ZDNet UK: Monitor Linux Routers and Firewalls with MRTG

“MRTG, or Multi Router Traffic Grapher, is a popular monitoring
and statistics tool for use on Linux platforms. It was designed to
monitor the traffic load on network links, but it’s highly
extensible and configurable. Not only can you watch interfaces on
routers and switches, but you can also analyze Linux system
variables. Although this is usually done with the Simple Network
Management Protocol (SNMP), MRTG also supports the use of local
scripts to feed it data. The data is then converted into HTML with
graphs in PNG format for a visual representation of your
network.

“Before we delve too deeply into the installation and
configuration of MRTG, it is important to understand how MRTG and
SNMP work together. By default, MRTG will take an SNMP community
string and a device hostname or IP address and discover what it
needs to know. This is done by polling Management Information Base
(MIB) objects predefined for all SNMP-ready devices. A MIB is
basically a database of variables that corresponds to a system
value. Basic examples include information such as system name,
interface type, and uptime…”

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