Home > Articles > Cisco Network Technology > IP Communications/VoIP > Building Resilient IP Networks: The Access Module

Building Resilient IP Networks: The Access Module

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Jun 9, 2006.

Chapter Description

This chapter focuses on Ethernet switching technology, specifically Layer 2 network resiliency and how it should be built to provide a solid foundation for the Layer 3 network.

This chapter covers the following topics:

  • Multilayer Campus Design
  • Access Module Building Blocks
  • Layer 2 Domain
  • Layer 3 Domain

The access module is a network's interface to the users or end stations, and challenges in the access module are often related to the physical or Layer 2 connectivity problems. Many Layer 2 technologies can be used to build the access module; however, the focus of this chapter is on the Ethernet technology because Ethernet has emerged as the de facto connectivity standard for end devices.

The ubiquity of the Ethernet technology lies in its simplicity and cost-effectiveness. The availability of Layer 3 switching technology brings IP and Ethernet together, and this has a profound impact on IP network design. For the first time, it is possible to build a complete network for an entire company using IP+Ethernet strategy, including workstation connections, servers in the data center, and connecting branches via a metro Ethernet offering from a service provider. The integration between IP and Ethernet here is so tightly coupled that problems found in the Layer 2 network directly impact the overall IP network availability.

This chapter focuses on Ethernet switching technology, specifically Layer 2 network resiliency and how it should be built to provide a solid foundation for the Layer 3 network.

Multilayer Campus Design

With the popularity of Layer 3 switching, the term multilayer campus design is almost synonymous with the Ethernet switching design. A multilayer campus design has two main characteristics:

  • Hierarchical— Each layer has a specific role to play.
  • Modular— The entire network is built by piecing building blocks together.

These two characteristics enable the network to scale in a deterministic manner, with efficient use of resources to provide a resilient network foundation.

Figure 6-1 shows the concept of a typical multilayer campus design. It has an access layer, which commonly consists of wiring closet switches. The access layer is connected to a distribution layer. The distribution layer is, in turn, connected to the core layer. From a high-level view, a group of access switches are connected to a pair of distribution switches to form a basic building block. Many of these building blocks exist within the network, and the core layer connects them. Designs such as this are also known as three-tier architecture.

06fig01.gif

Figure 6-1 Three-Tier Multilayer Campus Design

Although Figure 6-1 shows a typical three-tier architecture, a smaller network may be built without the need of the core module at all, which makes it a two-tier design, as shown in Figure 6-2.

06fig02.gif

Figure 6-2 Two-Tier Multilayer Campus Design

The benefit of adopting the multilayer campus design is clarity of roles performed by each layer. The role of each layer is translated to a set of features required, which in turn translates to which particular type of hardware is to be used.

Access Layer

The access layer within the multilayer campus design model is where users gain access to the network. Most of the features found within the access layer are geared toward collecting and conditioning the traffic that is coming in from the users' end stations. These features include the following:

  • Aggregating all the user endpoints
  • Providing traffic conditioning functions such as marking and policing
  • Providing intelligent network services such as automatic IP phone discovery
  • Providing network security services such as 802.1x and port security
  • Providing redundant links toward the distribution layer

In the classic multilayer campus design, the access layer is mainly made up of Layer 2 switches. Therefore, most of the work done here is in optimizing the Layer 2 protocol that governs this layer. This helps to provide a robust Layer 2 environment for the functioning of the IP network.

Distribution Layer

The distribution layer within the multilayer campus design model aggregates the access layer. One of the most important characteristics of the distribution layer is that it is the point where the Layer 2 domain ends and where the Layer 3 domain begins. The features at the distribution layer include the following:

  • Aggregating access layer switches
  • Terminating virtual LANs (VLANs) that are defined within the Layer 2 domain
  • Providing the first-hop gateway service for all the end stations
  • Providing traffic conditioning services such as security, quality of service (QoS), and queuing
  • Providing redundant links toward the core layer, if required

Because the distribution layer is the meeting place for both the Layer 2 and Layer 3 domains, it runs both Layer 2 and Layer 3 protocols. This is also the place where most of the network intelligence is found and is perhaps one of the most complex parts of the network.

Core Layer

The core layer within the multilayer campus design model has two important tasks:

  • Interconnect all the distribution layer blocks
  • Forward all the traffic as quickly as it can

As the backbone of the entire network, its function is quite different from that of the access layer and distribution layer. The features that are critical to the functioning of the core layer include the following:

  • Aggregating distribution layers to form an interconnected network
  • Providing high-speed transfer of traffic among the distribution layers
  • Providing a resilient IP routing environment

Because speed is of the essence here, the core layer usually does not provide services that may affect its performance (for example, security, access control, or any activities that require it to process every packet).

In the discussion of multilayer campus design, the inclusion of a core layer is always an interesting question. For a small network, it is common to see a two-tier design, as shown earlier in Figure 6-2, for cost reasons. However, for bigger networks, inclusion of the core layer is always recommended to scale the network in a manageable fashion.

2. Access Module Building Blocks | Next 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