So, the outside world only see the IP address of the Host machine. When the guest machine sends an IP packet to some remote machine, VirtualBox's NAT Engine will receive the packet and extracts the TCP/IP segments, and change the IP address to the IP address of the HOST machine. When a guest machine is set-up in this mode, then outside world will never be able to communicate with the Guest machine directly. Adapter 1 is NAT - for Internet connectivity.Note that we need to shutdown our guest OS: In the network settings for the virtual machine, set up adapters via VirtualBox Manager.In main Preferences of Virtualbox, under Network, add the Host-only network vboxnet0. Instead, a virtual network interface (similar to a loopback interface) is created on the host, providing connectivity among virtual machines and the host. This can be used to create a network containing the host and a set of virtual machines, without the need for the host's physical network interface. The Host-only network is a virtual network provided by VirtualBox that is visible only to the Host OS and its virtual machines. To enable static IP addresses on our VirtualBox VMs, we'll first need to setup a Host-only network.Our Ubuntu will be able to reach the Internet and see other Virtualbox machines as well. Now we want to setup the networks so that we can SSH from our Mac OS X into the Ubuntu. It is now mounted as a CD on our Ubuntu guest.

Click on it and select the VBoxGuestAdditions.iso on desktop and click on 'Open' and then on 'OK'. On the right side of the window is a small CD icon. Browse to 'Storage' and click on the empty disc under Controller:IDE.Now close all Finder windows and head back to the running Virtualbox application.

Search the file VBoxGuestAdditions.iso and copy it to Mac's desktop.Now we're in the MacOS folder of the application Virtualbox.Click the folder 'Contents' and then on 'MacOS'.Right-click on the Virtualbox icon and select 'Show Package Contents'.In Mac OS X, open Finder and browse to Applications folder.Via guest additions, we can access local files in our host machine.

We may want to install the Virtualbox Guest Additions to enable features like shared folders, etc.

Virtualbox guest additions mac