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VMware ACE Administrator’s Manual
Before any such communication can occur, the NAT device must set up a mapping
between the virtual machine’s address on the private NAT network and the host’s
network address on the external network.
When a virtual machine initiates a network connection with another network
resource, this mapping is created automatically. The operation is perfectly transparent
to the user of the virtual machine on the NAT network. No additional work needs to
be done to let the virtual machine access the external network.
The same cannot be said for network connections that are initiated from the external
network to a virtual machine on the NAT network.
When a machine on the external network attempts to initiate a connection with a
virtual machine on the NAT network, it cannot reach the virtual machine because the
NAT device does not forward the request. Network connections that are initiated from
outside the NAT network are not transparent.
File sharing of the type used by Windows operating systems and Samba is possible
among computers on the NAT network — including virtual machines and the host
computer. If you are using WINS servers on your network, a virtual machine using NAT
networking can access shared files and folders on the host that are known by the
WINS server so long as those shared files and folders are in the same workgroup or
domain.
Considerations for Using NAT
Because NAT requires that every packet sent and received from virtual machines is in
the NAT network, there is an unavoidable performance penalty. Our experiments
show that the penalty is minor for dial-up and DSL connections and performance is
adequate for most VMware ACE uses.
NAT is not perfectly transparent. It does not normally allow connections to be initiated
from outside the network, although you can set up server connections by manually
configuring the NAT device. The practical result is that some TCP and UDP protocols
that require a connection be initiated from the server machine — some peer to peer
applications, for example — do not work automatically, and some may not work at all.
A standard NAT configuration provides basic-level firewall protection because the NAT
device can initiate connections from the private NAT network, but devices on the
external network cannot normally initiate connections to the private NAT network.
Using NAT with NetLogon
When using NAT networking in a virtual machine with a Windows guest operating
system running on a Windows host, you can use NetLogon to log on to a Windows