Adding a VLAN-transparent bridge to Linux (Debian)

Question

On my current Debian system I use VLAN tagging and I create bridges br-wan and br-lan that I use for LXC containers:

auto lo br-lan br-wan

iface lo inet loopback

iface br-wan inet manual
    bridge_ports eth0.3
    bridge_maxwait 0

iface br-lan inet static
    address 192.168.200.10
    netmask 255.255.255.0
    gateway 192.168.200.1
    bridge_ports eth0.2
    bridge_maxwait 0
      
iface eth0.1 inet static
    address 10.7.1.10
    netmask 255.255.255.0

Now I would like to add a KVM guest that gets transparent access to eth0 and in turn uses VLAN tagging internally (for example, to create a virtualized router routing between eth0.2 and eth0.3). To test, I did the following:

brctl addbr br-master
brctl addif eth0

And then I created a KVM guest with --network=bridge=br-master,model=virtio which creates an interface vnet0 that is also added as bridge port to br-master. Inside the guest added the VLAN interfaces.   On the host, I see tagged packets in vnet0 (tcpdump -i vnet0 -e vlan) and br-master (tcpdump -i br-master -e vlan).   However, the traffic never reaches eth0 on the host.

I am sure the story is not that simple. How can I add such a VLAN-transparent "master bridge" to my system, without disrupting my old config?

Answer 1

I have not tried this but it should work with the bridge vlan ... command.

For each VLAN ID you use on vnet0 you have to do this:

for vlanid in 1 2 3 4; do
    bridge vlan add dev eth0 vid $vlanid untagged
done