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CHAPTER 11 Networking Virtual Machines
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the NAT device can dynamically obtain their IP addresses by sending out DHCP
requests. The DHCP server on the NAT network, which is also used in host-only
networking configurations, dynamically allocates IP addresses in the range of
<net>.128 through <net>.254, where <net> is the network number assigned to your
NAT network. VMware ACE always uses a Class C address for NAT networks. IP
addresses <net>.3 through <net>.127 can be used for static IP addresses. IP address
<net>.1 is reserved for the host adapter; <net>.2 is reserved for the NAT device.
In addition to the IP address, the DHCP server on the NAT network also sends out
additional configuration information that enables the virtual machine to operate
automatically. This information includes the default gateway and the DNS server. In
the DHCP response, the NAT device instructs the virtual machine to use the IP address
<net>.2 as the default gateway and DNS server. This causes all IP packets destined for
the external network and DNS requests to be forwarded to the NAT device.
DNS on the NAT Network
The NAT device acts as a DNS server for the virtual machines on the NAT network.
Actually, the NAT device is a DNS proxy and merely forwards DNS requests from the
virtual machines to a DNS server that is known by the host. Responses come back to
the NAT device, which then forwards them to the virtual machines.
If they get their configuration information from DHCP, the virtual machines on the NAT
network automatically use the NAT device as the DNS server. However, the virtual
machines can be statically configured to use another DNS server.
The virtual machines in the private NAT network are not, themselves, accessible via
DNS. If you want the virtual machines running on the NAT network to access each
other by DNS names, you must set up a private DNS server connected to the NAT
network.
External Access from the NAT Network
In general, any protocol using TCP or UDP can be used automatically by a virtual
machine on the NAT network so long as the virtual machine initiates the network
connection. This is true for most client applications such as Web browsing, Telnet,
passive-mode FTP and downloading streaming video. Additional protocol support
has been built into the NAT device to allow FTP and ICMP echo (ping) to work
completely transparently through the NAT.
On the external network to which the host is connected, any virtual machine on the
NAT network appears to be the host itself, because its network traffic uses the host’s IP
address. It is able to send and receive data using TCP/IP to any machine that is
accessible from the host.