[mrtg] Re: MRTG Graphs - True CIR representation

PAUL WILLIAMSON pwilliamson at mandtbank.com
Thu Feb 2 19:46:55 MET 2006

>>> Steve <crunkmeister at gmail.com> 02/02/06 1:35 PM >>>
> Hello All,
> First off I want to say thanks in advance for any help I recieve!  
> Second, I want to say I am no perl expert, I have fumbled 
> through getting MRTG to work for me but I have little experience 
> with commands and such.  My question is:  I am monitoring T1, 
> Frame-Relay, CPU and Ethernet traffic.  The graphs only grow 
> to the maximum bandwidth being used.  The grow to the size of the
> spikes, they are not a true representation of the actual "pipe" ie. 

> A T1 would be 1.544 mbps or a 512 frame relay.  I'd like the 
> graphs to "always" stay at here true commited rate and have 
> the actual data benn represented within the graph.  I hope this 
> makes sense.  Thanks for the help!

You have a few problems wotrking against you here...

1.  CIR is measured per second, so that you're guaranteed 
at least that, but you can always go over.  We have that happen 
to us all the time, our vendor let's us leak over the CIR whenever 
we need to it seems like.

2.  MRTG is polling in 5 minute intervals.  It is not a detailed 
diagnostic tool like a sniffer.  MRTG will definitely miss the peaks 
and valleys of a very "bursty" network.  We have one of these 
as well, and have decided that the "burstieness" is something 
we live with, but will catch any traffic trends over the longer 
term measurements.

So, you do get the actual data within that polling period.  You may 
have exceeded that CIR 8 times during the polling period, but 
it may never show on the graphs.   Especially if you're using 
MRTG and polling at 5 minute intervals.  You could probably do 
a bit better with RRDTool and polling more frequently, but then 
you increase the error with which RRDTool will interpolate 
the values collected.

Or, just add Unscaled[ezwf]:ymwd to your configs.


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