[Nagiosplug-help] check_mrtg

[Ralph Green]

Howdy,
  I am looking for a good explanation of how to setup the check_mrtg
plugin.  I have been to the man page online at:
  http://nagiosplugins.org/man/check_mrtg
 That tells me what it is for, but nothing about how to set it up.  I'll
start with a real basic point.  Where is mrtg supposed to be running?
Do I run it on my router, or on the nagio machine.  That may be obvious
to someone, but not to me.  A pointer to a setup guide or howto would be
great.  I have searched on the nagio site and on google without finding
anything useful.
Have a good day,
Ralph