One example of how to use ESXi isolation and virtual networking features to configure a secure environment is the creation of a network demilitarized zone (DMZ) on a single host.
In this example, four virtual machines are configured to create a virtual DMZ on Standard Switch 2:
Virtual Machine 1 and Virtual Machine 4 run firewalls and are connected to physical network adapters through standard switches. Both of these virtual machines are using multiple switches.
Virtual Machine 2 runs a Web server, and Virtual Machine 3 runs as an application server. Both of these virtual machines are connected to one virtual switch.
The Web server and application server occupy the DMZ between the two firewalls. The conduit between these elements is Standard Switch 2, which connects the firewalls with the servers. This switch has no direct connection with any elements outside the DMZ and is isolated from external traffic by the two firewalls.
From an operational viewpoint, external traffic from the Internet enters Virtual Machine 1 through Hardware Network Adapter 1 (routed by Standard Switch 1) and is verified by the firewall installed on this machine. If the firewall authorizes the traffic, it is routed to the standard switch in the DMZ, Standard Switch 2. Because the Web server and application server are also connected to this switch, they can serve external requests.
Standard Switch 2 is also connected to Virtual Machine 4. This virtual machine provides a firewall between the DMZ and the internal corporate network. This firewall filters packets from the Web server and application server. If a packet is verified, it is routed to Hardware Network Adapter 2 through Standard Switch 3. Hardware Network Adapter 2 is connected to the internal corporate network.
When creating a DMZ on a single host, you can use fairly lightweight firewalls. Although a virtual machine in this configuration cannot exert direct control over another virtual machine or access its memory, all the virtual machines are still connected through a virtual network. This network could be used for virus propagation or targeted for other types of attacks. The security of the virtual machines in the DMZ is equivalent to separate physical machines connected to the same network.