CompTIA Network+ Rapid Review: Network Concepts

  • 12/15/2012

Objective 1.9: Identify virtual network components

In networking, virtualization is a process that adds a layer of abstraction between actual, physical hardware and the system making use of it. Virtualization is a relatively recent philosophy in network management. Although virtualization was originally a tool primarily employed for lab testing and pre-production work, administrators are now using virtual components throughout their networks, taking advantage of the flexibility that virtualization provides.

Exam need to know

  • Identify the function of a virtual desktop

    For example: For what applications are virtual desktop products suitable?

  • Identify the function of a virtual server

    For example: What are the advantages of virtual servers over physical servers?

  • Identify the function of a virtual switch

    For example: How is a virtual switch different from a physical switch?

  • Identify the function of a virtual PBX

    For example: Can a virtual PBX provide the same service as a standard telephone system?

  • Identify the difference between onsite vs. offsite virtualization

    For example: Why would you want to have virtual machines stored offsite?

  • Identify the function of Network as a Service (NaaS)

    For example: Is NaaS more cost effective that hosting your own virtual machines?

Virtual desktops

Administrators typically use Type I virtualization products, such as Hyper-V, for server virtualization. This type of virtualization can provide the performance levels needed to run high-volume production servers. Type II virtualization provides an excellent platform for education, laboratory testing, and software evaluation. It also enables desktop users to run an instance of another operating system on a single computer, without the complications of dual booting.

In this practice, often called desktop virtualization, a user can run applications that are not compatible with his or her primary operating system. For example, there are several products that enable Apple Macintosh users to run an instance of Windows. Other products run on Windows 7 and enable users to install an earlier version of Windows, allowing them to run an application that has not been updated.

Windows 7 even includes a feature called Windows XP Mode, which is a fully licensed version of Windows XP that you can install on a computer running Windows 7 with Microsoft Windows Virtual PC.

True or false: Desktop virtualization is a low-cost way of deploying multiple production servers as virtual machines on a single workstation.

Answer: False. Type II virtualization provides a suitable platform for virtual workstations or for servers in a laboratory or classroom, but not for a production environment.

True or false: Hardware virtualization support is required to run any type of hypervisor product.

Answer: False. There are hypervisor implementations that do not require hardware virtualization support.

Virtual servers

A virtual server is a separate instance of an installed operating system running on a physical computer. Instead of having the server access the computer’s hardware directly, an intervening component called a hypervisor creates a virtual machine (VM) environment, and the server operating system runs in that environment.

The hypervisor is responsible for handling all of the hardware calls that the virtual machine makes and passing them along to the correct physical hardware. When you create a virtual machine, you specify what (virtual) hardware should be in it.

The advantage of this capability is that the hypervisor can create multiple virtual machines on a single computer, sharing the physical hardware among them. Each virtual machine can then have a separate operating system instance installed on it. The instances appear to the network as separate computers, each with its own hardware, its own addresses, and its own applications. If one virtual machine suffers a software malfunction and crashes, the other virtual machines on the same computer are in most cases unaffected.

True or false: Virtual servers enable administrators to run multiple roles on a single computer without them interfering with each other.

Answer: True. Multiple applications running on a single operating system instance can interfere with each other, causing the whole system to crash. By running the applications on separate virtual machines, one can crash without affecting the others.

True or false: Virtual servers in a production environment typically run on a Type I hypervisor.

Answer: True. A Type I hypervisor provides better virtual machine performance than a Type II hypervisor, so production servers usually run in a Type I environment.

Virtual switches

One of the problems that any server or desktop virtualization solution has to solve is that of network access. A physical computer usually has only one network adapter in it, but if there are multiple VMs running on that computer, each one has its own virtual adapter that needs access to the network. One way that a hypervisor can accomplish this is to use virtual switching.

To keep communication within the hypervisor, most virtualization products can create a virtual switch that enables all of the VMs on a computer to communicate with each other, just as if their network adapters were connected to a physical switch. For Type I virtualization solutions, there are also third-party virtual switch products available. These are essentially software switches that provide additional security, management, and wide area networking (WAN) services.

True or false: Virtual switches can enable virtual machines to participate in a physical network.

Answer: True. Virtual switches can provide virtual machines with access to the physical network through the physical network adapter in the host computer.

Virtual PBX

A private branch exchange (PBX) is essentially a telephone exchange, that is, a switchboard, wholly owned and operated by a business or other private entity, rather than by a telephone company. As its core functionality, the PBX routes incoming calls to the proper extensions and provides outgoing callers with automatic access to a line. The original alternative to a PBX for a business was a key system, which required callers to push buttons to select their own lines.

Deciding on the correct telephone solution was always difficult for relatively small businesses lacking the knowledgeable staff required to maintain a PBX. This eventually led to the appearance of hosted PBX services, sometimes called virtual PBXs, in which a telephone company provided the PBX services to a customer but maintained the actual hardware at their own facility.

Another option is a software-based solution, running on a computer at the customer’s site, which provides the same services as a hardware-based PBX.

The recent emphasis on cloud computing has led to the development of several hosted PBX solutions that use VoIP to provide services to customers over the Internet. Because of their decentralized nature, the actual company telephones connected by the virtual PBX service can be located anywhere, whereas a traditional PBX was limited to extensions located in the same facility.

True or false: A virtual PBX provides the same PSTN-based telephone functionality as a physical PBX.

Answer: False. A virtual PBX provides telephony services based on VoIP, not the Public Switched Telephone Network (PSTN).

Onsite vs. offsite

Because virtual machines all interface with the same hypervisor, you can easily copy or move a virtual machine from one physical computer to another. This enables administrators to easily maintain offline copies of virtual machines, so that if a physical computer fails, duplicates of its virtual servers are immediately available. Administrators can also maintain copies offsite, for backups in the event of theft or natural disaster. Some organizations maintain their entire data centers offsite, in a facility belonging to a hosting service that is responsible for its security and environmental maintenance.

True or false: Offsite datacenter hosting can be more economical than hosting the systems yourself.

Answer: True. In an area where office space comes at a premium, hosting virtual machines offsite can be cheaper than leasing space locally.

Network as a Service (NaaS)

Some service providers are in the business of selling access to offsite networks of virtual machines to customers; for a monthly fee, you can create a server or a network of servers at another location that runs any applications you need, just as if you were hosting them onsite. Sometimes called Network as a Service (NaaS), this concept is a progenitor of cloud computing.

True or false: NaaS eliminates some of the traditional concerns of the network administrator, such as bandwidth, fault tolerance, and environmental services.

Answer: True. NaaS is a pay-as-you-go arrangement that enables you to select the services you want and upgrade them as needed. Part of the arrangement is an agreed quality of service that covers fault tolerance and allowable downtime.

Can you answer these questions?

Find the answers to these questions at the end of this chapter.

  1. How does a Type I hypervisor differ from a Type II hypervisor?
  2. What relatively new telephony service has made the virtual PBX possible?
  3. How do virtual servers provide network administrators with fault tolerance?

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