Whereas in Ubuntu the samba dc is local, Nethserver runs the samba domain controller in a systemd-nspawn container, see I still don't get why Samba has to be run in a container - #6 by davidep
There seem to be problems to reach the container from a virtualbox guest.
It should be possible with network scripts, I’ll post if I have something working…
https://www.itzgeek.com/how-tos/mini-howtos/create-a-network-bridge-on-centos-7-rhel-7.html