Many network problems are the result of human-initiated change. Finding the change can involve inspecting documentation and communicating with co-workers and outside vendors. Even unintended changes because of the "fat finger factor" can seriously damage a network, so it's worth considering where you've been, no matter how unrelated it might seem. You'll also want to figure out where others have been; however, don't rely solely on logbooks. (Although to document is divine, people aren't perfect. They'll sometimes forget to write down what they've done.) Vendors, including VARs, ISPs, or the telephone company can be problematic because there is no direct profit motive in being good at communicating change before it happens.
Before deploying any new network toy, whether software or hardware, it's worth considering whether the risk is worth the potential benefit. Risk is always much higher with new productsyou're better off waiting a couple of months before using what might be a pretty green product. Limited rollouts can also limit your potential network risk. You should also always think about a rollback plan, just in case things don't go as expected with a new project. When considering levels of risk, it helps to think about the change's attributes in terms of scope, distribution, inspection, reversibility, and interactivity.
In Hour 5, we'll look at dividing and conquering, another powerful troubleshooting technique.