Home > Articles > Cisco Network Technology > General Networking > Network Virtualization: A Basic Virtualized Enterprise

Network Virtualization: A Basic Virtualized Enterprise

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Oct 6, 2006.


  1. The Virtual Enterprise
  2. Transport VirtualizationVNs
  3. Central Services Access: Virtual Network Perimeter
  4. Summary

Chapter Description

The authors of Network Virtualization define the technical requirements posed by the need to virtualize the network. Based on these requirements, they propose an architectural framework comprised of the functional areas necessary to successfully support concurrent virtual networks (VNs) over a shared enterprise physical network.

From the Book

Network Virtualization

Network Virtualization


Central Services Access: Virtual Network Perimeter

The default state of a VN is to be totally isolated from other VNs. In this respect, VNs could be seen as physically separate networks. However, because VNs actually belong to a common physical network, it is desirable for these VNs to share certain services such as Internet access, management stations, DHCP services, Domain Name System (DNS) services, or server farms. These services will usually be located outside of the different VNs or in a VN of their own. So, it is necessary for these VNs to have a gateway to connect to the "outside world." The outside world is basically any network outside the VN such as the Internet or other VNs. Because this is the perimeter of the VN, it is also desirable for this perimeter to be protected by security devices such as firewalls and intrusion detection systems (IDSs). Typically, the perimeter is deployed at a common physical location for most VNs. Hence, this location is known as the central services site, and the security devices here deployed can be shared by many VNs.

The creation of VNs could be seen as the creation of security zones, each of which has a unique and controlled entry/exit point at the VN perimeter. Routing within the VNs should be configured so that traffic is steered to the common services site as required. Figure 3-8 illustrates a typical perimeter deployment for multiple VNs accessing common services. Because the services accessed through the VN perimeter are protected by firewalls, we refer to these as "protected services."


Figure 3-8 Central Site Providing VN Perimeter Security

As shown in Figure 3-8, each VN is head ended by a dedicated firewall. This allows the creation of security policies specific to each VN and independent from each other. To access the shared services, all firewalls are connected to a "fusion" router. The fusion router can provide the VNs with connectivity to the common services, the Internet, or even inter-VN connectivity. The presence of this fusion router should raise two main concerns:

  • The potential for traffic leaking between VNs
  • The risk of routes from one VN being announced to another VN

The presence of dedicated per-VN firewalls prevents the leaking of traffic between VNs through the fusion router by only allowing established connections (connections initiated from "inside" the firewall) to return through the VN perimeter. It is key to configure the routing on the fusion device so that routes from one VN are not advertised to another through the fusion router. The details of the routing configuration at the central site are discussed in Chapter 8, "Traffic Steering and Service Centralization."

Figure 3-8 shows an additional firewall separating the fusion area from the Internet. This firewall is optional. Whether to use it or not depends on the need to keep common services or transit traffic in the fusion area protected from the Internet.

As mentioned, the common services could exist in a central location or in their own VN and therefore distributed throughout the enterprise. Depending on where the common services are located, the VN perimeter topology will vary. Figure 3-9 illustrates the different scenarios for common services positioning and the Internet firewall.


Figure 3-9 Common Services Positioning

When the common services are not present, or are placed in their own VN (and therefore front-ended by a dedicated firewall context) the additional Internet firewall can be removed, as shown in scenario B.2 of Figure 3-9. If concern exists about transit traffic (between VNs or between a VN and the shared services area) being on the Internet, the firewall can be kept (see diagram A.2). The common services could be separated from the rest of the network by having their own firewall, yet not be included in a VN; this is shown in scenario B.1 in Figure 3-9.

For scenarios B.1 and B.2 in Figure 3-9, it is important to note that the fusion router is actually part of the Internet; therefore the Network Address Translation (NAT) pool used at the firewalls must use valid Internet addresses. The deployment of the optional Internet firewall should follow standard Internet edge design guidance, which has been extensively documented across networking literature. The reference designs proposed by Cisco and published at http://www.cisco.com/go/srnd are good sources of information. The "Data Center: Internet Edge Design" document contains a comprehensive discussion on the topic. We use scenario A.1 from Figure 3-9 to illustrate the relevant design and deployment considerations, but these considerations are applicable to other scenarios.

Unprotected Services

In contrast with circuit-based technologies such as ATM or Frame Relay, most Layer 3 VPN technologies allow enough flexibility for traffic to be leaked between VNs in a controlled manner by importing and exporting routes between VNs to provide IP connectivity between the VNs. Thus, the exchange of traffic between the VNs may happen within the IP core and not have to pass through the VN perimeter firewalls at the central site. This type of inter-VN connectivity can be used to provide services, such as DHCP or DNS, that do not need to be protected by the central site firewall, or that would represent an unnecessary burden to the VN perimeter firewalls. Because of the any-to-any nature of an IP cloud, there is little chance of controlling inter-VN traffic after the routes have been exchanged. We refer to these as "unprotected services." This type of connectivity must be deployed carefully because it can potentially create unwanted back doors between VNs and break the concept of the VN as a "security zone" protected by a robust VN perimeter front end. Another consideration that must be made is the fact that importing and exporting routes between VNs precludes the use of overlapping address spaces between the VNs. We discuss the use of route-importing mechanisms for the creation of common services extranet VNs in detail in Chapter 8.

The deployment of protected services does not preclude the deployment of unprotected services and vice versa. In a virtualized network, a combination of protected and unprotected services is usually provided for the different VNs. For example, the DHCP and DNS services for several VNs may be shared and accessed in an unprotected manner, while all server farms and the Internet are also shared among the different VNs, but their access must be controlled by firewall policies and an IDS.

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020