I replaced it with a newer version gs108tv3.

I have the same setup:

3 VLANs: one for DMZ (port 3&4), Internet (port 1&2) and LAN (port 5-8)
All in untagged mode
Netgate connected to ports 2 (Internet), 4 (DMZ) and 5 (LAN)

But, as all the interfaces of the Netgate have the same IPs, the Netgear thinks it's a loopback and autodisable the interfaces:
PORT-4-ERR_DISABLE rsd_port.c(950) %% loopback-detection error detected on GigabitEthernet4, putting GigabitEthernet4 in err-disable state
PORT-4-ERR_DISABLE rsd_port.c(950) %% loopback-detection error detected on GigabitEthernet2, putting GigabitEthernet2 in err-disable state

I would prefer not to remove the anti-loopback protection so I wanted to change the FW MAC addresses for each interface but when I go to Interface / Assignement and choose one of my interface, the MAC Address field is greyed and cannot be modified and the message "The MAC address of a VLAN interface must be set on its parent interface" is displayed.

My assumption is that there are no real 3 interfaces on the Netgate 1100 but only a switch with different VLANs.

What are your suggestions ?
What should I change in my setup ?

Many thanks.

Freyja