[mrtg] Re: Formula for calculating Network Utilisation

[PAUL WILLIAMSON]

Why do you say it is wrong?  This is exactly how it should be
calculated.
The ThreshMaxI and ThreshMaxO are computed based on the interval. 

What is wrong about it?  If MRTG polls in 5 minute intervals, the only 
threshold it knows about is the 5 minute window.  If you want it to 
compute the thresholds on a lower interval (like 1 minute), you need 
to poll that often and set the threshold accordingly.  How is MRTG
supposed 
to alert you of a threshold that has been crossed at any one point
during 
the interval?  This is what you are asking for.  MRTG is not a packet 
sniffing real-time application.  If you want to be alerted at any one
point 
(down to a second) during a burst of traffic, you need to deploy RMON 
probes out to your network that can listen to traffic real-time (a few 
that come to mind are ntop, nGenuis, NetVigil and Nebula).  MRTG is 
not the tool to accomplish this.  ntop uses RRDTool however...

Paul

>>> "Meng Keng Lee" <mengkenglee at yahoo.com> 06/24/04 1:02 AM >>>
Hello Alex,
then how do we deploy this formula to MRTG to monitor network threshold?
 
 
I did some testing and found that I did to divide by 300sec to derive a
correct network utilisation percentage to be monitored for threshold
alert.
 
Furthermore, in MRTG, ThresMaxi derives its percentage from MaxBytes
which is wrong then.
 
Regards
Alex van den Bogaerdt <alex at ergens.op.het.net> wrote:
On Tue, Jun 22, 2004 at 08:38:34PM -0700, Meng Keng Lee wrote:
> Hello,
> 
> Can I check with you whether the formula for calculating Network
Utilisation (Input/Ouput) is correct?
> 
> Network Utilisation (Input in %) = ifInOctets/ifSpeed * 800
> 
> Network Utilisation (Output in %) = ifOutOctets/ifSpeed * 800

___if___ the ifInOctets counter counts bytes and ifSpeed is in bits
then it is correct. This is __not__ the case.

Both counters are of the same type (both bits or both bytes) and thus
a percentage is 100 * x/y.

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