Security administrators use firewalls to safeguard the network or selected components in the network from intrusion.
Firewalls control access to devices within their perimeter by closing all communication pathways, except for those that the administrator explicitly or implicitly designates as authorized. The pathways, or ports, that administrators open in the firewall allow traffic between devices on different sides of the firewall.
The ESXi firewall in ESXi 5.5 does not allow per-network filtering of vMotion traffic. Therefore, you must install rules on your external firewall to ensure that no incoming connections can be made to the vMotion socket.
In a virtual machine environment, you can plan the layout for firewalls between components.
Firewalls between physical machines such as vCenter Server systems and ESXi hosts.
Firewalls between one virtual machine and another—for example, between a virtual machine acting as an external Web server and a virtual machine connected to your company’s internal network.
Firewalls between a physical machine and a virtual machine, such as when you place a firewall between a physical network adapter card and a virtual machine.
How you use firewalls in your ESXi configuration is based on how you plan to use the network and how secure any given component needs to be. For example, if you create a virtual network where each virtual machine is dedicated to running a different benchmark test suite for the same department, the risk of unwanted access from one virtual machine to the next is minimal. Therefore, a configuration where firewalls are present between the virtual machines is not necessary. However, to prevent interruption of a test run from an outside host, you might set up the configuration so that a firewall is present at the entry point of the virtual network to protect the entire set of virtual machines.