So, you are new to networking. You might have seen or heard about different topics relating to networking, but you are only just now getting serious about learning the details. Like many people, your perspective about networks might be that of a user of the network, as opposed to the network engineer who builds networks. For some, that perspective is as a dialup user of the Internet. Others might use a computer at a job or at school; that computer is typically connected to a network via some cable. Figure 1-1 shows the basic end-user perspective of networking.
Figure 1-1 End-User Perspective on Networks
Home User PC with Modem
The top part of the figure shows a typical dialup user of the Internet. The user has a PC, and the user plugs in the phone line from the wall into a modem in a PC. By dialing the
Office User PC with Ethernet Card
right phone number, the user connects to the Internet. After connecting, the user can send e-mail, browse web sites, and use other tools and applications as well.
Similarly, an employee of a company or a student at a university views the world as a connection through a wall plug. Typically, this connection uses a type of local-area network (LAN) called Ethernet. Instead of a phone cord between a PC modem and the wall plug at your house, you have an Ethernet cable between a PC Ethernet card and a wall plug near where you are sitting at work or at school. The Ethernet connection does not require the PC to "dial" a phone number—it's always there waiting to be used, similar to the power outlet.
From the end-user perspective, whether at home, at work, or at school, what happens behind the wall plug is magic. Just as most people do not really understand how cars work, how TVs work, and so on, most people who use networks do not understand how they work. Nor do they want to! But if you have read this much into Chapter 1, you obviously have a little more interest in networking than an end user. By the end of this book, you will have a pretty thorough understanding of what's behind that wall plug.
The concepts, protocols, and devices covered on the CCNA exam are used to help build the network cloud shown in Figure 1-1. However, the CCNA exam focuses on technology that is used to build a network at a single company or school. These same technologies are used to build the Internet, but the CCNA exam topics focus on things that matter most to what Cisco calls "enterprise" networks—networks owned by a single enterprise or company. Figure 12 shows an alternative view of the world of networking, with several enterprise networks.
Figure 1-2 Enterprise Networks and the Internet
Figure 1-2 Enterprise Networks and the Internet
When you go to your school or your job and connect to "the network," you are most likely connecting to the private network, or enterprise network, for that school or company. That network, in turn, is connected to the Internet. Conversely, if you dial into some Internet service provider (ISP) from home, you are not connected to an Enterprise network, but you are connected directly to the Internet. However, if you then use a web browser to browse some web site, the web site itself might be inside that company's enterprise network.
In either case, practically every company or school that uses computers also has an enterprise network. To communicate, many enterprise networks connect to the Internet. The Internet itself is really a collection of ISPs that, in turn, connect to each other. By having the various enterprise networks connect to the Internet, most computer users around the world can use applications to communicate with each other—worldwide.
The CCNA exams focus on the technology used to build enterprise networks, with some coverage of technology more often used in the Internet. However, a lot of the protocols and concepts used in an enterprise network also happen inside the Internet. Because CCNA topics encompass the typical features found in enterprise networks, and because a much larger number of people work on enterprise networks than ISP networks, most of the examples in this book focus on enterprise networks.
Most of the details about standards for enterprise networks were created in the last quarter of the 20th century. You might have gotten interested in networking after most of the conventions and rules used for basic networking were created—if so, you missed out on the opportunity to help create the standards. However, taking the time to pause and think about what you would do if you were creating these standards can be helpful. The next section takes you through a somewhat silly example, but with real value in terms of thinking through some of the basic concepts behind enterprise networking and some of the design trade-offs.
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