I've talked to many network administrators over the years, and I've visited and consulted for a variety of operations that had anywhere from 10 to 600 clients. The one characteristic that all the organizations have had in common is the lack of good network documentation. Even in my own business, my documentation has, at times, been quite weak. Creating documentation is time-consuming, detail-oriented, and boring. It is also absolutely essential to the health of your network. An administrator's handbook containing network documentation could even save your job.
To help ease the process and show the value of creating such documentation, I recently gave my admin students a class project. They were to find out everything they could about our network, but they couldn't leave their computers to do it. After a few classes of pulling together all the pieces of what each student thought was critical information, I made a checklist of the sum total of the items. The question afterward was "What did we miss?" I decided that the best way to make sure we had covered all the bases was to apply the seven-layer OSI Reference Model to our checklist and see whether we had addressed the documentation of each layer. Most of our items fell within the parameters of one of the seven layers. A few spanned multiple layers or all layers. Below is a list of the seven layers and what needs to be documented at each one. I've also put together a network documentation outline that breaks these items down into an easy-to-read list.