Network Testing and Troubleshooting
So what do you do if you've followed this (and maybe other) home networking guides step-by-step, but still something's not right. Everything works except .... Or everything has been working great for weeks, but now one of the computers can't connect, and you don't know why. This section is dedicated to troubleshooting those pesky network problems. When I started writing this "quick" guide to home networking, which later turned in to the full-length novel it is today, this is the section I was most interested in writing. Network problems are bound to happen given enough time. I play with my home network a lot, so I tend to cause my own problems. (First rule of engineering: If you mess around with something long enough, you will eventually be successful in breaking it.)
These steps are the ones that I follow myself, so I'm certain they can help at least some of you out of a jam. The first time you are bringing up a new home network or adding new device (e.g., computer, Xbox 360) to an existing network, it's a good idea to follow the steps in order. However, when troubleshooting a device that had been working you might want to skip right to test 4 or test 5. I don't usually start with test 1 in that case myself. I start farther down and if a test fails, I work my way backwards towards test 1. After you've done this for a while, you'll get a feel for where to start just by the way the failure behaves, but these steps are always here in case you encounter a problem that resists being solved.
The subsections here fall into four categories of testing: testing the Ethernet Adapter (test 1 and 2), testing LAN Functionality (tests 3, 4 and 5), testing Internet connectivity (tests 6 and 7), and diagnosing a slow network (tests 8, 9 and 10). Within each category, there are two or three tests to perform. The basic approach is to check the adapter itself to see if the problem is within the computer's own hardware. If these tests pass, we move out from the system under test to the LAN. Network-wise, this is the next link in the change. If the LAN tests pass then we move outward again to the Internet connection (also called the Wide Area Network or WAN). The four category covers the case where the Internet connection is not down, but the performance is not what it once was or seems slower than it is advertised at. Finally, there is a short section that discusses useful tools for diagnosing networks.