VirtualBox 6.1.28 on OSX Big Sur
I'm testing a device whose traffic I'd like to dump and I don't have a switch which supports promiscuous mode.
I decided to create an Ubuntu VM with the following setup: a VirtualBox network adaptor(NAT) <> software BRIDGE <> VirtualBox network adaptor (Bridge to physical device).
Within Ubuntu I create a bridge between the two interfaces, with netplan.
The Ubuntu VM works perfectly, and can ping Google DNS.
The other device however cannot ping Google DNS.
I checked its networking configuration, and it receives and IP address in the same range as the Ubuntu VM has on the bridge.
But traffic just doesn't flow.
Now, a reading through documentation I figured out that this has to do with Promiscuous mode, so I decided to look at that, and came up with the following:
From the point of the bridged adaptor:
Promiscuous mode Deny:
Ubuntu VM: works perfectly, can contact the world
Device: gets IP from DHCP, but cannot ping, not even Ubuntu VM
Promiscuous mode Allow VMs:
Ubuntu VM: works perfectly, can contact the world
Device: gets IP from DHCP, but cannot ping, not even Ubuntu VM
Promiscuous mode Allow All:
Ubuntu VM: Fails to contact the world, 99% packets lost
Device: gets IP from DHCP, can ping Ubuntu VM, but not further (which I think relates to the fact that the Ubuntu VM itself doesn't know where to send traffic)
I think that there's something wrong on the Ubuntu VM that it doesn't know over which interface to send the traffic (?) when in full Promiscuous mode, BUT I am not sure if that mode is actually needed and that I'm doing something else wrong.
Any thoughts?