Keep and Maintain Network Documentation
One element for any troubleshooting philosophy to work is frequently absent: documentation. Many administrators neglect to document their network, or if they do, they do not keep the documentation up to date. Documentation provides the framework to answer fundamental questions such as, "What changed?" or "What connects to device X?" or "What Layer 2 paths exist from point A to point B?" Reconstructing the network topology documentation during a crisis does not lend itself to an efficient or structured troubleshooting approach. You are not doing yourself, your career, or your users any good when you have to take time during the crisis event to determine the network topology.
Document your network with both electronic media and old-fashioned paper. Electronically, use spreadsheets, graphics programs, network management tools, or any other means at your disposal to keep the documentation up to date. Electronic documentation has the advantage of portability; however, it has the disadvantage of limited access and vulnerability to outages. If you keep the documentation on your laptop or desktop, but make it inaccessible to others on your staff by either taking it with you or using passwords, they cannot use the documentation when you are not around. For security reasons (or to satisfy company politics), you might desire this, but in most cases this is not a good practice.
Paper versions offer non-dependence upon the electronic device, but frequently tend to be outdated through neglect. When you make an electronic change, make sure that the paper copy reflects the change as well.
Another underutilized documentation tool exists in your network equipment. Most equipment has built-in documentation features such as description strings for interfaces, modules, chassis, and so forth. Use these to prompt your memory for connectivity. It takes only a few seconds to put a description string on the port configuration. On the Catalyst 5000/6000, use the set port name mod_num/port_num [port_name] command to document interfaces with useful information. For example, you might indicate who or what attaches to the port. If the port is a trunk, indicate what Catalyst it connects to. As with previous documentation discussions, be sure to keep the descriptions current. You will see the port name if you use the show port status command as shown in Example 16-1. Here, Ports 1/1 and 3/1 have assigned names indicating the device the port attaches to.
Continue reading here: Troubleshooting Philosophy 2 Evaluate Layers of the OSI Model
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