So I needed to upgrade my home "web hosting" server from a Raspberry Pi 3b to something more flexible where I could even simulate a Raspberry Pi 3b given power. The new server hardware is now an Intel NUC i7 16GB / 250Gb SSD NVME. 😁
I order to accomplish this task I had to find a way to bridge the wireless interface which is the faster one on my actual home network setup.
I've also tried to mix the functionnality from another Rapsberry Pi (3b+ this time) who's acting as WLAN to LAN bridge. More details on this setup. But this was finally a bad idea and I was not able to make it work along the virtual network bridge created by libvirt or manually created... (I will explain why later)
The main difficulty was to use the DMZ IP address given by the router and route the traffic to the guest VM's.