In the real estate world, the mantra is location, location, location. In the network and server administration world, the mantra is visibility, visibility, visibility. If you don't know what your network and servers are doing at every second of the day, you're flying blind. Sooner or later, you're going to meet with disaster.
Fortunately, many good tools, both commercial and open source, are available to shine much-needed light into your environment. Because good and free always beat good and costly, I've compiled a list of my favorite open source tools that prove their worth day in and day out in networks of any size. From network and server monitoring to trending, graphing, and even switch and router configuration backups, these utilities will see you through.
First, there was MRTG. Back in the heady 1990s, Tobi Oetiker saw fit to write a simple graphing tool built on a round-robin database scheme that was perfectly suited to displaying router throughput. MRTG begat RRDTool, which is the self-contained round-robin database and graphing solution in use in a staggering number of open source tools today. Cacti is the current standard-bearer of open source network graphing, and it takes the original goals of MRTG to whole new levels.
Cacti is a LAMP application that provides a complete graphing framework for data of nearly every sort. In some of my more advanced installations of Cacti, I collect data on everything from fluid return temperatures in data center cooling units to free space on filer volumes to FLEXlm license utilization. If a device or service returns numeric data, it can probably be integrated into Cacti. There are templates to monitor a wide variety of devices, from Linux and Windows servers to Cisco routers and switches -- basically anything that speaks SNMP. There are also collections of contributed templates for an even greater array of hardware and software.
While Cacti's default collection method is SNMP, local Perl or PHP scripts can be used as well. The framework deftly separates data collection and graphing into discrete instances, so it's easy to rework and reorganize existing data into different displays. In addition, you can easily select specific timeframes and sections of graphs simply by clicking and dragging. In some of my installations, I have data going back several years, which proves invaluable when determining if current behavior of a network device or server is truly anomalous or, in fact, occurs regularly.
Using the PHP Network Weathermap plug-in for Cacti, you can easily create live network maps showing link utilization between network devices, complete with graphs that appear when you hover over a depiction of a network link. In many places where I've implemented Cacti, these maps wind up running 24/7 on 42-inch LCD monitors mounted high on the wall, providing the IT staff with at-a-glance updates on network utilization and link status.
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