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Chapter 1: Building a Simple Network

Cisco Press

By By Stephen McQuerry, Network World
May 29, 2008 02:19 PM ET

This chapter includes the following sections:

  • Chapter Objectives

  • Exploring the Functions of Networking

  • Securing the Network

  • Understanding the Host-to-Host Communications Model

  • Understanding TCP/IP's Internet Layer

  • IP Network Addressing

  • Understanding TCP/IP's Transport and Application Layers

  • Exploring the Packet Delivery Process

  • Understanding Ethernet

  • Connecting to an Ethernet LAN

  • Chapter Summary

  • Review Questions

When you are building a network, the tasks and components can sometimes be overwhelming. The key to understanding how to build a computer network lies in understanding the foundations of network communications. The key to building a complex network involves gaining an understanding of the physical and logical components of a simple point-to-point network. To become proficient in networking, you must gain knowledge of why networks are built and the protocols used in modern network designs. This chapter explores the basics of networking and provides a solid foundation on which to build a comprehensive knowledge of networking technology.

Chapter Objectives

Upon completing this chapter, you will be able to create a simple point-to-point network and describe network components and functions. These abilities include meeting these objectives:

  • Identify the benefits of computer networks and how they function

  • Identify common threats to a network and threat-mitigation methods

  • Identify and compare the Open System Interconnection (OSI) and TCP/IP layered models that control host-to-host communications

  • Describe IP address classification and how a host can obtain an address

  • Describe the process that TCP uses to establish a reliable connection

  • Describe the host-to-host packet delivery process

  • Describe how Ethernet operates at Layer 1 and Layer 2 of the OSI model

  • Explain how to connect to an Ethernet LAN

Exploring the Functions of Networking

To understand how networks function, you need to become familiar with the basic elements of a network. This chapter explains networks by introducing fundamental computer and network concepts and the characteristics, functions, benefits, metrics, and attributes used to describe network features and performance. This chapter also introduces the Open System Interconnection (OSI) reference model, data communications terms and concepts, and the TCP/IP protocol, which serves as the de facto standard for most of today's computer networks. Finally, this chapter provides you with an opportunity to connect two PCs in a point-to-point serial network.

What Is a Network?

The first task in understanding how to build a computer network is defining what a network is and understanding how it is used to help a business meet its objectives. A network is a connected collection of devices and end systems, such as computers and servers, that can communicate with each other.

Networks carry data in many types of environments, including homes, small businesses, and large enterprises. In a large enterprise, a number of locations might need to communicate with each other, and you can describe those locations as follows:

  • Main office: A main office is a site where everyone is connected via a network and where the bulk of corporate information is located. A main office can have hundreds or even thousands of people who depend on network access to do their jobs. A main office might use several connected networks, which can span many floors in an office building or cover a campus that contains several buildings.

  • Remote locations: A variety of remote access locations use networks to connect to the main office or to each other.

  • Branch offices: In branch offices, smaller groups of people work and communicate with each other via a network. Although some corporate information might be stored at a branch office, it is more likely that branch offices have local network resources, such as printers, but must access information directly from the main office.

  • Home offices: When individuals work from home, the location is called a home office. Home office workers often require on-demand connections to the main or branch offices to access information or to use network resources such as file servers.

  • Mobile users: Mobile users connect to the main office network while at the main office, at the branch office, or traveling. The network access needs of mobile users are based on where the mobile users are located.

Figure 1-1 shows some of the common locations of networks that can be used to connect users to business applications.

Figure 1-1

Figure 1-1
Network Locations

Many different types and locations of networks exist. You might use a network in your home or home office to communicate via the Internet, to locate information, to place orders for merchandise, and to send messages to friends. You might have work in a small office that is set up with a network that connects other computers and printers in the office. You might work in a large enterprise in which many computers, printers, storage devices, and servers communicate and store information from many departments over large geographic areas. All of these networks share many common components.

Common Physical Components of a Network

The physical components are the hardware devices that are interconnected to form a computer network. Depending on the size of the network, the number and size of these components varies, but most computer networks consist of the basic components shown in Figure 1-2.

Figure 1-2

Figure 1-2
Common Network Components

These are the four major categories of physical components in a computer network:

  • Personal computers (PCs): The PCs serve as endpoints in the network, sending and receiving data.

  • Interconnections: The interconnections consist of components that provide a means for data to travel from one point to another point in the network. This category includes components such as the following:

    • Network interface cards (NICs) that translate the data produced by the computer into a format that can be transmitted over the local network

    • Network media, such as cables or wireless media, that provide the means by which the signals are transmitted from one networked device to another

    • Connectors that provide the connection points for the media

  • Switches: Switches are devices that provide network attachment to the end systems and intelligent switching of the data within the local network.

  • Routers: Routers interconnect networks and choose the best paths between networks.

Interpreting a Network Diagram

When designing and describing a computer network, you use a drawing or diagram to describe the physical components and how they are interconnected.

The network diagram uses common symbols to capture information related to the network for planning, reference, and troubleshooting purposes. The amount of information and the details of that information differ from organization to organization. The network topology is commonly represented by a series of lines and icons. Figure 1-3 shows a typical network diagram.

In this diagram:

  • A cloud represents the Internet or WAN connection.

  • A cylinder with arrows represents a router.

  • A rectangular box with arrows represents a workgroup switch.

  • A tower PC represents a server.

  • A laptop or computer and monitor represent an end user PC.

  • A straight line represents an Ethernet link.

  • A Z-shaped line represents a serial link.

Figure 1-3

Figure 1-3
Typical Network Diagram

Other information can be included as space allows. For example, it is sometimes desirable to identify the interface on a device in the format of s0/0/0 for a serial interface or fa0/0 for a Fast Ethernet interface. It is also common to include the network address of the segment in the format such as, where indicates the network address and /24 indicates the subnet mask.

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