If a VM is set up/changed to shared networking. it gets and shared ip address from DHCP (Parallels) 10.211.x.x If your Mac firewall is enabled Stealth.. your mac would not visible to outside users.. (ping replies etc..) Since the Parallels DHCP in shared networking mode. users your Airport to route network traffic through and from Parallels, does this mean your VM is also Stealthy? Just wondering if a firewall on the VM is necessary in such a situation (apart from virus scanning) that is.
There is a good description in our documentation, here. As you can see, the virtual machine gets an internal IP, so this is similar to the LAN and your VM can not be easily reached from outside. However, I would not say that firewall is not needed in that case, i.e. there are many ways like backdoors and viruses that can still harm your system.
