What is the difference between NAT / Bridged / Host-Only networking?

Host-only only permits network operations with the Host OS.

NAT mode will mask all network activity as if it came from your Host OS, although the VM can access external resources.

Bridged mode replicates another node on the physical network and your VM will receive it's own IP address if DHCP is enabled in the network.

Same concept as the normal network setup :)

• Host-Only: The VM will be assigned one IP, but it's only accessible by the box VM is running on. No other computers can access it.

• NAT: Just like your home network with a wireless router, the VM will be assigned in a separate subnet, like 192.168.6.1 is your host computer, and VM is 192.168.6.3, then your VM can access outside network like your host, but no outside access to your VM directly, it's protected.

• Bridged: Your VM will be in the same network as your host, if your host IP is 172.16.120.45 then your VM will be like 172.16.120.50. It can be accessed by all computers in your host network.

The below table, from the Virtualbox documentation site, shows the connectivity between VM and Host for different network types: