I understand that this Guide will describe bonding into the guest OS.
However, I have a bond0 interface on host site and want to mapp this to the bridged eth0 interface of the guest.
In Settings -> Network I can mapp the bond0 (of the Host OS) to eth0 (of the Guest OS)
But I cannot connect (ping, ssh, etc.) from guest to os or vice versa.
The bridged adapter in VirtualBox requires a physical network adapter. Its operation relies on a special device driver on the host system to inject and intercept network communication. Network bonding on your Linux host system relies on dynamically shifting physical network adapters, which is probably not compatible with the VirtualBox bridged network driver. It might work if you use Link Aggregation though, but it requires a managed switch.
It might be a better idea to post this question in the VirtualBox forum at https://forums.virtualbox.org/
sorry - what do you mean Link Aggregation?
How to implement?
or does exist a workaround there?
Back to my original question:
How to solve the issue to connect eth0 (guest) to physical network adapter
when I either use eth0 or wlan0 - depending on the environment I'm working?
Is there no solution to this question?
at the moment the forums.virtualbox.org is not available ...
You may have more luck searching for a solution in the VirtualBox for Ubuntu forum. Make sure people understand you are trying to attach the virtual machine to a bonded network interface on the host system.
P.S. I somehow remember that VirtualBox will automatically pick your primary network adapter and route traffic to your ethernet or wlan interface, whatever is active, but perhaps I'm confusing it with other virtualization software or it requires the NAT interface.