Tools for watching the network

Now that you know some basics of how networking works, let's run through some quick introductions to some tools. Many of these tools are very powerful and have lots of options. Make sure to read their documentation to understand everything they can do. I will mainly be talking about one action you can use each tool for and will not provide an exhaustive list of their capabilities or possible uses.

netstat

netstat is a tool for evaluating the state of open connections on a Linux box. The tool can do a lot, but the main thing I use it for is to see which services are using which ports. I would suggest reading the man page for netstat by running man netstat. netstat can also list active outgoing connections and all sorts of cool stuff about your computer's active networking. Like every other tool in this book, though, read the documentation to find out lots of cool ways to use it.

The following example shows which ports are open on one of my computers...