Open source network monitoring tools you should care about: MRTG and RRDtool

In today's "mash-up" application development craze, the innovation is being driven largely by the fact that APIs are now more open and accessible, and presentation layer technologies such as AJAX are creating very compelling new ways to visualize data streams from multiple services. Developers can get to services more easily, and with XML they can deliver the data in much more dynamic ways via web applications.

Similar trends are driving software development innovation today in network monitoring. Tools such as MRTG (Multi-Router Traffic Grapher) and RRD (Round Robin Database) make it possible to more easily collect data from a greater number of devices on the network, and convert the data into XML for easy consumption on the front end.

According to Alex van den Bogaerdt, who wrote a very good tutorial on RRD -- "MRTG started as a tiny little script for graphing the use of a university's connection to the Internet. MRTG was later used as a tool for graphing other data sources including temperature, speed, voltage, number of printouts and the like."

Free under the GNU GPL, network professionals started using MRTG to poll network devices, retrieve MIB (Management Information Base) and SNMP (Simple Network Management Protocol) values, and use Perl scripts to post the results on graphs on web pages. Because MRTG is so good at polling devices and producing graphs, it quickly became widely used not only by the open source folks cobbling their own solutions together, but also by very large proprietary vendors such as HP who, according to this site, borrow from some of MRTG's capabilities for OpenView.

In network monitoring, the whole goal is to be able to monitor the right things. You don't want too much data, or you'll be flooded. Too little, and you miss important info. So there's this very fine line you have to walk to "right size" your monitoring system.

With MRTG and RRDTool (creator Tobias Oetiker's next generation MRTG, which extends the scalability and functionality), polling devices and getting just the information you want has become much, much easier. And because they use open C APIs and the info is dumped into XML format, these open source tools are interoperable with just about everything.