The ability to monitor your network over time is very important tool for a network administrator. It will help you to identify normal traffic flows and patterns and establish a benchmark for normal performance. There are many tools for monitoring networks and workstations in a network. Using Linux you can setup a network monitoring server that monitors your network using free open source tools. Cactii is a rrdtool a round robin database tool that polls the network, gathers information, and charting and graphs that information over time.