I have a Proxmox 8.3.0 host with two network interfaces:
vmbr0 is the LAN/management interface
vmbr1 is the WAN interface.
On the Proxmox host I've installed opnsense 25.1 with two virtual nics:
vtnet0 is the WAN interface that is connected to vmbr1
vtnet1 is the LAN interface that is connected...