The Multi Router Traffic Grapher
3.1 Overview of MRTG
MRTG is the Multi Router Traffic Grapher, a piece of free software released under the GNU General Public License.1 It was written primarily by Tobias Oetiker and Dave Rand. MRTG produces Web pages that display graphs of bandwidth use on network links on daily, weekly, monthly, and yearly scales. This can be an invaluable tool for diagnosing network problems because it not only indicates the current status of the network but also lets you visually compare this with the history of network utilization.
MRTG relies on SNMP version one, and optionally SNMP version two, to obtain data from routers or other network hardware. Using the variables described in Chapter 1, MRTG sends SNMP requests every five minutes and stores the responses in a specialized data format. This format allows MRTG to present the daily, weekly, monthly, and yearly graphs without the data files forever growing larger. It does this by summarizing the older data as necessary. The graphs themselves are created in Portable Network Graphics (PNG) format and can be included in Web pages or used in other applications.