It looks like you already have a bridge and want to bridge the bridge interface.
If you already have a br0 interface you’re done and don’t need another bridge for the VMs in NethServer.
Yes, I think you are right. Then I miss something else here:
On my NS I have a virtual machine that hosts another NS to test stuff. I know little about it and this way when I make mistakes my NS is still up an running because I make the mistakes in the virtual machine first.
I have the NS in the virtual machine running. Now I don’t know how to access the apache, the Server Manager webpage of the NS on the virtual machine … . Seems like I am not getting the concept of a bridge. Can you tell me how to do that?
edit: Maybe my mistake was here at setting up the virtual machine:
Your VM Nethserver should be in the same network as your Host Nethserver as they share the bridged interface. If you use DHCP in your network or on your Host Nethserver, the VM NS will get an IP and you should be able to reach your VM Nethserver.