I have a new tutorial on analyzing networks, in terms of understanding your basic network configuration, the other machines and devices on the network, and the general topology. From the intro:
When accessing a new UNIX system, or even understanding an existing one, a key part of the puzzle to how the system operates is the network configuration. There are many aspects of the network that you need to know and understand to correctly identify problems and prevent future problems. By using some basic tools and commands you can determine a lot about the configuration of a single system, and through this basic understanding, a good idea of the configuration of the rest of the network. With some additional tools, you can expand that knowledge to cover more systems and services within your network.In this tutorial you will use some basic tools within the UNIX environment that can disclose information about the configuration of your system. By understanding these tools and the information they output, you will be able to gain a greater understanding of your system network configuration and how it works. You will also examine tools and solutions that can look at the wider network and gain more detailed information about your network, its potential security issues, and key points of information that will help you identify and diagnose problems when they do occur.