[mrtg] Re: clearing of counters on Cisco - again

[Greg.Volk at edwardjones.com]

}After spending a couple of days on this now, I have determined 
}that MRTG,
}when used alone, does not show this behavior.  The problem is only with
}MRTG + RRDTOOL + 14all.cgi.  I've even downloaded and set up the newest
}versions of each only to get the same result.  Does anyone how 
}I can have
}RRDTOOL and 14all.cgi follow the same logic as MRTG when 
}creating graphs
}(eliminating this spike)?
}
}More info on my setup:
}- Switches are Cisco Cat 4006 and 5XXX
}- Our NMS is resetting all port counters by doing an snmpset on
}  private.1.9.5.1.1.13.0.  Most people do not believe me, but this DOES
}  reset the ifOctets value to 0, by design.
}

You may want to try using the DERIVE data source type in your RRDs. 
When 
I did this in the past, I just loaded the MRTG script up in vi, and 
changed all occurances of COUNTER to DERIVE. Probably not the safest
method to use, but I wasn't in production with it. That was v2.9.17, 
so it may or may not work in older/newer versions. Going from 
COUNTER to DERIVE eliminates the overflow checks as the following 
rrdtool man page excerpt mentions:

}DERIVE
}
}will store the derivative of the line going from the last to the 
}current value of the data source. This can be useful for gauges, 
}for example, to measure the rate of people entering or leaving a 
}room. Internally, derive works exaclty like COUNTER but without 
}overflow checks. So if your counter does not reset at 32 or 64 
}bit you might want to use DERIVE and combine it with a MIN value 
}of 0. 
}

Give it a shot in a test environment, it may be what you're after.



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