After you identify the symptoms of the issue, the first goal in troubleshooting is to identify the problem space. Essentially, this means determining (as best you can) where the problem is most likely to reside, and how many systems and services are affected. Sometimes the problem space is obvious. For example, if none of your computers are receiving an IP address from your Ubuntu-based DHCP server, then you'll know straight away to start investigating the logs on that particular server in regards to its ability (or inability), to do the job designated for it. In other cases, the problem space may not be obvious. Perhaps you have an application that exhibits problems every now and then, but isn't something you can reliably reproduce. In that case, it may take some digging before you know just how large the scope of the problem might be. Sometimes, the culprit is the last thing you expect.
Each component on your network works together with other components, or...