Explanation/Reference:
Section: Considerations for Expanding an Existing Network Explanation
Explanation/Reference:
Multiple virtual machines (VMs) can be running simultaneously on a single host computer. A VM is an isolated environment running a separate operating system (OS) while sharing hardware resources with a host machine's OS. For example, you can configure a Windows 7 VM that can run within Windows 8? both OSs can run at the same time if virtualization software, such as Microsoft HyperV, is used. The Windows 7 VM could then be used as a testing environment for patch or application deployment.
Depending on a computer's hardware capabilities, multiple VMs can be installed on a single computer, which can help provide more efficient utilization of hardware resources. For example, VMWare ESXi Server provides a hypervisor that runs on bare metal, meaning without a host OS, and that can efficiently manage multiple VMs on a single server. A VM can access the physical network through a network adapter shared by the host computer. Alternatively, a VM could access virtualized networking devices on the host, such as routers or switches, to access network resources.
Before a VM is installed, it is important to ensure that the hardware on the host in which you are configuring the VM has enough CPU process availability and random access memory (RAM) to support the simultaneous use of multiple OSs and to ensure that the client you are accessing the VM from has sufficient network bandwidth.
The VMs on a host computer can, but are not required to, run the same version of an OS as the host computer. For example, you can install Windows 8 on a VM that is hosted on a Windows 8 computer.
Alternatively, as in the example given previously, you can configure a Windows 7 VM that can run within Windows 8.
Installing virus protection on the host computer will not automatically protect any VMs running on that host computer. Securing the host computer does not secure all virtual computers running on that host computer. You must manually manage the security of each VM installed on a host computer. For example, installing patches and security software on the host computer will not also configure the patches and software to be installed on the VMs.
Although a VM shares the hardware resources of the host computer, the software remains separate.
Software installed on the host is not accessible from within the VM. For example, Microsoft Office might be installed on the host computer, but in order to access Microsoft Office from within a VM you must also install Microsoft Office on the VM. Separate instances of software on the host computer and on each VM can help protect the host computer from potentially harmful changes made within a VM. For example, if a VM user accidentally deletes a system file or installs malicious software, the host computer will not be affected. This applies to drivers as well? if the network adapter driver is removed from the VM, the host computer and the other VMs will not be affected.
Reference:
CCDA 200-310 Official Cert Guide, Chapter 4, Server Virtualization, p. 155