Setup :

internet -- VirtualBoxHost -- WIFI-switch -- clients

VirtualBoxHost hosts several Virtual Machines and has 2 interfaces.

Wan-interface is not used by VirtualBoxHost, but is directly mapped to the Virtual Machine Endian Firewall.

What I want :
Access to VM's for the Wifi-clients AND access from Wifi-clients to VirtualBoxHost.

What I have tried :

- create bridge
- add LAN-interface to bridge
- create tap0
- add tap0 to bridge

Virtual Machine uses tap0
Wifi-clients are connected via LAN-interface, via bridge, to VM's.

But my host-machine is not accessible from a WLAN-client and also I can not access a VirtualMachine from my host-machine.
A WLAN-client can connect to a VirtualMachine without problem.

I think with my bridge the local LAN and the VM's are now connected.

How to put also my host-machine in the LAN ??? As a LAN-client.

You can put any machine in a network as-long-as you add it to a proper bridge port.
Add a physical interface through which you want information to go out in a bridge
and then keep adding all the virtual tap interfaces to the brige. This will be equivalent
to having a physical switch with lots of port and connecting them all together.