My need was to run a virtual Linux System inside VirtualBox. The bridged drivers of the VirtualBox has broken the WakeOnLan functionality of my server, so had to uninstall this driver and use NAT connection (source). The problem with the NAT connection was, that all packages were given from the Host OS with their IP address as the client address.
To solve this problem and get NAT trasparent, you need to call the following command in the Host System (source):
"C:\Program Files\Oracle\VirtualBox\VBoxManage.exe" modifyvm "HomeServer Linux" --nataliasmode1 proxyonly
Fixes apache client ip on virtual system e.g.: