[mrtg] Re: Need some light!! MRTG options

Lightfoot.Michael Lightfoot.Michael at comcare.gov.au
Thu Nov 28 01:01:30 MET 2002

> -----Original Message-----
> From: PAUL WILLIAMSON [mailto:pwilliamson at mandtbank.com] 
> Sent: Thursday, 28 November 2002 1:11 AM
> To: mrtg at list.ee.ethz.ch; pouellet at microtecsecurite.com
> Subject: [mrtg] Re: Need some light!! MRTG options
> It is the maximum number of bytes per second 
> (typically) the device will see.
> Anything over this amount will be ignored.
It is slighhtly more complicated than this.

MaxBytes has two functions.  It represents the "maximum expected value"
of any data being plotted.  Used by itself it will be the absolute
maximum of any data and it will be used if percentages are involved.

For example, a 100 Mbps ethernet has a maximum value of 12500000 (bytes)
so MaxBytes would be set to that and any value higher than that would be
truncated to 12500000 as an obviously erroneous value; similarly,
percent CPU values have a maximum of 100.

OTOH, some data has a "maximum expected value" or perhaps an "expected
maximum sustained value" but could quite easily exceed that.  Examples
are frame relay PVCs which have a CIR and the maximum value of the whole
FR cloud and we are often interested in the amount of bursting over the
CIR.  A compressed link would also have no real maximum, but anything
that exceeds the uncompressed link speed would show the efficiency of
the compression.  A third example would be a value which represents some
sort of SLA threshhold.  In these cases MaxBytes can be exceeded by
using the AbsMax tag to indicate the value above which data would be
ingored, but percentages are still based on MaxBytes and that value is
indicated on the graphs by a red dotted horizontal line.

For example a FR PVC of 128 Kbps CIR on a FR of 1.5 Mbps would have a
MaxBytes of 16000 but an AbsMax of 193000.  Another example would be a
squid proxy server where median response times above 1 second would be
considered "unacceptable" but nothing would be consiered out of band
(the Internet is a stochastic thing) so that Maxbytes would be set to
1000 (ms) but AbsMax to some arbitrarily huge value (say 4 billion).
> >>> "Patrick Ouellet" <pouellet at microtecsecurite.com> 
> 11/27/02 08:43 AM 
> >>> >>>
> What's the use of the MaxByte parameter?
> How do you configure this param.... 

Michael Lightfoot
Unix Consultant
ISG Host Systems
+61 2 62750680
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