Home > Articles > Cisco Certification > CCDP > Designing Cisco Network Service Architectures (ARCH): Developing an Optimum Design for Layer 3 (CCDP)

Designing Cisco Network Service Architectures (ARCH): Developing an Optimum Design for Layer 3 (CCDP)

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Dec 8, 2011.

Chapter Description

This chapter examines a select number of topics on both advance IP addressing and design issues with Border Gateway Protocol (BGP), Enhanced Interior Gateway Routing Protocol (EIGRP), and Open Shortest Path First (OSPF).

Design Considerations for IPv6 in Campus Networks

This section discusses the three different IPv6 deployment models that can be used in the enterprise campus.

IPv6 Campus Design Considerations

As mentioned earlier, three major deployment models can be used to implement IPv6 support in the enterprise campus environment: the dual-stack model, the hybrid model, and the service block model. The choice of deployment model strongly depends on whether IPv6 switching in hardware is supported in the different areas of the network.

Dual stack is the preferred, most versatile, and highest-performance way to deploy IPv6 in existing IPv4 environments. IPv6 can be enabled wherever IPv4 is commissioned along with the associated features that are required to make IPv6 routable, highly available, and secure. In some cases, IPv6 may not be enabled on a specific interface or device because of the presence of legacy applications or hosts for which IPv6 is not supported. Inversely, IPv6 may be enabled on interfaces and devices for which IPv4 support is no longer necessary.

A key requirement for the deployment of the dual-stack model is that IPv6 switching must be performed in hardware on all switches in the campus. If some areas of the campus network do not support IPv6 switching in hardware, tunneling mechanisms are leveraged to integrate these areas into the IPv6 network. The hybrid model combines a dual-stack approach for IPv6-capable areas of the network with tunneling mechanisms such as Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) and manual IPv6 tunnels where needed.

The hybrid model adapts as much as possible to the characteristics of the existing network infrastructure. Transition mechanisms are selected based on multiple criteria, such as IPv6 hardware capabilities of the network elements, number of hosts, types of applications, location of IPv6 services, and network infrastructure feature support for various transition mechanisms.

The service block model uses a different approach to IPv6 deployment. It centralizes IPv6 as a service, similar to how other services such as voice or guest access can be provided at a central location. The service block model is unique in that it can be deployed as an overlay network without any impact to the existing IPv4 network, and it is completely centralized. This overlay network can be implemented rapidly while allowing for high availability of IPv6 services, QoS capabilities, and restriction of access to IPv6 resources with little or no changes to the existing IPv4 network. As the existing campus network becomes IPv6-capable, the service block model can become decentralized. Connections into the service block are changed from tunnels (ISATAP or manually configured) to dual-stack connections. When all the campus layers are dual-stack capable, the service block can be dismantled and repurposed for other uses.

These three models are not exclusive. Elements from each of these models can be combined to support specific network requirements.

Ultimately, a dual-stack deployment is preferred. The hybrid and service block models are transitory solutions. The models can be leveraged to migrate to a dual stack design in a graceful manner, without a need for forced hardware upgrades throughout the entire campus. From an address-planning standpoint, this means that the IPv6 address plan should be designed to support a complete dual-stack design in the future.

Dual-Stack Model

The dual-stack model deploys IPv4 and IPv6 in parallel without any tunneling or translation between the two protocols. IPv6 is enabled in the access, distribution, and core layers of the campus network. This model makes IPv6 simple to deploy, and is very scalable. No dependencies exist between the IPv4 and IPv6 design, which results in easier implementation and troubleshooting.

Deploying IPv6 in the campus using the dual-stack model offers several advantages over the hybrid and service block models. The primary advantage of the dual-stack model is that it does not require tunneling within the campus network. The dual-stack model runs the two protocols as "ships in the night," meaning that IPv4 and IPv6 run alongside one another and have no dependency on each other to function except that they share network resources. Both IPv4 and IPv6 have independent routing, high availability, QoS, security, and multicast policies. The dual-stack model also offers processing performance advantages, because packets are natively forwarded without having to account for additional encapsulation and lookup overhead.

These advantages make the dual-stack model the preferred deployment model. The stack model requires all switches in the campus to support IPv6 forwarding.

Hybrid Model

The hybrid model strategy is to employ two or more independent transition mechanisms with the same deployment design goals. Flexibility is the key aspect of the hybrid approach. Any combination of transition mechanisms can be leveraged to best fit a given network environment. The hybrid model uses dual stack in all areas of the network where the equipment supports IPv6. Tunneling mechanisms are deployed for areas that do not currently support IPv6 in hardware. These areas can be transitioned to dual stack as hardware is upgraded later.

Various tunneling mechanisms and deployment scenarios can be part of a hybrid model deployment. This section highlights two common scenarios.

The first scenario that may require the use of a hybrid model is when the campus core is not enabled for IPv6. Common reasons why the core layer might not be enabled for IPv6 are either that the core layer does not have hardware-based IPv6 support at all, or has limited IPv6 support but with low performance.

In this scenario, manually configured tunnels are used exclusively from the distribution to aggregation layers. Two tunnels from each switch are used for redundancy and load balancing. From an IPv6 perspective, the tunnels can be viewed as virtual links between the distribution and aggregation layer switches. On the tunnels, routing and IPv6 multicast are configured in the same manner as with a dual-stack configuration.

The scalability of this model is limited, and a dual-stack model is preferred. However, this is a good model to use if the campus core is being upgraded or has plans to be upgraded, and access to IPv6 services is required before the completion of the core upgrade.

The second scenario focuses on the situation where hosts that are located in the campus access layer need to use IPv6 services, but the distribution layer is not IPv6 capable or enabled. The distribution layer switch is most commonly the first Layer 3 gateway for the access layer devices. If IPv6 capabilities are not present in the existing distribution layer switches, the hosts cannot gain access to IPv6 addressing router information (stateless autoconfiguration or Dynamic Host Configuration Protocol [DHCP] for IPv6), and then cannot access the rest of the IPv6-enabled network.

In this scenario, tunneling can be used on the IPv6-enabled hosts to provide access to IPv6 services that are located beyond the distribution layer. For example, the ISATAP tunneling mechanisms on the hosts in the access layer to provide IPv6 addressing and off-link routing. The Microsoft Windows XP and Vista hosts in the access layer must have IPv6 enabled and either a static ISATAP router definition or Domain Name System (DNS) A record entry that is configured for the ISATAP router address.

Using the ISATAP IPv4 address, the hosts establish tunnels to the IPv6-enabled core routers, obtain IPv6 addresses, and tunnel IPv6 traffic across the IPv4 distribution switches to the IPv6 enabled part of the network.

Terminating ISATAP tunnels in the core layer makes the layer appear as an access layer to the IPv6 traffic, which may be undesirable from a high-level design perspective. To avoid the blending of core and access layer functions, the ISATAP can be terminated on a different set of switches, such as the data center aggregation switches.

The main reason to choose the hybrid deployment model is to deploy IPv6 without having to go through an immediate hardware upgrade for parts of the network. It allows switches that have not reached the end of their normal life cycle to remain deployed and avoids the added cost that is associated with upgrading equipment before its time with the sole purpose of enabling IPv6.

Some drawbacks apply to the hybrid model. The use of ISATAP tunnels is not compatible with IPv6 multicast. Therefore, any access or distribution layer blocks that require the use of IPv6 multicast applications should be deployed using the dual-stack model. Manual tunnels support IPv6 multicast and can still be used to carry IPv6 across an IPv4 core. Another drawback of the hybrid model is the added complexity that is associated with tunneling. Considerations that must be accounted for include performance, management, security, scalability, and availability.

Service Block Model

The service block model has several similarities to the hybrid model. The underlying IPv4 network is used as the foundation for the overlay IPv6 network that is being deployed. ISATAP provides access to hosts in the access layer. Manually configured tunnels are utilized from the data center aggregation layer to provide IPv6 access to the applications and services that are located in the data center access layer. IPv4 routing is configured between the core layer and service block switches to allow visibility to the service block switches for terminating IPv6-in-IPv4 tunnels.

The biggest difference with the hybrid model is that the service block model centralizes IPv6 connectivity through a separate redundant pair of switches. The service block deployment model is based on a redundant pair of Cisco Catalyst 6500 series switches with a Cisco Supervisor Engine 32 or Supervisor Engine 720 card. The key to maintaining a highly scalable and redundant configuration in the service block is to ensure that a high-performance switch, supervisor, and modules are used to manage the load of the ISATAP, manually configured tunnels, and dual-stack connections for an entire campus network.

The biggest benefit of this model compared with the hybrid model is that the centralized approach enables you to pace the IPv6 deployment in a very controlled manner.

In essence, the service block model provides control over the pace of IPv6 service introduction by leveraging the following:

  • Per-user or per-VLAN tunnels, or both, can be configured via ISATAP to control the flow of connections and allow for the measurement of IPv6 traffic use.
  • Access on a per-server or per-application basis can be controlled via access lists and routing policies that are implemented on the service block switches. This level of control allows for access to one, a few, or even many IPv6-enabled services, while all other services remain on IPv4 until those services can be upgraded or replaced. This enables a "per-service" deployment of IPv6.
  • The use of separate dual redundant switches in the service block allows for high availability of ISATAP and manually configured tunnels as well as all dual-stack connections.
  • Flexible options allow hosts access to the IPv6-enabled ISP connections, either by allowing a segregated IPv6 connection that is used only for IPv6-based Internet traffic or by providing links to the existing Internet edge connections that have both IPv4 and IPv6 ISP connections.
  • Implementation of the service block model does not disrupt the existing network infrastructure and services. Because of its similarity to the hybrid model, the service block model suffers from the same drawbacks that are associated with the use of tunneling. In addition to those drawbacks, there is the cost that is associated with the service block switches.
3. Designing Advanced Routing | Next Section Previous Section

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