Introduction

New business practices are driving changes in enterprise networks. The transition from an industrial to an information economy has changed how employees do their jobs, and the emergence of a global economy of unprecedented competitiveness has accelerated the speed at which companies must adapt to technological and financial changes.

To reduce the time to develop and market products, companies are empowering employees to make strategic decisions that require access to sales, marketing, financial, and engineering data. Employees at corporate headquarters and in worldwide field offices, and telecommuters in home offices, need immediate access to data, regardless of whether the data is on centralized or departmental servers.

To develop, sell, and distribute products into domestic and foreign markets, businesses are forming alliances with local and international partners. Businesses are carefully planning their network designs to meet security goals while also offering network access to resellers, vendors, customers, prospective customers, and contract workers located all over the world.

To accommodate increasing requirements for remote access, security, bandwidth, scalability, and reliability, vendors and standards bodies introduce new protocols and technologies at a rapid rate. Network designers are challenged to develop state-of-the-art networks even though the state of the art is continually changing.

Whether you are a novice network designer or a seasoned network architect, you probably have concerns about how to design a network that can keep pace with the accelerating changes in the internetworking industry. The goal of this book is to teach a systematic design methodology that can help you meet an organization’s requirements, regardless of the newness or complexity of applications and technologies.

Objectives

The purpose of Top-Down Network Design, Third Edition, is to help you design networks that meet a customer’s business and technical goals. Whether your customer is another department within your own company or an external client, this book provides you with tested processes and tools to help you understand traffic flow, protocol behavior, and internetworking technologies. After completing this book, you will be equipped to design enterprise networks that meet a customer’s requirements for functionality, capacity, performance, availability, scalability, affordability, security, and manageability.

Audience

This book is for you if you are an internetworking professional responsible for designing and maintaining medium- to large-sized enterprise networks. If you are a network engineer, architect, or technician who has a working knowledge of network protocols and technologies, this book will provide you with practical advice on applying your knowledge to internetwork design.

This book also includes useful information for consultants, systems engineers, and sales engineers who design corporate networks for clients. In the fast-paced presales environment of many systems engineers, it often is difficult to slow down and insist on a top-down, structured systems analysis approach. Wherever possible, this book includes shortcuts and assumptions that can be made to speed up the network design process.

Finally, this book is useful for undergraduate and graduate students in computer science and information technology disciplines. Students who have taken one or two courses in networking theory will find Top-Down Network Design, Third Edition, an approachable introduction to the engineering and business issues related to developing real-world networks that solve typical business problems.

Changes for the Third Edition

Networks have changed in many ways since the second edition was published. Many legacy technologies have disappeared and are no longer covered in the book. In addition, modern networks have become multifaceted, providing support for numerous bandwidth-hungry applications and a variety of devices, ranging from smart phones to tablet PCs to high-end servers.

Modern users expect the network to be available all the time, from any device, and to let them securely collaborate with coworkers, friends, and family. Networks today support voice, video, high-definition TV, desktop sharing, virtual meetings, online training, virtual reality, and applications that we can’t even imagine that brilliant college students are busily creating in their dorm rooms.

As applications rapidly change and put more demand on networks, the need to teach a systematic approach to network design is even more important than ever. With that need in mind, the third edition has been retooled to make it an ideal textbook for college students. The third edition features review questions and design scenarios at the end of each chapter to help students learn top-down network design.

To address new demands on modern networks, the third edition of Top-Down Network Design also has updated material on the following topics:

• Network redundancy

• Modularity in network designs

• The Cisco SAFE security reference architecture

• The Rapid Spanning Tree Protocol (RSTP)

• Internet Protocol version 6 (IPv6)

• Ethernet scalability options, including 10-Gbps Ethernet and Metro Ethernet

• Network design and management tools

Organization

This book is built around the steps for top-down network design. It is organized into four parts that correspond to the major phases of network design.

Part I: Identifying Your Customer’s Needs and Goals

Part I covers the requirements-analysis phase. This phase starts with identifying business goals and technical requirements. The task of characterizing the existing network, including the architecture and performance of major network segments and devices, follows. The last step in this phase is to analyze network traffic, including traffic flow and load, protocol behavior, and quality of service (QoS) requirements.

Part II: Logical Network Design

During the logical network design phase, the network designer develops a network topology. Depending on the size of the network and traffic characteristics, the topology can range from simple to complex, requiring hierarchy and modularity. During this phase, the network designer also devises a network layer addressing model and selects switching and routing protocols. Logical design also includes security planning, network management design, and the initial investigation into which service providers can meet WAN and remote-access requirements.

Part III: Physical Network Design

During the physical design phase, specific technologies and products that realize the logical design are selected. Physical network design starts with the selection of technologies and devices for campus networks, including cabling, Ethernet switches, wireless access points, wireless bridges, and routers. Selecting technologies and devices for remote-access and WAN needs follows. Also, the investigation into service providers, which began during the logical design phase, must be completed during this phase.

Part IV: Testing, Optimizing, and Documenting Your Network Design

The final steps in top-down network design are to write and implement a test plan, build a prototype or pilot, optimize the network design, and document your work with a network design proposal. If your test results indicate any performance problems, during this phase you should update your design to include such optimization features as traffic shaping and advanced router queuing and switching mechanisms. A glossary of networking terms concludes the book.

Companion Website

Top-Down Network Design, Third Edition, has a companion website at www.topdownbook.com. The companion website includes updates to the book, links to white papers, and supplemental information about design resources.