Part II Hands-on Knowledge This page intentionally left blank 209 Chapter 15 Designing a Network 210 Networking: A Beginner’s Guide N etworking professionals rarely have the opportunity to walk into a company and design a new network from the ground up, but those who do are certainly lucky. It’s true that such an effort involves long hours, stress, deadlines, and the nagging worry that maybe you’re forgetting something. But in return, you get to shape the computing environment of a large number of users, and—in many companies—set the tone for how efficiently the company itself can function in coming years. In some companies that rely heavily on information technology, a smoothly running network might even determine whether or not the company will be successful. It’s an enormous responsibility, but also one of the most rewarding jobs you can have. In practice, you usually start with some sort of network already in place. Networks start small and simply grow over time. Networks are almost like skin, where you’re sure to replace each and every cell every few years, but only a few at a time. The process is usually evolutionary rather than revolutionary. Exceptions exist to this rule, though. For example, a company might move to a new building, decide to scrap the old network during the process, and install an entirely new one. Likewise, a well-funded startup company that goes from 5 to 500 employees in six months is likely to see the need for a new network. Regardless of whether you’re building a brand-new network from scratch or renovating an existing network, the tools you use are much the same, and the process of designing the network is also much the same. The concept is actually simple: You assess the needs that the network must meet and then you design to meet those needs. In practice, this process is much more involved, but the idea is straightforward. Even in an evolving network, using network planning to formulate a long-term plan to renovate the network makes sense. This chapter describes how to design a network. It relies on all the information you learned in the preceding chapters. Think of this chapter as the one that brings together into a coherent whole all the information that you have already learned. Preceding chapters have focused on the bits and bytes of networks, while this chapter is the view from 30,000 feet where you start to see how everything works together. The Network Design Process Network design is not an exact science. Getting it exactly right the first time is nearly impossible, even with the best design tools and resources available. This is because every network has different demands placed on it, and these demands often interact in surprising ways. Moreover, predicting what new demands will be placed on the network over time, how users will use the network resources, and what other changes you might need to make is almost impossible. The entire situation is both fluid and chaotic. The trick is to do a good job of estimating needs, and then do the best job possible to create a design to meet those needs. Having fallback plans is also important, in case some part of the network doesn’t perform the way you intended. For instance, once the network is up and running, 211 Chapter 15: Designing a Network you might find that the distribution of bandwidth across segments is poor. You want to know in advance how you can measure and address these types of problems. You might also find storage requirements are much higher or lower than you expected. You need to know what to do if this happens. The point is that network design is a process, often an iterative one. Your job as a network designer is to get as close as possible to the needed design, and then fine-tune the design as needed. A lot of the network design process is what you decide to make of it. There are simple network design processes, and there are horrendously complicated processes that involve dozens of people, complex statistical modeling, and even network simulation software to test a planned design and see if it holds together under load. In this chapter, you learn a relatively comprehensive process that is straightforward and simple. Using the information in this chapter, along with a good dose of experience, will yield a flexible network that should easily meet the needs of hundreds of users. TIP You can’t design a network of any size without plenty of experience running similar networks. You can manage the overall process by understanding the methodology, but you can’t create a good design without hands-on experience. If you’re new to networking and you are asked to design a network, make sure you get experienced people on the team—either as consultants or as part of a supplier-led team—and listen carefully to their advice. Listening well pays off with a design that will work, rather than one that might look good on paper but won’t hold up to actual use. Assessing Network Needs “Measure twice and cut once” is a common adage that conveys the importance of planning. “Ready, fire, aim,” is one that pokes fun at people who don’t properly set goals. Assessing the needs that a network must meet corresponds to taking those measurements and aiming before you shoot. Before you even think about any specifics—network topology; network operating system (NOS) platform; a structure for hubs, bridges, and routers; or the grade of wiring—you must first know what the network needs to accomplish. Doing a proper job can be tedious, but assessing needs is where you should place the most emphasis during a design process. Failing to do so almost certainly will result in a network that isn’t productive for its users. NOTE Many IT professionals are, at heart, technologists who love to play with the latest technologies. It’s very tempting to design the network around the “hot” technologies, and then try to figure out how the needs fit into those technologies. However, this is not the way to go about designing a network. Instead, start with the needs, and then find out what technologies support those needs. . Part II Hands-on Knowledge This page intentionally left blank 209 Chapter 15 Designing a Network 210 Networking: A Beginner’s Guide N etworking professionals rarely have the opportunity to walk. relies on all the information you learned in the preceding chapters. Think of this chapter as the one that brings together into a coherent whole all the information that you have already learned that will work, rather than one that might look good on paper but won’t hold up to actual use. Assessing Network Needs “Measure twice and cut once” is a common adage that conveys the importance