 CHAPTER 35 Designing Networks There are hundreds of books out there that will tell you how to build a three-tier cor- porate network. This is not one of them. Instead, I'm going to show you what you need to do before you build your network. Then I'll show you some real-world examples of network designs. This is not the sort of technical information you learn from getting certified. This is information that will help you do your job better. For the most part, this chapter is written with the assumption that you'll be designing a network from scratch. While that's not often the case, the information contained herein is applicable to any network project. Documentation Documentation is the bane of many an engineer's existence. I'm not entirely sure why this is the case, but an engineer who likes to write documentation seems to be a rarity. Writing is hard work (try writing a book!), but the payoffs are enormous. Some engineers seem to believe that if they hoard information, they become irreplace- able. Trust me on this one-you and I are replaceable. In fact, I've made a living by coming in to document networks when "irreplaceable" engineers were fired. Well-written documentation saves time and money. If someone can fix your network by reading your documentation, you've done a good job. If no one but you can fix your network, you're not doing a good job. Whenever possible, even on small networks, you should document every detail of your network. Just because a network is small enough for you to memorize every IP address doesn't mean it should not be documented. Start with your home network. My home network has better documentation than many company networks, but to be fair, it's likely more complicated than many company networks as well. I take great pride in my documentation, and samples of my work have landed me jobs. Given two equally skil- led engineers, I'll hire the one with better documentation skills every time. Requirements Documents One of the things you should do at the start of any project, regardless of 