Re: [VBox-users] vlan trunking and promiscuous mode

[Gregory N. <gr...@gr...>]

On Sun, Jan 25, 2026 at 03:37:51PM +0100, Marco Moock wrote:
> I run Virtualbox on Debian with a network bridge to a real ethernet
> interface that is a trunk (transports multiple vlans with tags).
> 
> My goal is to bring that trunk into the VM, so one bridge exists to the
> trunk interface and the VM will create subinterfaces. Although, the
> bridge doesn't detect that those subinterfaces have multiple MAC
> addresses and doesn't forward ethernet traffic to them unless I enable
> promiscuous mode in the VM (e.g. start sniffing using tcpdump). If I
> disable promiscuous mode in the VM, the traffic with dst of the
> subinterfaces with different MAC will stop.
> 
> How do I configure that properly, so the bridge behaves like a real
> bridge that ust learns which MAC addresses are connected to which port
> and don't filter.

Use vboxmanage, like:

vboxmanage modifyvm vmname --nic-promisc1=allow-all

I believe this is chapter 8 of the VirtualBox user guide.

Greg


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