Designing Cisco Networks

Designing Cisco Networks

by Diane Teare, Cisco Systems, Inc. Staff, Cisco Systems, Inc.

There are no books available that can compete with the actual Cisco training courseware provided in this book!

  • Prepare for CCDA certification while mastering the network design process
  • Learn to characterize existing networks and determine new customer requirements
  • Develop appropriate network topologies for various environments
  • Design device


There are no books available that can compete with the actual Cisco training courseware provided in this book!

  • Prepare for CCDA certification while mastering the network design process
  • Learn to characterize existing networks and determine new customer requirements
  • Develop appropriate network topologies for various environments
  • Design device naming schemes and IP and IPX addressing schemes
  • Understand how to selet the best routing and bridging protocols and provision software featues and hardware for LANs and WANs
  • Learn how to create design documents and build prototypes and pilots
  • Optimize your network with valuable information on PIX firewalls, router performance, ISDN, and Windows NT

Improving network security based on the Cisco System instructor-led and self-study course available worldwide, Designing Cisco Networks teaches you how to become proficient in network design methodologies. Created for those seeking to attain CCDA certification, this book focuses on small- to medium-sized networks and provides a step-by-step process to follow when designing internetworks to ensure that all important issues are considered, resulting in optimal network design. By using this book you will be able to identify customer needs, design LAN and WAN network structures, create network management strategies, write design documents, and build and test prototypes and pilots.

Filled with case studies, procedures, charts, and checklists, Designing Cisco Networks will help you understand how to analyze and solve existing network problems while building a framework that supports the functionality, performance, and scalability required of any given environment. Self-assessment through exercises and chapter-ending tests starts you down the path for attaining your CCDA certification.

Product Details

Cisco Press
Publication date:
Ccda Certification and Training Series
Product dimensions:
7.60(w) x 9.33(h) x 2.08(d)

Read an Excerpt

Chapter 2: Analyzing Small- to Medium-Sized Business Networks

This chapter introduces the role that a Cisco Certified Design Associate (CCDA) will play in designing networks, and presents a framework for you to use in your designs.

Role of the Cisco Certified Design Associate

Your role as a Cisco Certified Design Associate is to be a network design consultant. You will act like an architect, building comprehensive designs that solve your customer's internetworking problems and provide the required functionality, performance, and scalability. In the same way that an architect designs a building or house for a client, you will develop blueprints for an overall internetwork design, as well as component plans for various pieces of the internetwork.


Cisco has developed an integrated network architecture, called CiscoFusion. With the CiscoFusion architecture, multiple networking technologies operating at different networking layers, can provide the best capabilities to handle different networking issues.

Many of your customers may already be aware of the recent internetworking trend toward an integrated view of networking technologies. As a Cisco Certified Design Associate, you will be uniquely positioned to produce network designs, based on CiscoFusion, that meet the needs of state-of-the-art networks that integrate Layer 2, Layer 3, and Asynchronous Transfer Mode (ATM) services. For example, the intelligent networking services associated with Layer 3 can be combined with the cost-effective, high-capacity services provided by Layer 2 in both local-area networks and wide-area networks.

Evolution of Layer 2 and Layer 3 Services

Layer 2, also known as the data link layer, operates within a specific local-area network (LAN) or wide-area network (WAN) segment. In the last two years, LANs have been revolutionized by the exploding use of switching at Layer 2. Companies are replacing hubs with switches at a quick pace. LAN switches provide performance enhancements for new and existing data networking applications by increasing bandwidth and throughput for workgroups and local servers.

Layer 3, also known as the network layer, operates between and across segments. Protocols such as Internet Protocol (IP), Internetwork Packet Exchange (IPX), and AppleTalk's Datagram Delivery Protocol (DDP) operate at Layer 3. In WANs, Layer 3 networking allows businesses to build global data networks. As an example, the global Internet is based on Layer 3 IP technology.

Layer 3 networking, implemented with routing, interconnects the switched workgroups and provides services such as security, Quality of Service (QoS) options, and traffic management. Routing provides the control needed to build functional, scalable networks.

NOTE    Traditionally, Layer 2 switching has been provided by LAN switches, and Layer 3 networking has been provided by routers. Increasingly, these two networking functions are being integrated into one common platform.

There will still be a wide range of platforms providing different performance and capacity ranges for each networking function, but users will gain fundamental benefits from integration of the layers. Users will be able to reduce the number of networking devices that need to be purchased, installed, supported, and serviced. In addition, users will be able to efficiently apply Layer 3 services, such as security and QoS capabilities, to specific individual users and applications.

Mirroring the integration of Layer 3 networking technology into LAN switching devices, WAN switching equipment likely will increasingly incorporate Layer 3 networking capabilities. As traditional Layer 3 routers gain support for higher capacity and bandwidth, the integration of Layer 2 technologies will enable routers to achieve optimum levels of performance, port density, and cost effectiveness.

Figure 2-1 shows how Layer 2 and Layer 3 switching can be used to facilitate communications between Client X and Server Y, with or without routing.

When To Use Layer 2 or Layer 3 Functionality

The decision to use Layer 2 or Layer 3 functionality in a network design depends on which problems you are trying to solve for your customer. These problems can be any of the following:
  • Media problems
  • Protocol problems
  • The need to transport large payloads
Each of these problems is discussed in more detail in the following sections. A solution framework for these problems, using Layer 2 and Layer 3 devices, is then presented.

Media Problems

Media problems occur when too many devices contend for access to a LAN segment, causing an excessive number of collisions on Ethernet networks and long waits for the token on Token Ring or FDDI networks. The level of contention can be estimated by examining network utilization and, in the case of Ethernet, the collision rate. Media contention problems are obvious from complaints from users about slow response time and difficulties accessing services.

Protocol Problems

Problems are caused by protocols that do not scale well. For example, some protocols send too many broadcasts. The number of broadcasts becomes excessive when there are too many clients looking for services, too many servers announcing services, and too many bridge protocol data unit (BPDU) frames. Protocol problems occur when a protocol that was designed for small workgroups is being used for larger networks or for a network that has outgrown the capability of the protocol. The protocol no longer provides the scale required for the business.

Example scenarios of when protocol problems can result include the following:

  • Network layer addressing issues, including running out of addresses.
  • The requirement to use variable-length subnet masks.
  • The need for physically discontiguous subnets.
  • The need for a private address space.
Chapter 8, "Designing a Network-Layer Addressing and Naming Model," discusses these issues.

The Need to Transport Large Payloads

The need to transport large payloads, such as multicast video, can require much more bandwidth than is available on a customer's network or backbone. Multicast video will need more bandwidth than standard data. Multicast video may also require support for low and predictable latency.

A Framework for Solving Small- to Medium-Sized Business Network Problems

To help reduce the complexity associated with identifying and analyzing customer problems and designing solutions, Cisco developed a basic framework into which most customer problems fit. The small- to medium-sized business solutions framework is represented as a triangle, as shown in Figure 2-2.

As illustrated in Figure 2-2, use the following simple rules when designing solutions to customer problems:

  • If the problems involve media contention, use LAN switching.
  • If the problems are protocol related -- for example, resulting in an excessive number of broadcasts -- use routing.
  • If the customer needs to transport payloads that require high bandwidth, use Fast Ethernet switching. In large networks where high bandwidth and predictable low latency are required, consider ATM switching.


Now that you have an understanding of the problems that customers may encounter on their networks and potential solutions available to you in a network, you are ready to start the network design process.

In the next part of the book, you will learn how to identify customer needs. While reading the chapter content and performing the chapter exercises, keep in mind the small- to medium-sized business solutions framework identified in this chapter to help you understand typical customer problems. At the end of Part III of this book, you will be able to determine whether the needs are related to media, protocols, or bandwidth.

Meet the Author

Diane Teare is a Senior Network Architect with GeoTrain Corporation, Cisco's largest worldwide training partner, where she provides training and consulting services to customers in North America and Europe. Diane is a Cisco Certified Systems Instructor with more than 14 years experience in teaching; course design; design, implementation, and troubleshooting of network hardware and software; and project management. She is the Master Instructor for the ICRC, ACRC, and DCN courses at GeoTrain. Diane has a Bachelors of Applied Science in Electrical Engineering and a Masters of Applied Science in Management Science.

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