VirtualBox network modes
As covered in the VirtualBox networking docs, the quickest overview into different networking modes is the following table:
|VM ↔ VM||VM → Host||Host → VM||VM → Net/LAN||Net/LAN → VM|
|NAT||-||+||forwarded ports||+||forwarded ports|
|NAT Network||+||+||forwarded ports||+||forwarded ports|
In short, bridged networking happily allows everything, while other less permissive modes give you granular control over your network security.