Home > Articles > Cisco Network Technology > General Networking > MPLS/VPN Architecture Overview

MPLS/VPN Architecture Overview

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Aug 2, 2002.

Chapter Description

MPLS/VPN concepts are introduced in this mock case study of service provider SuperCom and its two key customers. Learn how VPNs based on MPLS combine the benefits of the overlay VPN model with the benefits of the peer-to-peer VPN model.

VPN Packet Forwarding

In the previous section, you saw that the IP addresses used within a VPN must be prepended with a 64-bit prefix called a route distinguisher (RD) to make them unique.

Similarly, when the VPN-originated IP packets are forwarded across the service provider backbone (the P network), they must be augmented to make them uniquely recognizable. Yet again, several technology options are possible:

  • The IP packet is rewritten to include 96-bit addresses in the packet header. This operation would be slow and complex.

  • The IP packet is tunneled across the network in VPN-over-IP tunnels. This choice would make MPLS/VPN as complex as traditional IP-over-IP VPN solutions using the overlay VPN model.

With the introduction of MPLS, a third technology option was made possible: Each VPN packet is labeled by the ingress PE router with a label uniquely identifying the egress PE router, and is sent across the network. All the routers in the network subsequently switch labels without having to look into the packet itself. The preparatory steps for this process are illustrated in Figure 9-8.

Figure 9-8Figure 9-8 VPN Packet Forwarding—Preparatory Steps

Each PE router needs a unique identifier (a host route—usually the loopback IP address is used), which is then propagated throughout the P network using the usual IGP (Step 1). This IP address is also used as the BGP next-hop attribute of all VPN routes announced by the PE router. A label is assigned in each P router for that host route and is propagated to each of its neighbors (Step 2). Finally, all other PE routers receive a label associated with the egress PE router through an MPLS label distribution process (Step 3). After the label for the egress PE router is received by the ingress PE router, the VPN packet exchange can start.

However, when the egress PE router receives the VPN packet, it has no information to tell it which VPN the packet is destined for. To make the communication between VPN sites unique, a second set of labels is introduced, as illustrated in Figure 9-9.

Figure 9-9Figure 9-9 VPN Label Allocation

Each PE router allocates a unique label for each route in each VPN routing and forwarding (VRF) instance (Step 1). These labels are propagated together with the corresponding routes through MP-BGP to all other PE routers (Step 2). The PE routers receiving the MP-BGP update and installing the received routes in their VRF tables (see Figure 9-7 for additional details) also install the label assigned by the egress router in their VRF tables. The MPLS/VPN network is now ready to forward VPN packets.

When a VPN packet is received by the ingress PE router, the corresponding VRF is examined, and the label associated with the destination address by the egress PE router is fetched. Another label, pointing toward the egress PE router, is obtained from the global forwarding table. Both labels are combined into an MPLS label stack, are attached in front of the VPN packet, and are sent toward the egress PE router.

All the P routers in the network switch the VPN packet based only on the top label in the stack, which points toward the egress PE router. Because of the normal MPLS forwarding rules, the P routers never look beyond the first label and are thus completely unaware of the second label or the VPN packet carried across the network.

The egress PE router receives the labeled packet, drops the first label, and performs a lookup on the second label, which uniquely identifies the target VRF and sometimes even the outgoing interface on the PE router. A lookup is performed in the target VRF (if needed), and the packet is sent toward the proper CE router.

NOTE

The egress PE router assigns labels to VPN routes in such a way that the need for additional Layer 3 lookup in the target VRF is minimized. The additional Layer 3 lookup is needed only for summary VPN routes advertised between the PE routers.

The router just before the egress PE router might also remove the first label in the label stack through a mechanism called penultimate hop popping. Refer to Chapter 2, "Frame-mode MPLS Operation," for a detailed description of this mechanism.

In the best case (no summary VPN routes and network topology that supports penultimate hop popping), the egress PE router would perform only a single label lookup, resulting in maximum forwarding performance.

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.

Overview

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.

Surveys

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.

Newsletters

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.

Security

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

Children

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

Marketing

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.

Choice/Opt-out

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.

Links

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