I'm using Debian on a Virtualbox VM, the default network mode is NAT which according to the Virtualbox documentation is "the simplest way of accessing an external network from a virtual machine. Usually, it does not require any configuration on the host network and guest system. For this reason, it is the default networking mode in Oracle VM VirtualBox.", and for some reason it's not possible to directly FTP in to my VM from my host machine without adding port forwarding.
I don't understand why I need to port forward to be able to access SFTP if this is the simplest networking method to/from a VM. Why is this?