I cannot understand what is the actual difference between settings "Share with my Mac" and "Private to my Mac" of VMware Fusion Network Adapter. Here's a screenshot:
The only difference I see is that on "Share with my Mac", the VM is in the same network as my "vmnet1" host's adapter, while on "Private to my Mac" it's on "vmnet8".
Here're these networks (on host):
vmnet1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet 192.168.198.1 netmask 0xffffff00 broadcast 192.168.198.255
vmnet8: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet 172.16.66.1 netmask 0xffffff00 broadcast 172.16.66.255
I see that "Share with my Mac" enables Internet access from my VM, while the other setting disables Internet access.
How does it work? Why these settings are so different, although they look almost same - just the network subnet changes.
Ok .. where to start.....
The difference in IP subnets is part and parcel of what makes it work. The build-in DHCP server hands out addresses in subnets that depend on how that adapter is configured. So for example, 'Share with my Mac' gets a subnet that is routed internally to a NAT server and that address is then changed --- just like your home router does. 'Bridged Networking' sets other subnets so the internal routing in Fusion can pass those packets through to the real adapter unchanged.
For a better understanding go pull the source for VirtualBox from Oracle -- it does about the same thing in its network stack.
Ok, so although to me it might look like a simple change of subnet, VmWare's internals listen on those subnets and do different things there.
Well, looking through source code of a big project like VirtualBox must not be a simple task I think. I wouldn't even know which files to look at.
vmnet1 and vmnet8 both install a virtual Nic on your host.
For both virtual nics you enable a DHCP-server which assigns an IP to VMs that use vmnet1 or vmnet8.
So your observation that both look similar is correct.
Your host does not forward any traffic on vmnet1 to the internet via your local router.
Thats why this vmnet is labelled as "Private to my Mac"
On vmnet8 your host also runs a NAT-service - so VMs that are connected to vmnet8 can use your hosts internet connection.
VMs connected to vmnet8 send traffic to the internet or physical network as if it was coming from your hosts IP address.
This type is called "Share with my Mac"
One more suggestion is to click the "?" icon at the bottom right of that screen.
The VMware Fusion team did a proper job writing the help contents for the network adapter screen.