Essential SNMP

Pitfalls

Many SNMP-capable devices change the order of interfaces in the interfaces table whenever a new interface card is inserted or an old one is removed. If you run a fairly static router environment (i.e., you hardly ever add or remove cards from your routers), the configuration examples we’ve shown should work well for you. But in today’s fast-paced network environments, stability is rare. MRTG’s cfgmaker command provides a command-line option, - -ifref, to help with this problem. It doesn’t solve the problem, but it does allow you to generate graphs in which interfaces are labeled with their addresses, descriptions, or names; with this information, you don’t have to remember whether interface 1 is your local network interface or your T1 connection. Table 13-2 summarizes the usage of - -ifref.

Table 13-2. Summary of --ifref Options

Option	Description
--ifref=ip	Identify each interface by its IP address.
--ifref=eth	Use the Ethernet address to identify the interface.
--ifref=descr	Use the interface description to identify the interface.
--ifref=name	Use the interface name to identify the interface.

Thus, to label interfaces with their IP addresses, run cfgmaker like so:

[root][linuxserver] ~/mrtg-2.9.10> cfgmaker 
            --global 'WorkDir: /mrtg/images' \
            --output /mrtg/run/mrtg.cfg --ifref=ip public@router

Be sure to read the cfgmaker manual that comes with the MRTG documentation.