[mrtg] Re: Wierd traffic spike problem

Danny Brando dannyb at dannyb.net
Tue Sep 18 17:25:20 MEST 2001

On Tue, 18 Sep 2001, Bill Wichers wrote:

> I've been seeing this strange problem that I can't seem to track down. When
> my monitoring system looses connectivity and this outage happens to be
> during a sample (actually it has to be more than just one sample), the
> result is a *huge* spike on the graphs into the many megabits. Normally
> MRTG would just do the "assume last" thing, but not in this case -- and
> that's what I can't figure out.

Its because when you lose connectivity, it writes a -1 to the logs as the 
counter value (I have no idea why).  So when the next time you get a 
"real" counter value, it gets the difference between "new counter value"  
and -1, and if that number falls in the MaxBytes....you get a spike (or   

I have added some code so it exits the entire process and emails me 
letting me know there was a problem, rather than showing wacky dips and   


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